Category Archives: C. diff. Research & Development

Children with inflammatory bowel diseases (IBD) are particularly vulnerable to infection with Clostridioides difficile (CDI)

Multi-omic Analysis of the Interaction between Clostridioides difficile Infection and Pediatric Inflammatory Bowel Disease


  • Multi-omics reveals markers of CDI in pediatric IBD patients
  • Identification of metabolites reveals distinctive features for IBD and CDI
  • Isocaproyltaurine is made by C. difficile and associates with active IBD
  • Identifies biomarkers potentially useful for distinguishing disease processes


Children with inflammatory bowel diseases (IBD) are particularly vulnerable to infection with Clostridioides difficile (CDI). IBD and IBD + CDI have overlapping symptoms but respond to distinctive treatments, highlighting the need for diagnostic biomarkers. Here, we studied pediatric patients with IBD and IBD + CDI, comparing longitudinal data on the gut microbiome, metabolome, and other measures. The microbiome is dysbiotic and heterogeneous in both disease states, but the metabolome reveals disease-specific patterns. The IBD group shows increased concentrations of markers of inflammation and tissue damage compared with healthy controls, and metabolic changes associate with susceptibility to CDI. In IBD + CDI, we detect both metabolites associated with inflammation/tissue damage and fermentation products produced by C. difficile. The most discriminating metabolite found is isocaproyltaurine, a covalent conjugate of a distinctive C. difficile fermentation product (isocaproate) and an amino acid associated with tissue damage (taurine), which may be useful as a joint marker of the two disease processes.

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Accessible Database for Clostridioides difficile Genome Sequences Supporting Transmission and Epidemics

  • Martinique Frentrup1​, Zhemin Zhou2​, Matthias Steglich1​,3​, Jan P. Meier-Kolthoff1​, Markus Göker1​, Thomas Riedel1​,3​, Boyke Bunk1​, Cathrin Spröer1​, Jörg Overmann1​,3​,4​, Marion Blaschitz5​, Alexander Indra5​, Lutz von Müller6​, Thomas A. Kohl7​,8​, Stefan Niemann7​,8​, Christian Seyboldt9​, Frank Klawonn10​,11​, Nitin Kumar12​, Trevor D. Lawley12​, Sergio García-Fernández13​,14​, Rafael Cantón13​,14​, Rosa del Campo13​,14​, Ortrud Zimmermann15​, Uwe Groß15​, Mark Achtman2​, Ulrich Nübel1​,3​,4​


Clostridioides difficile is the primary infectious cause of antibiotic-associated diarrhea. Local transmissions and international outbreaks of this pathogen have been previously elucidated by bacterial whole-genome sequencing, but comparative genomic analyses at the global scale were hampered by the lack of specific bioinformatic tools. Here we introduce a publicly accessible database within EnteroBase ( that automatically retrieves and assembles 

C. difficile short-reads from the public domain, and calls alleles for core-genome multilocus sequence typing (cgMLST). We demonstrate that comparable levels of resolution and precision are attained by EnteroBase cgMLST and single-nucleotide polymorphism analysis. EnteroBase currently contains 18 254 quality-controlled 

C. difficile genomes, which have been assigned to hierarchical sets of single-linkage clusters by cgMLST distances. This hierarchical clustering is used to identify and name populations of C. difficile at all epidemiological levels, from recent transmission chains through to epidemic and endemic strains. Moreover, it puts newly collected isolates into phylogenetic and epidemiological context by identifying related strains among all previously published genome data. For example, HC2 clusters (i.e. chains of genomes with pairwise distances of up to two cgMLST alleles) were statistically associated with specific hospitals (P<10−4) or single wards (P=0.01) within hospitals, indicating they represented local transmission clusters. We also detected several HC2 clusters spanning more than one hospital that by retrospective epidemiological analysis were confirmed to be associated with inter-hospital patient transfers. In contrast, clustering at level HC150 correlated with k-mer-based classification and was largely compatible with PCR ribotyping, thus enabling comparisons to earlier surveillance data. EnteroBase enables contextual interpretation of a growing collection of assembled, quality-controlled C. difficile genome sequences and their associated metadata. Hierarchical clustering rapidly identifies database entries that are related at multiple levels of genetic distance, facilitating communication among researchers, clinicians, and public-health officials who are combatting disease caused by C. difficile.


  • Clostridioides (Clostridium) difficile
  • nosocomial infection, 
  • genomic population structure, 
  • outbreak, 
  • cgMLST, 
  • hierarchical clustering

Author NotesAll supporting data, code and protocols have been provided within the article or through supplementary data files. Three supplementary tables and eight supplementary figures are available with the online version of this article.Sequence accession numbers: PRJEB33768, PRJEB33779, PRJEB33780.†These authors contributed equally to this work‡These authors also contributed equally to this work


CC, cgST complex; CDI, Clostridioides difficile infection; cgMLST, core-genome MLST; cgST, core-genome sequence type; HC150, hierarchical cluster with pairwise distances of up to 150 cgMLST alleles; HC, hierarchial cluster; HierCC, hierarchical clustering; MLST, multilocus sequence typing; ORF, open reading frame; rMLST, ribosomal MLST; rST, ribosomal sequence type; RT, PCR ribotype; SNP, single-nucleotide polymorphism; wgMLST, whole-genome MLST.Impact Statement

Clostridioides difficile is a major cause of healthcare-associated diarrhea and causes large infection outbreaks. Whole-genome sequencing is increasingly applied for genotyping C. difficile, with the objectives to monitor and curb the pathogen’s spread. We present a publicly accessible database for quality-controlled genome sequences from C. difficile that enables contextual interpretation of newly collected isolates by identifying related strains among published data. It also provides a nomenclature for genomic types to facilitate communication about transmission chains, epidemics, and phylogenetic lineages. Finally, we demonstrate that genome-based hierarchical clustering is largely compatible with previously used molecular typing techniques, thus enabling comparisons to earlier surveillance data.

Data Summary

All genome sequencing data were submitted to the European Nucleotide Archive ( under study numbers PRJEB33768, PRJEB33779 and PRJEB33780. The Clostridioides database within EnteroBase is publicly accessible at In addition, stand-alone versions of all EnteroBase tools are available at


The anaerobic gut bacterium Clostridioides difficile (formerly Clostridium difficile) [1] is the primary cause of antibiotic-associated diarrhea in Europe and North America [2]. Molecular genotyping of C. difficile isolates has demonstrated international dissemination of diverse strains through healthcare systems [3–5], the community [6] and livestock production facilities [7, 8]. Previously, genotyping was commonly performed by PCR ribotyping or DNA macrorestriction. More recent publications have documented that genome-wide single-nucleotide polymorphisms (SNPs) from whole-genome sequences provide improved discrimination, and such analyses have enabled dramatic progress in our understanding of the emergence and spread of epidemic strains [9–12] and the epidemiology of local transmission [13, 14]. Eyre and colleagues have argued that transmission of C. difficile isolates within a hospital environment can be recognized with high probability as chains of genomes, which differ by up to two SNPs whereas genomes, which differ by at least ten genomic SNPs represent unrelated bacteria [13, 15]. However, SNP analyses require sophisticated bioinformatic tools and are difficult to standardize [16, 17]. A convenient alternative to SNP-based genotyping is offered by the commercial software SeqSphere, which implements a core-genome multilocus sequence typing scheme (cgMLST) for the analysis of genomic diversity in 

