The pathogenicity of Clostridium difficile

A role for TLR4 in Clostridium difficile infection and the recognition of surface layer proteins

Clostridium difficile is the etiological agent of antibiotic-associated diarrhoea (AAD) and pseudomembranous colitis in humans. The role of the surface layer proteins (SLPs) in this disease has not yet been fully explored. The aim of this study was to investigate a role for SLPs in the recognition of C. difficile and the subsequent activation of the immune system. Bone marrow derived dendritic cells (DCs) exposed to SLPs were assessed for production of inflammatory cytokines, expression of cell surface markers and their ability to generate T helper (Th) cell responses. DCs isolated from C3H/HeN and C3H/HeJ mice were used in order to examine whether SLPs are recognised by TLR4. The role of TLR4 in infection was examined in TLR4-deficient mice. SLPs induced maturation of DCs characterised by production of IL-12, TNFα and IL-10 and expression of MHC class II, CD40, CD80 and CD86. Furthermore, SLP-activated DCs generated Th cells producing IFNγ and IL-17. SLPs were unable to activate DCs isolated from TLR4-mutant C3H/HeJ mice and failed to induce a subsequent Th cell response. TLR4⁻/⁻ and Myd88⁻/⁻, but not TRIF⁻/⁻ mice were more susceptible than wild-type mice to C. difficile infection. Furthermore, SLPs activated NFκB, but not IRF3, downstream of TLR4. Our results indicate that SLPs isolated from C. difficile can activate innate and adaptive immunity and that these effects are mediated by TLR4, with TLR4 having a functional role in experimental C. difficile infection. This suggests an important role for SLPs in the recognition of C. difficile by the immune system.

Role of fibronectin-binding protein A in Clostridium difficile intestinal colonization

Clostridium difficile is a frequent cause of severe, recurrent, post-antibiotic diarrhoea and pseudomembranous colitis. Its pathogenicity is mediated mainly by two toxins, TcdA and TcdB. However, different adhesins have also been described as important colonization factors which are implicated in the first step of the intestinal infection. In this study, we focused our interest on one of these adhesins, fibronectin-binding protein A (FbpA), and on its role in the intestinal colonization process. A mutant of FbpA (CDΔFbpA) was constructed in C. difficile strain 630Δerm by using ClosTron technology. This mutant was characterized in vitro and in vivo and compared to the isogenic wild-type strain. Adhesion of the CDΔFbpA mutant to the human colonic epithelial cell line Caco-2 and to mucus-secreting HT29-MTX cells was examined. Surprisingly, the CDΔFbpA mutant adhered more than the wild-type parental strain. The CDΔFbpA mutant was also analysed in three different mouse models by following the intestinal implantation kinetics (faecal shedding) and caecal colonization (7 days post-challenge). We showed that in monoxenic mice, CDΔFbpA shed C. difficile in faeces at the same rate as that of the isogenic wild-type strain but its colonization of the caecal wall was significantly reduced. In dixenic mice, the shedding rate was slower for the CDΔFbpA mutant than for the isogenic wild-type strain during the first days of infection, but no significant difference was observed in caecal colonization. Similar rates of intestinal implantation and caecal colonization were observed for both strains in assays performed in human microbiota-associated mice. Taken together, our data suggest that FbpA plays a role in intestinal colonization by C. difficile.

Clostridium difficile infection: epidemiology and control measurements

Clostridium difficile (C. difficile) is the most commonly recognized cause of nosocomial infection and antibiotic-associated diarrhea in healthcare settings. C. difficile infection (CDI) can result in pseudomembranous colitis. The diagnosis of CDI should be based on a combination of clinical and laboratory findings. The majority of CDIs are acquired from external sources, and healthcare facilities are the main sources of transmission. Rational use of antibiotics is the most effective method to prevent CDI. Effective control measurements for nosocomial infection should be emphasized in healthcare settings to prevent the transmission of CDI. Limited data have shown that probiotics may be effective for the prevention of CDI.

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.

Clostridium difficile toxin B differentially affects GPCR-stimulated Ca2+ responses in macrophages: independent roles for Rho and PLA2

Clostridium difficile toxins cause acute colitis by disrupting the enterocyte barrier and promoting inflammation. ToxB from C. difficile inactivates Rho family GTPases and causes release of cytokines and eicosanoids by macrophages. We studied the effects of ToxB on GPCR signaling in murine RAW264.7 macrophages and found that ToxB elevated Ca(2+) responses to Galphai-linked receptors, including the C5aR, but reduced responses to Galphaq-linked receptors, including the UDP receptors. Other Rho inhibitors also reduced UDP Ca(2+) responses, but they did not affect C5a responses, suggesting that ToxB inhibited UDP responses by inhibiting Rho but enhanced C5a responses by other mechanisms. By using PLCbeta isoform-deficient BMDM, we found that ToxB inhibited Ca(2+) signaling through PLCbeta4 but enhanced signaling through PLCbeta3. Effects of ToxB on GPCR Ca(2+) responses correlated with GPCR use of PLCbeta3 versus PLCbeta4. ToxB inhibited UDP Ca(2+) signaling without reducing InsP3 production or the sensitivity of cellular Ca(2+) stores to exogenous InsP3, suggesting that ToxB impairs UDP signaling at the level of InsP3/Ca(2+)coupling. In contrast, ToxB elevated InsP3 production by C5a, and the enhancement of Ca(2+) signaling by C5a was prevented by inhibition of PLA(2) or 5-LOX but not COX, implicating LTs but not prostanoids in the mechanism. In sum, ToxB has opposing, independently regulated effects on Ca(2+) signaling by different GPCR-linked PLCbeta isoforms in macrophages.

