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Bile acid recognition by the Clostridium difficile germinant receptor, CspC, is important for establishing infection.

ABSTRACT: Clostridium difficile spores must germinate in vivo to become actively growing bacteria in order to produce the toxins that are necessary for disease. C. difficile spores germinate in vitro in response to certain bile acids and glycine. In other sporulating bacteria, proteins embedded within the inner membrane of the spore sense the presence of germinants and trigger the release of Ca??-dipicolinic acid (Ca??-DPA) from the spore core and subsequent hydrolysis of the spore cortex, a specialized peptidoglycan. Based upon homology searches of known germinant receptors from other spore-forming bacteria, C. difficile likely uses unique mechanisms to recognize germinants. Here, we identify the germination-specific protease, CspC, as the C. difficile bile acid germinant receptor and show that bile acid-mediated germination is important for establishing C. difficile disease in the hamster model of infection. These results highlight the importance of bile acids in triggering in vivo germination and provide the first description of a C. difficile spore germinant receptor. Blocking the interaction of bile acids with the C. difficile spore may represent an attractive target for novel therapeutics.

SUBMITTER: Francis MB

PROVIDER: S-EPMC3649964 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature

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Bile acid recognition by the Clostridium difficile germinant receptor, CspC, is important for establishing infection.

Francis Michael B MB Allen Charlotte A CA Shrestha Ritu R Sorg Joseph A JA

PLoS pathogens 20130509 5

Clostridium difficile spores must germinate in vivo to become actively growing bacteria in order to produce the toxins that are necessary for disease. C. difficile spores germinate in vitro in response to certain bile acids and glycine. In other sporulating bacteria, proteins embedded within the inner membrane of the spore sense the presence of germinants and trigger the release of Ca⁺⁺-dipicolinic acid (Ca⁺⁺-DPA) from the spore core and subsequent hydrolysis of the spore cortex, a specialized p ...[more]

PMID: 23675301

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Project description:UnlabelledClostridium difficile spore germination is essential for colonization and disease. The signals that initiate C. difficile spore germination are a combination of taurocholic acid (a bile acid) and glycine. Interestingly, the chenodeoxycholic acid class (CDCA) bile acids competitively inhibit taurocholic acid-mediated germination, suggesting that compounds that inhibit spore germination could be developed into drugs that prophylactically prevent C. difficile infection or reduce recurring disease. However, a recent report called into question the utility of such a strategy to prevent infection by describing C. difficile strains that germinated in the apparent absence of bile acids or germinated in the presence of the CDCA inhibitor. Because the mechanisms of C. difficile spore germination are beginning to be elucidated, the mechanism of germination in these particular strains could yield important information on how C. difficile spores initiate germination. Therefore, we quantified the interaction of these strains with taurocholic acid and CDCA, the rates of spore germination, the release of DPA from the spore core, and the abundance of the germinant receptor complex (CspC, CspB, and SleC). We found that strains previously observed to germinate in the absence of taurocholic acid correspond to more potent 50% effective concentrations (EC50 values; the concentrations that achieve a half-maximum germination rate) of the germinant and are still inhibited by CDCA, possibly explaining the previous observations. By comparing the germination kinetics and the abundance of proteins in the germinant receptor complex, we revised our original model for CspC-mediated activation of spore germination and propose that CspC may activate spore germination and then inhibit downstream processes.ImportanceClostridium difficile forms metabolically dormant spores that persist in the health care environment. In susceptible hosts, C. difficile spores germinate in response to certain bile acids and glycine. Blocking germination by C. difficile spores is an attractive strategy to prevent the initiation of disease or to block recurring infection. However, certain C. difficile strains have been identified whose spores germinate in the absence of bile acids or are not blocked by known inhibitors of C. difficile spore germination (calling into question the utility of such strategies). Here, we further investigate these strains and reestablish that bile acid activators and inhibitors of germination affect these strains and use these data to suggest another role for the C. difficile bile acid germinant receptor.

Project description:Bile acids, important mediators of lipid absorption, also act as hormone-like regulators and as antimicrobial molecules. In all these functions their potency is modulated by a variety of chemical modifications catalyzed by bacteria of the healthy gut microbiota, generating a complex variety of secondary bile acids. Intestinal commensal organisms are well-adapted to normal concentrations of bile acids in the gut. In contrast, physiological concentrations of the various intestinal bile acid species play an important role in the resistance to intestinal colonization by pathogens such as Clostridium difficile. Antibiotic therapy can perturb the gut microbiota and thereby impair the production of protective secondary bile acids. The most important bile acid transformation is 7α-dehydroxylation, producing deoxycholic acid (DCA) and lithocholic acid (LCA). The enzymatic pathway carrying out 7α-dehydroxylation is restricted to a narrow phylogenetic group of commensal bacteria, the best-characterized of which is Clostridium scindens. Like many other intestinal commensal species, 7-dehydroxylating bacteria are understudied in vivo. Conventional animals contain variable and uncharacterized indigenous 7α-dehydroxylating organisms that cannot be selectively removed, making controlled colonization with a specific strain in the context of an undisturbed microbiota unfeasible. In the present study, we used a recently established, standardized gnotobiotic mouse model that is stably associated with a simplified murine 12-species "oligo-mouse microbiota" (Oligo-MM12). It is representative of the major murine intestinal bacterial phyla, but is deficient for 7α-dehydroxylation. We find that the Oligo-MM12 consortium carries out bile acid deconjugation, a prerequisite for 7α-dehydroxylation, and confers no resistance to C. difficile infection (CDI). Amendment of Oligo-MM12 with C. scindens normalized the large intestinal bile acid composition by reconstituting 7α-dehydroxylation. These changes had only minor effects on the composition of the native Oligo-MM12, but significantly decreased early large intestinal C. difficile colonization and pathogenesis. The delayed pathogenesis of C. difficile in C. scindens-colonized mice was associated with breakdown of cecal microbial bile acid transformation.

Dataset Information

Bile acid recognition by the Clostridium difficile germinant receptor, CspC, is important for establishing infection.

Publications

Bile acid recognition by the Clostridium difficile germinant receptor, CspC, is important for establishing infection.

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