Bile salts and glycine as cogerminants for Clostridium difficile spores. J Bacteriol. 2008;190:2505-2512. [PMID: 18245298 DOI: 10.1128/jb.01765-07]

Muricholic acids inhibit Clostridium difficile spore germination and growth

Infections caused by Clostridium difficile have increased steadily over the past several years. While studies on C. difficile virulence and physiology have been hindered, in the past, by lack of genetic approaches and suitable animal models, newly developed technologies and animal models allow these processes to be studied in detail. One such advance is the generation of a mouse-model of C. difficile infection. The development of this system is a major step forward in analyzing the genetic requirements for colonization and infection. While important, it is equally as important in understanding what differences exist between mice and humans. One of these differences is the natural bile acid composition. Bile acid-mediated spore germination is an important step in C. difficile colonization. Mice produce several different bile acids that are not found in humans. These muricholic acids have the potential to impact C. difficile spore germination. Here we find that the three muricholic acids (α-muricholic acid, β-muricholic acid and ω-muricholic acid) inhibit C. difficile spore germination and can impact the growth of vegetative cells. These results highlight an important difference between humans and mice and may have an impact on C. difficile virulence in the mouse-model of C. difficile infection.

Fate of ingested Clostridium difficile spores in mice

Clostridium difficile infection (CDI) is a leading cause of antibiotic-associated diarrhea, a major nosocomial complication. The infective form of C. difficile is the spore, a dormant and resistant structure that forms under stress. Although spore germination is the first committed step in CDI onset, the temporal and spatial distribution of ingested C. difficile spores is not clearly understood. We recently reported that CamSA, a synthetic bile salt analog, inhibits C. difficile spore germination in vitro and in vivo. In this study, we took advantage of the anti-germination activity of bile salts to determine the fate of ingested C. difficile spores. We tested four different bile salts for efficacy in preventing CDI. Since CamSA was the only anti-germinant tested able to prevent signs of CDI, we characterized CamSa’s in vitro stability, distribution, and cytotoxicity. We report that CamSA is stable to simulated gastrointestinal (GI) environments, but will be degraded by members of the natural microbiota found in a healthy gut. Our data suggest that CamSA will not be systemically available, but instead will be localized to the GI tract. Since in vitro pharmacological parameters were acceptable, CamSA was used to probe the mouse model of CDI. By varying the timing of CamSA dosage, we estimated that C. difficile spores germinated and established infection less than 10 hours after ingestion. We also showed that ingested C. difficile spores rapidly transited through the GI tract and accumulated in the colon and cecum of CamSA-treated mice. From there, C. difficile spores were slowly shed over a 96-hour period. To our knowledge, this is the first report of using molecular probes to obtain disease progression information for C. difficile infection.

The protective effect of recombinant Lactococcus lactis oral vaccine on a Clostridium difficile-infected animal model

Background

Oral immunization with vaccines may be an effective strategy for prevention of Clostridium difficile infection (CDI). However, application of previously developed vaccines for preventing CDI has been limited due to various reasons. Here, we developed a recombinant Lactococcus lactis oral vaccine and evaluated its effect on a C. difficile-infected animal model established in golden hamsters in attempt to provide an alternative strategy for CDI prevention.

Methods

Recombinant L. lactis vaccine was developed using the pTRKH2 plasmid, a high-copy-number Escherichia coli-L. shuttle vector: 1) L. lactis expressing secreted proteins was constructed with recombinant pTRKH2 (secreted-protein plasmid) carrying the Usp45 signal peptide (SPUsp45), nontoxic adjuvanted tetanus toxin fragment C (TETC), and 14 of the 38 C-terminal repeats (14CDTA) of nontoxic C. difficile toxin A (TcdA); and 2) L. lactis expressing secreted and membrane proteins was constructed with recombinant pTRKH2 (membrane-anchored plasmid) carrying SPUsp45, TETC, 14CDTA, and the cell wall-anchored sequence of protein M6 (cwaM6). Then, 32 male Syrian golden hamsters were randomly divided into 4 groups (n = 8 each) for gavage of normal saline (blank control) and L. lactis carrying the empty shuttle vector, secreted-protein plasmid, and membrane-anchored plasmid, respectively. After 1-week gavage of clindamycin, the animals were administered with C. difficile spore suspension. General symptoms and intestinal pathological changes of the animals were examined by naked eye and microscopy, respectively. Protein levels of anti-TcdA IgG/IgA antibodies in intestinal tissue and fluid were analyzed by enzyme-linked immunosorbent assay (ELISA). A cell culture cytotoxicity neutralization assay was done by TcdA treatment with or without anti-TcdA serum pre-incubation or treatment. Apoptosis of intestinal epithelial cells was examined by flow cytometry (FL) assay. Expression of mucosal inflammatory cytokines in the animals was detected by polymer chain reaction (PCR) assay.

Results

After the C. difficile challenge, the animals of control group had severe diarrhea symptoms on day 1 and all died on day 4, indicating that the CDI animal model was established in hamster. Of the 3 immunization groups, secreted-protein and membrane-anchored plasmid groups had significantly lower mortalities, body weight decreases, and pathological scores, with higher survival rate/time than the empty plasmid group (P < 0.05). The tilter of IgG antibody directed against TcdA was significantly higher in serum and intestinal fluid of secreted-protein and membrane-anchored plasmid groups than in the empty plasmid group (P < 0.05) while the corresponding titer of IgA antibody directed against TcdA had no substantial differences (P > 0.05). The anti-TcdA serum of membrane-anchored plasmid group neutralized the cytotoxicity of 200 ng/ml TcdA with the best protective effect achieved by anti-TcdA serum pre-incubation. The incidences of TcdA-induced death and apoptosis of intestinal epithelial cells were significantly reduced by cell pre-incubation or treatment with anti-TcdA serum of membrane-anchored plasmid group (P < 0.05). MCP-1, ICAM-1, IL-6, and Gro-1 mRNA expression levels were the lowest in cecum tissue of the membrane-anchored groups compared to the other groups.

Conclusion

Recombinant L. lactis live vaccine is effective for preventing CDI in the hamster model, thus providing an alternative for immunization of C. difficile-associated diseases.

Novel strategies for enhanced removal of persistent Bacillus anthracis surrogates and Clostridium difficile spores from skin

Background

Removing spores of Clostridium difficile and Bacillus anthracis from skin is challenging because they are resistant to commonly used antimicrobials and soap and water washing provides only modest efficacy. We hypothesized that hygiene interventions incorporating a sporicidal electrochemically generated hypochlorous acid solution (Vashe^®) would reduce the burden of spores on skin.

Methods

Hands of volunteers were inoculated with non-toxigenic C. difficile spores or B. anthracis spore surrogates to assess the effectiveness of Vashe solution for reducing spores on skin. Reduction in spores was compared for Vashe hygiene interventions versus soap and water (control). To determine the effectiveness of Vashe solution for removal of C. difficile spores from the skin of patients with C. difficile infection (CDI), reductions in levels of spores on skin were compared for soap and water versus Vashe bed baths.