SleC is essential for germination of Clostridium difficile spores in nutrient-rich medium supplemented with the bile salt taurocholate

Clostridium difficile is the major cause of infectious diarrhea and a major burden to health care services. The ability of this organism to form endospores plays a pivotal role in infection and disease transmission. Spores are highly resistant to many forms of disinfection and thus are able to persist on hospital surfaces and disseminate infection. In order to cause disease, the spores must germinate and the organism must grow vegetatively. Spore germination in Bacillus is well understood, and genes important for this process have recently been identified in Clostridium perfringens; however, little is known about C. difficile. Apparent homologues of the spore cortex lytic enzyme genes cwlJ and sleB (Bacillus subtilis) and sleC (C. perfringens) are present in the C. difficile genome, and we describe inactivation of these homologues in C. difficile 630Delta erm and a B1/NAP1/027 clinical isolate. Spores of a sleC mutant were unable to form colonies when germination was induced with taurocholate, although decoated sleC spores formed the same number of heat-resistant colonies as the parental control, even in the absence of germinants. This suggests that sleC is absolutely required for conversion of spores to vegetative cells, in contrast to CD3563 (a cwlJ/sleB homologue), inactivation of which had no effect on germination and outgrowth of C. difficile spores under the same conditions. The B1/NAP1/027 strain R20291 was found to sporulate more slowly and produce fewer spores than 630Delta erm. Furthermore, fewer R20291 spores germinated, indicating that there are differences in both sporulation and germination between these epidemic and nonepidemic C. difficile isolates.

Modulation of pathogen-induced CCL20 secretion from HT-29 human intestinal epithelial cells by commensal bacteria

Background

Human intestinal epithelial cells (IECs) secrete the chemokine CCL20 in response to infection by various enteropathogenic bacteria or exposure to bacterial flagellin. CCL20 recruits immature dendritic cells and lymphocytes to target sites. Here we investigated IEC responses to various pathogenic and commensal bacteria as well as the modulatory effects of commensal bacteria on pathogen-induced CCL20 secretion. HT-29 human IECs were incubated with commensal bacteria (Bifidobacterium infantis or Lactobacillus salivarius), or with Salmonella typhimurium, its flagellin, Clostridium difficile, Mycobacterium paratuberculosis, or Mycobacterium smegmatis for varying times. In some studies, HT-29 cells were pre-treated with a commensal strain for 2 hr prior to infection or flagellin stimulation. CCL20 and interleukin (IL)-8 secretion and nuclear factor (NF)-κB activation were measured using enzyme-linked immunosorbent assays.

Results

Compared to untreated cells, S. typhimurium, C. difficile, M. paratuberculosis, and flagellin activated NF-κB and stimulated significant secretion of CCL20 and IL-8 by HT-29 cells. Conversely, B. infantis, L. salivarius or M. smegmatis did not activate NF-κB or augment CCL20 or IL-8 production. Treatment with B. infantis, but not L. salivarius, dose-dependently inhibited the baseline secretion of CCL20. In cells pre-treated with B. infantis, C. difficile-, S. typhimurium-, and flagellin-induced CCL20 were significantly attenuated. B. infantis did not limit M. Paratuberculosis-induced CCL20 secretion.

Conclusion

This study is the first to demonstrate that a commensal strain can attenuate CCL20 secretion in HT-29 IECs. Collectively, the data indicate that M. paratuberculosis may mediate mucosal damage and that B. infantis can exert immunomodulatory effects on IECs that mediate host responses to flagellin and flagellated enteric pathogens.

A novel genetic switch controls phase variable expression of CwpV, a Clostridium difficile cell wall protein

Clostridium difficile is a nosocomial pathogen that can cause severe gastrointestinal infections. C. difficile encodes a family of cell wall proteins, some of which are implicated in pathogenesis. Here we have characterized CwpV, the largest member of this family. CwpV is surface expressed and post-translationally processed in a manner analogous to the major S-layer protein SlpA. Expression of cwpV is phase variable, with approximately 5% of cells in a population expressing the protein under standard laboratory growth conditions. Upstream of cwpV, inverted repeats flank a 195 bp sequence which undergoes DNA inversion. Use of a gusA transcriptional reporter demonstrated that phase variation is mediated by DNA inversion; in one orientation cwpV is expressed while in the opposite orientation the gene is silent. The inversion region contains neither the promoter nor any of the open reading frame, therefore this system differs from previously described phase variation mechanisms. The cwpV promoter is located upstream of the inversion region and we propose a model of phase variation based on intrinsic terminator formation in the OFF transcript. A C. difficile site-specific recombinase able to catalyse the inversion has been identified.

Mass spectrometric analysis of the S-layer proteins from Clostridium difficile demonstrates the absence of glycosylation

Like many other bacterial cell surfaces, the cell wall of Clostridium difficile is also encapsulated by a proteinaceous paracrystalline layer, the surface (S)-layer. In many bacterial species, the S-layer proteins (SLPs) have been shown to be glycosylated, whereas in other species glycosylation is absent. Unusually, the S-layer of C. difficile is composed of two distinct proteins, the high-molecular weight (HMW) and low-molecular-weight (LMW) SLPs. Previous investigations have reported that one or both of these SLPs are glycosylated, though no definitive study has been conducted. We have used a variety of mass spectrometric approaches to analyse SLPs from a number of strains of C. difficile for the presence of associated glycans. Analysis of intact SLPs by matrix assisted laser desorption/ionisation time of flight (MALDI-ToF) mass spectrometry demonstrated that the observed molecular masses matched the predicted masses of the LMW and HMW SLPs. Furthermore, analysis of Cyanogen bromide (CNBr) and tryptic peptides displayed no evidence of post-translational modification. In the first in-depth study of its kind, we unequivocally demonstrate that the S-layer proteins from the C. difficile strains investigated are not glycosylated.

Induction of toxins in Clostridium difficile is associated with dramatic changes of its metabolism

Certain amino acids, and cysteine in particular, promptly blocked toxin expression in Clostridium difficile strain VPI 10463 when added to late-exponential-phase peptone-yeast cultures, i.e. prior to normal induction of toxins A and B. Glucose reduced toxin yields by 80-fold, but only when supplemented at inoculation. Forty upregulated C. difficile proteins were identified during maximum toxin expression, and most of these were enzymes involved in energy exchange, e.g. succinate, CO/folate and butyrate metabolism. Transcription of tcdA (toxin operon) and folD (CO/folate operon) was induced by 20- and 10-fold, respectively, and with strikingly similar kinetics between OD 0.8 and 1.2. The sigma factors tcdR and sigH were upregulated simultaneously with tcdA and folD (3.5-fold increase of mRNA level), whereas transcription of tcdC, codY, sigB and sigL showed little or no correlation with that of tcdA and folD. The results suggest a connection between toxin expression, alternative energy metabolism and initial sporulation events in C. difficile.

