Clostridium difficile: its disease and toxins

Multicenter evaluation of a new enzyme immunoassay for detection of Clostridium difficile enterotoxin A

The Premier Clostridium difficile toxin A enzyme immunoassay (PTA EIA) (Meridian Diagnostics, Inc., Cincinnati, Ohio) for rapid diagnosis of antibiotic-associated colitis (AAC) was evaluated in a multicenter study. Stool samples from 421 patients suspected of having AAC were tested for toxin A by the PTA EIA and for toxin B by three tissue culture assays (TCA) employing WI-38 cells (New England Deaconess Hospital) in conventional tubes or foreskin fibroblasts (Children's Hospital) or Vero cells (Beth Israel Hospital) in microwells. The tubes and plates were examined at 24 and 48 h for cytotoxicity. Clinical criteria, repeat testing at another site, and culture of frozen stool samples for C. difficile were used to evaluate discrepant results. Of 504 samples, 66 were positive and 409 were negative by both tests. Eight samples had indeterminate PTA EIA results and were excluded from this analysis. Of 21 discrepancies, 9 were PTA EIA positive and TCA negative and 12 were PTA EIA negative TCA positive. Following resolution of the discrepancies, 11 of 12 PTA EIA-negative-TCA-positive and 5 of 9 PTA EIA-positive-TCA-negative samples were considered true positive for AAC. The sensitivity and specificity were, respectively, 86.6 and 99.0% for the PTA EIA and 93.9 and 99.8% for TCA. The predictive values of positive and negative tests were, respectively, 94.7 and 97.4% for the PTA EIA and 98.7 and 98.8% for TCA. We conclude that the PTA EIA is a rapid, simple EIA technique whose accuracy in detecting enterotoxin A approaches that of reference TCA methods for detection of cytotoxin B.

Sensitivity in culture of epithelial cells from rhesus monkey kidney and human colon carcinoma to toxins A and B from Clostridium difficile

The effect of toxins A and B from Clostridium difficile on human colon carcinoma cells (HT-29, epithelial), rhesus monkey kidney cells (MA-104, epithelial) and green monkey kidney cells (VERO, fibroblast) was studied. Both toxins caused rounding of HT-29 cells and rounding with projections remaining attached to the substrate in MA-104 and VERO cells; however, the sensitivity to each toxin varies considerably. Toxin A was detected in ng by VERO, pg by HT-29 and fractions of pg by MA-104 cells; for toxin B, pg were detected by VERO, ng by MA-104 and micrograms by HT-29 cells. HT-29 cells were grown with galactose to allow their differentiation to enterocytes, and their sensitivity to the toxins during the process was studied. At early stages, the sensitivity to both toxins was similar, and as the differentiation proceeded, the response to both toxins decreased continuously, and after 16 days no evident morphological effect was observed, even with micrograms amounts of either toxin. In contrast to all cell lines reported to date, HT-29 and MA-104 epithelial cells are exquisitely sensitive to toxin A and less responsive to toxin B. The rounding of HT-29 by these toxins depends on the degree of differentiation of the cell.

Identification of toxigenic Clostridium difficile strains using a toxin B gene-specific oligonucleotide probe

We describe the use of a new specific synthetic oligonucleotide probe, deduced from the sequence of the gene for Clostridium difficile toxin B, to identify toxigenic strains of C. difficile. This probe does not hybridize to the DNA of non-toxigenic strains of C. difficile nor to DNA isolated from different Clostridium species, including C. sordellii. None of the enteric pathogenic bacteria tested were seen to hybridize with the probe. A preliminary study of direct probing of faecal specimens indicates a potential for the use of this DNA probe in the clinical laboratory for the rapid identification of toxigenic strains of C. difficile.

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

A new, commercially available enzyme immunoassay for the detection of toxin A in stool specimens, the Premier Clostridium difficile Toxin A test (Meridian Diagnostics), was evaluated using 228 diarrhoeal stool specimens. Using a cytotoxin assay on HeLa cells as the reference method, this new test resulted in a sensitivity of 88% and a specificity of 95%. Using the presence or absence of a toxigenic strain in the stools as the reference method, the sensitivity was similar to that of the cytotoxin assay (71.7+ versus 70.5%) and the overall correlation was even better (89.4% versus 82%). The Premier Clostridium difficile Toxin A assay is rapid and easy to perform and is an excellent alternative to the usual toxin B assay.

Human colonic aspirates containing immunoglobulin A antibody to Clostridium difficile toxin A inhibit toxin A-receptor binding