Results

Spore removal from hands was enhanced with Vashe soak (>2.5 log₁₀ reduction) versus soap and water wash or soak (~2.0 log₁₀ reduction; P<0.05) and Vashe wipes versus alcohol wipes (P<0.01). A combined approach of soap and water wash followed by soaking in Vashe removed >3.5 log₁₀ spores from hands (P<0.01 compared to washing or soaking alone). Bed baths using soap and water (N =26 patients) did not reduce the percentage of positive skin cultures for CDI patients (64% before versus 57% after bathing; P =0.5), whereas bathing with Vashe solution (N =21 patients) significantly reduced skin contamination (54% before versus 8% after bathing; P =0.0001). Vashe was well-tolerated with no evidence of adverse effects on skin.

Conclusions

Vashe was safe and effective for reducing the burden of B. anthracis surrogates and C. difficile spores on hands. Bed baths with Vashe were effective for reducing C. difficile on skin. These findings suggest a novel strategy to reduce the burden of spores on skin.

The Clostridium difficile exosporium cysteine (CdeC)-rich protein is required for exosporium morphogenesis and coat assembly

Clostridium difficile is an important nosocomial pathogen that has become a major cause of antibiotic-associated diarrhea. There is a general consensus that C. difficile spores play an important role in C. difficile pathogenesis, contributing to infection, persistence, and transmission. Evidence has demonstrated that C. difficile spores have an outermost layer, termed the exosporium, that plays some role in adherence to intestinal epithelial cells. Recently, the protein encoded by CD1067 was shown to be present in trypsin-exosporium extracts of C. difficile 630 spores. In this study, we renamed the CD1067 protein Clostridium difficile exosporium cysteine-rich protein (CdeC) and characterized its role in the structure and properties of C. difficile spores. CdeC is expressed under sporulation conditions and localizes to the C. difficile spore. Through the construction of an ΔcdeC isogenic knockout mutant derivative of C. difficile strain R20291, we demonstrated that (i) the distinctive nap layer is largely missing in ΔcdeC spores; (ii) CdeC is localized in the exosporium-like layer and is accessible to IgGs; (iii) ΔcdeC spores were more sensitive to lysozyme, ethanol, and heat treatment than wild-type spores; and (iv) despite the almost complete absence of the exosporium layer, ΔcdeC spores adhered at higher levels than wild-type spores to intestinal epithelium cell lines (i.e., HT-29 and Caco-2 cells). Collectively, these results indicate that CdeC is essential for exosporium morphogenesis and the correct assembly of the spore coat of C. difficile.

Transcriptional analysis of temporal gene expression in germinating Clostridium difficile 630 endospores

Clostridium difficile is the leading cause of hospital acquired diarrhoea in industrialised countries. Under conditions that are not favourable for growth, the pathogen produces metabolically dormant endospores via asymmetric cell division. These are extremely resistant to both chemical and physical stress and provide the mechanism by which C. difficile can evade the potentially fatal consequences of exposure to heat, oxygen, alcohol, and certain disinfectants. Spores are the primary infective agent and must germinate to allow for vegetative cell growth and toxin production. While spore germination in Bacillus is well understood, little is known about C. difficile germination and outgrowth. Here we use genome-wide transcriptional analysis to elucidate the temporal gene expression patterns in C. difficile 630 endospore germination. We have optimized methods for large scale production and purification of spores. The germination characteristics of purified spores have been characterized and RNA extraction protocols have been optimized. Gene expression was highly dynamic during germination and outgrowth, and was found to involve a large number of genes. Using this genome-wide, microarray approach we have identified 511 genes that are significantly up- or down-regulated during C. difficile germination (p≤0.01). A number of functional groups of genes appeared to be co-regulated. These included transport, protein synthesis and secretion, motility and chemotaxis as well as cell wall biogenesis. These data give insight into how C. difficile re-establishes its metabolism, re-builds the basic structures of the vegetative cell and resumes growth.

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

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.

Germination efficiency of clinical Clostridium difficile spores and correlation with ribotype, disease severity and therapy failure

Spore germination is an important part of the pathogenesis of Clostridium difficile infection (CDI). Spores are resistant to antibiotics, including those therapeutically administered for CDI and strains with a high germination rate are significantly more likely to be implicated in recurrent CDI. The role of germination efficiency in cases of refractory CDI where first-line therapy fails remains unclear. We investigated spore germination efficiencies of clinical C. difficile isolates by measuring drop in OD600 and colony forming efficiency. Ribotype 027 isolates exhibited significantly higher germination efficiencies in the presence of 0.1 % (w/v) sodium taurocholate (51.66 ± 8.75 %; 95 % confidence interval (CI) 47.37-55.95 %) than ribotype 106 (41.91 ± 8.35 %; 95 % CI 37.82-46 %) (P<0.05) and ribotype 078 (42.07 ± 8.57 %, 95 % CI 37.22-46.92 %) (P<0.05). Spore outgrowth rates were comparable between the ribotype groups but the exponential phase occurred approximately 4 h later in the absence of sodium taurocholate. Spore germination efficiencies for isolates implicated in severe CDI were significantly higher (49.68 ± 10.00 %, 95 % CI 47.06-52.30 %) than non-severe CDI (40.92 ± 9.29 %, 95 % CI 37.48-44.36 %); P<0.01. Germination efficiencies were also significantly higher in recurrent CDI or when metronidazole therapy failed than when therapy was successful [(49.00 ± 10.49 %, 95 % CI 46.25-51.75 %) versus (41.42 ± 9.43 %, 95 % CI 37.93-44.91 %); P<0.01]. This study suggests an important link between C. difficile spore germination, CDI pathogenesis and response to treatment; however, further work is warranted before the complex interplay between germination dynamics and CDI outcome can be fully understood.

A new strategy for the prevention of Clostridium difficile infection

BACKGROUND

Clostridium difficile infection (CDI) is a leading cause of antibiotic-associated diarrhea. The infective form of C. difficile is the spore, but the vegetative bacterium causes the disease. Because C. difficile spore germination is required for symptomatic infection, antigermination approaches could lead to the prevention of CDI. We recently reported that CamSA, a bile salt analog, inhibits C. difficile spore germination in vitro.

METHODS

Mice infected with massive inocula of C. difficile spores were treated with different concentrations of CamSA and monitored for CDI signs. C. difficile spore and vegetative cells were counted in feces from infected mice.

RESULTS

A single 50-mg/kg dose of CamSA prevented CDI in mice without any observable toxicity. Lower CamSA doses resulted in delayed CDI onset and less severe signs of disease. Ingested C. difficile spores were quantitatively recovered from feces of CamSA-protected mice.

CONCLUSIONS

Our results support a mechanism whereby the antigermination effect of CamSA is responsible for preventing CDI signs. This approach represents a new paradigm in CDI treatment. Instead of further compromising the microbiota of CDI patients with strong antibiotics, antigermination therapy could serve as a microbiota surrogate to curtail C. difficile colonization of antibiotic-treated patients.