Peripartum Clostridium difficile infection: case series and review of the literature

Clostridium difficile infection (CDI) in nonhospitalized patients has been reported with increased frequency. An association between CDI and pregnancy has not been stressed. This review will report 4 cases of peripartum CDI with characterization of the infecting strain and a literature review. A PubMed search identified 24 recorded cases of peripartum CDI; information was available for 14 cases. Most patients (91%) received prophylactic antibiotics during delivery or for treatment of bacterial infections (50%). All patients reported diarrhea. Two of our reported cases without known risk factors were found by polymerase chain reaction analysis to be infected with an epidemic and hypervirulent C difficile strain. These cases demonstrate the need for clinicians to consider CDI in patients with severe diarrhea, even if they do not have the traditional risk factors for CDI, such as antibiotic use or concurrent hospitalizations. Further research into the scope and risk factors for peripartum CDI is warranted.

Enhanced resistance of restraint-stressed mice to sepsis

Sepsis remains a major health concern across the world. The effects of stress on host resistance to sepsis are still not very clear. To explore the effects of chronic stress on sepsis(') we examined the impact of restraint stress on the resistance of mice to sepsis. Interestingly, it was found that restraint stress enhanced the antisepsis resistance of mice and the concentrations of the proinflammatory cytokines IL-1, IL-6, IL-12, and TNF-alpha in the blood of stressed mice were dramatically reduced post Escherichia coli infection or LPS treatment as compared with that of controls (p < 0.05). In addition, the mRNA expressions of glucocorticoid-induced leucine zipper (GILZ) were up-regulated in the spleen and peritoneal macrophages of mice receiving restraint stress or dexamethasone treatment. These results demonstrate that restraint stress enhances the resistance of mice to sepsis, supporting corticotherapy for sepsis and proposing restraint-stressed mouse as an animal model to elucidate mechanisms of stress-associated, antisepsis resistance.

Immunoreactive cell wall proteins of Clostridium difficile identified by human sera

Clostridium difficile is a leading cause of nosocomial infection in the developed world, causing antibiotic-associated disease in susceptible populations. The identity of immunogenic proteins is important in understanding the pathogenesis of disease and in the design of vaccines. This study analysed the sera of six patients infected during a hospital outbreak of a C. difficile ribotype 017 strain. Using a proteomics-based approach, cell wall proteins were separated by two-dimensional PAGE, and immunoreactive proteins were revealed by reaction with patient sera. The identity of immunoreactive proteins was established by MS. Forty-two different proteins were identified in total. All patient sera reacted with at least one component of the surface-layer protein (SLP), four reacted with both components (high- and low-molecular-mass SLPs), and five reacted with one other cell wall protein, suggesting that these are immunodominant antigens. The role of these proteins as potential vaccine candidates and their roles in pathogenesis deserve further study.

Enhancement of the cytotoxic activity of Clostridium difficile toxin A by surface-associated antigens

Cell-surface antigens of Clostridium difficile and LPS from Escherichia coli were investigated for modulating effects on the activity of C. difficile toxin A on Vero and Caco2 cells. The antigens of C. difficile tested comprised: (i) an EDTA extract, which contained several major and minor cell-surface proteins and the membrane-associated lipocarbohydrate (LC); (ii) a guanidine hydrochloride extract, which mainly contained the surface-layer proteins; (iii) an aqueous phenol-extracted, protein-free LC. On their own, none of the antigens had a detrimental effect on the cells, with the EDTA extract and LC having a marginally protective effect. When these antigens were added to suboptimal levels of toxin A, there was significant enhancement of its cytotoxicity by the EDTA and LC preparations on both cell types. LPS showed some enhancement of the effect of toxin on Vero cells at the lowest levels of toxin investigated. It was concluded that this effect seen in vitro may have a role to play in the colon during infection with C. difficile.

The changing spectrum of clostridium difficile associated disease: implications for dentistry

BACKGROUND

Clostridium difficile is an anaerobic, spore-forming bacterium that causes a wide range of diseases of the gastrointestinal tract. It is best known for its association with uncomplicated antimicrobial-agent-associated diarrhea.

CASE DESCRIPTION

The authors describe two previously published cases of Clostridium difficile-associated disease (CDAD) to highlight its varied clinical manifestations. A 48-year-old woman had mild CDAD after receiving antibiotics after undergoing endodontic surgery. She took metronidazole, and her C. difficile infection resolved. A 31-year-old pregnant woman developed severe CDAD after receiving antibiotics for a urinary tract infection. She underwent surgery to remove part of her colon, but her condition worsened, and she died.

CLINICAL IMPLICATIONS

Dentists often prescribe antimicrobial agents to treat infections. Until recently, these agents also were recommended as prophylaxis for infective endocarditis during invasive oral procedures. An important risk factor for CDAD and recurrent CDAD is antimicrobial agent exposure. Dentists should be aware of CDAD to help prevent its spread and facilitate early recognition and treatment to minimize severe outcomes.

