Comparison of bacterial isolation, cytotoxicity assay, and counterimmunoelectrophoresis for the detection of Clostridium difficile and its toxin

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.

Comparison of a dot immunobinding assay, latex agglutination, and cytotoxin assay for laboratory diagnosis of Clostridium difficile-associated diarrhea

C. diff-CUBE, a dot immunobinding assay (DIA) (Difco Laboratories, Ann Arbor, Mich.) for detection of Clostridium difficile toxin A in stool specimens, was compared with latex agglutination (LA) (Marion Laboratories, Kansas City, Mo.) and cytotoxin assay (CTA) for the laboratory diagnosis of C. difficile-associated diarrhea. A total of 200 stool specimens collected from 169 patients with suspected C. difficile diarrhea were tested. Of the 198 specimens evaluated by all three methods, 36 (18%) from 36 patients were positive by one or more of the tests. Twenty-five, 26, and 23 specimens were positive by CTA, DIA, and LA, respectively; 14 were positive by all three methods. Eight specimens yielded nonspecific LA test results; all eight were negative by CTA, and one was positive by DIA. DIA results agreed with CTA results in 183 (92%) cases and with LA results in 175 (88%) cases. CTA and LA results agreed in 179 (90%) cases. Freezing of the specimen did not appear to adversely affect either the DIA or LA test. These preliminary results suggest that C. diff-CUBE may be useful as a rapid screen for the diagnosis of C. difficile-associated diarrhea. However, for optimum laboratory diagnosis, further testing of all stools that are negative by DIA is warranted.

Laboratory diagnosis of Clostridium difficile-associated diarrhoea

This paper reviews the various laboratory procedures available for the isolation and identification of Clostridium difficile and the detection of toxins produced by this organism. Laboratories should be selective in determining which patients require investigation for Clostridium difficile-associated diarrhoea. Transport and storage of stool specimens at 4 degrees C is recommended when delays in processing may occur. Tissue culture techniques are still the best method for detection of cytotoxin and a variety of cell lines can be used. Other methods for detecting cytotoxin, and methods for detecting other toxins are not sufficiently developed yet to warrant introduction into diagnostic laboratories. Culture techniques remain the most sensitive for diagnosis, particularly since the development of a variety of enrichment techniques. Cycloserine cefoxitin fructose agar is still adequate, although reduced concentrations of antimicrobial agents are necessary, and improvements, such as the addition of sodium taurocholate, increase the recovery of spores. Enrichment cultures have markedly increased isolation rates for Clostridium difficile but the significance of these isolates needs to be carefully evaluated. Until simpler and more reliable tests are available in clinical laboratories for the detection of toxins, the isolation of Clostridium difficile from patients with diarrhoeal disease should be considered paramount.

Clostridium difficile: its disease and toxins

Clostridium difficile is the etiologic agent of pseudomembranous colitis, a severe, sometimes fatal disease that occurs in adults undergoing antimicrobial therapy. The disease, ironically, has been most effectively treated with antibiotics, although some of the newer methods of treatment such as the replacement of the bowel flora may prove more beneficial for patients who continue to relapse with pseudomembranous colitis. The organism produces two potent exotoxins designated toxin A and toxin B. Toxin A is an enterotoxin believed to be responsible for the diarrhea and mucosal tissue damage which occur during the disease. Toxin B is an extremely potent cytotoxin, but its role in the disease has not been as well studied. There appears to be a cascade of events which result in the expression of the activity of these toxins, and these events, ranging from the recognition of a trisaccharide receptor by toxin A to the synergistic action of the toxins and their possible dissemination in the body, are discussed in this review. The advantages and disadvantages of the various assays, including tissue culture assay, enzyme immunoassay, and latex agglutination, currently used in the clinical diagnosis of the disease also are discussed.