Clostridium difficile toxin A, a 308-kilodalton protein exotoxin, is the principal causative agent of antibiotic-associated, C. difficile-induced colitis. In the current study, the prevalence of specific human serum and secretory antibody to toxin A and the possible protective effect of secretory, intestinal anti-toxin A antibody are examined. Serum (n = 35), colonic aspirates (n = 35), and duodenal aspirates (n = 20) were collected from adults at diagnostic endoscopy. Patients with evidence of colitis or a history of recent antibiotic use were excluded from the study. Specific serum immunoglobulin (Ig) A and IgG antitoxin A antibodies were detected in 60% and 57% of subjects, respectively, by enzyme-linked immunosorbent assay. Fifty-seven percent of colonic aspirates contained IgA antitoxin, whereas only 10% of duodenal aspirates were positive (P = 0.002). Binding of toxin A to its intestinal receptor was studied using [3H]toxin A and purified rabbit ileal brush border membranes. Toxin A binding was significantly inhibited by colonic aspirates with high IgA anti-toxin A antibody levels (0.503 +/- 0.055 pmol toxin A bound per milligram of brush border membrane protein, mean +/- SE) in comparison with antitoxin A-negative aspirates (0.778 +/- 0.089 pmol; P = 0.02) and control (0.766 +/- 0.004 pmol; P = 0.03). In the current study, a specific intestinal secretory IgA antibody response to C. difficile toxin A in humans is reported. This antibody response is more evident in the colon, the site of C. difficile infection, than in the upper intestinal tract. Our data suggest that human colonic IgA antitoxin may protect against C. difficile colitis by inhibiting the binding of toxin A to its intestinal epithelial cell receptor.

Effect of yogurt on clindamycin-induced Clostridium difficile colitis in hamsters

Yogurt exhibits in vitro bactericidal activity against a variety of pathogenic microorganisms, including Clostridium difficile. In the present studies, we tested whether yogurt ingestion could prevent or ameliorate antibiotic associated colitis in the clindamycin-treated hamster model. Male golden Syrian hamsters were given 5 mg/kg clindamycin subcutaneously 24 hr before and 6 hr following inoculation with 0.5 ml of less than 10, 10(3), 10(5), or 10(6) CFU/ml of C. difficile. Hamsters in the control group ingested chow and water ad libitum, whereas the experimental group ingested chow and a 1:1 (v/v) mixture of yogurt and water ad libitum, beginning 24 hr before the first injection of clindamycin and continuing throughout the course of the study. Animals were monitored for colonization with C. difficile, pathological evidence of colitis, and death. Mortality was 100% in yogurt-treated animals, and all animals showed histological changes of severe colitis. Fecal and intestinal segment cultures were positive for C. difficile in all animals. Thus, in the hamster model, we found no evidence to support the possible efficacy of yogurt in the prevention of C. difficile colitis.

Development of a rapid enzyme immunoassay for Clostridium difficile toxin A and its use in the diagnosis of C. difficile-associated disease

A rapid (2.5 h) direct enzyme immunoassay (EIA) for Clostridium difficile toxin A was developed for clinical use. Specimen centrifugation and filtration were not required. The EIA detected toxin A levels in patient stool as low as 20 pg (2 ng/ml of stool). The test was 5,000 times more sensitive for toxin A than it was for toxin B and did not react with a panel of other bacterial species with the exception of one highly toxigenic strain of Clostridium sordellii. The EIA was compared with the cytotoxin assay, culture of toxigenic C. difficile (toxigenic culture), and latex agglutination by using 313 fresh stool specimens submitted from patients with suspected C. difficile-associated disease. Results read visually and with a plate reader were similar. Sixty-two specimens were positive by one or more tests, but only 22 (35%) were positive by all four laboratory methods. The EIA was 84.1% sensitive and 98.9% specific when it was compared with the cytotoxin assay. The use of toxigenic culture to referee discrepant results (EIA versus cytotoxin assay) showed the EIA sensitivity and specificity to be 95.1 and 99.3%, respectively, with respect to other laboratory methods. Patient charts were reviewed for antibiotic-associated diarrhea on 108 specimens, including all those that were positive by at least one test method. Of 34 patients determined to have C. difficile-associated disease, 29 (85.3%) were positive by EIA, 32 (94.1%) were positive by the cytotoxin assay, 27 (79.4%) were positive by toxigenic culture, and 20 (58.8%) were positive by latex agglutination. Seven patients with antibiotic-associated diarrhea had a positive latex result, but results were negative by EIA, the cytotoxin assay, and toxigenic culture. The EIA demonstrated high specificity and good sensitivity for C. difficile-associated disease cases. The test can be used alone or in combination with the cytotoxin assay or toxigenic culture to provide rapid and sensitive results.

Tetracyclines, chloramphenicol, erythromycin, clindamycin, and metronidazole

The tetracyclines are effective in the treatment of Chlamydia, Mycoplasma pneumoniae, and rickettsial infections and also can be used for gonococcal infections in patients unable to tolerate penicillin. These drugs may cause gastrointestinal irritation, diarrhea, phototoxic dermatitis, and vestibular damage, and fatal reactions due to hepatotoxicity have occurred in pregnant women. Chloramphenicol has a broad spectrum of bacteriostatic activity, but its association with suppression of the bone marrow and aplastic anemia has relegated it to a historical role. Erythromycin is the drug of choice for the treatment of infections caused by M. pneumoniae, Legionella species, group A beta-hemolytic streptococci, and Streptococcus pneumoniae. The frequency of serious adverse effects associated with the use of erythromycin is low; dose-related epigastric distress may occur. Clindamycin is bactericidal to most nonenterococcal gram-positive aerobic bacteria and many anaerobic microorganisms. Although historically it was a frequent cause of antibiotic-associated diarrhea and colitis, clindamycin is considered an excellent alternative to beta-lactam antibiotics for treatment of many staphylococcal infections, and it has therapeutic utility in anaerobic infections and in several protozoan infections in immunosuppressed patients. Metronidazole is efficacious for treating nonpulmonary anaerobic infections, various parasitic infections (trichomoniasis, amebiasis, and giardiasis), nonspecific vaginitis, and Clostridium difficile-mediated colitis. With use of metronidazole, mild side effects such as epigastric discomfort, diarrhea, reversible neutropenia, and allergic-type cutaneous reactions may occur.