Clostridium difficile colitis in solid organ transplantation--a single-center experience

Clostridium difficile (CD) is one of the most common causes of diarrhea in solid organ transplantation (SOT). Between 1996 and 2005, a total of 2474 solid organ transplants were performed at our institution, of which 43 patients developed CD-associated diarrhea. There were 3 lung, 3 heart, 20 liver, 8 kidney-pancreas, 6 kidney, 1 composite tissue, and 2 multivisceral recipients. Onset of CD infection ranged from 5 to 2453 days posttransplant. All patients presented with abdominal pain and watery diarrhea. Toxins A and B were detected using rapid immunoassay or enzyme immunoassay. Treatment consisted of reduction of immunosuppression, fluid and electrolyte replacement, metronidazole (n=20), oral vancomycin (n=20), and a combination of metronidazole and vancomycin (n=2). Toxic megacolon was seen in five patients. Two of them had colonoscopic decompression, and the remaining three required colonic resection. One of these patients died due to multiorgan failure after cured CD enteritis. The remaining patients were discharged with well-functioning grafts and all are currently alive. CD colitis was a rare complication prior to 2000; 38 of the 43 cases occurred thereafter. We conclude that CD colitis represents a severe complication following SOT. Recently, a dramatic increase in the incidence of this complication has been observed. The development of life-threatening toxic megacolon must be considered in solid organ recipients.

Early and late onset Clostridium difficile-associated colitis following liver transplantation

Clostridium difficile colitis (CDC) remains a serious and common complication after liver transplantation (LT). Four hundred and sixty-seven consecutive LTs in 402 individuals were performed between 1998 and 2001 at our center. Standard immunosuppression consisted of tacrolimus, mycophenolate, and steroids. CD toxins A and B were detected by using a rapid immunoassay or enzyme immunoassay. CDC was diagnosed in 32 patients (5-1999 days post-LT), with 93.8% (30/32) of patients developing CDC during the first year post-LT; three individuals had CDC more than 3 years post-LT, one of which also had early CDC. All patients presented with abdominal pain and watery diarrhea. Patients who developed CDC within 1-year post-LT were significantly more likely to have a hemorrhagic, biliary, or infectious complication. Patients who developed CDC within 28 days post-LT had a significantly higher model end-stage liver disease score. Treatment consisted of fluid and electrolyte replacement and metronidazole and no patients developed toxic megacolon, required colonic resection, or died from CDC. CDC represents a potentially severe complication following LT. Most cases occur early post-LT. Development of a hemorrhagic, biliary, or infectious complication is associated with the development of CDC.

Enterocolitis due to simultaneous infection with rotavirus and Clostridium difficile in adult and pediatric solid organ transplantation

Diarrhea is a well-known complication of immunosuppression but is also frequently caused by pathogens such as Clostridium difficile (CD) and rotavirus (RV). Three adult and five pediatric solid organ recipients (SORs) developed diarrhea with simultaneous identification of CD and RV. Rotavirus was identified using an immunochromatografic- or enzyme-linked immunosorbent assay; CD was identified using a rapid immunoassay or enzyme immunoassay. One adult renal, one adult kidney-pancreas, one adult liver, and five pediatric liver recipients were affected. Onset of RV/CD infection ranged from 2 weeks to 4 years posttransplant. All patients presented with enterocolitis causing significant fluid and electrolyte loss. In adults, CD was treated with metronidazole and in children with oral vancomycin. RV infection was treated with fluid/electrolyte replacement. During diarrhea, a significant rise in tacrolimus serum level was noted. All patients cleared CD. One child developed recurrent episodes of RV infection and died from bacterial sepsis; the renal recipient died 6 months posttransplant from myocardial infarction. The remaining six patients are currently alive with well-functioning grafts. Simultaneous infection with CD and RV may lead to severe diarrhea in SORs. Both pathogens should be considered in SOR presenting with diarrhea.

Bacteriophage-encoded toxins: the ?-holin protein causes caspase-independent non-apoptotic cell death of eukaryotic cells

The bacteriophage-encoded holin proteins are known to promote bacterial cell lysis by forming lesions within the cytoplasmic membrane. Recently, we have shown that the bacteriophage lambda-holin protein exerts cytotoxic activity also in eukaryotic cells accounting for a reduced tumour growth in vivo. In order to elucidate the mechanisms of lambda-holin-induced mammalian cell death, detailed biochemical and morphological analyses were performed. Colocalization analyses by subcellular fractionation and organelle-specific fluorescence immunocytochemistry indicated the presence of the lambda-holin protein in the endoplasmic reticulum and in mitochondria. Functional studies using the mitochondria-specific fluorochrome JC-1 demonstrated a loss of mitochondrial transmembrane potential in response to lambda-holin expression. Morphologically, these cells exhibited unfragmented nuclei but severe cytoplasmic vacuolization representing signs of oncosis/necrosis rather than apoptosis. Consistently, Western blot analyses indicated neither an activation of effector caspases 3 and 7 nor cleavage of the respective substrate poly(ADP-ribose) polymerase (PARP) in an apoptosis-specific manner. These findings suggest that the lambda-holin protein mediates a caspase-independent non-apoptotic mode of cell death.

Toxin production by and adhesive properties of Clostridium difficile isolated from humans and horses with antibiotic-associated diarrhea

Clostridium difficile is a common nosocomial pathogen in humans and animals that causes diarrhea and colitis following antibiotic therapy. Isolates of C. difficile obtained from faecal material from 20 human patients and 6 equine subjects with antibiotic-associated diarrhea were investigated regarding production of toxins A and B, their capacity to adhere to the human intestinal Caco-2 cell line and equine intestinal cells, and for the presence of fimbriae. The results showed that most (17/20) of the human clinical isolates produced both toxins A and B. One of the human isolates proved toxin A-negative/toxin B-positive. All (6/6) horse isolates were positive for both toxins A and B. Both the human and horse isolates possessed the capacity to adhere, to varying degree, to human and equine intestinal cells. It appeared that human isolates produced greater amounts of toxin B, and that there was a host-species dependency on ability to attach to intestinal epithelial cells. No fimbriae were found in any of the investigated isolates.

