Evaluation of a new commercial Clostridium difficile toxin A enzyme immunoassay using diarrhoeal stools

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.

Increasing seroprevalence of Clostridium difficile in an adult Danish general population

The incidence of Clostridium difficile-associated infections is increasing, but it remains to be defined whether any change in the seroprevalence of C. difficile has also occurred. In a population-based study of the general adult population, 734 subjects, aged 15-69 years, were examined on two occasions 8 years apart (1990 and 1998) for the presence of antibodies against C. difficile in serum. The overall seroprevalence of C. difficile increased significantly from 19% in 1990 to 27% in 1998 (P<0.0001). The seroprevalence increased with increasing age in both 1990 and 1998, but the increase was about four times higher in 1998 than in 1990. In conclusion, the observed increase in seroprevalence suggests a higher exposure to C. difficile in the general Danish adult population.

A European survey of diagnostic methods and testing protocols for Clostridium difficile

OBJECTIVE

To conduct a survey of the methods used in clinical microbiology laboratories in Europe to diagnose infection with Clostridium difficile.

METHODS

A questionnaire was devised and sent to a co-ordinating member of the Study Group in each of eight European countries. This co-ordinator was in charge of forwarding the questionnaire to hospital laboratories arbitrarily selected. The number of laboratories in each country was determined on the basis of one laboratory for 10,000 beds of hospitalization. This questionnaire covered different aspects pertaining to Clostridium difficile associated to diarrhea (CDAD) diagnosis such as circumstances of request, criteria used for undertaking C. difficile investigations, methods used for the diagnosis, etc.

RESULTS

A total of 212 questionnaires were completed and submitted for analysis: 87.7% of laboratories reported routinely performing C. difficile diagnostic tests. Methods used included toxin detection (93%), culture (55%), and glutamate dehydrogenase (GDH) detection (5.9%). Among the laboratories detecting toxins, different enzyme immunoassays (EIA) and cytotoxicity assays were used in 79% and 17.3% of cases, respectively. Among the different strategies reported, 4.8% were considered suboptimal for the diagnosis of C. difficile infections, but marked discrepancies could be observed between countries. The overall incidence (median) of CDAD was estimated at 1.1 for 1,000 patient admissions.

CONCLUSION

The results of this study suggest marked discrepancies between laboratories and also between countries regarding the criteria by which C. difficile is investigated for, and the methods and the strategies that are used for the diagnosis of C. difficile. These discrepancies could be explained by the lack of clear guidelines for C. difficile diagnosis in each country, and by the importance that physicians attach to C. difficile. Precise guidelines for C. difficile diagnosis would be the first step to make possible accurate comparison of the incidence and the epidemiology of CDAD from one hospital to another or from one country to another.

Survey of incidence of Clostridium difficile infection in Canadian hospitals and diagnostic approaches

A questionnaire relating to Clostridium difficile disease incidence and diagnostic practices was sent to 380 Canadian hospitals (all with > 50 beds). The national questionnaire response rate was 63%. In-house testing was performed in 17.6, 61.5, and 74.2% of the hospitals with < 300, 300 to 500, and > 500 beds, respectively. The average test positivity rates were 17.2, 15.3, and 13.2% for hospitals with < 300, 300 to 500, and > 500 beds, respectively. The average disease incidences were 23.5, 30.8, and 40.3 cases per 100,000 patient days in the hospitals with < 300, 300 to 500, and > 500 beds, respectively. In the 81 hospitals where in-house testing was performed, cytotoxin testing utilizing tissue culture was most common (44.4%), followed by enzyme-linked immunosorbent assay (38.3%), culture for toxigenic C. difficile (32.1%), and latex agglutination (13.6%). The clinical criteria for C. difficile testing were variable, with 85% of hospitals indicating that a test was done automatically if ordered by a doctor. Our results show that C. difficile-associated diarrhea is a major problem in hospitals with > or = 200 beds. Despite a lower disease incidence in smaller hospitals, there was a higher diagnostic test positivity rate. This may reflect the preference of smaller hospitals for culture and latex agglutination tests.

