The pathogenicity of Clostridium difficile

Expression of Clostridium difficile toxins A and B and their sigma factor TcdD is controlled by temperature

Growth temperature was found to control the expression of toxins A and B in Clostridium difficile VPI 10463, with a maximum at 37 degrees C and low levels at 22 and 42 degrees C in both peptone yeast (PY) and defined media. The up-regulation of toxin A and B mRNA and protein levels upon temperature upshift from 22 to 37 degrees C followed the same kinetics, showing that temperature control occurred at the level of transcription. Experiments with Clostridium perfringens using gusA as a reporter gene demonstrated that both toxin gene promoters were temperature controlled and that their high activity at 37 degrees C was dependent on the alternative sigma factor TcdD. Furthermore, tcdD was found to be autoinduced at 37 degrees C. Glucose down-regulated all these responses in the C. perfringens constructs, similar to its impact on toxin production in C. difficile PY broth cultures. C. difficile proteins induced at 37 degrees C and thus coregulated with the toxins by temperature were demonstrated by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified as enzymes involved in butyric acid production and as electron carriers in oxidation-reduction reactions. The regulation of toxin production in C. difficile by temperature is a novel finding apparently reflecting an adaptation of the expression of its virulence to mammalian hosts.

Clostridium difficile

Clostridium difficile is the most commonly identified infective cause of antibiotic associated diarrhoea. Broad spectrum antibiotics, are most frequently incriminated, although short (<3 day) antibiotic courses cause fewer episodes. Gold standard cell-culture based cytotoxin assays have been compared to rapid immunoassays, which are less effective, especially since toxin A negative, toxin B positive strains have been shown to be truly virulent. Details of colonization and adherence mechanisms have been revealed, and clonal spread has been demonstrated. The mainstay of treatment of C. difficile infection remains metronidazole. Justified fears over resistance are leading to development of alternative therapeutic strategies. These include a toxin binding polymer and ongoing biotherapy research. An antibody rise to toxin A during an episode of C. difficile diarrhoea protects against recurrence, and trials are in progress to investigate immunization: a toxoid vaccine which is immunogenic and safe in healthy volunteers shows promise for the future.

Detection of toxin production in Clostridium difficile strains by three different methods

OBJECTIVE

To compare two immunoassays for detection of toxins produced in vitro by isolates of Clostridium difficile with the standard tissue culture assay, to help in the diagnosis of C. difficile-associated diarrhoea.

METHODS

Toxin production was investigated in 42 strains of C. difficile of various serotypes, ribotypes and S-protein types. These included strains from our laboratory collection, strains freshly isolated from stool specimens of patients suspected of suffering from C. difficile-associated disease or of carrying it asymptomatically, and one reference strain (NCTC 11223). Toxin was assayed by (i) a rapid slide immunoassay (C. difficile toxin A test, Clearview, Oxoid), (ii) an enzyme-linked microplate immunoassay (C. difficile toxin A/B test, Techlab), and (iii) a tissue culture assay. The rapid slide assay and the enzyme immunoassay were performed according to the manufacturers' recommendations. The tissue culture assay was performed using Vero cells.

RESULTS

Thirty of the 42 strains (71%) were shown to be positive for toxin A by the slide immunoassay and 34 of the strains (81%) were found to be toxin A/B producers by the enzyme immunoassay. The same 34 strains that were positive in the enzyme immunoassay also produced toxin B (cytotoxin) in the tissue culture assay. The sensitivity, specificity, and positive and negative predictive values for the rapid slide immunoassay method were calculated to be 88.2%, 100.0%, 100.0% and 66.7%, respectively, when compared to tissue culture assay results as the reference method. These values for the enzyme immunoassay method were all 100.0%. In this study eight strains were found to be non-toxin-producing by all methods. It is possible that there were four strains that only produced toxin B (A- B+), and were missed by the rapid A-only assay.

CONCLUSIONS

We can recommend the use of the Techlab A + B enzyme immunoassay for the detection of toxin production by C. difficile strains because of its high sensitivity and specificity, its ease of use, and its capability of detecting both A- and B-type toxins.

Epidemiology of Clostridium difficile-associated infections

Clostridium difficile is responsible for 15-25% of cases of antibiotic-associated diarrhea (AAD) and for virtually all cases of antibiotic-associated pseudomembranous colitis (PMC). This anaerobic bacterium has been identified as the leading cause of nosocomial infectious diarrhea in adults and can be responsible for large outbreaks. Nosocomial C. difficile infection results in an increased length of stay in hospital ranging from 8 to 21 days. Risk factors for C. difficile-associated diarrhea include antimicrobial therapy, older age (>65 years), antineoplastic chemotherapy and length of hospital stay. Other interventions with high risk associations are enemas, nasogastric tubes, gastrointestinal surgery and antiperistaltic drugs. Prospective studies have shown that nosocomial transmission of C. difficile is frequent but often remains asymptomatic. Patients can be contaminated from environmental surfaces, shared instrumentation, hospital personnel hands and infected roommates. Once an outbreak starts, C. difficile may be spread rapidly throughout the hospital environment where spores may persist for months. Measures that are effective in reducing incidence of C. difficile infections and cross-infection include: (i) an accurate and rapid diagnosis, (ii) appropriate treatment, (iii) implementation of enteric precautions for symptomatic patients, (iv) reinforcement of hand-washing, (v) daily environmental disinfection, and (vi) a restrictive antibiotic policy. C. difficile is a common cause of infectious diarrhea and should be therefore systematically investigated in patients with nosocomial diarrhea.