The emergence ofClostridium difficileas a pathogen of food animals

Clostridium difficilecauses pseudomembranous colitis in humans, usually after disruption of the bowel flora by antibiotic therapy. Factors mediating the frank disease include the dose and toxigenicity of the colonizing strain, its ability to adhere to colonic epithelium, the concurrent presence of organisms that affect multiplication and toxin production or activity, and the susceptibility of the host. Toxins A (an enterotoxin) and B (a cytotoxin) play the major role in pathogenesis and the detection of toxins in gut contents is the gold standard for diagnosis. Disease in horses takes the form of often-fatal foal hemorrhagic enteritis. Nosocomial, antibiotic-associated, disease is increasingly common in adult horses. Enteric clinical signs are reported in ostriches, companion animals and recently calves.Clostridium difficilecolitis is now a common diagnosis in neonatal pigs in the USA and elsewhere. Clinical features include onset at 1–5 days of age, sometimes with dyspnea, mild abdominal distension and scrotal edema, and commonly with yellow, pasty diarrhea. There is mesocolonic edema grossly, with microscopic diffuse colitis, mucosal edema, crypt distension, epithelial necrosis and superficial mucosal erosion. Neutrophil infiltration of the lamina propria is common, and fibrin and numerous rod-shaped bacteria are observed on the surface. About two-thirds of litters and one-third of piglets will be affected (based upon positive toxin tests), although this appears to vary with the season. The case fatality rate is probably low if considering only direct effects ofC. difficileinfection. The significance of toxin-positive non-diarrheic pigs and the nature of the interaction of toxins A and B with enterocytes are unknown. Given the widespread occurrence of the disease, there is substantial effort to develop immunoprophylactic products.

Evaluation of three rapid assays for detection of Clostridium difficile toxin A and toxin B in stool specimens

Diagnosis of Clostridium difficile-associated disease continues to be difficult for clinical microbiology laboratories. The aim of this study was to evaluate the performance of three enzyme immunoassays for detection of C. difficile toxins A and B: the recently marketed rapid enzyme immunoassay Ridascreen Clostridium difficile Toxin A/B (R-Biopharm, Darmstadt, Germany) and two established enzyme immunoassays, the C. difficile Tox A/B II Assay (TechLab, Blacksburg, VA, USA) and the ProSpecT C. difficile Toxin A/B Microplate Assay (Remel, Lenexa, KS, USA). Stool specimens (n = 383) from patients with a clinical diagnosis of antibiotic-associated diarrhea were examined by these three enzyme immunoassays and were additionally cultured for C. difficile on selective agar. Samples giving discordant enzyme immunoassay results underwent confirmatory testing by tissue culture cytotoxin B assay and by PCR for toxin A (tcdA) and toxin B (tcdB) genes from C. difficile. Using the criteria adopted for this study, 60 (15.7%) samples tested positive for toxins A and/or B. Sensitivity and specificity of the enzyme immunoassays were, respectively, 88.3 and 100% for the TechLab enzyme immunoassay, 91.7 and 100% for the R-Biopharm enzyme immunoassay, and 93.3 and 100% for the Remel enzyme immunoassay. The differences between these results are statistically not significant (p > 0.05). The results show that all three enzyme immunoassays are acceptable tests for the detection of C. difficile toxins A and B directly in fecal specimens or in toxigenic cultures.

Regulation of Apoptosis by Gram-Positive Bacteria: Mechanistic Diversity and Consequences for Immunity

Apoptosis, or programmed cell death (PCD), is an important physiological mechanism, through which the human immune system regulates homeostasis and responds to diverse forms of cellular damage. PCD may also be involved in immune counteraction to microbial infection. Over the past decade, the amount of research on bacteria-induced PCD has grown tremendously, and the implications of this mechanism on immunity are being elucidated. Some pathogenic bacteria actively trigger the suicide response in critical lineages of leukocytes that orchestrate both the innate and adaptive immune responses; other bacteria proactively prevent PCD to benefit their own survival and persistence. Currently, the microbial virulence factors, which represent the keys to unlocking the suicide response in host cells, are a primary focus of this field. In this review, we discuss these bacterial "apoptosis regulatory molecules" and the apoptotic events they either trigger or prevent, the host target cells of this regulatory activity, and the possible ramifications for immunity to infection. Gram-positive pathogens including Staphylococcus, Streptococcus, Bacillus, Listeria, and Clostridia species are discussed as important agents of human infection that modulate PCD pathways in eukaryotic cells.

Clostridium difficile: An important pathogen of food animals

Human Clostridium difficile-associated disease (CDAD) is of unquestioned importance in humans, and has been a not-uncommon cause of enteric disease in horses, dogs, and ratites. Over the past 5 years, C. difficile has emerged as a major cause of neonatal enteritis in pigs. Piglets 1-7 days of age are affected, with gross lesions frequently including mesocolonic edema. Colonic contents may be pasty-to-watery and yellow, although some piglets are constipated or obstipated. Focal suppuration and segmental necrosis are seen on microscopic examination of cecal and colonic lamina propria, and exudation of neutrophils and fibrin into the lumen gives rise to the so-called volcano lesions. Results of one study revealed that more than one-third of piglets with enteritis were affected by C. difficile alone, while an additional quarter of affected piglets may have had mixed infections. C. difficile may be the most important uncontrolled cause of neonatal diarrhea in pigs.

A predominantly clonal multi-institutional outbreak of Clostridium difficile-associated diarrhea with high morbidity and mortality

BACKGROUND

In March 2003, several hospitals in Quebec, Canada, noted a marked increase in the incidence of Clostridium difficile-associated diarrhea.

METHODS

In 2004 we conducted a prospective study at 12 Quebec hospitals to determine the incidence of nosocomial C. difficile-associated diarrhea and its complications and a case-control study to identify risk factors for the disease. Isolates of C. difficile were typed by pulsed-field gel electrophoresis and analyzed for binary toxin genes and partial deletions in the toxin A and B repressor gene tcdC. Antimicrobial susceptibility was evaluated in a subgroup of isolates.

RESULTS

A total of 1703 patients with 1719 episodes of nosocomial C. difficile-associated diarrhea were identified. The incidence was 22.5 per 1000 admissions. The 30-day attributable mortality rate was 6.9 percent. Case patients were more likely than matched controls to have received fluoroquinolones (odds ratio, 3.9; 95 percent confidence interval, 2.3 to 6.6) or cephalosporins (odds ratio, 3.8; 95 percent confidence interval, 2.2 to 6.6). A predominant strain, resistant to fluoroquinolones, was found in 129 of 157 isolates (82.2 percent), and the binary toxin genes and partial deletions in the tcdC gene were present in 132 isolates (84.1 percent).