Recent trends in diagnosis and treatment of Clostridium difficile in a tertiary care facility

BACKGROUND

With the prevalence of antibiotic use, the diagnosis and management of Clostridium difficile disease requires assessment.

METHODS

In a retrospective review, patients with a positive culture, toxin, or both during 1 year were identified. Recent literature was reviewed. Results of culture and toxin, prior antibiotic use, antibiotic treatment history and cost were analyzed.

RESULTS

Of 592 patients tested, 101 were positive; 96 of 101 were available for review. Of those positive tested for both, 45% were positive for toxin and culture. Sixty-two of 96 were treated with antibiotics; metronidazole was used in 90%. Ten of 62 antibiotic treatments were changed (mean 3 days). Ten days of metronidazole is 1/200th the cost of vancomycin.

CONCLUSIONS

In 55% of the positive cases in which culture and toxin were obtained, one test was negative. As metronidazole's efficacy and cost compares favorably with vancomycin, metronidazole is the drug of choice. Any changes made to antibiotic regimens occurred prior to the 6 days recommended in the literature.

Evaluation of a new enzyme immunoassay for Clostridium difficile toxin A

AIM

To evaluate a new enzyme immunoassay (EIA) method for detection of Clostridium difficile toxin by comparing it to cytotoxicity assay. To investigate the nature of false negative and false positive EIA results by evaluating clinical and therapeutic parameters.

METHODS

737 consecutive diarrhoeal specimens collected from patients clinically suspected of having C difficile colitis were tested for the presence of C difficile toxin by EIA for toxin A and by cytotoxicity assay. Clinical data were evaluated in all cases positive by either method.

RESULTS

With the cytotoxicity assay as a gold standard, the specificity of EIA for toxin detection was 99.3% and the sensitivity was 62.2%. No false negative EIA specimens were obtained from patients already being treated for C difficile colitis. Among patients with cytotoxicity positive specimens, those with EIA positive samples had no clinical features distinguishing them from patients with EIA negative samples.

CONCLUSIONS

Although specific, the new EIA method directed against toxin A lacks sensitivity compared to cytotoxicity. False negative EIA tests are not associated with concurrent treatment for C difficile colitis nor with any specific clinical features examined in our study.

Rapid detection of Clostridium difficile toxin A in stool specimens

OBJECTIVE: To evaluate a rapid (15-min) enzyme immunoassay in the format of an individual cassette (ImmunoCard toxin A, Meridian, BMD, Marne-la-Vallée, France) for the detection of Clostridium difficile toxin A in stool specimens. METHODS: We compared this new test with the cytotoxicity assay using MRC-5 cells, the ToxA test (TechLab, BioWhittaker, Fontenay-sous-bois, France) and toxigenic culture for the diagnosis of C. difficile-associated diseases (CDAD). A total of 236 stool specimens collected from 220 patients was simultaneously tested with the four methods. Discordant results were resolved by reviewing patients' clinical records. RESULTS: The prevalence of CDAD was 13.9%. Test sensitivities and specificities were 100% and 99% respectively for the cytotoxicity assay, 87.5% and 100% for ImmunoCard toxin A, 77.4% and 100% for the ToxA test and 100% and 98% for toxigenic culture. CONCLUSIONS: The ImmunoCard Toxin A is a very rapid, individual and easy-to-perform test for the diagnosis of CDAD. It provides same-day results and may be useful for both guiding appropriate treatment and controlling nosocomial spread of C. difficile.

Multicenter evaluation of four methods for Clostridium difficile detection: ImmunoCard C. difficile, cytotoxin assay, culture, and latex agglutination