Isolation of a fibroblast mutant resistant to Clostridium difficile toxins A and B

A mutant of Chinese hamster lung fibroblasts (Don cells), resistant against Clostridium difficile toxins A and B, was isolated after mutagenization with ethylmethanesulphonate and a two-step selection with toxin B. The mutant, termed CdtR-Q, was 10(4) times more resistant to toxin B than wild-type cells and cross-resistant to toxin A (10(3) times more resistant). The resistance was overcome by increasing the dose of toxin. The resistance has been stable after cultivation for 40 generations in the absence of toxin. The morphology of the mutant was more epithelial-like than that of the fibroblast parental cells. The plating efficiency was about half that of the wild-type, whereas the growth rate was the same. The mutant was significantly less sensitive than the wild-type to the microfilament-interacting cytochalasins B and D. It was as sensitive as the wild-type to endocytosed toxins (diphtheria, pertussis, ricin), to microtubule-interacting agents (colchicine, gossypol, nocodazole, taxol, vinblastine), and to membrane-damaging toxins with different mechanisms of action, with one exception; the mutant was more highly sensitive to the action of phospholipase C (with broad substrate-specificity) than the wild-type. The results suggest that the mutant has a normal endocytosis, and that the mutation does not affect the microtubuli. The results are consistent with a mutation affecting the microfilaments in the cytoskeleton.

Identification of the latex test-reactive protein of Clostridium difficile as glutamate dehydrogenase

Computer analysis showed that the gene encoding the latex test-reactive protein of Clostridium difficile exhibited high levels of homology with glutamate dehydrogenases from various sources. Further analysis demonstrated that the recombinant protein possessed glutamate dehydrogenase activity. Our results show that the protein that reacts in commercial latex tests for C. difficile is a glutamate dehydrogenase.

Control of nosocomial transmission of Clostridium difficile based on sporadic case surveillance

The recognition of a cluster of antibiotic-associated nosocomial Clostridium difficile disease (NCDD) caused by serotype C in a surgical ward led to a hospital-wide NCDD surveillance and control program. The initial step included: (a) gas-liquid chromatography screening of inpatients' diarrheal stools; (b) enteric isolation precautions, cohorting and terminal room disinfection in wards with a cluster of two or more NCDD cases per month. During a 12-month period, the quarterly incidence of NCDD remained unchanged and six new clusters of serotype C, K, and H infections occurred, giving a global incidence of 1.5/1,000 admissions. C. difficile spores were recovered from 36.7% surfaces of case patient rooms versus 6.7% in control rooms. More intensive control measures were evaluated: (a) culture screening of inpatients' diarrheal stools; (b) early therapy, enteric isolation precautions, and daily meticulous room disinfection for each sporadic NCDD case. Surface disinfection reduced the contamination level four-fold (p = 0.04). In the following 12 months, no cluster occurred and the incidence of NCDD fell to 0.3/1,000 admission (protective efficacy 73%, 95% confidence interval: 46-87%). These observations suggest that early therapy, isolation precautions, and surface disinfection, focused on patients with sporadic NCDD detected by active surveillance, can prevent nosocomial transmission of C. difficile.

Antigenic cross-reactivity and functional inhibition by antibodies to Clostridium difficile toxin A, Streptococcus mutans glucan-binding protein, and a synthetic peptide

A 10-amino-acid repeating sequence of the hemagglutinating portion of Clostridium difficile toxin A has been synthesized and used to produce antisera in rabbits. Antipeptide antibody inhibited toxin A-mediated hemagglutination and neutralized cytotoxic activity. Immunoblot analysis with the antipeptide antibody revealed cross-reactivity with native toxin, a recombinant protein containing the toxin A repeats, and a glucan-binding protein from Streptococcus mutans whose primary structure has repeating amino acid motifs similar to those of the synthetic peptide. A polyclonal antibody against the glucan-binding protein, which cross-reacted with purified toxin A, also inhibited toxin A-mediated hemagglutination and neutralized cytotoxic activity. We recently identified toxin A and the glucan-binding protein as members of a novel family of clostridial and streptococcal binding proteins based on conserved repeating amino acid motifs at the C-terminal region of the molecules. This study provides immunological and functional evidence of the predicted relationship between toxin A and the glucan-binding protein and further implicates the repeating subunits as ligand-binding domains in this family of proteins.

Usefulness of semi-quantitative cultures in the diagnosis of Clostridium difficile associated disease

Semi-quantitative stool cultures on CCFA were compared to cytotoxic assays for the diagnosis of Clostridium difficile associated disease (CAD). There was a significant correlation between the amount of Clostridium difficile growth on CCFA, the presence of cytotoxin and a clinical diagnosis of CAD in the 541 initial stool specimens tested.