CONCLUSIONS

A strain of C. difficile that was resistant to fluoroquinolones and had binary toxin and a partial deletion of the tcdC gene was responsible for this outbreak of C. difficile-associated diarrhea. Exposure to fluoroquinolones or cephalosporins was a risk factor.

Clostridium difficile in emergency room

Clostridium difficile strains are known as etiological agents of pseudomembranous colitis (PMC), antibiotic-associated diarrhea (AAC) and colitis (AAC) and hospital-acquired infections. The aim of this study was to determine the frequency of C. difficile infection among patients in the emergency room and to compare isolated strains by phenotypic and genotypic characteristics. During a period of 11 months, 56 stool samples taken from diarrheic patients hospitalized in the emergency room of the Medical Center UC Davis and 14 environmental samples were cultured for isolation of C. difficile strains. Eighteen C. difficile strains were isolated from stool samples cultured on selective TCCCA plates and 5 strains from environmental samples using Rodac plates. Eleven toxigenic (TcdA+/TcdB+), 6 non-toxigenic (TcdA-/TcdB-) and unique toxin A-negative/toxin B-positive (TcdA-/TcdB+) C. difficile strains were detected among patients' isolates and 3 toxigenic and 2 non-toxigenic strains-among environmental samples. The majority of C. difficile-positive patients were treated previously by antibiotics. Four strains isolated from patients' fecal samples and one strain isolated from the environment demonstrated high-level resistance to erythromycin and clindamycin (MIC >256mug/mL). The results obtained by AP-PCR and PCR-ribotyping revealed genetic heterogeneity among the strains isolated from patients' fecal samples. However, similarity was observed among environmental strains and strains isolated from patients' fecal samples. Considering the importance of emergency room patients as a potential source of C. difficile strains, it appears to be important examine these patients for C. difficile before transfer to the other hospital units.

Pathogenesis and treatment of Clostridium difficile infection

This paper reviews the pathogenesis and management of Clostridium difficile diarrhoea, in particular the management of recurrent episodes.

Toxigenic C. difficile induced inflammatory marker expression by human intestinal epithelial cells is asymmetrical

Clostridium difficile infection of the intestinal epithelium and consequent pseudomembranous colitis is an important cause of morbidity and mortality. Pathogenesis has been ascribed exclusively to toxin production. Using in vitro models of human intestinal epithelial layers, we show that exposure to toxigenic C. difficile upregulates epithelial expression of IL-8 and ICAM-1, two molecules important in neutrophil chemoattraction and adhesion and subsequent inflammation. IL-8 production was also stimulated by toxin-containing supernatants. C difficile induced IL-8 release was inhibited by specific antiserum. Increased ICAM-1 expression only occurred after basolateral exposure to C. difficile while apical exposure had no effect on ICAM-1 expression. However, transepithelial electrical resistance was impaired by apical exposure to bacterial suspensions. We suggest that apical exposure to C. difficile induces changes in epithelial layer integrity which allows the bacteria and/or the toxin access to the basolateral compartment where pathogenic inflammatory mechanisms are activated.

A survey of metronidazole and vancomycin resistance in strains of Clostridium difficile isolated in Warsaw, Poland

The drug of choice used to treat Clostridium difficile-associated diarroea (CDAD) are metronidazole and vancomycin. Information about emergence of antimicrobial resistance among C. difficile strains to metronidazole and intermediate resistance to vancomycin in some countries are alarming. This study was performed to determine the susceptibility to metronidazole and vancomycin of 193 C. difficile strains isolated in our diagnostic laboratory between year 1998 and 2003 from patients adults and children suffering from CDAD. Among these strains, 142 produced toxin A and B (TcdA(+)TcdB(+)), 43 only B (TcdA(-)TcdB(+)) and 8 were nontoxigenic. We have not observed any differences in susceptibility to metronidazole and vancomycin between all C. difficile strains under investigation (toxinogenic and non-toxinogenic). Resistance to metronidazole and vancomycin was not observed.

Analysis of Clostridium difficile-associated diarrhea among patients hospitalized in tertiary care academic hospital

The frequency of Clostridium difficile strains in stool samples of patients with diarrhea hospitalized in the hematology/oncology, surgery, orthopedics, transplantology ward, and emergency room of Davis Medical Center was analyzed. A total of 786 stool samples collected from patients with diarrhea and 180 samples taken from the hospital environment were cultured for C. difficile by routine methods. There were 119 strains of C. difficile isolated: 97 (12.3%) strains from patients' stools (no enteropathogen other than C. difficile was detected in these stool samples) and 22 (12.2%) strains from the hospital environment. It was confirmed that hospital environment plays an important role in transmission of C. difficile by AP-PCR and PCR ribotyping. Among 97 C. difficile strains isolated from patient' stools 25 were nontoxigenic (A-/B-), 67 were toxigenic (A+/B+), and 5 strains were toxin B-positive/toxin A-negative. Analysis of concomitant symptoms among hospitalized patients with diarrhea demonstrated significantly longer duration of diarrhea caused by nontoxigenic strains than in cases of diarrhea caused by toxigenic strains. On the other hand, among patients infected by toxigenic strains, significantly higher leukocytosis and longer duration of fever were observed. The resistance of isolated C. difficile strains to erythromycin and clindamycin indicated the possibility of transmission in the hospital strains with macrolide-lincosamide-streptogramin B resistance type.