C. difficile [18] and other organisms. Indeed, cgMLST [18] confirmed the prior conclusion from genomic SNP analyses [19] that a common clone of C. difficile had been isolated over two successive years at a hospital in China [18]. However, a recent quantitative comparison of the two methods showed that SeqSphere’s cgMLST achieved a low predictive value (41 %) for identifying isolate pairs that were closely related by the ≤2 SNPs’ criterion [20]. cgMLST of genomic sequences of a variety of bacterial pathogens can also be performed with EnteroBase (, which has been developed over the last few years with the goal of facilitating genomic analyses by microbiologists [21]. EnteroBase automatically retrieves Illumina short-read sequences from public short-read archives. It uses a consistent assembly pipeline to automatically assemble these short-reads into draft genomes consisting of multiple contigs, and presents the assembled genomes together with their metadata for public access [22]. It also performs the same procedures on sequencing data uploaded by its registered users. Assembled genomes that pass quality control are genotyped by MLST at the levels of seven-gene MLST, ribosomal MLST (rMLST), cgMLST and whole-genome MLST (wgMLST) [21, 22]. EnteroBase supports subsequent analyses based on either SNPs or cgMLST alleles using the GrapeTree or Dendrogram visualization tools [23]. EnteroBase also assigns these genotypes to populations by hierarchical clustering (HierCC), which supports the identification of close relatives at the global level [22]. Originally, EnteroBase was restricted to the bacterial genera Salmonella, Escherichia, Yersinia and Moraxella but since January 2018, EnteroBase has included a database for genomes and their metadata for the genus Clostridioides. In June 2020, EnteroBase contained 18 254 draft genomes of C. difficile plus one genome of C. mangenotii. These included over 900 unpublished draft genomes that were sequenced at the Leibniz Institute DSMZ, as well as 80 complete genome sequences based on Pacific Biosciences plus Illumina sequencing technologies. It also included 862 unpublished draft genomes that were sequenced at the Wellcome Sanger Institute.

Here we show that comparable levels of resolution and precision are attained by EnteroBase cgMLST as by SNP analyses. We also summarize the genomic diversity that accumulated during recurring infections within single patients as well as transmission chains within individual hospitals and between neighbouring hospitals in Germany, and show that it can be detected by HierCC. We also demonstrate that HierCC can be used to identify bacterial populations at various epidemiological levels ranging from recent transmission chains through to epidemic and endemic spread, and relate these HierCC clusters to genotypes that were identified by PCR ribotyping and k-mer-based diversity analysis. These observations indicate that cgMLST and HierCC within EnteroBase can provide a common language for communications and interactions by the global community who is combatting disease caused by C. difficile.Results

Implementation of MLST schemes in EnteroBase

cgMLST in EnteroBase consists of a defined subset of genes within a whole-genome MLST scheme that represents all single-copy orthologues within the pan-genome of a representative set of bacterial isolates. To this end, we assembled the draft genomes of 5232 isolates of C. difficile from public short-read archives, and assigned them to ribosomal sequence types (rSTs) according to rMLST, which indexes diversity at 53 loci encoding ribosomal protein subunits on the basis of existing exemplar alleles at PubMLST [24]. We then created a reference set of 442 genomes consisting of one genome of C. mangenotii [1], 18 complete genomes from GenBank, 81 closed genomes from our work and the draft genome with the smallest number of contigs from each of the 343 rSTs ( The Clostridioides pan-genome was calculated with PEPPA [25] and used to define a wgMLST scheme consisting of 13 763 genetic loci ( EnteroBase uses the wgMLST scheme to call loci and alleles from each assembly and extracts the allelic assignments for the subsets corresponding to cgMLST, rMLST and seven-gene MLST from those allelic calls [22]. The cgMLST subset consists of 2556 core genes, which were present in ≥98% of the reference set, intact in ≥94%, and were not excessively divergent (Fig. 1).Fig. 1.Criteria for inclusion in a cgMLST scheme of a subset of wgMLST genes based on their properties in a reference set of 442 genomes ( (a) Numbers of genes versus frequency (% presence) within the reference set. In total, 2634 genes satisfied the cut-off criterion of ≥98 % presence (dashed line). (b) Numbers of genes versus intact ORF (% intact ORF) within the 2634 genes from (a). Overall, 2560 genes satisfied the cut-off criterion of ≥94 % intact ORF (dashed line). (c) Frequency of allelic variants versus gene size among the 2560 genes from (b). The genetic diversity was calculated using the GaussianProcessRegressor function in the sklearn module in Python. This function calculates the Gaussian process regression of the frequency of genetic variants on gene sizes, using a linear combination of a radial basis function kernel (RBF) and a white kernel [57]. The shadowed region shows a single-tailed 99.9% confidence interval (≤3 sigma) of the prediction. Altogether, 2556 loci fell within this area and were retained for the cgMLST scheme, while four were excluded due to excessive numbers of alleles.Click to view

Comparison of cgMLST and SNPs for analyses of transmission chains

We compared the numbers of cgMLST allelic differences and the numbers of non-recombinant SNPs in isolates from multiple epidemiological chains. These included 176 isolates from four patients with recurring CDI (C. difficile infection), 63 isolates from four transmission chains in multiple hospitals [14, 19, 26], and a comprehensive sample of 1158 isolates collected over several years in four hospitals in Oxfordshire, UK [13]. A strong linear relationship (R2, 0.71–0.93) was found in all three analyses between the pairwise differences in cgMLST alleles and non-recombinant SNPs (Fig. S1, available in the online version of this article). The slope of the regression lines was close to 1.0, indicating a 1 : 1 increase in cgMLST allelic differences with numbers of SNPs. The same data were also investigated with cgMLST calculated with the commercial program SeqSphere [18], with similar correlation coefficients but a lower slope due to lesser discriminatory power of the SeqSphere cgMLST scheme (lower panels in Fig. S1).

Eyre et al. [13] concluded that direct transmission between two hospital patients can be detected because their bacterial genomes differ by two SNPs or less. Our analysis indicated that these transmission chains in the Oxfordshire dataset would also have been recognized by cgMLST in EnteroBase. Genomes that differed by two cgMLST alleles usually also differed by ≤2 SNPs according to a binary logistic regression model (probability=89%; 95% confidence interval, 88–89%) (Fig. 2). Of 3807 pairs of genomes with ≤2 allelic differences, 3474 also differed by ≤2 SNPs, yielding a positive predictive value of 91 % for identifying isolate pairs with ≤2 SNPs by EnteroBase cgMLST and a sensitivity of 62 % (≤2 cgMLST allelic differences were found in 3474 of 5707 pairs with ≤2 SNPs). The comparable values for SeqSphere were 78 % positive predictive value and 99% sensitivity.Fig. 2.Binary logistic regression model to determine the probability that two genomes are related at ≤2 SNPs, given a certain difference in their cgMLST allelic profiles, based on the Oxfordshire dataset [13]. The number of SNPs was encoded as a binary dependent variable (1 if ≤2 SNPs, 0 if otherwise) and the number of allelic differences was used as a predictor variable.Click to view

We also compared the genetic distances between 242 genomes from Oxfordshire, which had been isolated during the initial 6 months and 916 genomes from the actual testing period (April 2008 to March 2011) [13]. Overall, 35% (318/916) of the latter genomes matched at least one genome collected earlier by two or less EnteroBase cgMLST alleles and 34% (316/916) matched an earlier genome by ≤2 SNPs. The two sets of genomes were 89% concordant. Thus, cgMLST is equivalent to SNP analysis for detecting inter-patient transmission chains.

