Clostridium difficile-associated diarrhoea

Harnessing the glucosyltransferase activities of Clostridium difficile for functional studies of toxins A and B

The incidence of Clostridium difficile infection (CDI) has been increasing within the last decade. Pathogenic strains of C. difficile produce toxin A and/or toxin B, which are important virulence factors in the pathogenesis of this bacterium. Current methods for diagnosing CDI are mostly qualitative tests that detect either the bacterium or the toxins. We have developed an assay (Cdifftox activity assay) to detect C. difficile toxin A and B activities that is quantitative and cost-efficient and utilizes a substrate that is stereochemically similar to the native substrate of the toxins (UDP-glucose). To characterize toxin activity, toxins A and B were purified from culture supernatants by ammonium sulfate precipitation and chromatography through DEAE-Sepharose and gel filtration columns. The activities of the final fractions were quantitated using the Cdifftox activity assay and compared to the results of a toxin A- and B-specific enzyme-linked immunosorbent assay (ELISA). The affinity for the substrate was >4-fold higher for toxin B than for toxin A. Moreover, the rate of cleavage of the substrate was 4.3-fold higher for toxin B than for toxin A. The optimum temperature for both toxins ranged from 35 to 40°C at pH 8. Culture supernatants from clinical isolates obtained from the stools of patients suspected to be suffering from CDI were tested using the Cdifftox activity assay, and the results were compared to those of ELISA and PCR amplification of the toxin genes. Our results demonstrate that this new assay is comparable to the current commercial ELISA for detecting the toxins in the samples tested and has the added advantage of quantitating toxin activity.

Both, toxin A and toxin B, are important in Clostridium difficile infection

The bacterium Clostridium difficile is the leading cause of healthcare associated diarrhoea in the developed world and thus presents a major financial burden. The main virulence factors of C. difficile are two large toxins, A and B. Over the years there has been some debate over the respective roles and importance of these two toxins. To address this, we recently constructed stable toxin mutants of C. difficile and found that they were virulent if either toxin A or toxin B was functional. This underlined the importance of each toxin and the necessity to consider both when developing countermeasures against Clostridium difficile infection (CDI). In this article we discuss our findings in the context of previous work and outline some of the challenges which face the field as a result.

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.

The enterotoxicity of Clostridium difficile toxins

The major virulence factors of Clostridium difficile infection (CDI) are two large exotoxins A (TcdA) and B (TcdB). However, our understanding of the specific roles of these toxins in CDI is still evolving. It is now accepted that both toxins are enterotoxic and proinflammatory in the human intestine. Both purified TcdA and TcdB are capable of inducing the pathophysiology of CDI, although most studies have focused on TcdA. C. difficile toxins exert a wide array of biological activities by acting directly on intestinal epithelial cells. Alternatively, the toxins may target immune cells and neurons once the intestinal epithelial barrier is disrupted. The toxins may also act indirectly by stimulating cells to produce chemokines, proinflammatory cytokines, neuropeptides and other neuroimmune signals. This review considers the mechanisms of TcdA- and TcdB-induced enterotoxicity, and recent developments in this field.

Piglet models of acute or chronic Clostridium difficile illness

We examined the piglet model of Clostridium difficile illness (CDI) in humans, because swine are naturally susceptible to C. difficile. The piglet is a reproducible model of acute or chronic CDI with characteristic pseudomembranous colitis. Germ-free piglets were consistently and extensively colonized after oral challenge with the human strain 027/BI/NAP1, establishing an infectious dose-age relationship. This allowed a demarcation between acute fatal and chronic models. The clinical manifestations of disease inclusive of gastrointestinal and systemic symptoms and characteristic mucosal lesions of the large bowel (including pseudomembranous colitis) are described. Additionally, we demonstrate the presence of toxins in feces, body fluids, and serum and a significant elevation in interleukin 8 levels in animals with severe disease. We conclude that piglets infected with C. difficile mimic many of the key characteristics observed in humans with CDI and are suitable animals in which to investigate the role played by virulence attributes, drug efficacy, and vaccine candidates.

Characterization of the sporulation initiation pathway of Clostridium difficile and its role in toxin production

Clostridium difficile is responsible for significant mortality and morbidity in the hospitalized elderly. C. difficile spores are infectious and are a major factor contributing to nosocomial transmission. The Spo0A response regulator is the master regulator for sporulation initiation and can influence many other cellular processes. Using the ClosTron gene knockout system, we inactivated genes encoding Spo0A and a putative sporulation-associated sensor histidine kinase in C. difficile. Inactivation of spo0A resulted in an asporogeneous phenotype, whereas inactivation of the kinase reduced C. difficile sporulation capacity by 3.5-fold, suggesting that this kinase also has a role in sporulation initiation. Furthermore, inactivation of either spo0A or the kinase resulted in a marked defect in C. difficile toxin production. Therefore, Spo0A and the signaling pathway that modulates its activity appear to be involved in regulation of toxin synthesis in C. difficile. In addition, Spo0A was directly phosphorylated by a putative sporulation-associated kinase, supporting the hypothesis that sporulation initiation in C. difficile is controlled by a two-component signal transduction system rather than a multicomponent phosphorelay. The implications of these findings for C. difficile sporulation, virulence, and transmission are discussed.