Proteomic analysis of cell surface proteins fromClostridium difficile

Clostridium difficile is a bacterium that causes disease of the large intestine, particularly after treatment with antibiotics. The bacterium produces two toxins (A and B) that are responsible for the pathology of the disease. In addition, a number of bacterial virulence factors associated with adhesion to the gut have previously been identified, including the cell wall protein Cwp66, the high-molecular weight surface layer protein (HMW-SLP) and the flagella. As the genome sequence predicts many other cell wall associated proteins, we have investigated the diversity of proteins in cell wall extracts, with the aim of identifying further virulence factors. We have used a number of methods to remove the proteins associated with the cell wall of C. difficile. Two of the resulting extracts, obtained using low pH glycine treatment and lysozyme digestion of the cell wall, have been analysed in detail by two-dimensional electrophoresis and mass spectrometry. One hundred and nineteen spots, comprising 49 different proteins, have been identified. The two surface layer proteins (SLPs) are the most abundant proteins, and we have also found components of the flagellum. Interestingly, we have also determined that a number of paralogs of the HMW-SLP are expressed, and these could represent targets for further investigation as virulence factors.

Generation of an erythromycin-sensitive derivative of Clostridium difficile strain 630 (630Δerm) and demonstration that the conjugative transposon Tn916ΔE enters the genome of this strain at multiple sites

Erythromycin resistance in Clostridium difficile strain 630 is conferred by a genetic element termed Tn5398 which contains two erm(B) genes: erm1(B) and erm2(B). An erythromycin-sensitive derivative of strain 630 (designated 630Deltaerm) was generated by spontaneous mutation after continuous subculture for 30 days. This strain had lost the erm2(B) gene from within Tn5398 but retained erm1(B). However, the strain could revert to erythromycin resistance at a frequency of 2.79 x 10(-8), although it still contained the deletion of erm2(B). The availability of C. difficile 630Deltaerm allowed the behaviour of Tn916DeltaE to be investigated in this strain. This element entered the genome at multiple sites indicating that it could be useful as an insertional mutagen.

Steroid-refractory ulcerative colitis treated with corticosteroids, metronidazole and vancomycin: a case report

BACKGROUND

Increasing evidence elucidating the pathogenic mechanisms of ulcerative colitis (UC) has accumulated and the disease is widely assumed to be the consequence of genetic susceptibility and an abnormal immune response to commensal bacteria. However evidence regarding an infectious etiology in UC remains elusive.

CASE PRESENTATION

We report a provocative case of UC with profound rheumatologic involvement directly preceded by Clostridium difficile infection and accompanying fever, vomiting, bloody diarrhea, and arthritis. Colonic biopsy revealed a histopathology suggestive of UC. Antibiotic treatment eliminated detectable levels of enteric pathogens but did not abate symptoms. Resolution of symptoms was procurable with oral prednisone, but tapering of corticosteroids was only achievable in combination therapy with vancomycin and metronidazole.

CONCLUSIONS

An infectious pathogen may have both precipitated and exacerbated autoimmune disease attributes in UC, symptoms of which could be resolved only with a combination of corticosteroids, vancomycin and metronidazole. This may warrant the need for more perceptive scrutiny of C. difficile and the like in patients with UC.

[Characterization of an extracellular protease from Clostridium difficile]

Clostridium difficile is an intestinal pathogen, which produces two main virulence factors, the exotoxins A and B. Other bacterial structures have been implicated in the colonization of the gastrointestinal tract, which is the first step of the pathogenic process. C. difficile expresses adherence factors and also, displays some surface-associated proteolytic activity, which could play a role in the physiopathology of this bacterium. The aim of this work was to study the protein named Cwp84 which displays significant homologies with many cysteine proteases. The coding catalytic domain of this protein has been cloned in the expression system pGEX-6P-1, as an in-frame fusion with the gluthatione S-transferase, and subsequently purified. The purified fraction showed proteolytic activity on gelatine and BAPNA, but not on azocoll, suggesting a highly selective substrate specificity. The results obtained from inhibition experiments confirmed that Cwp84 belongs to the cysteine protease family. Cwp84 could play a role in degrading some specific host proteins or in the maturation of surface-associated bacterial proteins.

Large clostridial cytotoxins

The large clostridial cytotoxins are a family of structurally and functionally related exotoxins from Clostridium difficile (toxins A and B), C. sordellii (lethal and hemorrhagic toxin) and C. novyi (alpha-toxin). The exotoxins are major pathogenicity factors which in addition to their in vivo effects are cytotoxic to cultured cell lines causing reorganization of the cytoskeleton accompanied by morphological changes. The exotoxins are single-chain protein toxins, which are constructed of three domains: receptor-binding, translocation and catalytic domain. These domains reflect the self-mediated cell entry via receptor-mediated endocytosis, translocation into the cytoplasm, and execution of their cytotoxic activity by an inherent enzyme activity. Enzymatically, the toxins catalyze the transfer of a glucosyl moiety from UDP-glucose to the intracellular target proteins which are the Rho and Ras GTPases. The covalent attachment of the glucose moiety to a conserved threonine within the effector region of the GTPases renders the Rho-GTPases functionally inactive. Whereas the molecular mode of cytotoxic effects is fully understood, the mechanisms leading to inflammatory processes in the context of disease (e.g., antibiotic-associated pseudomembranous colitis caused by Clostridium difficile) are less clear.

Clostridium difficile-associated diarrhea in adults

Clostridium difficile is the most important cause of nosocomial diarrhea in adults. Illness may range from mild watery diarrhea to life-threatening colitis. An antecedent disruption of the normal colonic flora followed by exposure to a toxigenic strain of C. difficile are necessary first steps in the pathogenesis of disease. Diagnosis is based primarily on the detection of C. difficile toxin A or toxin B. First-line treatment is with oral metronidazole therapy. Treatment with oral vancomycin therapy should be reserved for patients who have contraindications or intolerance to metronidazole or who fail to respond to first-line therapy.