Hierarchical clustering for tracing local and regional spread

SNP analyses are computer intensive, and are only feasible with limited numbers of genomes [27]. cgMLST-based relationships can be analysed for up to 100 000 genomes with GrapeTree, but analyses involving more than 10 000 genomes remain computer intensive [23]. EnteroBase implements single-linkage hierarchical clustering (HierCC V1) of cgMLST data in pairwise comparisons at multiple levels of relationship after excluding missing data [22]. These are designated as HC0 for hierarchical clusters of indistinguishable core-genome sequence types (cgSTs), HC2 for clusters with pairwise distances of up to two cgMLST alleles, etc. EnteroBase presents cluster assignments for C. difficile at the levels of HC0, HC2, HC5, HC10, HC20, HC50, HC100, HC150, HC200, HC500, HC950, HC200 and HC2500. Here we address the nature of the genetic relationships that are associated with these multiple levels of HierCC among 13 515 publicly available C. difficile genomes, and examine which levels of pairwise allelic distances correspond to epidemic outbreaks and to endemic populations.

In our analyses of 176 C. difficile isolates from four patients with two recurrent episodes of CDI, multiple genomes were assigned to patient-specific HC2 clusters, some of which were isolated from the initial episode as well as the recurrence 80–153 days later (Fig. 3, patients D, F and G; 4 to 36 isolates had been collected per episode; Table S1). For these patients, relapsing disease likely reflected continued colonization after initially successful therapy. However, some isolates from patient F differed by 12–21 cgMLST alleles from the bulk population (Fig. 3), which indicates that the patient was co-infected simultaneously with multiple related strains. In patient E, the two genomes from the two CDI episodes differed by >2000 allelic differences (Fig. 3), which indicates that the second incident of CDI represented an independent infection with an unrelated strain. Hence, discrimination between relapse and reinfection based on cgMLST appears to be straightforward except that two episodes of CDI might arise by reinfection with identical strains from an environment that is heavily contaminated with C. difficile spores [28]. We note that the time intervals (16–22 weeks) investigated here exceeded the currently recommended threshold of 8 weeks for surveillance-based detection of CDI relapses [29, 30] but still yielded almost identical strains in three of four patients.Fig. 3.Minimum-spanning trees indicating the population structure of C. difficile in four patients with recurrent CDI episodes. Red, first episode; blue, second episode.Click to view

Our examinations of multiple local outbreaks have revealed individual, outbreak-specific HC2 clusters. However, it is also conceivable that multiple HC2 clusters might be isolated from a single epidemiological outbreak due to the accumulation of genetic diversity over time. Alternatively, multiple HC2 clusters within a single outbreak may represent the absence of crucial links due to incomplete sampling. Incomplete sampling of outbreaks is not unlikely because asymptomatic patients are only rarely examined for colonization with C. difficile [31–33] even though they may constitute an important reservoir for transmission. Indeed, some of the outbreaks investigated here did consist of more than one HC2 cluster (Fig. 4). For example, nine isolates from a recently reported ribotype 018 (RT018) outbreak in Germany [26] encompassed four related HC2 clusters, and outbreaks with RT027 and RT106 in a hospital in Spain [14] were each affiliated with two or three HC2 clusters (Fig. 4).Fig. 4.Neighbour-joining trees based on cgMLST showing the phylogenetic relationships among C. difficile isolates from previously published CDI outbreaks as indicated [14, 19, 26]. Nodes are coloured by HC2. CC, cgST complex, i.e. related at level HC150; RT, PCR ribotype. The scale, indicating one allelic difference, applies to all trees.Click to view

We identified 23 HC2 clusters encompassing 133 genome sequences in a dataset of 309 C. difficile genome sequences collected from CDI patients in six neighbouring hospitals in Germany. These HC2 clusters were associated with individual hospitals (Χ2P=8.6×10−5; Shannon entropy, P=4.2×10−5) and even with single wards in these hospitals (Χ2P=0.01; Shannon entropy, P=6.2×10−3). We investigated whether these HC2 clusters reflected the local spread of C. difficile within institutions by retrospective analyses of patient location data. Sixty-six patients (50 %) were found to have had ward contacts with another patient with the same HC2 cluster (median time interval between ward occupancy: 63 days; range, 0 to 521). These results are consistent with the direct transmission on wards of C. difficile isolates of the same HC2 cluster (Fig. 5). For patients such as P1 and P2 where the shared ward contacts were separated in time (Fig. 5), transmission may have occurred indirectly through asymptomatically colonized patients or from a common reservoir, such as environmental spore contamination [14, 31, 32]. We also detected 15 HC2 clusters that included isolates from two or more hospitals in the region. Subsequent analyses of patient location data confirmed that some of these HC2 clusters were associated with patient transferrals between the hospitals (Fig. 5). Hence, hierarchical clustering of C. difficile genome sequences in conjunction with retrospective analysis of patient movements revealed multiple likely nosocomial transmission events, none of which had been detected previously by routine surveillance.Fig. 5. Timelines of two transmission chains discovered retrospectively through inspection of files from CDI patients with closely related C. difficile isolates (HC2). Colours indicate hospital wards, ‘X’ indicates a diagnosis of CDI, and arrows indicate presumed transmission pathways. Minimum-spanning trees indicating genomic distances among C. difficile isolates are shown on the right. Upper panel: patient P1 was diagnosed with CDI in hospital H2 and transferred to hospital H3 15 days later. Another five and 6 days later, respectively, patients P2 in hospital H2 and P3 in hospital H3 got diagnosed with CDI with closely related strains. Both these patients were on the same wards as the initial patient, who probably had been the source for the pathogen. Since there was no temporal overlap between patient P2 and the other patients in hospital H2, the transmission may have occurred indirectly, possibly through environmental contamination. Lower panel: another putative transmission chain involved three patients that had shared time in hospital H2. Patients P4 and P5 got diagnosed with CDI on the same day after they had shared 7 days in this hospital, albeit on different medical wards. The third patient developed CDI with the same C. difficile cgST 4 days after being transferred to another hospital (h5), but had previously stayed at hospital H2 during the time when CDI got diagnosed in the first two patients. Since the three patients stayed on different wards in hospital H2, transmission presumably occurred indirectly.Click to view

Hierarchical clustering for identification of epidemic strains and endemic populations

The international epidemic spread of C. difficile over up to 25 years has been inferred previously on the basis of molecular epidemiology with lower resolution techniques [34]. For multiple representatives of those epidemic strains in EnteroBase, the majority of these epidemic groups corresponded to HC10 clusters, including epidemic RT017 [11] (HC10_17), the two fluoroquinolone-resistant lineages of RT027 [9] (HC10_4, HC10_9), or livestock-associated RT078/126 [35] (HC10_1) (Fig. 6).Fig. 6.Phylogenetic structure of three international C. difficile epidemics, each of which has spread for about 25 years [9, 11]. Within each epidemic, the majority of isolates are related at level HC10, as indicated by the colours. CC, cgST complex, i.e. related at level HC150; RT, PCR ribotype.Click to view

Endemic populations have also been described by ribotyping and phylogenetic analyses, some of which have acted as sources for the emergence of epidemic strains [2, 9]. Many endemic populations seem to be represented by HC150 clusters. Clustering at HC150 was well supported statistically (Fig. S2), and the frequency distribution of pairwise genomic distances indicated that multiple database entries clustered at <150 cgMLST allelic differences (Fig. S3). HC150 clusters also correlated well with k-mer-based classification [36]. When applied to the dataset of 309 C. difficile genomes from six hospitals in Germany, the two methods implemented in EnteroBase and PopPUNK found 51 and 48 clusters, respectively, the majority of which coincided (adjusted Rand coefficient, 0.97).