The clinical significance of antibiotic-associated pseudomembranous colitis in the 1990s

Antibiotic-associated pseudomembranous colitis is an uncommon but potentially serious adverse reaction, resulting in acute diarrhoea and characterised by colonic pseudomembranes. A direct relationship between the disease, recent antibiotic therapy and proliferation of Clostridium difficile in the colonic lumen was established in the late 1970s. It is thought that antibiotic therapy may alter the enteric flora, enabling C. difficile to proliferate and produce toxins with cytopathic (toxin B or cytotoxin) and hypersecretory (toxin A or enterotoxin) effects on the mucosa. Apart from clindamycin, the first antibiotic recognised to be clearly associated with pseudomembranous colitis, the antimicrobial agents most commonly responsible are cephalosporins and ampicillin (or amoxicillin). However, virtually all antibiotics except parenterally administered aminoglycosides can cause the disease. Vancomycin and metronidazole, 2 drugs used to treat antibiotic-associated pseudomembranous colitis, have also been reported to be responsible for the complication when used parenterally. Pseudomembranous colitis may develop after perioperative prophylactic antibiotic therapy with cephalosporins. Antibiotic-associated pseudomembranous colitis is most frequent in elderly and debilitated patients and in intensive care units. Nosocomial acquisition of C. difficile has been documented. Therefore it has been recommended that enteric isolation precautions should be taken with patients with this disease. The clinical symptoms include watery diarrhoea, abdominal cramping, and frequently fever, leucocytosis and hypoalbuminaemia. Toxic megacolon and acute peritonitis secondary to perforation of the colon are the most serious complications. The pseudomembranes are usually seen during endoscopic procedures, sigmoidoscopy or, if possible, colonoscopy; the most useful microbiological tests for confirmation of the diagnosis include cycloserine cefoxitin fructose agar (CCFA) stool cultures and stool toxin assays on tissues or by immunological techniques. However, cultures and toxin tests may be positive in patients without pseudomembranous colitis or C. difficile-associated diarrhoea. Mild cases may respond to discontinuation of the drug responsible, but therapy with an anticlostridial antibiotic is often necessary: a 10-day course of oral vancomycin, metronidazole or bacitracin should be given. Relapses are seen in 5 to 50% of patients treated. Antibiotic treatment should avoid sporulation leading to other relapses. 'Biotherapy' (lactobacilli, Saccharomyces) has also been proposed.

Clostridium difficile toxin A induces a specific antisecretory factor which protects against intestinal mucosal damage

Peroral challenge with toxin A from Clostridium difficile induced the formation of antisecretory factor in rats. The animals were given 100 micrograms of the toxin, which was followed by a pronounced diarrhoea and by the appearance of antisecretory factor in the pituitary gland. In electrofocusing, the induced antisecretory factor separated in two peaks (pI 5.4 and 5.0); both fractions showed a lectin-like binding to agarose. The pI 5.4 fraction inhibited cholera toxin as well as toxin A induced fluid secretion, while pI 5.0 inhibited toxin A induced secretion only. Immunohistochemistry showed that an antisecretory factor of pI 5.0 protected the mucosa from the cytotoxic effect of toxin A, but did not affect the binding of toxin A to the intestinal epithelium. Sodium dodecyl-sulphate-polyacrylamide gel electrophoresis of the pI 5.0 protein showed two major fractions to be present, one of molecular weight 60 kDa, the other of 30 kDa, the latter probably being a degradation product of the former.

Correlation of immunoblot type, enterotoxin production, and cytotoxin production with clinical manifestations of Clostridium difficile infection in a cohort of hospitalized patients

To determine whether strain-specific differences in immunoblot type, enterotoxin production, or cytotoxin production correlated with clinical presentation of Clostridium difficile infection, we evaluated isolates obtained from 428 prospectively studied hospitalized patients. Of 99 isolates available for immunoblot typing, 61 were recovered from asymptomatic carriers and 38 were from patients with C. difficile-associated diarrhea. Of 17 immunoblot types, the seven types comprising the majority of isolates (82 of 99; 83%) were variably associated with disease. Neither the presence of cytotoxin in the stool nor the production of cytotoxin or enterotoxin by isolates in vitro was significantly different for symptomatic versus asymptomatic patients. Selected host factors were more predictive of symptomatic disease than was the specific infecting C. difficile strain. These results suggest that variations in the clinical severity of C. difficile infection in different patients are not solely strain-specific phenomena related to immunoblot type or to the production of cytotoxin or enterotoxin.

Passive immunization of hamsters against disease caused by Clostridium difficile by use of bovine immunoglobulin G concentrate

Gestating Holstein cows were vaccinated with Clostridium difficile toxoid prepared from the culture filtrate of a strain that produces high levels of toxins A and B and other antigens. A bovine immunoglobulin G (IgG) concentrate was prepared from colostrum collected at parturition. The results of our studies showed that hamsters treated prophylactically with the hyperimmune bovine IgG concentrate were protected against C. difficile disease. These results suggest that orally administered hyperimmune bovine IgG specific for C. difficile culture filtrate may be useful in prophylaxis against C. difficile disease.