Low occurrence of Clostridium difficile in retail ground meat in Sweden

This pilot study was conducted to evaluate the occurrence of Clostridium difficile in samples of ground meat in Sweden. From April to September 2008, 82 meat samples were collected from randomly selected retail shops in Uppsala County (central Sweden). C. difficile was isolated from 2 (2.4%; both ground beef) of the 82 meat samples. No C. difficile was detected in pork, hamburger, sheep, poultry, or other type of meat samples. The two C. difficile isolates produced both toxin A and toxin B. These findings indicate that C. difficile might be present in ground meat samples in Sweden. However, further studies are necessary to confirm these preliminary data and to elucidate the public health significance of meat contamination by C. difficile in Sweden.

Long-term follow-up of patients with fulminant Clostridium difficile colitis

PURPOSE

The purpose of this study was to determine the long-term survival rate, rate of gastrointestinal continuity restoration, and rate of recurrence following an attack of fulminant Clostridium difficile colitis.

MATERIAL AND METHODS

Fulminant C. difficile colitis was defined as any patient who had a bout of C. difficile colitis and required surgical intervention after failing medical therapy. These patients were found through a pathological database search. Follow-up phone calls were made to any patient who survived at least 30 days after being discharged from the hospital following surgical intervention (long-term survivor group).

RESULTS

A total of 49 patients were involved in the study. The 30-day mortality rate was 57% (28/49), with an in-hospital mortality rate of 49%. The 5-year survival rate for the long-term survival group was 38% (8/21) and 16.3% for all patients. Gastrointestinal continuity was restored in 20% of the patients. There was one documented recurrence of C. difficile colitis

CONCLUSION

Patients who have a bout of fulminant C. difficile colitis have a poor prognosis of surviving longer than 5 years. Restoring gastrointestinal continuity is uncommon and usually reserved for patients with few co-morbidities. Recurrent C. difficile colitis after surgical resection is a rare occurrence.

Clostridium difficile-associated enteric disease after percutaneous endoscopic gastrostomy

BACKGROUND

Percutaneous endoscopic gastrostomy (PEG) has become established as a useful enteral nutrition technique. Although various adverse events related to PEG are known, few reports have described Clostridium difficile-associated enteric disease (CDED) after PEG. We encountered several cases of CDED with onset soon after PEG. The present study examined these cases in detail and analyzed potential risk factors.

METHODS

A total of 239 patients underwent PEG at our hospital from 1999, and the subjects comprised 233 patients for whom data could be statistically analyzed. CDED with onset soon after PEG was defined for cases with symptoms within 1 month after PEG. We investigated features and prognosis of these cases. A total of 19 predictors were chosen, and logistic regression analysis was performed using CDED with onset soon after PEG as a dependent variable.

RESULTS

Mean patient age was high, and about 65% were men. Their body weights were low and their general condition was markedly poor. CDED with onset soon after PEG was shown in 15 patients (6.4%). Although oral administration of vancomycin resulted in prompt recovery in most cases, enteral nutrition was interrupted for a long period, and the general condition deteriorated markedly in two patients. Logistic regression analysis identified "past history of CDED" and "antibiotic dosing period at PEG" as risk factors for CDED onset soon after PEG.

CONCLUSIONS

CDED occurred with onset soon after PEG at a comparatively high rate. Our analysis suggested "past history of CDED" and "antibiotic dosing period at PEG" as risk factors for CDED after PEG.

Laboratory maintenance of Clostridium difficile

Clostridium difficile is a Gram-positive, spore-forming, anaerobe and is the leading cause of antibiotic-associated diarrhea, pseudomembranous colitis, and toxic megacolon. Essential to the lifestyle of C. difficile is the ability to form a metabolically dormant spore, germinate, and grow out upon appropriate signals and elicit disease with the secretion of two toxins. To aid in the study of this organism, this unit describes the growth and maintenance of C. difficile. Included are methods to isolate C. difficile from environmental samples, grow in laboratory medium, and produce and purify spores.

What have we learned about antimicrobial use and the risks for Clostridium difficile-associated diarrhoea?

Clostridium difficile is recognized as a major cause of antibiotic-associated diarrhoea and colitis. Antimicrobial agents have been repeatedly recognized as a causative risk for C. difficile-associated diarrhoea (CDAD) and more recently fluoroquinolones have been particularly implicated. Unfortunately, not all reports of antimicrobial associations with CDAD have excluded variables other than antimicrobial use. Prevention of CDAD usually involves infection control interventions and antimicrobial restriction policies may not be fully substantiated by currently available data; however, antimicrobial drug restriction seems prudent in outbreak situations.

Molecular characterization of a Clostridium difficile bacteriophage and its cloned biologically active endolysin

Clostridium difficile infection is increasing in both frequency and severity, with the emergence of new highly virulent strains highlighting the need for more rapid and effective methods of control. Here, we show that bacteriophage endolysin can be used to inhibit and kill C. difficile. The genome sequence of a novel bacteriophage that is active against C. difficile was determined, and the bacteriophage endolysin gene was subcloned and expressed in Escherichia coli. The partially purified endolysin was active against 30 diverse strains of C. difficile, and importantly, this group included strains of the major epidemic ribotype 027 (B1/NAP1). In contrast, a range of commensal species that inhabit the gastrointestinal tract, including several representatives of the clostridium-like Firmicutes, were insensitive to the endolysin. This endolysin provides a platform for the generation of both therapeutic and detection systems to combat the C. difficile problem. To investigate a method for the protected delivery and production of the lysin in the gastrointestinal tract, we demonstrated the expression of active CD27L endolysin in the lactic acid bacterium Lactococcus lactis MG1363.