A cgMLST-based phylogenetic tree of 13515 C. difficile genomes showed 201 well-separated HC150 clusters, each encompassing a set of related isolates, plus 209 singletons (Fig. 7). Because these HC150 clusters are based on cgMLST genetic distances, we refer to them as ‘cgST complexes’, abbreviated as CCs. Genomes from each of the major CCs have been collected over many years in multiple countries, indicating their long-term persistence over wide geographic ranges (Table 1).Fig. 7.Rapid-neighbour-joining phylogenetic tree based on cgMLST variation from 13 515 C. difficile genomes. Colours and numerals indicate CCs (HC150 clusters) with ≥10 entries, and information on predominant PCR ribotypes is provided in brackets.Click to view

Table 1.

Characteristics of cgST complexes (CC) with ≥100 entriesToggle display:Table 1.  Open Table 1. fullscreen 

CC (HC150)PCR RibotypeNumber of entriesSampling yearsNumber of countries% isolates in HC2>21% isolates from animal hosts
1078, 126, 06612221994–2018266117
6020, 4047681995–201714431
22106, 5005311997–20177593
71014, 0203152004–201716401
178018, 3562432006–20177520
141001, 0261072007–2016270
49011, 056, 4461032001–20175350
1isolates in HC2 clusters with >2 entries.

We compared HC150 clustering with PCR ribotyping for 2263 genomes spanning 84 PCR ribotypes for which PCR ribotyping data were available in EnteroBase. These included 905 genomes, which we ribotyped (Table S2), as well as several hundred other genomes for which ribotype information was manually retrieved from published data. The correlation between HC150 clustering and ribotyping was high (adjusted Rand coefficient, 0.92; 95% confidence interval, 0.90–0.93). However, our analysis also revealed that PCR ribotypes did not always correspond to phylogenetically coherent groupings. PCR ribotypes 002, 015 and 018 were each distributed across multiple phylogenetic branches (Fig. 8). Furthermore, some genomes with indistinguishable cgMLST alleles were assigned to multiple ribotypes, including RT001/RT241, RT106/RT500 and RT126/RT078 (Fig. 8Table 1). In these cases, both ribotypes occurred in several, closely related clades (Fig. 8), indicating that similar ribotype banding patterns had evolved multiple times. In contrast, HC150 clusters corresponded to clear-cut phylogenetic groupings within a phylogenetic tree of core genes (Fig. 8b).Fig. 8.Rapid-neighbour-joining phylogenetic tree based on cgMLST variation from 2263 C. difficile genomes, for which PCR ribotyping information is available. Upper panel: nodes are coloured by PCR ribotype as indicated. Lower panel: nodes are coloured by CC (HC150 clusters).Click to view

Higher population levels

HierCC can also identify clusters at still higher taxonomic levels, up to the levels of species and sub-species [22]. In C. difficile, HC950 clusters seem to correspond to deep evolutionary branches (Fig. S4) and HC2000 clusters were congruent with the major clades reported previously [37], except that cluster HC2000_2 encompassed clade 1 plus clade 2 (Fig. S5). Finally, HC2500 may correspond to the subspecies level, because it distinguished between C. difficile and distantly related ‘cryptic clades’ (Fig. S6).Discussion

Infectious disease epidemiologists frequently seek to know if new isolates of bacterial pathogens are closely related to others from the different geographical origin, i.e. if they are part of a widespread outbreak. Unlike a previous cgMLST implementation [18], EnteroBase supports this goal by taking full advantage of rapidly growing, public repositories of short-read genome sequences [22]. In contrast to short-read archives, however, where stored sequence data are not readily interpretable without specialized bioinformatic tools [38], EnteroBase enables contextual interpretation of a growing collection (18 254 entries as of June 2020) of assembled, quality-controlled C. difficile genome sequences and their associated metadata. At least the collection date (year), the geographic origin (country), and the source (host species) are available for the majority of database entries. Importantly, phylogenetic trees based on cgMLST allelic profiles from many thousand bacterial genomes can be reconstructed within a few minutes, whereas such calculations are currently prohibitively slow based on SNP alignments [22]. Genome-sequencing reads from newly sampled C. difficile isolates can be uploaded to EnteroBase and compared to all publicly available genome data within hours, without requiring any command-line skills.

We demonstrate that the application of cgMLST to investigations of local C. difficile epidemiology yields results that are quantitatively equivalent to those from SNP analyses. This is a major advance because SNP analyses require specific bioinformatic skills and infrastructure, are time-consuming and not easily standardized [16]. A web platform for centralized, automated SNP analyses on bacterial genomes is limited to food pathogens currently and does not offer any analyses on C. difficile genomes [39]. Even though a cgMLST scheme for C. difficile had been published recently [18], its ability to identify closely related isolates and the inferred genomic distances was shown to be inferior to SNP analyses due to an excess of errors introduced by the de novo assembly of sequencing reads and a lack of per-base quality control [20]. In EnteroBase, cgMLST is also based on de novo assembly, but EnteroBase uses Pilon [40] to polish the assembled scaffolds and evaluate the reliability of consensus bases of the scaffolds, thereby achieving comparable accuracy to mapping-based SNP analyses. When applied to a large dataset of C. difficile genomes from hospital patients in the Oxfordshire region (UK), cgMLST and SNP analysis were largely consistent (89% match) at discriminating between isolates that were sufficiently closely related to have arisen during transmissions chains from others that were epidemiologically unrelated.

After assembly, draft genomes contain missing data and many cgSTs have unique cgST numbers but are identical to other cgSTs, except for missing data. Hence, individual cgST numbers are only rarely informative. However, indistinguishable cgSTs are clustered in common HierCC HC0 clusters, which ignore missing data. In June 2020, the Clostridioides database contained >12 000 HC0 clusters, indicating that the majority of genomes was unique. Similarly, EnteroBase provides cluster designations at multiple levels of HierCC, enabling rapid identification of all cgSTs that are related at multiple levels of genetic distance. The data presented here shows that HierCC designations can facilitate communications between researchers, clinicians and public-health officials about transmission chains, epidemic outbreaks, endemic populations and higher phylogenetic lineages up to the level of subspecies.

EnteroBase cgMLST identified numerous HC2 clusters of strains in C. difficile isolates that seem to have arisen during transmission chains in six neighboring hospitals in Germany. These assignments were in part consistent with retrospective investigation of patient location data, although none of the nosocomial outbreaks (defined by German law as two or more infections with likely epidemiological connections []) had been detected previously by standard epidemiological surveillance by skilled clinical microbiologists. Recent publications propose that prospective genome sequencing of nosocomial pathogens should be applied routinely at the hospital level to guide epidemiological surveillance [41]. Our data indicates that the combination of genome sequencing with cgMLST and HierCC may identify nosocomial transmission routes of C. difficile more effectively than presently common practice, and hence could help to reduce pathogen spread and the burden of disease. Reliable identification of transmission chains requires interpretation of pathogen genome sequence data in its epidemiological context, however [42].