Etiology and mechanisms of acute infectious diarrhea in infants in the United States

Infectious diarrhea, caused by a wide variety of viral, bacterial and parasitic pathogens, is a common reason for morbidity and hospitalization for children in the United States. Overall, rotavirus is the most common cause of acute diarrheal disease in infants. Salmonella, Shigella, and Campylobacter are the most frequently isolated bacterial pathogens, and Giardia and Cryptosporidium are the parasites that most commonly produce acute infectious diarrhea. The mechanisms by which these enteropathogens cause diarrhea are highly variable, and include crypt cell proliferation, cellular invasion, elaboration of enterotoxins or cytotoxins, and enteroadhesion. In infants the incidence of diarrheal disease is higher and the severity of the illness is greater than in older children and adults. An increased rate of exposure to enteropathogens, as a result of fecal-oral contamination, may explain some of the increased incidence of diarrhea in infants. However, age-specific differences in host defense mechanisms may also account for the increased susceptibility to and severity of certain enteric infections in infants.

Treatment with intravenously administered gamma globulin of chronic relapsing colitis induced by Clostridium difficile toxin

We tested the hypothesis that children with chronic relapsing colitis induced by Clostridium difficile toxin have defective antibody responses to C. difficile toxins as a cause of their underlying illness. Six such children were tested for serum IgG and IgA antibody to C. difficile toxin A. These six children had lower IgG anti-toxin A levels than 24 healthy children (p = 0.026) and 18 healthy adults (p = 0.0008). Five patients treated with 400 mg intravenously administered gamma-globulin per kilogram every 3 weeks had significant increases in IgG (p = 0.01) but not IgA anti-toxin A (p = 0.406) levels, and all five had clinical resolution of their gastrointestinal symptoms as well as clearing of C. difficile cytotoxin B from their stools. These observations suggest that a deficiency of IgG anti-toxin A may predispose children to the development of chronic relapsing C. difficile-induced colitis. In such cases, intravenous gamma-globulin therapy may be effective in producing clinical remission.

Protection against experimental pseudomembranous colitis in gnotobiotic mice by use of monoclonal antibodies against Clostridium difficile toxin A

The pathogenicity of Clostridium difficile is due to the production of two toxins (toxins A and B). We prepared monoclonal antibodies against toxin A and determined whether axenic mice passively immunized with the monoclonal antibodies were protected against C. difficile disease. The mice were kept in an isolator and were given ascites fluid intravenously prior to challenge with a toxinogenic strain of C. difficile. Control mice and mice receiving ascites fluid devoid of toxin antibody died within 2 days and had high levels of toxins A and B in their feces. Mice that received ascites fluid containing high amounts of toxin A monoclonal antibodies directed against the repeating units of the toxin survived. In protected mice, toxin B levels were similar to those in dying mice, but toxin A levels were greatly reduced. These data show that passive immunity induced by monoclonal antibodies against toxin A was effective against pseudomembranous cecitis.

Clostridium difficile--a common and costly colitis

Clostridium difficile infection manifests as a self-limiting diarrhea, protracted colitis, or toxic pseudomembranous colitis. The incidence of C. difficile in a 514-bed community hospital was studied retrospectively; 155 patients of a total 18,262 admitted during 1988 were identified with C. difficile as an admitting or subsequent diagnosis. The method of diagnosis, mode of therapy, and related costs were analyzed. We have determined that education, with an emphasis on pathogenesis and prevention, is necessary to reduce the incidence in the hospital and the cost to the patient.

ADP-ribosylation in Clostridium difficile toxin-treated cells is not related to cytopathogenicity of toxin B

ADP-ribosylation of a protein in human fibroblasts treated with partially purified Clostridium difficile toxin B was previously reported. Here we show that the same protein was ADP-ribosylated also in human fibroblasts exposed to supernatant from a C. difficile strain producing neither toxin A nor toxin B. Furthermore, in Chinese hamster ovary and in Vero cells, showing toxin B-induced cytopathogenic effect, the protein was not significantly ADP-ribosylated. The results indicate that the ADP-ribosylation is unrelated to the cytopathogenic effect of toxin B. It appears to be caused by another unidentified factor from C. difficile, and the substrate may correspond to a protein modified endogenously in cells exposed to stressful situations. Cellular actin was not ADP-ribosylated by toxin B.

Clostridium difficile toxin A and its effects on cells

Clostridium difficile toxin A in its native form is a high molecular weight (520-540 K) aggregate with five major biological activities. It is lethal, enterotoxic, cytotoxic and cytotonic, and induces hemagglutination of rabbit red blood cells. Possibly these activities are contained in separate components. A major subunit of c. 230-310 K has been defined but lower molecular weight components cannot be excluded. The major component has been cloned, and sequence analysis indicated a complicated pattern of repeating sequences in the C-terminal third of the molecule. This review deals mainly with the effects of toxin A on cultured cells. Most mammalian cells are sensitive to toxin A whose major effect is to stop cell division irreversibly. The toxin binds via its repeat sequences to a trisaccharide receptor expressed on rabbit red cells and on brush border membranes from hamster intestine. This receptor seems to be functional in the hemagglutination reaction and the enterotoxicity. Its role in the cytotoxic effect of the toxin is not clear, but no other receptor structure has as yet been identified. In order to exert its cytotoxic (antiproliferative) effect toxin A must first be internalized by endocytosis. Thus a latency period of at least 30 min after toxin binding to cells is consistently observed, and all cytotoxic effects can be prevented by blocking the endocytosis pathway. The first microscopically visible signs of cytotoxicity consist in retraction and rounding of intoxicated cells. In addition the nucleus becomes polarized to one side of the cell while other cell organelles are not significantly affected. These morphological changes seem to be the consequence of a cytoskeletal rearrangement, mainly involving some components of the microfilament system. Inhibition of macromolecular syntheses as well as permeabilization of the plasma membrane may follow the early cytoskeletal effects and finally lead to cell death. Attempts to identify metabolic pathways of significance in the cytotoxicity suggest that the cytosolic level of Ca2+ is not important, thus excluding certain mechanisms for cell killing. In this respect the cytotoxic mode of action of toxin A clearly differs from that of toxin B. However, the biochemical basis for the antiproliferative effect of toxin A remains unknown.

