Tag Archives: Clostridioides difficile research

Study Hypothesized Commensal Clostridia are Important for Providing Colonization Resistance Against C. difficile Due to Their Ability to Produce Secondary Bile Acids

ABSTRACT

Clostridioides difficile is one of the leading causes of antibiotic-associated diarrhea.

Gut microbiota-derived secondary bile acids and commensal Clostridia that carry the bile acid-inducible (bai) operon are associated with protection from C. difficile infection (CDI), although the mechanism is not known.

In this study, we hypothesized that commensal Clostridia are important for providing colonization resistance against C. difficile due to their ability to produce secondary bile acids, as well as potentially competing against C. difficile for similar nutrients.

To test this hypothesis, we examined the abilities of four commensal Clostridia carrying the bai operon (Clostridium scindens VPI 12708, C. scindens ATCC 35704, Clostridium hiranonis, and Clostridium hylemonae) to convert cholate (CA) to deoxycholate (DCA) in vitro, and we determined whether the amount of DCA produced was sufficient to inhibit the growth of a clinically relevant C. difficile strain.

We also investigated the competitive relationships between these commensals and
C. difficile using an in vitro coculture system.

We found that inhibition of C. difficile growth by commensal Clostridia supplemented with CA was strain dependent, correlated with the production of ∼2 mM  DCA, and increased the expression of bai operon genes.

We also found that C. difficile was able to outcompete all four commensal Clostridia in an in vitro coculture system. These studies are instrumental in understanding the relationship between commensal Clostridia and C. difficile in the gut, which is vital for designing targeted bacterial therapeutics. Future studies dissecting the regulation of the bai operon in vitro and in vivo and how this affects CDI will be important.

IMPORTANCE : Commensal Clostridia carrying the bai operon, such as C. scindens, have been associated with protection against CDI; however, the mechanism for this protection is unknown. Herein, we show four commensal Clostridia that carry the bai operon and affect                                C. difficile growth in a strain-dependent manner, with and without the addition of cholate. Inhibition of C. difficile by commensals correlated with the efficient conversion of cholate to deoxycholate, a secondary bile acid that inhibits C. difficile germination, growth, and toxin production.

Competition studies also revealed that C. difficile was able to outcompete the commensals in an in vitro coculture system.

These studies are instrumental in understanding the relationship between commensal Clostridia and C. difficile in the gut, which is vital for designing targeted bacterial therapeutics.

 

 

 

 

 

 

SOURCE: https://jb.asm.org/content/202/11/e00039-20

Biologists Develop Models to Aid Development of Novel Therapies to Fight Clostridioides difficile (C. diff.) Pathogen

The Clostridium difficile pathogen takes its name from the French word for “difficult.” A bacterium that is known to cause symptoms ranging from diarrhea to life-threatening colon damage,

 

 

 

C. difficile is part of a growing epidemic of concern for the elderly and patients on antibiotics.

Outbreaks of C. difficile-infected cases have progressively increased in Western countries, with 29,000 reported deaths per year in the United States alone.

Now, biologists at the University of California San Diego are drawing parallels from newly developed models of the common fruit fly to help lay the foundation for novel therapies to fight the pathogen’s spread. Their report is published in the journal iScience.

C. difficile infections pose a serious risk to hospitalized patients,” said Ethan Bier, a distinguished professor in the Division of Biological Sciences and science director of the UC San Diego unit of the Tata Institute for Genetics and Society (TIGS). “This research opens a new avenue for understanding how this pathogen gains an advantage over other beneficial bacteria in the human microbiome through its production of toxic factors. Such knowledge could aid in devising strategies to contain this pathogen and reduce the great suffering it causes.”

As with most bacterial pathogens, C. difficile secretes toxins that enter host cells, disrupt key signaling pathways and weaken the host’s normal defense mechanisms. The most potent strains of C. difficile unleash a two-component toxin that triggers a string of complex cellular responses, culminating in the formation of long membrane protrusions that allow the bacteria to attach more effectively to host cells.