Structural and functional analysis of the CspB protease required for Clostridium spore germination

Spores are the major transmissive form of the nosocomial pathogen Clostridium difficile, a leading cause of healthcare-associated diarrhea worldwide. Successful transmission of C. difficile requires that its hardy, resistant spores germinate into vegetative cells in the gastrointestinal tract. A critical step during this process is the degradation of the spore cortex, a thick layer of peptidoglycan surrounding the spore core. In Clostridium sp., cortex degradation depends on the proteolytic activation of the cortex hydrolase, SleC. Previous studies have implicated Csps as being necessary for SleC cleavage during germination; however, their mechanism of action has remained poorly characterized. In this study, we demonstrate that CspB is a subtilisin-like serine protease whose activity is essential for efficient SleC cleavage and C. difficile spore germination. By solving the first crystal structure of a Csp family member, CspB, to 1.6 Å, we identify key structural domains within CspB. In contrast with all previously solved structures of prokaryotic subtilases, the CspB prodomain remains tightly bound to the wildtype subtilase domain and sterically occludes a catalytically competent active site. The structure, combined with biochemical and genetic analyses, reveals that Csp proteases contain a unique jellyroll domain insertion critical for stabilizing the protease in vitro and in C. difficile. Collectively, our study provides the first molecular insight into CspB activity and function. These studies may inform the development of inhibitors that can prevent clostridial spore germination and thus disease transmission.

Clostridium difficile is the leading cause of health-care associated diarrhea worldwide. C. difficile infections begin when its spores transform into vegetative cells during a process called germination. In Clostridium sp., germination requires that the spore cortex, a thick, protective layer, be removed by the cortex hydrolase SleC. While previous studies have shown that SleC activity depends on a subtilisin-like protease, CspB, the mechanisms regulating CspB function have not been characterized. In this study, we solved the first crystal structure of the Csp family of proteases and identified its key functional regions. We determined that CspB carries a unique jellyroll domain required for stabilizing the protein both in vitro and in C. difficile and a prodomain required for proper folding of the protease. Unlike all other prokaryotic subtilisin-like proteases, the prodomain remains bound to CspB and inhibits its protease activity until the germination signal is sensed. Our study provides new insight into how germination is regulated in C. difficile and may inform the development of inhibitors that can prevent germination and thus C. difficile transmission.

Activate to eradicate: inhibition of Clostridium difficile spore outgrowth by the synergistic effects of osmotic activation and nisin

BACKGROUND

Germination is the irreversible loss of spore-specific properties prior to outgrowth. Because germinating spores become more susceptible to killing by stressors, induction of germination has been proposed as a spore control strategy. However, this strategy is limited by superdormant spores that remain unaffected by germinants. Harsh chemicals and heat activation are effective for stimulating germination of superdormant spores but are impractical for use in a hospital setting, where Clostridium difficile spores present a challenge. Here, we tested whether osmotic activation solutes will provide a mild alternative for stimulation of superdormant C. difficile spores in the presence of germinants as previously demonstrated in several species of Bacillus. In addition, we tested the hypothesis that the limitations of superdormancy can be circumvented with a combined approach using nisin, a FDA-approved safe bacteriocin, to inhibit outgrowth of germinated spores and osmotic activation solutes to enhance outgrowth inhibition by stimulating superdormant spores.

PRINCIPAL FINDINGS

Exposure to germination solution triggered ~1 log(10) colony forming units (CFU) of spores to germinate, and heat activation increased the spores that germinated to >2.5 log(10)CFU. Germinating spores, in contrast to dormant spores, became susceptible to inhibition by nisin. The presence of osmotic activation solutes did not stimulate germination of superdormant C. difficile spores exposed to germination solution. But, in the absence of germination solution, osmotic activation solutes enhanced nisin inhibition of superdormant spores to >3.5 log(10)CFU. The synergistic effects of osmotic activation solutes and nisin were associated with loss of membrane integrity.

CONCLUSIONS

These findings suggest that the synergistic effects of osmotic activation and nisin bypass the limitations of germination as a spore control strategy, and might be a novel method to safely and effectively reduce the burden of C.difficile spores on skin and environmental surfaces.

Molecular basis of early stages of Clostridium difficile infection: germination and colonization

Clostridium difficile infections (CDIs) occur when antibiotic therapy disrupts the gastrointestinal flora, favoring infected C. difficile spores to germinate, outgrow, colonize and produce toxins. During CDI, C. difficile vegetative cells initiate the process of sporulation allowing a fraction of the spores to remain adhered to the intestinal surfaces. These spores, which are unaffected by antibiotic therapy commonly used for CDIs, then germinate, outgrow and recolonize the host's GI tract causing relapse of CDI. Consequently, the germination and colonization processes can be considered as the earliest and most essential steps for the development as well as relapse of CDI. The aim of this review is to provide an overview on the molecular basis involved in C. difficile spore germination and colonization.

Both fidaxomicin and vancomycin inhibit outgrowth of Clostridium difficile spores

Fidaxomicin (FDX) is approved to treat Clostridium difficile-associated diarrhea and is superior to vancomycin in providing a sustained clinical response (cure without recurrence in the subsequent 25 days). The mechanism(s) behind the low recurrence rate of FDX-treated patients could be multifactorial. Here, we tested effects of FDX, its metabolite OP-1118, and vancomycin on spore germination and determined that none affected the initiation of spore germination but all inhibited outgrowth of vegetative cells from germinated spores.

Different antibiotic resistance and sporulation properties within multiclonal Clostridium difficile PCR ribotypes 078, 126, and 033 in a single calf farm

Clostridium difficile strains were sampled periodically from 50 animals at a single veal calf farm over a period of 6 months. At arrival, 10% of animals were C. difficile positive, and the peak incidence was determined to occur at the age of 18 days (16%). The prevalence then decreased, and at slaughter, C. difficile could not be isolated. Six different PCR ribotypes were detected, and strains within a single PCR ribotype could be differentiated further by pulsed-field gel electrophoresis (PFGE). The PCR ribotype diversity was high up to the animal age of 18 days, but at later sampling points, PCR ribotype 078 and the highly related PCR ribotype 126 predominated. Resistance to tetracycline, doxycycline, and erythromycin was detected, while all strains were susceptible to amoxicillin and metronidazole. Multiple variations of the resistance gene tet(M) were present at the same sampling point, and these changed over time. We have shown that PCR ribotypes often associated with cattle (ribotypes 078, 126, and 033) were not clonal but differed in PFGE type, sporulation properties, antibiotic sensitivities, and tetracycline resistance determinants, suggesting that multiple strains of the same PCR ribotype infected the calves and that calves were likely to be infected prior to arrival at the farm. Importantly, strains isolated at later time points were more likely to be resistant to tetracycline and erythromycin and showed higher early sporulation efficiencies in vitro, suggesting that these two properties converge to promote the persistence of C. difficile in the environment or in hosts.