Proteomics of protein secretion by Bacillus subtilis: separating the "secrets" of the secretome

Secretory proteins perform a variety of important "remote-control" functions for bacterial survival in the environment. The availability of complete genome sequences has allowed us to make predictions about the composition of bacterial machinery for protein secretion as well as the extracellular complement of bacterial proteomes. Recently, the power of proteomics was successfully employed to evaluate genome-based models of these so-called secretomes. Progress in this field is well illustrated by the proteomic analysis of protein secretion by the gram-positive bacterium Bacillus subtilis, for which approximately 90 extracellular proteins were identified. Analysis of these proteins disclosed various "secrets of the secretome," such as the residence of cytoplasmic and predicted cell envelope proteins in the extracellular proteome. This showed that genome-based predictions reflect only approximately 50% of the actual composition of the extracellular proteome of B. subtilis. Importantly, proteomics allowed the first verification of the impact of individual secretion machinery components on the total flow of proteins from the cytoplasm to the extracellular environment. In conclusion, proteomics has yielded a variety of novel leads for the analysis of protein traffic in B. subtilis and other gram-positive bacteria. Ultimately, such leads will serve to increase our understanding of virulence factor biogenesis in gram-positive pathogens, which is likely to be of high medical relevance.

Microbial-gut interactions in health and disease. Antibiotic-associated diarrhoea

Most cases of antibiotic-associated diarrhoea (AAD) are directly or indirectly due to the alteration of gut microflora by antibiotics. 'Functional' diarrhoea, usually limited to a mild and brief change in stool frequency, is considered as the most frequent pattern of AAD. Reduced carbohydrate fermentation and impaired metabolism of bile acids have been claimed as the potential causes of this transient digestive discomfort but a critical analysis of the data supporting these theories is necessary. Alternatively, changes in the gut flora ecosystem allow pathogens to proliferate. Clostridium difficile is responsible for approximately 10% of cases of AAD and almost all cases of antibiotic-associated pseudomembranous colitis. The level of evidence which supports the potential responsibility of other candidate pathogens (Klebsiella oxytoca, enterotoxin-producing Clostridium perfringens and Staphylococcus aureus, Candida) needs to be appreciated according to the updated postulates of causality relationships between a bacterium and a disease.

Development of an integrative vector for the expression of antisense RNA in Clostridium difficile

A method was developed to use the conjugative transposon Tn916 as a vector for introducing recombinant DNA into Clostridium difficile. This was used to introduce antisense RNA for the adhesin encoding gene cwp66 into C. difficile 79-685. RT-PCR demonstrated that cwp66 specific antisense RNA was produced. However, there was no statistically significant difference in the protein expression or in the adherence of recombinant C. difficile strains. This may be due to the amount of transcripts of the wild-type (sense) cwp66 outnumbering the antisense transcripts or secondary structures present within the cwp66 mRNA. Unlike in other strains of C. difficile, where Tn916 inserts into the genome at highly preferred sites, in C. difficile 79-685, it integrates into multiple sites opening up the possibility of using Tn916 as a mutagen in this strain.

Topical acne drugs: review of clinical properties, systemic exposure, and safety

This review examines the commonly available topical acne agents and factors that determine their percutaneous absorption. Reported and theoretical adverse effects from systemic exposure are detailed. The topical retinoid class, which includes tretinoin, adapalene and tazarotene, and the topical antibacterials, clindamycin and erythromycin, are regulated by prescription in most countries. Used appropriately, the above-mentioned drugs deliver, at most, miniscule amounts of active ingredient into the circulation. Clear-cut links to systemic toxicity in humans are practically nonexistent, except in the case of topical clindamycin, which has been associated with diarrhea rarely, and there have been 2 cases of pseudomembranous colitis reported. Birth defects have occurred in two patients treated with tretinoin and one patient treated with adapalene, but causation was not proven. Another prescription drug, 20% azelaic acid, is associated with relatively high systemic exposure, which is presumed innocuous because it is a normal dietary constituent whose endogenous levels are not altered by topical use. Benzoyl peroxide, salicylic acid, sulfur, and sodium sulfacetamide are available in concentrations of 2% or more in over-the-counter acne treatments and some prescription products. All of these agents are known to exhibit some degree of percutaneous absorption. They remain largely unregulated because, other than skin irritation, only local allergic contact dermatitis from benzoyl peroxide in about 2.5% of patients and rare local and systemic hypersensitivity reactions from sodium sulfacetamide have been reported. Salicylism has occurred using methyl salicylate ointments and high concentrations of salicylic acid on widespread areas of hyperkeratotic skin, but there are no known cases resulting from salicylic acid acne products. Caution is advised in special circumstances, such as during childhood, pregnancy, lactation and concomitant therapy with other drugs, because relevant studies are lacking. Animal data support avoidance of many topical agents, particularly known teratogens such as retinoids and salicylic acid, in pregnant women. Salicylate avoidance is advised during lactation, because aspirin use carries the risk of bleeding disorders in nursing infants.

Enteric flora and lymphocyte-derived cytokines determine expression of heat shock proteins in mouse colonic epithelial cells

BACKGROUND & AIMS

Inducible heat shock proteins (hsps), particularly hsp25 and hsp72, are expressed by surface colonocytes and may have a role in protecting intestinal epithelial cells against injury. This study is aimed at determining if enteric bacteria and/or immune signals regulate their physiologic expression.

METHODS

Intestinal hsp25, hsp72, and constitutive hsc73 expression were studied in immunodeficient RAG-1(-/-) mice and in normal mice. Mucosal permeability was measured by mannitol flux and transepithelial resistance. Hsp expression in intestinal YAMC cells was assessed after incubation with recombinant cytokines, activated lamina propria lymphocytes (LPLs), or Bacteroides fragilis.

RESULTS

Chronic metronidazole treatment decreases colonic mucosal hsp25 and hsp72 expression, an effect associated with increased susceptibility of mucosal barrier function to C. difficile toxin A. Hsp expression also was increased in YAMC cells incubated with B. fragilis, an effect mediated by lipopolysaccharide and other bacteria-derived factors. Colonic hsp72, but not hsp25 or hsc73, expression is decreased in RAG-1(-/-) mice. Recombinant IL-2 and other cytokines enhance YAMC hsp25 and/or hsp72 expression. Activated LPLs induce YAMC hsp expression, an effect blocked by IL-2 neutralizing antibody.

CONCLUSIONS

Enteric flora and mucosal lymphocytes play a role in maintaining physiologic expression of colonocyte hsp25 and hsp72.