A three-center study was undertaken to compare several test methods for the detection of Clostridium difficile, associated toxin, or related markers by using 927 stool specimens. Methods included direct assay of cytotoxin in stool by tissue culture, C. difficile bacterial culture followed by cytotoxin assay, bacterial culture alone, latex agglutination assay, and the ImmunoCard C. difficile test (Meridian Diagnostics, Inc.). The sensitivities, as determined against direct cytotoxin assay results, of the ImmunoCard C. difficile and latex agglutination assays were 84 and 67%, respectively (92 and 77%, respectively, when adjusted for bacterial culture outcomes). Evaluation for C. difficile-associated disease (CDAD) among 864 patients was based on clinical criteria for antibiotic-associated diarrhea combined with laboratory evidence of toxin or toxin-producing C. difficile in stool specimens. The sensitivity of each test method for screening of CDAD was as follows: bacterial culture, 95%; culture with cytotoxin assay of isolates, 90%; ImmunoCard C. difficile test, 83%; cytotoxin assay 82%; and latex agglutination assay, 67% (P < or = 0.05 versus all other methods). The standard deviations of the test sensitivity statistics between study sites were ranked as follows: cytotoxin assay (+/- 3.1%) < ImmunoCard C. difficile test (+/- 5.7%) < latex agglutination assay (+/- 12.3%) < culture (+/- 24.7%) < culture with cytotoxin assay (+/- 28.0%). The data support the use of the ImmunoCard C. difficile test as an adjunct for the diagnosis of CDAD.

Toxin A detection on Clostridium difficile colonies from 24-h cultures

OBJECTIVE: Performance of a combined approach for the detection of toxigenic strains in patients suspected of having Clostridium difficile-associated disease was evaluated. METHODS: In this approach, stools were cultured for 24 h on a selective medium supplemented with sodium taurocholate (TCCFA), in anaerobic conditions created with the Martreg Anoxomat system, and toxin A detection was performed directly on C. difficile colonies, by enzyme immunoassay (EIA). This method was compared with three others: cytotoxigenic culture consisting of a 48-h culture on selective medium followed by detection of in vitro cytotoxin production on cell monolayers, fecal cytotoxin detection and fecal toxin A detection by EIA. RESULTS: From 548 stools, 108 yielded a positive culture by at least one of the methods, and 81 isolates were cytotoxin producers. Cultures for 24 h on TCCFA were positive in 106 cases and EIA performed on colonies gave 73 positive results, giving a sensitivity of 90.1% and a specificity of 100%. By comparison, the sensitivity and specificity of cytotoxigenic culture, stool cytotoxin and stool toxin A were respectively 96.2% and 100%, 61.7% and 100%, and 66.7% and 95.9%. CONCLUSIONS: Performing EIA on colonies recovered after 24 h culture allows us to improve the detection of toxigenic strains in patients suspected of having C. difficile-associated disease.

Comparison of two commercial enzyme immunoassays with cytotoxicity assay and culture for the diagnosis of Clostridium difficile related diarrhea

184 stool samples were analysed for the presence of Clostridium difficile and toxins using the Meridian Premier Toxin A and TechLab Tox-A EIA kits, selective culture and cytotoxin assay. Of the 184 samples 36 stools tested positive for cytotoxin. In comparison the sensitivity and specificity of the EIAs and culture were as follows: Meridian, 72 and 87, TechLab, 64 and 95, and selective culture, 83 and 96%, respectively. The positive predictive values and negative predictive values for the various methods were: Meridian, 58 and 93, TechLab, 77 and 92, and selective culture, 83 and 96%, respectively. Discrepant results to those obtained by cytotoxicity assay were encountered with both EIA kits evaluated and less so by culture. In this study direct isolation of Clostridium difficile from stool samples most closely paralleled the findings of the "gold standard" cell line cytotoxicity assay. It appears that a single test for the determination of Clostridium difficile disease is adequate, although a second method improves the predictability of the diagnosis. Direct culture of feces provided a reliable secondary procedure to cytotoxicity assay. The EIAs were simple to use, labour efficient and provided a rapid result. However the lack of sensitivity and relative expense did not justify their routine use in our laboratory.

Clostridium difficile-associated diarrhea and colitis

OBJECTIVES

To review and summarize the status of diagnosis, epidemiology, infection control, and treatment of Clostridium difficile-associated disease (CDAD).