UC San Diego scientists in Bier’s lab-created strains of fruit flies that are capable of expressing the active component of this toxin, known as “CDTa.” The strains allowed them to study the elaborate mechanisms underlying CDTa toxicity in a live model system focused on the gut, which is key since the digestive system of these small flies is surprisingly similar to that of humans.

“The fly gut provides a rapid and surprisingly accurate model for the human intestine, which is the site of infection by C. difficile,” said Bier. “The vast array of sophisticated genetic tools in flies can identify new mechanisms for how toxic factors produced by bacteria disrupt cellular processes and molecular pathways. Such discoveries, once validated in a mammalian system or human cells, can lead to novel treatments for preventing or reducing the severity of C. difficile infections.”

The fruit fly model gave the researchers a clear path to examine genetic interactions disrupted at the hands of CDTa. They ultimately found that the toxin induces a collapse of networks that are essential for nutrient absorption. As a result, the model flies’ body weight, fecal output and overall lifespan were severely reduced, mimicking symptoms in human C. difficile-infected patients.

In addition to Bier, study coauthors include first-author Ruth Schwartz, Annabel Guichard, Nathalie Franc, and Sitara Roy.

The National Institutes of Health (R01 AI110713) funded the research.


Story Source:

Materials provided by the University of California – San Diego. Original written by Mario Aguilera. Note: Content may be edited for style and length.


Journal Reference:

  1. Ruth Schwartz, Annabel Guichard, Nathalie C. Franc, Sitara Roy, Ethan Bier. A Drosophila Model for Clostridium difficile Toxin CDT Reveals Interactions with Multiple Effector Pathways. iScience, 2020; 100865 DOI: 10.1016/j.isci.2020.100865

Transgenic fruit flies help scientists trace the cascade of symptoms caused by toxic infection

Date: February 7, 2020

Source: University of California – San Diego
Summary: Clostridium difficile, a bacterium is known to cause symptoms from diarrhea to life-threatening colon damage, is part of a growing epidemic for the elderly and hospitalized patients. Biologists have now developed models of the common fruit fly to help develop novel therapies to fight the pathogen

Researchers Find C. diff. a Major Cause of Nosocomial Diarrheal Disease Exhibits Phenotypic Heterogeneity Within a Clonal Population As a Result of Phase Variation

Recent work has revealed that Clostridioides difficile, a major cause of nosocomial diarrheal disease, exhibits phenotypic heterogeneity within a clonal population as a result of phase variation.

Many C. difficile strains representing multiple ribotypes develop two colony morphotypes, termed rough and smooth, but the biological implications of this phenomenon have not been explored. Here, we examine the molecular basis and physiological relevance of the distinct colony morphotypes produced by this bacterium. We show that C. difficile reversibly differentiates into rough and smooth colony morphologies and that bacteria derived from the isolates display discrete motility behaviors. We identified an atypical phase-variable signal transduction system consisting of a histidine kinase and two response regulators, named herein colony morphology regulators RST (CmrRST), which mediates the switch in colony morphology and motility behaviors. The CmrRST-regulated surface motility is independent of flagella and type IV pili, suggesting a novel mechanism of cell migration in C. difficile. Microscopic analysis of cell and colony structure indicates that CmrRST promotes the formation of elongated bacteria arranged in bundled chains, which may contribute to bacterial migration on surfaces. In a hamster model of acute C. difficile disease, the CmrRST system is required for disease development. Furthermore, we provide evidence that CmrRST phase varies during infection, suggesting that the intestinal environment impacts the proportion of CmrRST-expressing C. difficile. Our findings indicate that C. difficile employs phase variation of the CmrRST signal transduction system to generate phenotypic heterogeneity during infection, with concomitant effects on bacterial physiology and pathogenesis.

To read the article in its entirety please click on the following link:

https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000379