Improved recovery of Clostridium difficile spores with the incorporation of synthetic taurocholate in cycloserine-cefoxitin-fructose agar (CCFA)

AIM

Culture remains important for the detection and typing of Clostridium difficile. Culture of C. difficile spores can be enhanced on media supplemented with a germinant. Despite this, unsupplemented media continues to be used in some laboratories. The aim of this study was to quantify the effect of the known germinant sodium taurocholate on recovery of C. difficile spores and to determine if the supplement impacts on the recovery of vegetative C. difficile.

METHODS

The recovery on cycloserine-cefoxitin-fructose agar (CCFA) with and without taurocholate, of spore, vegetative, and total cell fractions of broth cultures of eight C. difficile isolates was compared.

RESULTS

Taurocholate in CCFA did not inhibit growth of vegetative C. difficile and significantly increased recovery of spores (p = 0.04).

CONCLUSIONS

The routine incorporation of taurocholate in CCFA is recommended for improved sensitivity in C. difficile culture from specimens.

Clostridium difficile spore-macrophage interactions: spore survival

BACKGROUND

Clostridium difficile is the main cause of nosocomial infections including antibiotic associated diarrhea, pseudomembranous colitis and toxic megacolon. During the course of Clostridium difficile infections (CDI), C. difficile undergoes sporulation and releases spores to the colonic environment. The elevated relapse rates of CDI suggest that C. difficile spores has a mechanism(s) to efficiently persist in the host colonic environment.

METHODOLOGY/PRINCIPAL FINDINGS

In this work, we provide evidence that C. difficile spores are well suited to survive the host's innate immune system. Electron microscopy results show that C. difficile spores are recognized by discrete patchy regions on the surface of macrophage Raw 264.7 cells, and phagocytosis was actin polymerization dependent. Fluorescence microscopy results show that >80% of Raw 264.7 cells had at least one C. difficile spore adhered, and that ∼60% of C. difficile spores were phagocytosed by Raw 264.7 cells. Strikingly, presence of complement decreased Raw 264.7 cells' ability to phagocytose C. difficile spores. Due to the ability of C. difficile spores to remain dormant inside Raw 264.7 cells, they were able to survive up to 72 h of macrophage infection. Interestingly, transmission electron micrographs showed interactions between the surface proteins of C. difficile spores and the phagosome membrane of Raw 264.7 cells. In addition, infection of Raw 264.7 cells with C. difficile spores for 48 h produced significant Raw 264.7 cell death as demonstrated by trypan blue assay, and nuclei staining by ethidium homodimer-1.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate that despite efficient recognition and phagocytosis of C. difficile spores by Raw 264.7 cells, spores remain dormant and are able to survive and produce cytotoxic effects on Raw 264.7 cells.

Contribution of spores to the ability of Clostridium difficile to adhere to surfaces

Clostridium difficile is the commonest cause of hospital-acquired infection in the United Kingdom. We characterized the abilities of 21 clinical isolates to form spores; to adhere to inorganic and organic surfaces, including stainless steel and human adenocarcinoma cells; and to germinate. The composition of culture media had a significant effect on spore formation, as significantly more spores were produced in brain heart infusion broth (Student's t test; P = 0.018). The spore surface relative hydrophobicity (RH) varied markedly (14 to 77%) and was correlated with the ability to adhere to stainless steel. We observed no correlation between the ribotype and the ability to adhere to steel. When the binding of hydrophobic (DS1813; ribotype 027; RH, 77%) and hydrophilic (DS1748; ribotype 002; RH, 14%) spores to human gut epithelial cells at different stages of cell development was examined, DS1813 spores adhered more strongly, suggesting the presence of surface properties that aid attachment to human cells. Electron microscopy studies revealed the presence of an exosporium surrounding DS1813 spores that was absent from spores of DS1748. Finally, the ability of spores to germinate was found to be strain and medium dependent. While the significance of these findings to the disease process has yet to be determined, this study has highlighted the importance of analyzing multiple isolates when attempting to characterize the behavior of a bacterial species.

Interaction between the intestinal microbiota and host in Clostridium difficile colonization resistance

Clostridium difficile infection (CDI) has become one of the most prevalent and costly nosocomial infections. In spite of the importance of CDI, our knowledge of the pathogenesis of this infection is still rudimentary. Although previous use of antibiotics is generally considered to be the sine qua non of CDI, the mechanisms by which antibiotics render the host susceptible to C. difficile are not well defined. In this review, we will explore what is known about how the indigenous microbiota acts in concert with the host to prevent colonization and virulence of C. difficile and how antibiotic administration disturbs host-microbiota homeostasis, leading to CDI.

Adherence of Clostridium difficile spores to Caco-2 cells in culture

Clostridium difficile is the causative agent of the majority of antibiotic associated diarrhoea cases. C. difficile spores are recognized as the persistent and infectious morphotype as well as the vehicle of transmission of CDI. However, there is a lack of knowledge on how C. difficile spores interact with the host's epithelial surfaces. In this context, we have characterized the ability of C. difficile spores to adhere to human Caco-2 cells. Despite the similarities in spore-surface hydrophobicity between spores of C. difficile and Clostridium perfringens (another enteric pathogen that also sporulates in the gut), spores of C. difficile adhere better to Caco-2 cells. Adherence to Caco-2 cells was significantly reduced when C. difficile spores were treated with trypsin. Sonication of C. difficile spores altered the ultrastructure of the outermost exosporium-like structure, releasing two protein species of ~40 kDa and significantly reduced spore hydrophobicity and adherence to Caco-2 cells. Using a trifunctional cross-linker, we were able to co-immunoprecipitate four protein species from the surface of Caco-2 cells. In conclusion, this study provides evidence that C. difficile spores adhere to human intestinal enterocyte-like cells through spore- and enterocytic-surface-specific ligand(s) and/or receptor(s).

Sensitive quantification of Clostridium difficile cells by reverse transcription-quantitative PCR targeting rRNA molecules

We established a sensitive and accurate quantification system for Clostridium difficile in human intestines, based on rRNA-targeted reverse transcription-quantitative PCR (RT-qPCR). We newly developed a species-specific primer set for C. difficile targeting 23S rRNA gene sequences. Both the vegetative cells and the spores of C. difficile in human feces were quantified by RT-qPCR, with a lower detection limit of 10(2.4) cells/g of feces. In an analysis of the feces of residents (n = 83; age, 85 ± 8 years) and staff (n = 19; age, 36 ± 10 years) at a care facility for the elderly, C. difficile was detected by RT-qPCR in 43% of the residents (average count, log(10) 4.0 ± 2.0 cells/g of feces) and 16% of the staff (average count, log(10) 2.2 ± 0.1 cells/g of feces); these rates were far higher than those detected by qPCR (residents, 19%; staff, 0%) or selective cultivation (residents, 18%; staff, 5%). Another analysis of healthy adults (n = 63; age, 41 ± 11 years) also revealed the significant carriage rate of C. difficile in the intestines (detection rate, 13%; average count, log(10) 4.9 ± 1.2 cells/g of feces). From these results, it was suggested that rRNA-targeted RT-qPCR should be an effective tool for analyzing population levels of C. difficile in the human intestine.