HierCC will also enable comparisons to previously published data because we have provided a correspondence table between HC150 clusters and PCR ribotypes (Table 1). Rarefaction analysis indicated that the currently available genome sequences represent about two-thirds of extant HC150 (CC) diversity, which extrapolated to about 600 CCs (Fig. S7). At least some of this enormous diversity may be due to the occupation of multiple, distinct ecological niches, as exemplified by differential propensities for colonizing non-human host species (Table 1) [43, 44]. Individual CCs may also differ in their aptitudes for epidemic spread, as indicated by drastically different proportions of genomes assigned to HC2 chains: only 7% of CC141 were assigned to HC2 clusters versus 35% of CC34 and 77% of CC4 (Table 1). A full understanding of the population structure of C. difficile and its relationship to epidemiological patterns will require additional study because many of the clusters described here have not yet been studied or described. However, this task can be addressed by the global community due to the free public access to such an unprecedented amount of genomic data from this important pathogen.Methods


In total, 309 C. difficile isolates were collected at a diagnostic laboratory providing clinical microbiology services to several hospitals in central Germany. To assemble a representative sample, we included the first 20 isolates from each of six hospitals from each of three consecutive calendar years (Table S2). For the investigation of recurrent CDI, a set of 176 C. difficile isolates were collected in a diagnostic laboratory in Saarland, Germany. Here, primary stool culture agar plates were stored at 4 °C for 5 months to eventually enable the analysis of multiple plates representing episodes of recurrent C. difficile infection from individual patients, who had developed the recurrent disease by then and could be chosen with hindsight. It was attempted to pick and cultivate as many bacterial colonies from each selected plate as possible, resulting in 6 to 36 isolates per CDI episode (Table S1). In addition, we sequenced the genomes from 383 isolates that had been characterized by PCR ribotyping previously, including 184 isolates sampled from piglets [8], 71 isolates from various hospitals in Germany [3], and 108 isolates from stool samples collected from nursing home residents (unpublished; Table S2).

PCR ribotyping

PCR ribotyping was performed as described previously [45], applying an ABI Prism 3100 apparatus for capillary electrophoresis and comparing banding patterns to the Webribo database ( sequencing

For Illumina sequencing, genomic DNA was extracted from bacterial isolates by using the DNeasy Blood and Tissue kit (Qiagen), and libraries were prepared as described previously [46] and sequenced on an Illumina NextSeq 500 machine using a Mid-Output kit (Illumina) with 300 cycles. For generating complete genome sequences, we applied SMRT long-read sequencing on an RSII instrument (Pacific Biosciences) in combination with Illumina sequencing as reported previously [46]. All genome sequencing data were submitted to the European Nucleotide Archive ( under study numbers PRJEB33768, PRJEB33779 and PRJEB33780

.SNP detection and phylogenetic analysis

Sequencing reads were mapped to the reference genome sequence from C. difficile strain R20291 (sequence accession number FN545816) by using BWA-MEM and sequence variation was detected by applying VarScan2 as reported previously [46]. Sequence variation likely generated by recombination was detected through analysis with ClonalFrameML [47] and removed prior to determination of pairwise sequence distances [15] and to construction of maximum-likelihood phylogenetic trees with RAxML (version 8.2.9) [48].Genome assembly, quality control and wgMLST allele calling

Genomic data was processed by automated pipelines within EnteroBase, which were described in detail previously [22]. Briefly, Illumina sequencing reads were assembled by using Spades v3.10 [49] and assemblies were improved by applying Pilon [40]. To pass quality control, assemblies were required to comply with the following thresholds: total length, 3.6 to 4.8 Mbp; N50, ≥20 000; the number of contigs, ≤600; number of unresolved nucleotides, ≤3%; the proportion of Clostridioides sequences, >65 % (as determined by Kraken with MiniKraken database [50]). Assemblies were aligned to exemplar alleles by using blastn [51] and the usearch module UblastP [52], and allele numbers, STs, and HC numbers assigned by using the EnteroBase module MLSType [22]. All EnteroBase tools are available at

To determine the probability that two genomes are related at ≤2 SNPs, given a certain difference in their cgMLST allelic profiles, we inferred a logistic regression model using R ([53], pp. 593–609). Genomic relatedness was encoded as a binary response variable (1 if ≤2 SNPs, 0 if otherwise) and the number of core-genome allelic differences was used as a predictor variable. We applied this model to a dataset of 1158 genome sequences from a previous study, representing almost all symptomatic CDI patients in Oxfordshire, UK, from 2007 through 2011 [13]. While that original study had encompassed a slightly larger number of sequences, we restricted our analysis to the data (95 %) that had passed quality control as implemented in EnteroBase [21]. We used the SNP data from Eyre’s report [13].

The hierarchical single-linkage clustering of cgMLST sequence types was carried out as described [22] for all levels of allelic distances between 0 and 2556. We searched for stable levels of differentiation by HierCC according to the Silhouette index [54], a measure of uniformity of the divergence within clusters. The Silhouette index was calculated based on d^’, a normalized genetic distance between pairs of STs, which was calculated from their allelic distance d as follows: d^’=1-(1-d)^(1/l), where l is the average length (937 bp) of the genes in the cgMLST scheme.

We further evaluated the ‘stability’ of hierarchical clustering using two other criteria. The Shannon index is a measure of diversity in a given population. The Shannon index drops from nearly 1 in HC0, because most cgSTs are assigned to a unique HC0 cluster, to 0 in HC2500, which assigns all sequence types to one cluster. The gradient of the Shannon index between the two extremes reflects the frequencies of coalescence of multiple clusters at a lower HC level. Thus, the plateaus in the curve correspond to stable hierarchical levels, where the Shannon index does not change dramatically with HC level. We also evaluated the stability of hierarchical clustering by pairwise comparison of the results from different levels based on the normalized mutual information score [55] (Fig. S3).

For clustering C. difficile diversity with PopPUNK [36], we used a sketch size of 105 and a K value (maximum number of mixture components) of 15. Of note, the resulting number of clusters for the tested dataset was identical for all K between 15 and 30.

To estimate concordance between cgMLST-based hierarchical clustering and PCR ribotyping or PopPUNK clustering, respectively, we calculated the adjusted Rand coefficient [56] by using the online tool available at To test statistical associations of HC2 clusters with specific hospitals and hospital wards, respectively, we compared Χ2 values and normalized Shannon entropy values (R package ‘entropy’ v.1.2.1) from contingency tables containing real isolate distributions (Table S3) and randomly permuted distributions (n=1000), by using the non-parametric, two-sided Mann–Whitney U test (R package ‘stats’ v.3.5.0).

This work was partially funded by the German Center for Infection Research (DZIF), by the Federal State of Lower Saxony (Niedersächsisches Vorab VWZN2889/3215/3266), by the EU Horizon 2020 programme (grant agreement number 643476), the Wellcome Trust (098051), and the UK Medical Research Council (PF451). EnteroBase development was funded by the BBSRC (BB/L020319/1) and the Wellcome Trust (202792/Z/16/Z), and the salary of Z.Z. was also provided by The Wellcome Trust. The funders had no role in the study design, preparation of the article, or decision to publish.


