Clostridium difficile: its disease and toxins

Toxins A and B of Clostridium difficile

The toxins produced by Clostridium difficile share several functional properties with other bacterial toxins, like the heat-labile enterotoxin of Escherichia coli and cholera toxin. However, functional and structural differences also exist. Like cholera toxin, their main target is the disruption of the microfilaments in the cell. However, since these effects are not reversible, as found with cholera toxin, additional mechanisms add to the cytotoxic potential of these toxins. Unlike most bacterial toxins, which are built from two structurally and functionally different small polypeptide chains, the functional and binding properties of the toxins of C. difficile are confined within one large polypeptide chain, making them the largest bacterial toxins known so far.

Comparison of two commercially available enzyme immunoassays for detection of Clostridium difficile in stool specimens

Clostridium difficile is the cause of most cases of pseudomembranous colitis, the most severe form of antibiotic-associated diarrhea. Rapid diagnosis guides both the treatment and the control of nosocomial spread of infection. Two enzyme immunoassay (EIA) kits developed for the rapid detection of C. difficile toxin A in fecal specimens, Premier (Meridian Diagnostics, Cincinnati, Ohio) and Tox-A test (TechLab, Virginia Polytechnic Institute Research Park, Blacksburg), were evaluated by using 410 fecal specimens. Seventy-six specimens were positive for C. difficile toxin B by the cytotoxin assay (prevalence rate, 19%). The Meridian EIA was positive for 71 of the 76 samples, yielding a sensitivity of 93%. The TechLab EIA detected 75 of the 76 positive samples, yielding a sensitivity of 99%. The Meridian and TechLab EIAs had specificities of 100 and 93%, respectively. These data indicate that both EIAs are suitable alternatives to the cytotoxin assay in routine diagnostic laboratories. However, confirmation of TechLab EIA-positive test results by the cytotoxin assay remains necessary.

Nutritional aspects of cytotoxin production by Clostridium difficile

Arginine was the only amino acid used by Clostridium difficile that permitted cytotoxin synthesis in a peptone-based medium. Synthesis of cytotoxin was delayed when glucose was used as the substrate. Addition of rifampin or puromycin to cultures prior to release of cytotoxin inhibited the release of cytotoxin, suggesting that a protein essential for cytotoxin release is synthesized after cytotoxin is synthesized.

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.

Comparison of four methods in the diagnosis of Clostridium difficile disease

Nine hundred forty-five stool specimens from patients suspected of having Clostridium difficile disease were examined using a cell culture cytotoxicity assay (CTA), two enzyme immunoassay (EIA) kits (Cytoclone for toxins A and B; VIDAS for toxin A) and a latex agglutination assay (CDT). One hundred nineteen specimens had positive titers (> or = 90) in the CTA; clinical review of 16 discordant samples and 49 controls supported the significance of 90 as the positive cut-off titer. The performance of the two EIAs and the latex assay was assessed relative to CTA titers of the samples. Sensitivity was < or = 50% for all three assays for the 24 specimens with CTA titers of 90, but it reached 97-100% for the two EIAs and 84% for the latex assay at titers of > or = 2,250. The Cytoclone EIA exhibited higher sensitivity at the lower positive titers. Overall, specificity of the methods ranged from 96.7% (CDT latex assay) to 99.1% (Cytoclone EIA).

Clostridium difficile toxin A elicits Ca(2+)-independent cytotoxic effects in cultured normal rat intestinal crypt cells

In rat intestinal crypt cells, Clostridium difficile toxin A induces (i) early cytoskeletal alterations involving the whole population and (ii) late effects in 30 to 40% of the cells, consisting mainly of surface blebbing and nuclear fragmentation. All these effects were Ca2+ independent and were not abolished by protein synthesis inhibitors.

Clostridia-associated enterocolitis in adult horses and foals

A review of the literature describing clostridia-associated enterocolitis is presented. The bacteria, their toxins, and possible factors that interact to contribute to the pathogenesis of enterocolitis are described. Clinical signs associated with clostridia-associated enterocolitis, methods of diagnosis, treatments, and preventive strategies are discussed.

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.