Rectal swab cultures for Clostridium difficile surveillance studies

We compared the recovery of Clostridium difficile from hospitalized patients by two collection methods: rectal swabs and stool cultures. Rectal swab cultures were as sensitive as stool cultures and were more easily obtained. Transport of swabs in an anaerobic VACUTAINER system resulted in longer survival times compared with transport in Amies medium.

Considerations in the laboratory diagnosis of antibiotic-associated gastroenteritis

Clostridium difficile has been shown to be the major cause of antibiotic-associated gastroenteritis in both humans and experimental animals. During the past few years an increasing number of laboratories have attempted to detect, isolate, and identify this organism and its toxin from clinical samples. Direct visualization of C. difficile in patient specimens using immunofluorescent microscopy has been proposed. The major disadvantage of this method was its lack of specificity due to crossreaction with other clostridial species. Attempts to absorb the antisera with crossreacting strains also failed. Laboratory diagnosis of C. difficile in clinical specimens has relied on either culture using one or more selective media or on the detection of specific cytotoxin in stool filtrates. Until recently the cytotoxicity assay was the only procedure available for the routine detection of cytotoxin and, as a result, has limited this test to laboratories with access to tissue culture facilities. As a result, there has been much interest in the development of immunochemical methods for the detection of C. difficile toxins. We originally reported on the detection of C. difficile toxin in stool filtrates using counterimmunoelectrophoresis. We examined 140 fecal specimens submitted for C. difficile toxin assay by counterimmunoelectrophoresis, using both unabsorbed and absorbed antitoxin, tissue culture, and bacterial culture. Using tissue culture assay as the reference method, the sensitivity of counterimmunoelectrophoresis and counterimmunoelectrophoresis-absorbed was 100% and the specificity 63.0% and 77.5%, respectively. Enzyme immunosorbent assays for the detection of toxin A from C. difficile have also been reported, however, at the present time they do not appear to be as sensitive as the cytotoxicity assay for toxin B (cytotoxin).(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of Clostridium difficile toxins by enzyme immunoassay

An enzyme-linked immunosorbent assay (ELISA) for the rapid diagnosis of antibiotic-associated colitis (AAC) is presented. Commercially available antisera to Clostridium difficile toxins contain antibodies to other antigens found in non-toxigenic C. difficile and other bacteria. Removal of these unwanted antibodies by absorption increased the specificity of ELISA for detection of C. difficile toxins. Specimens tested included 40 faecal extracts positive for cytotoxicity from cases of AAC, 30 diarrhoeic and 30 well-formed stools negative for cytotoxicity and 50 culture filtrates of toxigenic and non-toxigenic C. difficile and other clostridial species. Use of absorbed sera reduced false-positive reactions observed with faecal specimens from 23 to 8%. About 90% of specimens that were positive by the tissue culture cytotoxicity test were positive by ELISA using the absorbed sera. The relative merits of ELISA and other methods for the rapid diagnosis of AAC are discussed.

Latex particle agglutination for detecting and identifying Clostridium difficile

A total of 329 selective enrichment broth cultures were tested for detection of Clostridium difficile by latex particle agglutination (LPA), gas-liquid chromatography, and bacterial culture. Of 53 broths positive by LPA, 36 were positive by gas-liquid chromatography, and 42 were positive by bacterial culture. The sensitivity and specificity of LPA relative to bacterial culture was 95.6% and 96.3%, respectively, while the sensitivity and specificity of gas-liquid chromatography relative to bacterial culture was 84.6% and 100%, respectively. The high predictive value of a negative test (99%) should make LPA on broth cultures a good screening test for detecting C difficile. Of several other Clostridium spp tested in pure culture, strains of C sordellii and C bifermentans also gave a positive result by LPA. These results, together with the low cost and simple facilities required, suggest that the LPA test will be a useful procedure for the presumptive identification of C difficile in selective enrichment broths and for the identification of pure cultures.