We thank Vera Junker, Simone Severitt, Nicole Heyer and Carola Berg for excellent technical assistance, Johannes Sikorski for help with R, and David Eyre for supplying SNP data from his 2013 paper in tabular format.Author contributions

M.A. and U.N. designed the study. M.F., Z.Z., M.S., J.P.M., M.G., T.R., B.B., C.S., J.O., M.B., A.I., L.v.M., F.K., S.G.F., O.Z., U.G., M.A., and U.N. analyzed the data. L.v.M., C.S., O.Z., U.G., R.C., R.d.C., N.K., T.D.L., T.A.K. and S.N. acquired bacterial isolates and sequence data. M.F., Z.Z., M.A., and U.N. wrote the manuscript and all authors reviewed and edited the manuscript and approved the final version.

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Seres Therapeutics SER-109 Met Phase 3 Primary Endpoint, Positive Results From Pivotal Phase 3 ECOSPOR III Study Evaluating Investigational Oral Microbiome Therapeutic For Recurrent C. difficile Infection

– SER-109 met Phase 3 primary endpoint, showing a highly statistically significant 30.2% absolute reduction in the rate of C. difficile infection recurrence compared to placebo 

– SER-109 was well tolerated, with a safety profile comparable to placebo 

– Efficacy results substantially exceeded FDA regulatory guidance to support BLA filing as a single pivotal trial; Company to meet with the agency to discuss filing for product approval as soon as possible 

 Positive SER-109 Phase 3 data provide validation for Seres’ microbiome therapeutics platform and further development of its pipeline of product candidates 

 Seres Therapeutics, Inc. reported on August 10, 2020, positive topline results from the pivotal Phase 3 ECOSPOR III study evaluating its investigational oral microbiome therapeutic SER-109 for recurrent C. difficile infection (CDI). The study showed that SER-109 administration resulted in a highly statistically significant absolute decrease of 30.2% in the proportion of patients who experienced a recurrence in CDI within eight weeks of administration versus placebo, the study’s primary endpoint. 11.1% of patients administered SER-109 experienced a CDI recurrence, versus 41.3% of placebo patients. The study results were equally compelling when characterized by the alternative metric of sustained clinical response, where 88.9% of patients in the SER-109 arm achieved this objective.

The study’s efficacy results exceeded the statistical threshold previously provided in consultation with the U.S. Food and Drug Administration (FDA) that could allow this single clinical study to fulfill efficacy requirements for a Biologics License Application (BLA). The SER-109 safety results were favorable, with an adverse event profile comparable to placebo.

“We are extremely pleased with these highly clinically meaningful SER-109 Phase 3 study results, greatly exceeding the statistical threshold provided by the FDA. Based on our prior discussions with the FDA, we believe this trial should provide the efficacy basis for submitting an application for product approval. We look forward to meeting with the FDA as soon as possible to discuss the regulatory path forward with the goal of bringing SER-109 to patients as a first-in-class microbiome therapeutic,” said Eric D. Shaff, President and Chief Executive Officer of Seres. “Our results represent the first-ever positive pivotal clinical study results for a targeted microbiome drug candidate. We believe these Phase 3 data provide strong validation for our underlying microbiome therapeutics platform, which has been the scientific basis for the Company, as well as persuasive clinical evidence supporting our other active pipeline programs.”

“We would like to thank all those who participated in this landmark study. Based on these highly positive SER-109 ECOSPOR III results, we believe that this novel microbiome therapeutic candidate could potentially provide a much-needed effective oral treatment option for the approximately 170,000 patients in the U.S. that suffer from recurrent CDI annually,” said Lisa von Moltke, M.D., FCP, Chief Medical Officer of Seres. “Seres applied a data-driven and scientifically rigorous approach to develop SER-109. The proprietary scientific learnings we have obtained continue to drive our overall R&D efforts and the advancement of our other ongoing microbiome therapeutic programs.”

“Recurrent C. difficile infection is a serious disease that devastates patients’ quality of life, and in many severe cases may result in a patient’s death. Today’s treatment options have important shortcomings related to efficacy, safety and route of administration, and novel approaches that target the root causes of the disease are urgently needed. The SER-109 Phase 3 results are highly impressive and represent an exceptional advance in the fight against this disease. I believe that SER-109 has the potential to fundamentally transform the treatment of recurrent C. difficile infection,” said Mark Wilcox, M.D., Professor of Medical Microbiology, University of Leeds.

ECOSPOR III Study Design and Results

The ECOSPOR III study ( identifier: NCT03183128) is a multicenter, randomized, placebo-controlled study that enrolled 182 patients with multiply recurrent CDI. Patients were randomized 1:1 to receive either SER-109 or placebo, after standard of care antibiotic treatment. SER-109, or placebo, was administered orally for three consecutive days. All patients were required to have a positive C. difficile toxin diagnostic test both at study entry and in the case of suspected recurrence to ensure the selection of individuals with active disease and to confirm the accuracy of the primary endpoint.

The primary efficacy endpoint of ECOSPOR III was the proportion of patients with recurrent CDI at up to eight weeks following administration of SER-109 or placebo. As a secondary endpoint, patients are evaluated for CDI recurrence through 24 weeks post-treatment, and the Company plans to present those results at a future date.

SER-109 met the study’s primary endpoint with a significantly lower recurrence rate of 11.1% in SER-109 patients versus 41.3% in placebo patients at eight weeks; p<0.001 tested at the one-sided 0.25 level. Patients administered SER-109 experienced a 30.2% lower rate of recurrence, on an absolute basis, compared to placebo. The SER-109 treatment arm relative risk was 0.27 (95% CI=0.15 to 0.51) versus placebo. The ECOSPOR III recurrence rates translate into a sustained clinical response rate of 88.9% versus 58.7% with SER-109 and placebo, respectively. The SER-109 Number Needed to Treat (NNT) was approximately 3.

In prior discussions, the FDA communicated that demonstration of a statistically very persuasive efficacy finding in the ECOSPOR III primary endpoint, defined as demonstrating a 95% upper confidence level of relative risk lower than 0.833, could support a BLA submission on the basis of this single study. The results of ECOSPOR III demonstrated a SER-109 relative risk of 0.27 (95% CI=0.15 to 0.51) compared to placebo. As a result, Seres believes that this study should support the efficacy basis for BLA submission. SER-109 has obtained FDA Breakthrough Therapy and Orphan Drug designations.

SER-109 was well tolerated, with no treatment-related serious adverse events (SAEs) observed in the active arm, and an adverse event profile similar to placebo. The overall incidence of patients who experienced AEs during the eight-week study period was similar between SER-109 and placebo arms. The most commonly observed treatment-related AEs were flatulence, abdominal distention and abdominal pain, which were generally mild to moderate in nature, and these were observed at a similar rate in both the SER-109 and placebo arms.

A SER-109 open-label study is ongoing ( identifier: NCT03183141) at selected clinical sites that participated in the ECOSPOR III study, and the Company may initiate the program at additional clinical sites. The FDA has previously indicated that SER-109 administration to at least 300 patients, consistent with standard FDA guidance, would be required to support BLA submission. The ongoing SER-109 open-label study is continuing to contribute to the SER-109 safety database.

The Company plans to immediately request a Breakthrough Therapy designation meeting with the FDA to discuss the requirements to submit a BLA seeking regulatory approval of SER-109. Given the favorable efficacy and safety results seen in ECOSPOR III, the safety results observed in prior SER-109 clinical studies, and the critical unmet need for a therapeutic option for recurrent CDI patients, the Company plans to discuss with the FDA the safety data requirements for a BLA filing.