Purification and characterization of alpha-toxin produced by Clostridium novyi type A

Our study describes the production, purification, and properties of alpha-toxin from Clostridium novyi type A 19402. The bacterium produced maximal amounts of alpha-toxin when grown at 37 degrees C for 72 h in dialysis flask cultures containing brain heart infusion supplemented with 0.75% Tween 80 and 2% glycerol. The alpha-toxin was purified by precipitation with polyethylene glycol 6000, followed by chromatography on Q-Sepharose, phenyl-agarose, and Mono-Q. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the toxin exhibited a single band with an M(r) of 200,000. The toxin also exhibited a single immunoprecipitin arc by crossed immunoelectrophoresis with antiserum against crude toxin. It was stable when stored at 4 degrees C and also following exposure to buffers with pHs in the range of 4 to 7. The toxin had a minimum lethal dose in mice of 5 to 10 ng, caused rounding of a variety of cells in tissue culture, and was negative in the rabbit ileal loop assay. The cytotoxic activity was inhibited by agents that affect receptor-mediated processes, and the toxin was less active on a CHO mutant cell line that is defective in endosomal acidification. The analysis of the amino acid composition revealed an unusually high proline content. The N-terminal sequence is Met-Leu-Ile-Thr-Arg-Glu-Gln-Leu-Met-Lys.

Comparison of vidas Clostridium difficile toxin-A assay and premier C. difficile toxin-A assay to cytotoxin-B tissue culture assay for the detection of toxins of C. difficile

Damage to the intestinal mucosa by Clostridium difficile (CD) is toxin mediated. Two enzyme immunoassays (EIAs) for toxin-A detection, the automated Vitek immunodiagnostic assay system CDA (Vidas CDA), and the Premier toxin A (Premier) were tested for their ability to detect toxin A in 301 stool samples and compared with an in-house tissue culture assay for toxin B (TCA). Of these 301 samples, 49 were TCA positive and 252 were TCA negative. Agreement between Vidas CDA and TCA on the initial run was 85% (255 of 301) and increased to 94% (278 of 296) when discordant samples were retested from available frozen specimens. Corresponding levels of agreement for Premier were 91% (272 of 301) and 98% (284 of 288), respectively. If tissue culture positivity at any titer was used as the sole criterion for positivity of the specimen, agreement with positive TCA before and after repeat testing was 57% (26 of 49) and 74% (34 of 46) for Vidas CDA and 65% (32 of 49) and 95% (36 of 38) for Premier. Agreement with negative TCA titers was good: 90% for Vidas CDA and 95% for Premier, and 98% for Vidas CDA and 99% for Premier after repeat testing. Predictive values positive and negative after repeat testing were, respectively, 88% and 96% for Vidas CDA, and 95% and 99% for Premier. Results for the automated and manual EIA methods for detection of C. difficile toxin A were obtained in 2.5 h as compared with 36-48 h for tissue culture.

Identification of a Clostridium cocleatum strain involved in an anti-Clostridium difficile barrier effect and determination of its mucin-degrading enzymes

We isolated Gram-positive circular bacterium HB1 from intestinal microflora showing resistance to colonization by Clostridium difficile in mice (Su et. al., 1986a,b). We studied its enzymatic capacity to degrade mucin the first potential barrier to implantation of strains in the intestine. Its biochemical characteristics, terminal metabolites and the electrophoretic profiles of proteins and DNA-DNA homology indicated that it was a strain of Clostridium cocleatum. This strain displayed numerous glucosidase activities which were assumed to play a role in the degradation of mucin oligosaccharide chains in the digestive tract. These enzymes included alpha- and beta-galactosidases, beta-glucosidase, beta-N-acetylglucosaminidase, sialidase and alpha-N-acetylgalactosaminidase.