Detection of Clostridium difficile Toxin A by immunoblotting

A clinical isolate of Clostridium difficile has been tested for its toxin production. Both toxins, toxin A and toxin B, could be detected by tissue culture and in animal models as well. Antibodies against a crude toxin A preparation have been prepared. These antibodies are able to neutralize the toxin both in the mouse lethality test and tissue culture test systems. The specificity of this antiserum has been analysed by electroimmunoprecipitation methods. Using immunoblotting, it could be demonstrated that the antigenicity of toxin A after SDS polyacrylamide gel electrophoresis under denaturing and reducing conditions was still preserved. The molecular weight of toxin A has been estimated to be 250000. Immunoblotting offers a simple and reliable procedure for toxin A detection from culture supernatants of C. difficile.

Diagnosis of Clostridium difficile-associated intestinal disease

Toxigenic Clostridium difficile is the major cause of antimicrobial agent-associated pseudomembranous colitis and is the etiological agent of approximately 30% of cases of nonspecific colitis and diarrhea (without colitis) induced by antimicrobial agents. In addition, C. difficile has been implicated in certain intestinal diseases not related to prior antimicrobial administration. C. difficile has been reported to be one of the most common enteropathogens isolated from stool specimens submitted to hospital laboratories. Thus, diagnosis of C. difficile-associated intestinal disease should now be routinely performed in diagnostic clinical laboratories. The diagnosis of C. difficile-associated intestinal disease relies on the demonstration of either the organism or the toxin(s) in stool specimens or antibody response in serum to the toxin(s). Several selective medium are available for the recovery of C. difficile from stool specimens. The toxin(s) of C. difficile can be demonstrated using a variety of techniques, including biological assays as well as immunological assays. This article will review the techniques currently available to aid in the diagnosis of C. difficile-associated intestinal disease.

Monoclonal and specific polyclonal antibodies for immunoassay of Clostridium difficile toxin A

Monoclonal antibody, affinity-purified antibody, and monospecific antiserum against toxin A were produced. The monoclonal antibody was an immunoglobulin G2a kappa chain isotype that immunoprecipitated toxin A, as shown by crossed immunoelectrophoresis. These antibodies were compared by counterimmunoelectrophoresis, latex agglutination, and indirect enzyme-linked immunosorbent assay for their sensitivity in detecting toxin A. Our findings indicate that these antibodies may be useful as immunodiagnostic reagents for Clostridium difficile disease.

Latex agglutination test for detection of Clostridium difficile toxin in stool samples

A total of 163 stool specimens were tested for detection of Clostridium difficile and its toxin by cytotoxicity assay with tissue culture, latex agglutination test, and isolation of the organism. From 33 specimens which were positive for toxin by cytotoxicity, 30 were positive by the latex agglutination test; the organism was isolated from 21. The total number of samples which were positive with the latex agglutination test was 44. The predictive value of a positive latex agglutination result relative to the cytotoxicity test was 68%, and the predictive value of a negative result was 97.5%. The specificity and sensitivity of the latex agglutination test relative to the cytotoxicity assay and the low cost and simple facilities required indicate that the latex agglutination test is a useful procedure for screening for C. difficile toxins, provided that positive latex results are confirmed by cytotoxicity assay.

Laboratory investigation of hemorrhagic colitis outbreaks associated with a rare Escherichia coli serotype

Two outbreaks of hemorrhagic colitis, a newly recognized syndrome characterized by bloody diarrhea, severe abdominal pain, and little or no fever, occurred in 1982. No previously recognized pathogens were recovered from stool specimens from persons in either outbreak. However, a rare E. coli serotype, O157:H7, was isolated from 9 of 20 cases and from no controls. It was also recovered from a meat patty from the implicated lot eaten by persons in one outbreak. No recovery of this organism was made from stools collected 7 or more days after onset of illness; whereas 9 of 12 culture-positive stools had been collected within 4 days of onset of illness. The isolate was not invasive or toxigenic by standard tests, and all strains has a unique biotype. Plasmid profile analysis indicates that all outbreak-associated E. coli O157:H7 isolates are closely related. These results suggest that E. coli O157:H7 was the causative agent of illness in the two outbreaks.