Clostridium difficile infection: toxins and non-toxin virulence factors, and their contributions to disease establishment and host response

Clostridium difficile infection is the leading cause of antibiotic- and healthcare-associated diarrhea, and its containment and treatment imposes a significant financial burden, estimated to be over $3 billion in the USA alone. Since the year 2000, CDI epidemics/outbreaks have occurred in North America, Europe and Asia. These outbreaks have been variously associated with, or attributed to, the emergence of Clostridium difficile strains with increased virulence, an increase in resistance to commonly used antimicrobials such as the fluoroquinolones, or host susceptibilities, including the use of gastric acid suppressants, to name a few. Efforts to elucidate C. difficile pathogenic mechanisms have been hampered by a lack of molecular tools, manipulatable animal models, and genetic intractability of clinical C. difficile isolates. However, in the past 5 y, painstaking efforts have resulted in the unraveling of multiple C. difficile virulence-associated pathways and mechanisms. We have recently reviewed the disease, its associated risk factors, transmission and interventions (Viswanathan, Gut Microbes 2010). This article summarizes genetics, non-toxin virulence factors, and host-cell biology associated with C. difficile pathogenesis as of 2011, and highlights those findings/factors that may be of interest as future intervention targets.

TcdB from hypervirulent Clostridium difficile exhibits increased efficiency of autoprocessing

TcdB, an intracellular bacterial toxin that inactivates small GTPases, is a major Clostridium difficile virulence factor. Recent studies have found that TcdB produced by emerging/hypervirulent strains of C. difficile is more potent than TcdB from historical strains, and in the current work, studies were performed to investigate the underlying mechanisms for this change in TcdB toxicity. Using a series of biochemical analyses we found that TcdB from a hypervirulent strain (TcdB(HV) ) was more efficient at autoprocessing than TcdB from a historical strain (TcdB(HIST) ). TcdB(HV) and TcdB(HIST) were activated by similar concentrations of IP6; however, the overall efficiency of processing was 20% higher for TcdB(HV) . Using an activity-based fluorescent probe (AWP19) an intermediate, activated but uncleaved, form of TcdB(HIST) was identified, while only a processed form of TcdB(HV) could be detected under the same conditions. Using a much higher concentration (200 µM) of the probe revealed an activated uncleaved form of TcdB(HV) , indicating a preferential and more efficient engagement of intramolecular substrate than TcdB(HIST) . Furthermore, a peptide-based inhibitor (Ac-GSL-AOMK) was found to block the cytotoxicity of TcdB(HIST) at a lower concentration than required to inhibit TcdB(HV) . These findings suggest that TcdB(HV) may cause increased cytotoxicity due to more efficient autoprocessing.

Spores of Clostridium difficile clinical isolates display a diverse germination response to bile salts

Clostridium difficile spores play a pivotal role in the transmission of infectious diarrhoea, but in order to cause disease spores must complete germination and return to vegetative cell growth. While the mechanisms of spore germination are well understood in Bacillus, knowledge of C. difficile germination remains limited. Previous studies have shown that bile salts and amino acids play an important role in regulating the germination response of C. difficile spores. Taurocholate, in combination with glycine, can stimulate germination, whereas chenodeoxycholate has been shown to inhibit spore germination in a C. difficile clinical isolate. Our recent studies of C. difficile sporulation characteristics have since pointed to substantial diversity among different clinical isolates. Consequently, in this study we investigated how the germination characteristics of different C. difficile isolates vary in response to bile salts. By analysing 29 isolates, including 16 belonging to the BI/NAP1/027 type, we show that considerable diversity exists in both the rate and extent of C. difficile germination in response to rich medium containing both taurocholate and glycine. Strikingly, we also show that although a potent inhibitor of germination for some isolates, chenodeoxycholate does not inhibit the germination, or outgrowth, of all C. difficile strains. Finally, we provide evidence that components of rich media may induce the germination of C. difficile spores, even in the absence of taurocholate. Taken together, these data suggest that the mechanisms of C. difficile spore germination in response to bile salts are complex and require further study. Furthermore, we stress the importance of studying multiple isolates in the future when analysing the nutrients or chemicals that either stimulate or inhibit C. difficile spore germination.

Molecular and microbiological characterization of Clostridium difficile isolates from single, relapse, and reinfection cases

In this study, we investigated the correlation between the microbiological characteristics of Clostridium difficile clinical isolates and the recurrence of C. difficile-associated disease (CDAD). Twenty C. difficile isolates recovered from 20 single infection cases and 53 isolates from 20 recurrent cases were analyzed by pulsed-field gel electrophoresis (PFGE) and PCR ribotyping, and the cytotoxicity, antimicrobial susceptibility, and sporulation/germination rates of the isolates were examined. Recurrent cases were divided into relapse or reinfection cases by the results of C. difficile DNA typing. Among the 20 recurrent cases, 16 cases (80%) were identified to be relapse cases caused by the initial strain and the remaining 4 cases (20%) were identified to be reinfection cases caused by different strains. All 73 isolates were susceptible to both vancomycin and metronidazole, but resistance against clindamycin, ceftriaxone, erythromycin, and ciprofloxacin was found in 87.7%, 93.2%, 87.7%, and 100% of the isolates, respectively. No correlations between DNA typing group, cytotoxicity, and sporulation rate of isolates and infection status, i.e., single, relapse, or reinfection, were observed. However, the isolates recovered from relapse cases showed a significantly higher germination rate when incubated in medium lacking the germination stimulant sodium taurocholate. These results indicate that the germination ability of C. difficile may be a potential risk factor for the recurrence of CDAD.

Reconsidering the sporulation characteristics of hypervirulent Clostridium difficile BI/NAP1/027

Clostridium difficile is the leading cause of antibiotic-associated diarrhoea and a major burden to healthcare services worldwide. In recent years, C. difficile strains belonging to the BI/NAP1/027 type have become highly represented among clinical isolates. These so-called 'hypervirulent' strains are associated with outbreaks of increased disease severity, higher relapse rates and an expanded repertoire of antibiotic resistance. Spores, formed during sporulation, play a pivotal role in disease transmission and it has been suggested that BI/NAP1/027 strains are more prolific in terms of sporulation in vitro than 'non-epidemic' C. difficile types. Work in our laboratory has since provided credible evidence to the contrary suggesting that the strain-to-strain variation in C. difficile sporulation characteristics is not type-associated. However, the BI/NAP1/027 type is still widely stated to have an increased rate of sporulation. In this study, we analysed the sporulation rates of 53 C. difficile strains, the largest sample size used to-date in such a study, including 28 BI/NAP1/027 isolates. Our data confirm that significant variation exists in the rate at which different C. difficile strains form spores. However, we clearly show that the sporulation rate of the BI/NAP1/027 type was no higher than that of non-BI/NAP1/027 strains. In addition, we observed substantial variation in sporulation characteristics within the BI/NAP1/027 type. This work highlights the danger of assuming that all strains of one type behave similarly without studying adequate sample sizes. Furthermore, we stress the need for more rigorous experimental procedures in order to quantify C. difficile sporulation more accurately in the future.