Ciprofloxacin as a cause of Clostridium difficile-associated diarrhoea in an HIV antibody-positive patient

Ciprofloxacin is an uncommon cause of pseudomembranous colitis. A case is described in which diarrhoea was associated with the presence of clostridial toxin in an HIV-infected patient and the possible implications are discussed.

Presumptive identification of Clostridium difficile by detection of p-cresol in prepared peptone yeast glucose broth supplemented with p-hydroxyphenylacetic acid

Prereduced, anaerobically sterilized peptone yeast glucose broth was supplemented with p-hydroxyphenylacetic acid and used for the presumptive identification of Clostridium difficile. Two hundred eighty-two organisms were grown in this medium for 18 h and tested for p-cresol production by gas-liquid chromatography. All 49 stock and reference strains of C. difficile and 19 organisms confirmed as C. difficile produced p-cresol. p-Cresol was not produced by 53 negative control or 161 test organisms. The system was convenient and effective.

Molecular characterization of the Clostridium difficile toxin A gene

The gene encoding the toxin A protein of Clostridium difficile (strain VPI 10463) was cloned and sequenced. The coding region of 8,133 base pairs had a mol% G + C of 26.9 and encodes 2,710 amino acids. The deduced polypeptide has a molecular mass of ca. 308 kilodaltons. Nearly a third of the gene, at the 3' end, consists of 38 repeating sequences. The repeating units were grouped into two classes, I and II, on the basis of length and the low levels of DNA sequence similarities between them. There were seven class I repeating units, each containing 90 nucleotides, and 31 class II units, which, with two exceptions, were either 60 or 63 nucleotides in length. On the basis of DNA sequence similarities, the class II repeating units were further segregated into subclasses: 7 class IIA, 13 class IIB, 5 class IIC, and 6 class IID. The dipeptide tyrosine-phenylalanine was found in all 38 repeating units, and other amino acid sequences were unique to a specific class or subclass. This region of the protein has epitopes for the monoclonal antibody PCG-4 and includes the binding region for the Gal alpha 1-3Gal beta 1-4GlcNAc carbohydrate receptor. Located 1,350 base pairs upstream from the toxin A translation start site is the 3' end of the toxin B gene. Between the two toxin genes is a small open reading frame, which encodes a deduced polypeptide of ca. 16 or 19 kilodaltons. The role of this open reading frame is unknown.

Toxigenic clostridia

Toxigenic clostridia belonging to 13 recognized species are discussed in this review. Each species or group of organisms is, in general, introduced by presenting the historical aspects of its discovery by early investigators of human and animal diseases. The diseases caused by each species or group are described and usually discussed in relation to the toxins involved in the pathology. Morphological and physiological characteristics of the organisms are described. Finally, the toxins produced by each organism are listed, with a presentation of their biological activities and physical and biochemical characteristics. The complete amino acid sequences for some are known, and some of the genes have been cloned. The term toxin is used loosely to include the various antigenic protein products of these organisms with biological and serological activities which have served as distinguishing characteristics for differentiation and classification. Some of these factors are not truly toxic and have no known role in pathogenicity. Some of the interesting factors common to more than one species or group are the following: neurotoxins, lethal toxins, lecithinases, oxygen-labile hemolysins, binary toxins, and ADP-ribosyltransferases. Problems in bacterial nomenclature and designation of biologically active factors are noted.

Update on pseudomembranous colitis

These discussions are selected from the weekly staff conferences in the Department of Medicine, University of California, San Francisco. Taken from transcriptions, they are prepared by Homer A. Boushey, MD, Professor of Medicine, under the direction of Lloyd H. Smith, Jr, MD, Professor of Medicine and Associate Dean in the School of Medicine. Requests for reprints should be sent to the Department of Medicine, University of California, San Francisco, School of Medicine, San Francisco, CA 94143.

Effect of Clostridium difficile enterotoxin A on ultrastructure of Chinese hamster ovary cells

Electron microscopical immunocytochemistry and light microscopy were used to study the effect of Clostridium difficile enterotoxin A (EA) on cultured Chinese hamster ovary (CHO) cells. At 4 degrees C, immunocytochemically detected EA was randomly distributed along the plasma membrane; when cells were subsequently transferred to 37 degrees C, the EA moved into coated pits and coated vesicles within 2 min. Within 2 h of incubation at 37 degrees C with EA, the perinuclear cytoplasm of the CHO cells became highly refractile, and in 4 h, most of the cells were round; however, the majority of rounded cells excluded erythrosin B while remaining firmly attached to the culture dish plastic. When EA was removed from the cultured cells within 2 h, the cells returned to a normal morphology and formed a confluent monolayer. The nuclei of rounded cells were irregularly shaped; cytoplasmic intermediate filaments were collapsed toward the nucleus. Long bundles of parallel, 11-nm-diameter filaments appeared in the nuclei after 3 h of incubation with EA and disappeared by the fourth hour of incubation. Intoxicated cells did not undergo mitosis. Thus, EA was internalized, at least in part, by receptor-mediated endocytosis and subsequently affected the nuclei of CHO cells.