Seres continues to advance its commercial readiness for the potential launch of SER-109. In June 2020, Seres appointed Terri Young, Ph.D., R.Ph., as Chief Commercial and Strategy Officer. The Company has been conducting activities to support successful future potential commercialization. Seres believes that the commercial opportunity for SER-109 could be substantial, given the dire need for an effective, safe, oral therapeutic, and the strength of the SER-109 Phase 3 study results.

Conference Call Information

Seres’ management will host a conference call today, August 10, 2020, at 8:30 a.m. ET. To access the conference call, please dial 844-277-9450 (domestic) or 336-525-7139 (international) and reference the conference ID number 3216859. Accompanying slides will be posted on the Seres website ahead of the conference call. To join the live webcast, and to view the accompanying slides, please visit the “Investors and Media” section of the Seres website at

A webcast replay will be available on the Seres website beginning approximately two hours after the event and will be archived for approximately 21 days.

About SER-109

SER-109 is an investigational, oral, biologically-derived microbiome therapeutic that is designed to reduce recurrence of C. difficile infection (CDI), enabling patients to achieve a sustained clinical response by breaking the vicious cycle of CDI recurrence and restoring the diversity of the gastrointestinal microbiome. SER-109 is a consortium of purified bacterial spores of multiple Firmicute species, manufactured by fractionating targeted bacteria from the stool of healthy human donors with further steps to inactivate potential pathogens. The FDA has granted SER-109 Breakthrough Therapy designation and Orphan Drug designation for the treatment of CDI.

SER-109 is fundamentally distinct from fecal microbiota transplantation (FMT). SER-109 is comprised of a highly-purified consortia of spore-based commensal bacteria and designed to be manufactured in accordance with Good Manufacturing Practice conditions using stringent standards to ensure product quality and consistency. To support product safety, Seres utilizes a unique manufacturing process that inactivates numerous potential pathogens, including species of non-spore bacteria, such as Escherichia coli, and viruses such as SARS-CoV-2.

About C. difficile Infection (CDI) and Current Treatments

C. difficile infection (CDI) is one of the top three most urgent antibiotic-resistant bacterial threats in the U.S., according to the Centers for Disease Control, and is a leading cause of hospital-acquired infection in the U.S. It is responsible for the deaths of approximately 20,000 Americans each year. CDI is associated with debilitating diarrhea, which significantly impacts quality of life in every functional domain. Since the discovery of C. difficile more than four decades ago, vancomycin has been the most commonly used drug for patient management. Current approaches provide only modest improvements in sustained clinical response rates, leaving behind a significant pool of patients with recurrent disease. Unapproved FMT, used in cases that are not responsive to approved drugs, remains poorly characterized clinically and has been associated with serious safety concerns, including the transmission of bacterial pathogens and the potential transmission of viruses such as SARS-CoV-2, the virus that causes COVID-19. The recent quarantine and shipping hold of FMT from a major stool bank highlights the urgent need for an approved effective and safe treatment for recurrent CDI.

About Seres Therapeutics

Seres Therapeutics, Inc., (Nasdaq: MCRB) is a leading microbiome therapeutics platform company developing a novel class of multifunctional bacterial consortia that are designed to functionally interact with host cells and tissues to treat disease. Seres’ SER-109 program achieved the first-ever positive pivotal clinical results for a targeted microbiome drug candidate and has obtained Breakthrough Therapy and Orphan Drug designations from the FDA. The SER-109 program is being advanced for the treatment of recurrent C. difficile infection and has the potential to become a first-in-class FDA-approved microbiome therapeutic. Seres’ SER-287 program has obtained Fast Track and Orphan Drug designations from the FDA and is being evaluated in a Phase 2b study in patients with active mild-to-moderate ulcerative colitis. Seres is developing SER-401 in a Phase 1b study in patients with metastatic melanoma, SER-301 for ulcerative colitis and SER-155 to prevent mortality due to gastrointestinal infections, bacteremia, and graft versus host disease. For more information, please visit

SOURCE: Seres Therapeutics

DEINOVE: DNV3837 Antibiotic Candidate: the Phase II Clinical Trial to Treat CDI Continues in the USA

DEINOVE is a French biotech company that uses its lead generation platform to develop innovative anti-infective drugs, is pursuing the Phase II clinical trial of its antibiotic candidate DNV3837, in a context where U.S. hospitals are still fighting the COVID-19 pandemic. The Company thanks the clinicians for their commitment to this trial, as they face an unprecedented health crisis.

DNV3837 targets the treatment of Clostridioides difficile gastrointestinal infections (CDI), a pathogen classified as urgent threat by the U.S. Centers for Disease Control and Prevention (CDC). A Phase II clinical trial, launched in early 2020 in the United States, is evaluating the efficacy of DNV3837 in patients, following promising Phase I data. To date, DEINOVE is the only French biotech with a small molecule in clinical development, fully owned by the company, in the field of antibiotics.

This trial continues in the United States despite the COVID-19 outbreak. Several of the investigation centers have maintained their clinical research activities and continue to screen and include patients. DEINOVE scientific team and the CRO Medpace are closely monitoring the situation.

« We are grateful to the clinicians for doing their utmost to ensure that the clinical trial runs smoothly. We are surrounded by a team that is aware of the therapeutic stakes and the potential of our solution in development, and we thank them for this. In the current health conditions in the United States, where hospitals are overcrowded, we could have feared a suspension of the trial, » says Dr. Yannick Plétan, Acting Chief Medical Officer responsible for the clinical trial. «Conversely, the COVID-19 outbreak – which mainly affects the elderly – and the heavy antibiotic treatments administered to combat possible bacterial co-infections, are factors conducive to the development of severe Clostridioides difficile infections targeted by DNV3837. We are concerned, however, about the irrational use of antibiotics, which would have long-term public health consequences. »

On June 1st of this year, the WHO warned of the increasing rates of antimicrobial resistance, boosted by the current health crisis. ” The COVID19 pandemic has led to an increased use of antibiotics, which ultimately will lead to higher bacterial resistance rates that will impact the burden of disease and deaths during the pandemic and beyond,”worried Dr Tedros Adhanom Ghebreyesus, WHO Director-General1. According to him, the threat of antimicrobial resistance is “one of the most urgent challenges of our time “. He also recalled that only small proportion of COVID-19 patients need antibiotics to treat subsequent bacterial infections.


40% of patients suffering a Clostridioides difficile infection (CDI) have severe forms, with mortality rates as high as 50%. Over the past 20 years, CDIs tended to increase significantly in incidence and severity, particularly due to the development of new hypervirulent strains and the high risk of recurrence. The US Center for Disease Control and Prevention (CDC) recently identified CDIs as one of the leading causes of healthcare-associated infections before Staphylococcus aureus (MRSA2) infections. In 2017, in the United States, there were an estimated 223,900 cases in hospitalized patients and 12,800 deaths3. This disease does not affect the United States only, recent studies4 show that the incidence of this type of infection is vastly underestimated in other parts of the world such as Europe and Asia.

To date, there are no therapeutic solutions for patients with severe gastrointestinal infections. Since the oral route is compromised, the available treatments, which are mostly oral treatments, struggle to reach the intestine because of the patient’s pathological condition (reduced gastrointestinal motility, intubation, intestinal perforation, etc.), and the few antibiotics that could be administered intravenously (IV), do not cross the gastrointestinal barrier and therefore do not reach the site of infection.


DNV3837 – a prodrug5 of the DNV3681 molecule (also known as MCB3681) – is a narrow-spectrum, hybrid oxazolidinone-quinolone synthetic antibiotic targeting only Gram-positive bacteria. It is developed as a highly active 1st line treatment targeting Clostridioides difficile.