Sporulation studies in Clostridium difficile

Clostridium difficile is a leading cause of healthcare-associated diarrhoea. In recent years, certain C. difficile types have become highly represented among clinical isolates and are associated with outbreaks of increased disease severity, higher relapse rates and an expanded repertoire of antibiotic resistance. Endospores, produced during sporulation, play a pivotal role in infection and disease transmission and it has been suggested in the literature that these so-called 'hypervirulent' C. difficile types are more prolific in terms of sporulation in vitro. However, work in our laboratory has provided evidence to the contrary suggesting that although there is significant strain-to-strain variation in C. difficile sporulation characteristics this variation does not appear to be type-associated. On analysis of the literature, it is apparent that the methods used to quantify sporulation in previous studies have varied greatly and sample sizes have remained small. The conflicting data in the literature may, therefore, not necessarily be generally representative of C. difficile sporulation. Instead, these inconsistencies may reflect differences in the experimental design of each study. In this review, the need for further investigations of C. difficile sporulation rates is highlighted. Specifically, the advantages and disadvantages of the different experimental approaches previously used are discussed and a standard set of principles for measuring C. difficile sporulation in the future is proposed.

Progesterone analogs influence germination of Clostridium sordellii and Clostridium difficile spores in vitro

Clostridium sordellii and Clostridium difficile are closely related anaerobic Gram-positive, spore-forming human pathogens. C. sordellii and C. difficile form spores that are believed to be the infectious form of these bacteria. These spores return to toxin-producing vegetative cells upon binding to small molecule germinants. The endogenous compounds that regulate clostridial spore germination are not fully understood. While C. sordellii spores require three structurally distinct amino acids to germinate, the occurrence of postpregnancy C. sordellii infections suggests that steroidal sex hormones might regulate its capacity to germinate. On the other hand, C. difficile spores require taurocholate (a bile salt) and glycine (an amino acid) to germinate. Bile salts and steroid hormones are biosynthesized from cholesterol, suggesting that the common sterane structure can affect the germination of both C. sordellii and C. difficile spores. Therefore, we tested the effect of sterane compounds on C. sordellii and C. difficile spore germination. Our results show that both steroid hormones and bile salts are able to increase C. sordellii spore germination rates. In contrast, a subset of steroid hormones acted as competitive inhibitors of C. difficile spore germination. Thus, even though C. sordellii and C. difficile are phylogenetically related, the two species' spores respond differently to steroidal compounds.

Germination response of spores of the pathogenic bacterium Clostridium perfringens and Clostridium difficile to cultured human epithelial cells

Spores of pathogenic Clostridium perfringens and Clostridium difficile must germinate in the food vehicle and/or host's intestinal tract to cause disease. In this work, we examined the germination response of spores of C. perfringens and C. difficile upon incubation with cultured human epithelial cell lines (Caco-2, HeLa and HT-29). C. perfringens spores of various sources were able to germinate to different extents; while spores of a non-food-borne isolate germinated very well, spores of food-borne and animal isolates germinated poorly in human epithelial cells. In contrast, no detectable spore germination (i.e., loss of spore heat resistance) was observed upon incubation of C. difficile spores with epithelial cells; instead, there was a significant (p < 0.01) increase in heat-resistant spore titers. In C. perfringens, the highest spore germination response observed with the HT-29 cell line, might be in part, due to the expression of germination factor with peptidoglycan cortex hydrolysis activity by HT-29 cells. Collectively, these findings might well have implications in understanding the mechanism of clostridial spore germination in vivo.

Germination of spores of Bacillales and Clostridiales species: mechanisms and proteins involved

Under conditions that are not conducive to growth, such as nutrient depletion, many members of the orders Bacillales and Clostridiales can sporulate, generating dormant and resistant spores that can survive in the absence of nutrients for years under harsh conditions. However, when nutrients are again present, these spores can return to active growth through the process of germination. Many of the components of the spore germination machinery are conserved between spore forming members of the Bacillales and Clostridiales orders. However, recent studies have revealed significant differences between the germination of spores of Clostridium perfringens and that of spores of a number of Bacillus species, both in the proteins and in the signal transduction pathways involved. In this review, the roles of components of the spore germination machinery of C. perfringens and several Bacillus species and the bioinformatic analysis of germination proteins in the Bacillales and Clostridiales orders are discussed and models for the germination of spores of these two orders are proposed.

Exit from dormancy in microbial organisms

Bacteria can exist in metabolically inactive states that allow them to survive conditions that are not conducive for growth. Such dormant cells may sense when conditions have improved and re-initiate growth, lest they be outcompeted by their neighbours. Growing bacteria turn over and release large quantities of their cell walls into the environment. Drawing from recent work on the germination of Bacillus subtilis spores, we propose that many microorganisms exit dormancy in response to cell wall muropeptides.

Mapping interactions between germinants and Clostridium difficile spores

Germination of Clostridium difficile spores is the first required step in establishing C. difficile-associated disease (CDAD). Taurocholate (a bile salt) and glycine (an amino acid) have been shown to be important germinants of C. difficile spores. In the present study, we tested a series of glycine and taurocholate analogs for the ability to induce or inhibit C. difficile spore germination. Testing of glycine analogs revealed that both the carboxy and amino groups are important epitopes for recognition and that the glycine binding site can accommodate compounds with more widely separated termini. The C. difficile germination machinery also recognizes other hydrophobic amino acids. In general, linear alkyl side chains are better activators of spore germination than their branched analogs. However, L-phenylalanine and L-arginine are also good germinants and are probably recognized by distinct binding sites. Testing of taurocholate analogs revealed that the 12-hydroxyl group of taurocholate is necessary, but not sufficient, to activate spore germination. In contrast, the 6- and 7-hydroxyl groups are required for inhibition of C. difficile spore germination. Similarly, C. difficile spores are able to detect taurocholate analogs with shorter, but not longer, alkyl amino sulfonic acid side chains. Furthermore, the sulfonic acid group can be partially substituted with other acidic groups. Finally, a taurocholate analog with an m-aminobenzenesulfonic acid side chain is a strong inhibitor of C. difficile spore germination. In conclusion, C. difficile spores recognize both amino acids and taurocholate through multiple interactions that are required to bind the germinants and/or activate the germination machinery.