Production, purification and characterization of Clostridium difficile toxic proteins different from toxin A and from toxin B

The purification and characterization of three new proteins called C1, C2, and C3 from Clostridium difficile are described. Their estimated molecular mass were about 350 (C1), 270 (C2) and 140 (C3) kDa, consisting of subunits of 39 (C1), 43 (C2) and 41 (C3) kDa, respectively. Immunodiffusion revealed that the three proteins contained similar but not identical antigenic determinants to toxin A. Each protein induced a cytotonic effect on hamster ovaric cells; the combined proteins, had a specific activity on cells 5-times higher than that of toxin A. In rat intestinal loops, they induced a clear fluid secretion, while toxin A elicited a haemorrhagic fluid response. The cytotonic activities of all three proteins were abolished by antiserum against toxin A, while antiserum against toxin B inhibited only the activity of the 270 kDa protein. In contrast to toxin A, the cytotoxicity of the three proteins was inactivated by trypsin. Thus, the chemical, antigenic and biological properties of these proteins differed from those of toxin A and toxin B.

Identification of Clostridium difficile in stool specimens by culture-enhanced gas-liquid chromatography

We have developed a sensitive and specific method for the identification of Clostridium difficile in stool specimens based on the detection of metabolic breakdown products of the organism by gas-liquid chromatography after incubation of stool samples in a selective broth medium containing cefoxitin. Use of this approach to test samples from two different populations of patients at separate medical centers showed this method to be superior to plate cultures or cytotoxin testing alone for both populations. The combined results from the two patient populations showed that 225 of 226 confirmed isolates were identified correctly, resulting in a sensitivity of 99.6% and a specificity of 99.0%. This method eliminates the delay caused by subculturing for tests requiring a pure isolate. The culture phase amplifies even low numbers of C. difficile in fecal samples (due to low in vivo concentrations or delayed transport) and thus increases sensitivity. Other advantages include the ability to detect C. difficile in the mixed flora of the stool and the ability of most clinical laboratories to use this procedure. Given the complexities of the detection of C. difficile toxins and the increasing importance of this organism as a nosocomial agent, culture-based methods remain the preferred approach to screening and routine workup for cases of diarrhea.

Comparison of media for screening of diarrheic stools for the recovery of Clostridium difficile

Recoveries of Clostridium difficile from stool specimens by using three media, cycloserine-mannitol agar (M-CMA), cycloserine-mannitol-blood agar (M-CMBA), and cycloserine-cefoxitin agar (M-CCA), were compared. Of 321 clinical specimens, 37 yielded C. difficile. Thirty-four were positive on M-CCA, 21 were positive on M-CMA, and 20 were positive on M-CMBA. M-CCA recovered significantly more C. difficile than did M-CMBA or M-CMA.

Prevention of antibiotic-associated diarrhea by Saccharomyces boulardii: a prospective study

Saccharomyces boulardii, a nonpathogenic yeast, has been widely used in Europe to prevent antibiotic-associated diarrhea (AAD). We performed a prospective double-blind controlled study to investigate AAD in hospitalized patients and to evaluate the effect of S. boulardii, a living yeast, given in capsule form concurrently with antibiotics. Over 23 mo, 180 patients completed the study. Of the patients receiving placebo, 22% experienced diarrhea compared with 9.5% of patients receiving S. boulardii (p = 0.038). Risk factors found to be associated with AAD were multiple antibiotic combinations (containing clindamycin, cephalosporins, or trimethoprim-sulfamethoxazole) and tube feeding. Clostridium difficile, an anaerobe found in the stools of most patients with pseudomembranous colitis, was variably associated with AAD. We evaluated the role of C. difficile in AAD in the study population and found no significant association between the presence of C. difficile or cytotoxin with AAD. Approximately 33% of the patients without diarrhea harbored at least one C. difficile-positive stool and nearly 50% of these patients had detectable cytotoxin. Similar values were obtained in patients with diarrhea. Of C. difficile-positive patients, 31% (5/16) on placebo developed diarrhea compared with 9.4% (3/32) on S. boulardii; this difference was not statistically significant (p = 0.07). There were no discernable adverse effects of yeast administration. We conclude that S. boulardii reduces the incidence of antibiotic-associated diarrhea in hospitalized patients.

Yield of stool cultures, ova and parasite tests, and Clostridium difficile determinations in nosocomial diarrheas

Stool cultures for bacterial pathogens, ova and parasites, and Clostridium difficile are usually ordered for patients with nosocomial diarrhea. In the interest of cost containment we undertook an 18-month retrospective study to assess the cost/benefit of performing each of these three tests. During the study period nosocomial diarrhea developed in 118 patients. Of 452 bacterial stool cultures ordered, only one was positive for Campylobacter jejuni and none for ova and parasites. However, of 126 cultures examined for C. difficile, 47 showed positive results. We conclude that bacterial stool culture and ova and parasite identification are not indicated for patients with nosocomial diarrhea. Elimination of these unnecessary stool tests (bacterial/ova and parasite) would have saved the hospital approximately +7530 in the 18-month study period.