DIAGNOSIS

A case definition of CDAD should include the presence of symptoms (usually diarrhea) and at least one of the following positive tests: endoscopy revealing pseudomembranes, stool cytotoxicity test for toxin B, stool enzyme immunoassay for toxin A or B, or stool culture for C difficile (preferably with confirmation of organism toxicity if a direct stool toxin test is negative or not done). Testing of asymptomatic patients, including those who are asymptomatic after treatment, is not recommended other than for epidemiologic purposes. Lower gastrointestinal endoscopy is the only diagnostic test for pseudomembranous colitis, but it is expensive, invasive, and insensitive (51% to 55%) for the diagnosis of CDAD. Stool culture is the most sensitive laboratory test currently in clinical use, but it is not as specific as the cell cytotoxicity assay.

EPIDEMIOLOGY

C difficile is the most frequently identified cause of nosocomial diarrhea. The majority of C difficile infections are acquired nosocomially, and most patients remain asymptomatic following acquisition. Antimicrobial exposure is the greatest risk factor for patients, especially clindamycin, cephalosporins, and penicillins, although virtually every antimicrobial has been implicated. Cases of CDAD unassociated with prior antimicrobial or antineoplastic use are very rare. Hands of personnel, as well as a variety of environmental sites within institutions, have been found to be contaminated with C difficile, which can persist as spores for many months. Contaminated commodes, bathing tubs, and electronic thermometers have been implicated as sources of C difficile. Symptomatic and asymptomatic infected patients are the major reservoirs and sources for environmental contamination. Both genotypic and phenotypic typing systems for C difficile are available and have enhanced epidemiologic investigation greatly.

INFECTION CONTROL

Successful infection control measures designed to prevent horizontal transmission include the use of gloves in handling body substances and replacement of electronic thermometers with disposable devices. Isolation, cohorting, handwashing, environmental disinfection, and treatment of asymptomatic carriers are recommended practices for which convincing data of efficacy are not available. The most successful control measure directed at reduction in symptomatic disease has been antimicrobial restriction.

TREATMENT

Treatment of symptomatic (but not asymptomatic) patients with metronidazole or vancomycin for 10 days is effective; metronidazole may be preferred to reduce risk of vancomycin resistance among other organisms in hospitals. Recurrence of symptoms occurs in 7% to 20% of patients and is due to both relapse and reinfection. Over 90% of first recurrences can be treated successfully in the same manner as initial cases. Combination treatment with vancomycin plus rifampin or the addition orally of the yeast Saccharomyces boulardii to vancomycin or metronidazole treatment has been shown to prevent subsequent diarrhea in patients with recurrent disease.

Cloning of a genetic determinant from Clostridium difficile involved in adherence to tissue culture cells and mucus

Our laboratory has previously shown that Clostridium difficile adherence to Caco-2 cells is greatly enhanced after heat shock at 60 degrees C and that it is mediated by a proteinaceous surface component. The experiments described here show that C. difficile could adhere to several types of tissue culture cells (Vero, HeLa, and KB) after heat shock. The type of culture medium (liquid or solid, with or without blood) had little effect on adhesion. To clone the adhesin gene, polyclonal antibodies against C. difficile heated at 60 degrees C were used to screen a genomic library of C. difficile constructed in lambda ZapII. Ten positive clones were identified in the library, one of which (pCL6) agglutinated several types of erythrocytes in the presence of mannose. In Western blots (immunoblots), this clone expressed in Escherichia coli a 40- and a 27-kDa protein; a 27-kDa protein has been previously identified in the surface extracts of heat-shocked C. difficile as a possible adhesin. The clone adhered to Vero, Caco-2, KB, and HeLa cells; the adherence was blocked by anti-C. difficile antibodies, by a surface extract of C. difficile, and by mucus isolated from axenic mice. Furthermore, the clone could attach ex vivo to intestinal mucus isolated from axenic mice. Preliminary studies on the receptor moieties implicated in C. difficile adhesion revealed that glucose and galactose could partially block adhesion to tissue culture cells, as did di- or trisaccharides containing these sugars, suggesting that the adhesin is a lectin. In addition, N-acetylgalactosamine, a component of mucus, and gelatin partially impeded cell attachment.