It has demonstrated significant efficacy and superiority to reference treatments (fidaxomicin in particular) against isolates of C. difficile, regardless of their virulence (including the hyper virulent BI/NAP1/027 strain).

DNV3837 is an intravenous antibiotic that, when converted to its active form DNV3681, crosses the gastrointestinal barrier and accumulates in the intestinal lumen, allowing it to precisely target the infection site. Several Phase I trials (on approx. a hundred healthy volunteers) have shown a high concentration of the antibiotic in stools, a strong marker of its presence in the intestine. It has also demonstrated its ability to eliminate Clostridioides bacteria without affecting the gut microbiota. It has also shown an acceptable tolerance profile.

FDA granted the DNV3837 drug with Qualified Infectious Disease Product (QIDP) designation and Fast Track status.


The antibiotic candidate DNV3837 has been in a Phase II trial since the end of January 2020. The purpose of this trial is to evaluate its efficacy in CDI (through monitoring of symptoms, stool analysis, etc.), as well as to consolidate the safety and pharmacokinetic data.

This trial is taking place in the United States in two stages:

  • In the first phase, a cohort of 10 patients with moderate to severe CDI is treated with DNV3837. At the end of this phase, the DSMB6 has scheduled to review the interim results.
  • The second phase involves 30 patients with severe CDI. This is an open-label randomized trial testing DNV3837 (in 2/3 of patients) against an approved standard of care7 (1/3 of patients) for comparison purposes.

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Acurx Pharmaceuticals Phase 2 Clinical Trial of ibezapolstat Is In Progress

Acurx Pharmaceuticals, LLC (“Acurx” or the “Company”), a privately held, clinical stage biopharmaceutical company developing new antibiotics for difficult-to-treat bacterial infections, announced on July 27th, 2020 that a Phase 2 clinical trial of the Company’s lead antibiotic product candidate is in progress. In this trial, orally-administered ibezapolstat given 450 mg twice daily for 10 days will be evaluated for the treatment of patients with CDI. FDA has granted Qualified Infectious Disease Product (QIDP) designation and Fast-Track status to ibezapolstat for patients with CDI.

Up to 6 study centers in the U.S. will participate in the first segment (Segment 2A) of the trial. Additional information about the trial, including eligibility criteria, can be found at (Study identifier: NCT04247542). This Phase 2, multicenter, open-label single-arm segment (Segment 2A) will be followed by a double-blind, randomized, active-controlled segment (Segment 2B), and is designed to evaluate both clinical cure and sustained clinical cure, safety, and pharmacokinetics. All patients in both segments will have stool samples tested for ibezapolstat concentrations and microbiome effects. Pharmacokinetic testing for systemic exposure will be performed on blood samples in Segment 2A. All of the first 6 patients enrolled in the trial have met the study’s primary endpoint, Clinical Cure at end of treatment. All patients who have reached the 30-day follow-up milestone, no recurrence of CDI, have achieved Sustained Clinical Cure, the study’s secondary endpoint. Ibezapolstat has been well-tolerated in all patients to date. After the first 10 patients have completed treatment, the study’s Trial Oversight Committee will assess the ibezapolstat safety profile in relationship to treatment outcomes and will advise the company on any recommended trial modifications which could include early termination of Phase 2A and acceleration of the double-blind Segment 2B.

Robert J. DeLuccia, Co-Founder & Managing Partner of Acurx, stated “With today’s heightened awareness of antimicrobial resistance, even more so in the current Covid-19 environment, and the need for new classes of antibiotics to fight this global crisis, we are very excited to advance ibezapolstat to this stage of clinical development.” He further stated, “This is a significant value-creating development milestone for our Company. We believe this now clinically validated target of inhibition of bacterial DNA pol IIIC will pave the way forward for our pipeline of new oral/I.V. antibiotics in pre-clinical development to treat other Gram-positive life-threatening infections in skin/skin structure, community acquired pneumonia, bone & joint and bacteremia. This will include pathogens resistant to currently available antibiotics, and classified as priority pathogens by the WHO, CDC and FDA, all of whom emphasize the need for new classes of antibiotics to prepare for the next global infectious disease threat.”

Additionally, the U.S. Center for Diseases Control recently issued its 2019 update on antimicrobial resistance and reaffirmed that CDI remains an URGENT threat causing at least 12,800 deaths in 2017, highlighting the need for new antibiotics, particularly those with a novel mechanism of action. It further reported that more than 2.8 million antibiotic-resistant infections occur in the U.S. each year and more than 35,000 people die as a result, nearly twice as many annual deaths than previously reported by CDC in 2013. These deaths are attributed to antimicrobial-resistant pathogens including Enterococcus (including vancomycin-resistant strains or VRE), Staphylococcus (including methicillin-resistant strains or MRSA), and Streptococcus (including antibiotic-resistant strains), which are the targets of Company’s second antibiotic candidate currently in preclinical development.

About the Phase 2 Clinical Trial.  In Segment 2A of this trial, up to 20 subjects with diarrhea caused by C. difficile will be treated with ibezapolstat 450 mg orally for 10 days and evaluated for clinical cure. All cured subjects will be followed for sustained clinical cure at 28 ± 2 days. In Segment 2B, approximately 64 additional subjects with CDI will be enrolled and randomized in a 1:1 ratio to either ibezapolstat 450 mg every 12 hours or vancomycin 125 mg orally every 6 hours for 10 days and followed for 28 ± 2 days for recurrence. The two treatments will be identical in appearance, dosing times, and number of capsules administered to maintain the blind. Subjects in both segments will be evaluated for clinical and sustained clinical cure, safety, and tolerability. All subjects in both segments will have stool samples tested for microbiome profiles.
Additional information about the trial, including eligibility criteria can be found at: (Study identifier: NCT04247542).

About ibezapolstat, FDA QIDP and Fast Track Designation.  In June 2018, FDA granted Qualified Infectious Disease Product (QIDP) designation to ibezapolstat as an oral treatment for patients with CDI. In addition, in January 2019, FDA granted Fast Track designation to ibezapolstat for the oral treatment for patients with CDI. 

FDA Fast Track Designation is a process designed to facilitate the development and expedite the regulatory pathway of new drugs to treat serious or life-threatening conditions and that fill a high unmet medical need. Ibezapolstat is a novel, first-in-class, orally administered antibacterial. It is the first of a novel class of DNA polymerase IIIC inhibitors under development by Acurx to treat bacterial infections. Acurx acquired ibezapolstat from GLSynthesis, Inc. in February 2018.

FDA’s QIDP Designation provides that ibezapolstat will be eligible to benefit from certain incentives for the development of new antibiotics provided under the Generating Antibiotic Incentives Now Act (the GAIN Act). These incentives include Priority Review and eligibility for Fast Track status, the latter of which Acurx has already applied for and been granted by FDA. Further, if ultimately approved by the FDA, ibezapolstat is eligible for an additional five-year extension of Hatch-Waxman marketing exclusivity. Ibezapolstat is being developed as a targeted, narrow spectrum oral antibiotic for the treatment of patients with CDI. Acurx is planning to advance ibezapolstat into a Phase 2 clinical trial in first quarter 2020. The CDC (Centers for Disease Control & Prevention) has designated Clostridium difficile bacteria as an urgent threat highlighting the need for new antibiotics to treat CDI.