Evaluation of a commercial latex test for Clostridium difficile for reactivity with C. difficile and cross-reactions with other bacteria

Seventy-eight species of bacteria (739 isolates) were tested for reactivity with a commercial latex test for Clostridium difficile. All noncytotoxic as well as cytotoxic strains of C. difficile reacted positively. Immuno-specific cross-reactions were found only with C. sporogenes, proteolytic C. botulinum, and Peptostreptococcus anaerobius.

An evaluation of a rapid latex test for the diagnosis of Clostridium difficile-associated diarrhea

We present here the results of an evaluation of a rapid latex test for detection of Cl. stridium difficile-associated in comparison with our standard cytotoxin assay and culture for C. difficile. Some 515 diarrheal stools were examined. C. difficile was cultured from 70 specimens (13.5%); 53 specimens (10.2%) were positive with the latex test, and 50 (9.6%) by cytotoxin assay. The latex test did not differ significantly from the cytotoxin assay in sensitivity or specificity compared to culture results. There was also no significant difference in the specificity of the latex test compared to cytotoxin assay in patients in whom the diagnosis of C. difficile-associated diarrhea was negative. Positive and negative predictive values of the latex test for C. difficile-associated diarrhea were similar to those of cytotoxin assay. The latex test thus appears to be a rapid and practical test for the laboratory diagnosis of C. difficile-associated diarrhea. To optimize specificity and sensitivity its use should be restricted to patients where the diagnosis is strongly suspected and a rapid answer is required. As it does not distinguish between toxigenic virulent C. difficile strains and non-toxigenic avirulent strains, it would seem prudent to confirm positive results subsequently by demonstrating in-vivo or in-vitro cytotoxin production.

Purification and characterisation of two forms of toxin B produced by Clostridium difficile

Toxin B from Clostridium difficile was purified to homogeneity by gel filtration and high resolution ion exchange chromatography. Two forms of toxin B were found. Form 1 which seemed to consist of two identical subunits of 220-300 kDa; femtogram amounts of this toxin induced rounding of fibroblast cells. Form 2 contained subunits of 43 kDa and 105 kDa; the stoichiometric ratio probably being 4:1; picogram amounts were needed to induce rounding of fibroblast cells. Immunological studies suggested that both subunit types were antigenic and had epitopes which were identical with those of form 1.

Results of a prospective, 18-month clinical evaluation of culture, cytotoxin testing, and culturette brand (CDT) latex testing in the diagnosis of Clostridium difficile-associated diarrhea

An 18-mo evaluation of culture, cytotoxin, and latex testing for Clostridium difficile was performed between July 1, 1985, and December 31, 1986, on 1,536 specimens from 1,406 patients during evaluation of diarrhea. All cases with at least one test positive were investigated for clinical status. There were 144 Clostridium difficile-associated diarrhea (CAD) patients; 139 (97%) were positive by culture, 96 (67%) by cytotoxin, and 98 (68%) by latex testing. In the 1,262 non-CAD patients with diarrheal stool, 89 (7.1%) were positive by culture, 18 (1.4%) by cytotoxin, and 68 (5.4%) by the latex test. No CAD patient was positive by cytotoxin testing only, and two were positive by latex testing only. The culture and cytotoxin positivity were similar to our previous reports of 90-97% and 70-73%, respectively. Latex sensitivity (68%) was comparable to that of cytotoxin testing in this large group of patients (p greater than 0.5). Overall, in the 1,262 patients without clinical evidence of Clostridium difficile disease, positive tests by latex testing (5.4%) were intermediate between those of culture (7.1%, p less than 0.1) and cytotoxin (1.4%, p less than 0.001).

Purification and characterization of Clostridium sordellii hemorrhagic toxin and cross-reactivity with Clostridium difficile toxin A (enterotoxin)

Hemorrhagic toxin (toxin HT) was purified from Clostridium sordellii culture filtrate. The purification steps included ultrafiltration through an XM-100 membrane filter and immunoaffinity chromatography, using a monoclonal antibody to toxin A of Clostridium difficile as the ligand. Toxin HT migrated as a major band with a molecular weight of 525,000 and a minor band at 450,000 on nondenaturing gradient polyacrylamide gel electrophoresis. The molecular weight was estimated at 300,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Isoelectric focusing indicated an apparent pI of 6.1. Toxin HT was cytotoxic for cultured cells and lethal for mice by intraperitoneal injection, and it elicited an accumulation of hemorrhagic fluid in rabbit ileal loops. Immunodiffusion analysis revealed a reaction of partial identity between toxins A and HT. Immunological cross-reactivity between these toxins was further demonstrated by immunoblotting and by neutralization of toxin HT biological activity with antibodies to toxin A. A sensitive indirect enzyme-linked immunosorbent assay was used to examine the affinity involved in homologous and heterologous antigen-antibody interactions. Our findings show that toxin HT has biological activities and immunological properties similar to those of toxin A; however, the toxins are not identical.