The diverse sporulation characteristics of Clostridium difficile clinical isolates are not associated with type

Clostridium difficile causes diarrhoeal diseases ranging from asymptomatic carriage to a fulminant, relapsing, and potentially fatal colitis. Endospore production plays a vital role in transmission of infection, and in order to cause disease these spores must then germinate and return to vegetative cell growth. Type BI/NAP1/027 strains of C. difficile have recently become highly represented among clinical isolates and are associated with increased disease severity. It has also been suggested that these 'epidemic' types generally sporulate more prolifically than 'non-epidemic' strains, although the few existing reports are inconclusive and encompass only a small number of isolates. In order to better understand any differences in sporulation rates between epidemic and non-epidemic C. difficile types, we analysed these characteristics using 14 C. difficile clinical isolates of a variety of types. Sporulation rates varied greatly between individual BI/NAP1/027 isolates, but this variation did not appear to be type-associated. Furthermore, a number of BI/NAP1/027 spores appeared to form colonies with a lower frequency than specific non-BI/NAP1/027 strains. The data suggest that (i) careful experimental design is required in order to accurately quantify sporulation; and (ii) current evidence cannot link differences in sporulation rates with the disease severity of the BI/NAP1/027 type.

Use of purified Clostridium difficile spores to facilitate evaluation of health care disinfection regimens

Clostridium difficile is a major cause of antibiotic-associated diarrheal disease in many parts of the world. In recent years, distinct genetic variants of C. difficile that cause severe disease and persist within health care settings have emerged. Highly resistant and infectious C. difficile spores are proposed to be the main vectors of environmental persistence and host transmission, so methods to accurately monitor spores and their inactivation are urgently needed. Here we describe simple quantitative methods, based on purified C. difficile spores and a murine transmission model, for evaluating health care disinfection regimens. We demonstrate that disinfectants that contain strong oxidizing active ingredients, such as hydrogen peroxide, are very effective in inactivating pure spores and blocking spore-mediated transmission. Complete inactivation of 10⁶ pure C. difficile spores on indicator strips, a six-log reduction, and a standard measure of stringent disinfection regimens require at least 5 min of exposure to hydrogen peroxide vapor (HPV; 400 ppm). In contrast, a 1-min treatment with HPV was required to disinfect an environment that was heavily contaminated with C. difficile spores (17 to 29 spores/cm²) and block host transmission. Thus, pure C. difficile spores facilitate practical methods for evaluating the efficacy of C. difficile spore disinfection regimens and bringing scientific acumen to C. difficile infection control.

Inhibiting the initiation of Clostridium difficile spore germination using analogs of chenodeoxycholic acid, a bile acid

To cause disease, Clostridium difficile spores must germinate in the host gastrointestinal tract. Germination is initiated upon exposure to glycine and certain bile acids, e.g., taurocholate. Chenodeoxycholate, another bile acid, inhibits taurocholate-mediated germination. By applying Michaelis-Menten kinetic analysis to C. difficile spore germination, we found that chenodeoxycholate is a competitive inhibitor of taurocholate-mediated germination and appears to interact with the spores with greater apparent affinity than does taurocholate. We also report that several analogs of chenodeoxycholate are even more effective inhibitors. Some of these compounds resist 7α-dehydroxylation by Clostridium scindens, a core member of the normal human colonic microbiota, suggesting that they are more stable than chenodeoxycholate in the colonic environment.

Clostridium difficile infection

Clostridium difficile is the leading cause of hospital-acquired diarrhea in Europe and North America and is a serious reemerging pathogen. Recent outbreaks have led to increasing morbidity and mortality and have been associated with a new strain (BI/NAP1/027) of C difficile that produces more toxin than historic strains. With the increasing incidence of C difficile infection, clinicians have also seen a change in the epidemiology with increased infections in previously low-risk populations. This chapter highlights the current knowledge on C difficile virulence, human disease, epidemic outbreaks and optimal treatment strategies.

Clostridium difficile spore germination: an update

Endospore production is vital for the spread of Clostridium difficile infection. However, in order to cause disease, these spores must germinate and return to vegetative cell growth. Knowledge of germination is therefore important, with potential practical implications for routine cleaning, outbreak management and potentially in the design of new therapeutics. Germination has been well studied in Bacillus, but until recently there had been few studies reported in C. difficile. The role of bile salts as germinants for C. difficile spores has now been described in some detail, which improves our understanding of how C. difficile spores interact with their environment following ingestion by susceptible individuals. Furthermore, with the aid of novel genetic tools, it has now become possible to study the germination of C. difficile spores using both a forward and reverse genetics approach. Significant progress is beginning to be made in the study of this important aspect of C. difficile disease.

The role of toxin A and toxin B in Clostridium difficile infection

Clostridium difficile infection is the leading cause of healthcare-associated diarrhoea in Europe and North America. During infection, C. difficile produces two key virulence determinants, toxin A and toxin B. Experiments with purified toxins have indicated that toxin A alone is able to evoke the symptoms of C. difficile infection, but toxin B is unable to do so unless it is mixed with toxin A or there is prior damage to the gut mucosa. However, a recent study indicated that toxin B is essential for C. difficile virulence and that a strain producing toxin A alone was avirulent. This creates a paradox over the individual importance of toxin A and toxin B. Here we show that isogenic mutants of C. difficile producing either toxin A or toxin B alone can cause fulminant disease in the hamster model of infection. By using a gene knockout system to inactivate the toxin genes permanently, we found that C. difficile producing either one or both toxins showed cytotoxic activity in vitro that translated directly into virulence in vivo. Furthermore, by constructing the first ever double-mutant strain of C. difficile, in which both toxin genes were inactivated, we were able to completely attenuate virulence. Our findings re-establish the importance of both toxin A and toxin B and highlight the need to continue to consider both toxins in the development of diagnostic tests and effective countermeasures against C. difficile.

Clostridium difficile

Clostridium difficile has re-emerged as a major hospital-acquired infection since 2001. Despite development of polymerase chain reaction-based testing, no single clinical diagnostic test has emerged with sufficient sensitivity, specificity, and turnaround time to be entirely reliable for disease diagnosis. The importance of C difficile acquired outside the hospital environment remains an unknown factor and awaits further epidemiologic investigation. This article discusses the changing epidemiology, clinical presentation, and pathogenesis of C difficile infection and highlights the ongoing challenges of laboratory diagnosis, treatment, and disease relapse.