Evaluation of three commercial enzyme immunoassay kits for detecting faecal Clostridium difficile toxins

The detection of faecal cytotoxicity using tissue culture was compared with three commercial Clostridium difficile enzyme immunoassay (EIA) kits; Premier C difficile toxin A (Meridian Diagnostic, Inc.); CD-TOX C difficile toxin A (Porton Cambridge); and Cytoclone A+B EIA (Cambridge Biotech Corporation). Of 160 faecal samples examined by all four methods, 52 (32.5%) were cytotoxic, 44 (27.5%) were positive by Premier, 48 (30%) by CD-TOX EIA, and 50 (31.3%) with Cytoclone. When compared with detection of cytotoxicity by tissue culture assay, the following performance indices were obtained: Premier, sensitivity 84.1%, specificity 99.1%, positive predictive value (PPV) 97.8%, negative predictive value (NPV) 93%; CD-TOX, sensitivity 92.3%, specificity 88.0%, PPV 78.7%, NPV 95.9%; Cytoclone, sensitivity 96.2%, specificity 93.5%, PPV 87.7%, NPV 98.1%. EIA results were available within three hours, whereas the results of the cytotoxin assay were available after 24-48 hours. All three kits provided satisfactory results and, although relatively expensive, all could be used in the laboratory effectively to screen for diarrhoeal disease associated with C difficile.

Evaluation of an enzyme immunoassay kit for the detection of Clostridium difficile enterotoxin

The Premier Clostridium difficile toxin A enzyme immunoassay (EIA) kit was evaluated for the detection of C. difficile enterotoxin in fecal samples. A total of 314 samples was tested by culture, cytotoxin detection and EIA kit. Compared to a combined culture/cytotoxin result the Premier EIA kit had a sensitivity of 88.3%, a specificity of 100%, a predictive value positive of 100% and a predictive value negative of 87.4%. Test results were available within 3 hrs providing a rapid and reliable means of detecting C. difficile enterotoxin.

Comparison of four commercially available rapid enzyme immunoassays with cytotoxin assay for detection of Clostridium difficile toxin(s) from stool specimens

Rapid (2.5- to 3.5-h) enzyme immunoassays (EIAs) for the detection of Clostridium difficile toxins have been developed. We report the results of simultaneous testing of 700 fresh stool specimens by the tissue culture cytotoxin assay and four EIAs (Bartels Prima System C. difficile Toxin A EIA, Cambridge Biotech Cytoclone A+B EIA, Meridian Diagnostics Premier C. difficile Toxin A EIA, and TechLab C. difficile Tox-A Test EIA). In cases of disagreement, culturing for toxigenic C. difficile was performed. A total of 61 (8.7%) specimens from 46 patients were positive for C. difficile toxin. The sensitivity of the cytotoxin assay was 87%, and that of culture was 93%. In comparison with the cytotoxin assay results, the sensitivity and specificity of the EIAs were as follows: Bartels, 87 and 96%; Cambridge, 89 and 99%; Meridian, 87 and 98%; and TechLab, 87 and 95%, respectively. In comparison with the cytotoxin assay plus toxigenic culture results, the sensitivity and specificity of the EIAs were as follows: Bartels, 84 and 97%; Cambridge, 85 and 99%; Meridian, 79 and 98%; and TechLab, 80 and 96%, respectively. The EIAs varied in positive predictive values (PPVs). A high PPV was seen with the Cambridge EIA (96%); lower PPVs were seen with the TechLab (64%), Bartels (72%), and Meridian (80%) EIAs because of high false-positive rates. The negative predictive values (98 to 99%) were excellent with all EIAs. Results were indeterminant with 0.3% of the samples by the Meridian EIA and 3% by all the other EIAs. Although the EIAs were less sensitive than the cytotoxin assay, they provide same-day results and may be useful in laboratories without tissue culture facilities.

Evaluation of four commercially available enzyme immunoassays for laboratory diagnosis of Clostridium difficile-associated diseases

Four commercial enzyme immunoassays (EIAs) for the detection of Clostridium difficile toxin A have recently been developed and marketed (Premier, Meridian Diagnostics, Cincinnati, Ohio; VIDAS, bioMerierux Vitek, Inc., Hazelwood, Mo.; Tox-A-Test, TechLab, Blacksburg, Va.; and Bartels, Baxter Diagnostics, McGaw Park, Ill.). The performances of these EIAs were compared with those of the tissue culture cytotoxicity assay and a definition of C. difficile-associated disease based on both laboratory and clinical criteria for 329 clinical specimens. Two EIAs (Premier and VIDAS) showed good overall agreement (96 and 95%, respectively) with the cytotoxicity assay. However, they were less sensitive (84 and 71%, respectively) than the Bartels (94%) or Tox-A-Test (93%) EIAs. The Bartels and Tox-A-Test assays were much less specific, resulting in poor positive predictive values (56%) of the two assays when compared with that of the cytotoxicity assay. Tox-A-Test had the added drawback of having a significant number of indeterminate results (6.4%). These data indicate that the four EIAs all have specific shortcomings. When using these EIAs, testing strategies that take these shortcomings into consideration should be developed.

Clostridium difficile: clinical disease and diagnosis

Clostridium difficile is an opportunistic pathogen that causes a spectrum of disease ranging from antibiotic-associated diarrhea to pseudomembranous colitis. Although the disease was first described in 1893, the etiologic agent was not isolated and identified until 1978. Since clinical and pathological features of C. difficile-associated disease are not easily distinguished from those of other gastrointestinal diseases, including ulcerative colitis, chronic inflammatory bowel disease, and Crohn's disease, diagnostic methods have relied on either isolation and identification of the microorganism or direct detection of bacterial antigens or toxins in stool specimens. The current review focuses on the sensitivity, specificity, and practical use of several diagnostic tests, including methods for culture of the etiologic agent, cellular cytotoxicity assays, latex agglutination tests, enzyme immunoassay systems, counterimmunoelectrophoresis, fluorescent-antibody assays, and polymerase chain reactions.

Shedding of Clostridium difficile, fecal beta-lactamase activity, and gastrointestinal symptoms in 51 volunteers treated with oral cefixime

Microbial changes including the shedding of Clostridium difficile, fecal beta-lactamase activity, and gastrointestinal symptoms were assessed in 51 healthy volunteers given 200 mg of cefixime twice daily for 8 days. The number of organisms of the family Enterobacteriaceae (means +/- standard deviations) dropped from 6.9 +/- 1.1 to 3.9 +/- 1.8 log CFU/g of feces (P < 0.01), whereas counts of enterococci rose from 7.0 +/- 1.5 to 9.0 +/- 1.0 log CFU/g of feces (P < 0.01). Both counts returned to their initial levels 50 days after the cessation of treatment. Cefixime did not significantly modify the frequency of fecal excretion of Pseudomonas aeruginosa, Staphylococcus spp., yeasts, or members of the Enterobacteriaceae resistant to ceftazidime or ampicillin. The proportion of subjects shedding C. difficile rose from 6% before treatment to 57% (P < 0.01) at the end of treatment but returned to 8% 50 days thereafter. No case of pseudomembranous colitis was observed. Stool changes occurred in 13 volunteers during treatment (25%) and in 2 others more than 10 days after the end of treatment (4%). These changes were not significantly associated with the shedding of toxigenic strains of C. difficile or with the presence of toxin A in feces. By contrast, during treatment, stool changes occurred in 8 of the 18 volunteers (44%) who had antibiotic activity in their feces but in only 5 of the 33 (15%) for whom no such activity was found (P < 0.05). The absence of antibiotic activity in the feces was itself linked with the presence of beta-lactamase activity in the feces. Since we had found earlier that fecal beta-lactamase activity afforded protection against alteration in stool consistency during treatments with oral cephalosporins, the present study confirmed our previous preliminary results in this respect.

Detection of toxigenic Clostridium difficile in fecal samples by colony blot hybridization

A hybridization assay for detection of toxigenic Clostridium difficile in fecal samples was developed and compared with the classical tissue culture cytotoxicity assay. A DNA fragment probe specific for the toxin B gene of Clostridium difficile was synthesized by the polymerase chain reaction and labelled with digoxigenin. Fecal samples were cultured for 24 hours, replica-plated and hybridized with the probe. The hybridization assay had a sensitivity of 100%, specificity of 96.7%, positive predictive value of 86.7% and negative predictive value of 100% compared with the cytotoxicity assay.