Kinetic evidence for the presence of putative germination receptors in Clostridium difficile spores

Clostridium difficile is a spore-forming bacterium that causes Clostridium difficile-associated disease (CDAD). Intestinal microflora keeps C. difficile in the spore state and prevents colonization. Following antimicrobial treatment, the microflora is disrupted, and C. difficile spores germinate in the intestines. The resulting vegetative cells are believed to fill empty niches left by the depleted microbial community and establish infection. Thus, germination of C. difficile spores is the first required step in CDAD. Interestingly, C. difficile genes encode most known spore-specific protein necessary for germination, except for germination (Ger) receptors. Even though C. difficile Ger receptors have not been identified, taurocholate (a bile salt) and glycine (an amino acid) have been shown to be required for spore germination. Furthermore, chenodeoxycholate, another bile salt, can inhibit taurocholate-induced C. difficile spore germination. In the present study, we examined C. difficile spore germination kinetics to determine whether taurocholate acts as a specific germinant that activates unknown germination receptors or acts nonspecifically by disrupting spores' membranes. Kinetic analysis of C. difficile spore germination suggested the presence of distinct receptors for taurocholate and glycine. Furthermore, taurocholate, glycine, and chenodeoxycholate seem to bind to C. difficile spores through a complex mechanism, where both receptor homo- and heterocomplexes are formed. The kinetic data also point to an ordered sequential progression of binding where taurocholate must be recognized first before detection of glycine can take place. Finally, comparing calculated kinetic parameters with intestinal concentrations of the two germinants suggests a mechanism for the preferential germination of C. difficile spores in antibiotic-treated individuals.

Spore-forming Bacilli and Clostridia in human disease

Many Gram-positive spore-forming bacteria in the Firmicute phylum are important members of the human commensal microbiota, which, in rare cases, cause opportunistic infections. Other spore-formers, however, have evolved to become dedicated pathogens that can cause a striking variety of diseases. Despite variations in disease presentation, the etiologic agent is often the spore, with bacterially produced toxins playing a central role in the pathophysiology of infection. This review will focus on the specific diseases caused by spores of the Clostridia and Bacilli.

Clostridial spore germination versus bacilli: genome mining and current insights

Bacilli and clostridia share the characteristic of forming metabolically inactive endospores. Spores are highly resistant to adverse environmental conditions including heat, and their ubiquitous presence in nature makes them inevitable contaminants of foods and food ingredients. Spores can germinate under favourable conditions, and the following outgrowth can lead to food spoilage and foodborne illness. Germination of spores has been best studied in Bacillus species, but the process of spore germination is less well understood in anaerobic clostridia. This paper describes a genome mining approach focusing on the genes related to spore germination of clostridia. To this end, 12 representative sequenced Bacillus genomes and 24 Clostridium genomes were analyzed for the distribution of known and putative germination-related genes and their homologues. Overall, the number of ger operons encoding germinant receptors is lower in clostridia than in bacilli, and some Clostridium species are predicted to produce cortex-lytic enzymes that are different from the ones encountered in bacilli. The in silico germination model constructed for clostridia was linked to recently obtained experimental data for selected germination determinants, mainly in Clostridium perfringens. Similarities and differences between germination mechanisms of bacilli and clostridia will be discussed.

Clostridium difficile infection and inflammatory bowel disease

The importance of Clostridium difficile (C. difficile) infection amongst patients with inflammatory bowel disease (IBD) is increasingly being recognized. Recent studies have demonstrated a concerning trend towards increased rates of infection, morbidity, mortality and health costs, and guidelines now promote testing for C. difficile in IBD patients experiencing a relapse. This critical review focuses on the epidemiology, risk factors, pathogenesis, treatment options and outcomes associated with C. difficile infection in patients with IBD.

Metabolism of bile salts in mice influences spore germination in Clostridium difficile

Clostridium difficile, a spore-forming bacterium, causes antibiotic-associated diarrhea. In order to produce toxins and cause disease, C. difficile spores must germinate and grow out as vegetative cells in the host. Although a few compounds capable of germinating C. difficile spores in vitro have been identified, the in vivo signal(s) to which the spores respond were not previously known. Examination of intestinal and cecal extracts from untreated and antibiotic-treated mice revealed that extracts from the antibiotic-treated mice can stimulate colony formation from spores to greater levels. Treatment of these extracts with cholestyramine, a bile salt binding resin, severely decreased the ability of the extracts to stimulate colony formation from spores. This result, along with the facts that the germination factor is small, heat-stable, and water-soluble, support the idea that bile salts stimulate germination of C. difficile spores in vivo. All extracts able to stimulate high level of colony formation from spores had a higher proportion of primary to secondary bile salts than extracts that could not. In addition, cecal flora from antibiotic-treated mice was less able to modify the germinant taurocholate relative to flora from untreated mice, indicating that the population of bile salt modifying bacteria differed between the two groups. Taken together, these data suggest that an in vivo-produced compound, likely bile salts, stimulates colony formation from C. difficile spores and that levels of this compound are influenced by the commensal gastrointestinal flora.

The Ger receptor family from sporulating bacteria

Bacterial spores are specialized cells that are exceptionally resistant to environmental stress. Spores convert back to actively growing cells, a process called germination, upon nutrient detection. The most common, initial step in the germination process is the recognition of small molecule germinants by germination (Ger) receptors. Ger receptors are inner-membrane heterocomplexes formed by three distinct protein products, the A-, B-, and C-subunits. In this review, we discuss and contrast published reports on representative Ger receptors from different Bacilli and Clostridia. We also present evidence for unrecognized germination pathways independent of Ger receptors. We further emphasize the function of L-alanine as a universal germinant. We also comment on biochemical aspects of germinant recognition and interaction between Ger receptor proteins. We propose that there are six general strategies used by Bacilli and Clostridia to integrate multiple germination signals. The use of different germinant recognition strategies results in germination response flexibility. Consequently, sporulating bacterial species that use the same biomolecules as germination signals can have different germination profiles. Finally, we discuss future directions for understanding the function of Ger receptors.

Clostridium difficile infection: An overview of the disease and its pathogenesis, epidemiology and interventions

Clostridium difficile infection (CDI) is the primary cause of antibiotic-associated diarrhea and is a significant nosocomial disease. In the past ten years, variant toxin-producing strains of C. difficile have emerged, that have been associated with severe disease as well as outbreaks worldwide. This review summarizes current information on C. difficile pathogenesis and disease, and highlights interventions used to combat single and recurrent episodes of CDI.

A mariner-based transposon system for in vivo random mutagenesis of Clostridium difficile

Understanding the molecular basis of Clostridium difficile infection is a prerequisite to the development of effective countermeasures. Although there are methods for constructing gene-specific mutants of C. difficile, currently there is no effective method for generating libraries of random mutants. In this study, we developed a novel mariner-based transposon system for in vivo random mutagenesis of C. difficile R20291, the BI/NAP1/027 epidemic strain at the center of the C. difficile outbreaks in Stoke Mandeville, United Kingdom, in 2003 to 2004 and 2004 to 2005. Transposition occurred at a frequency of 4.5 (+/-0.4) x 10(-4) per cell to give stable insertions at random genomic loci, which were defined only by the nucleotide sequence TA. Furthermore, mutants with just a single transposon insertion were generated in an overwhelming majority (98.3% in this study). Phenotypic screening of a C. difficile R20291 random mutant library yielded a sporulation/germination-defective clone with an insertion in the germination-specific protease gene cspBA and an auxotroph with an insertion in the pyrimidine biosynthesis gene pyrB. These results validate our mariner-based transposon system for use in forward genetic studies of C. difficile.