Activation of cellular phospholipase A2 by Clostridium difficile toxin B

C. difficile toxin B is a potent cytotoxin known to disrupt the microfilaments of cultured cells. We have recently shown also increased phospholipase A2 activity in cells treated with toxin B. The activity was detected as a toxin-induced, dose-dependent release of 14C-arachidonic acid from prelabeled fibroblasts. Here is shown that the toxin elicited a 14C-arachidonic acid release in a cell mutant resistant to the toxin B effect on the microfilaments. The toxin-induced release was further characterized using fibroblasts. Within 20 min high doses of toxin B (6 micrograms/ml) elicited a release which increased exponentially with time. Of the major membrane phospholipids the lipase activity affected mainly phosphatidyl ethanolamine. Neither cycloheximide nor pertussis toxin treatment or target cells inhibited the toxin-induced release, while it could be increased with 12-O-tetradecanoylphorbol-13-acetate. Our results also suggest a toxin-mediated increase in phospholipase C activity occurring at a later stage than the phospholipase A2 activation. We conclude that the ability of toxin B to induce phospholipase activation represents a hitherto unrecognized toxin B effect which is neither a cause nor a consequence of toxin-induced microfilament disorganization.

Intestinal carriage of Clostridium difficile in neonate dogs

A total of 70 puppies and their dams, distributed in 14 litters, were submitted to weekly fecal examinations for C. difficile during the first 10 weeks after birth. During the study, 94.3% of the puppies and 42.9% of the dams harboured C. difficile at least once in their feces. We calculated that 58% of the puppies carried toxigenic C. difficile at least once during the survey. In the puppies, C. difficile carriage rates ranging from 3.1% to 67.1% were observed at different moments of the observation period. In comparison, C. difficile carriage rate was 1.4% in a control group of healthy dogs more than 3 months old. Discrepancies in the toxigenic phenotype of the C. difficile strains isolated in the same litter showed that the neonate dogs were transiently infected with different strains, and that the dam is often not the source of infection with C. difficile. We could not demonstrate any pathogenicity of C. difficile for neonate dogs.

Fecal leukocytes in stool specimens submitted for Clostridium difficile toxin assay

To determine their diagnostic utility, fecal leukocytes were sought by methylene blue stain in 502 consecutive stool specimens submitted for Clostridium difficile toxin assay. In addition, the stability of fecal leukocytes was assessed by daily examination of 23 stool specimens stored at 4 degrees C and room temperature. The sensitivity, specificity, and positive and negative predictive values of fecal leukocytes in predicting C. difficile toxin assay results were 28%, 92%, 27%, and 93%, respectively. At 4 degrees C, fecal leukocytes retained morphology for a minimum of 3 days. Leukocytes survived as long in stool specimens containing either C. difficile toxin or an enteric pathogen as they did in stool specimens with neither finding. We conclude that testing stool specimens for fecal leukocytes is not useful for predicting the presence of C. difficile toxin, because 72% of stool specimens positive for C. difficile toxin are negative for fecal leukocytes despite their stability.

Signal transduction pathways and cellular intoxication with Clostridium difficile toxins

In cultured cells the cytopathic effects (CPE) of Clostridium difficile toxins A and B are superficially similar. The irreversible CPEs involve a reorganization of the cytoskeleton, but the molecular details of the mechanism(s) of action are unknown. As part of the work to elucidate the events leading to the CPE, cultured cells were preincubated with agents known to either stimulate or inhibit some major signal transduction pathways, whereupon toxin was added and the development of the CPE was followed. Both toxin-induced CPEs were enhanced by phorbol esters and mezerein, which stimulate protein kinase C, while they were inhibited by the phospholipase A2 inhibitors quinacrine and 4-bromophenacylbromide. Agents affecting certain G-proteins, cGMP and cAMP levels, phosphatases, prostacyclin, lipoxygenase, and phospholipase C did not affect the development of the CPE of either toxin. Thus, the cytoskeletal effect induced by toxins A or B appears to require PLA2 activity and involves at least part of a protein kinase C-dependent pathway, but not pertussis toxin-sensitive G-proteins, cyclic nucleotides, eicosanoid metabolites, or phospholipase C activity. In addition, both toxins were shown to activate phospholipase A2.

Comparison of three enzyme immunoassays, a cytotoxicity assay, and toxigenic culture for diagnosis of Clostridium difficile-associated diarrhea

Enzyme immunoassays (EIAs) based on monoclonal antibodies for the detection of Clostridium difficile toxins have recently been developed for clinical use. The aim of this study was to compare three commercially available EIAs, two for toxin A (Premier C. difficile Toxin A; Meridian, Osi, Elancourt, France; and Vidas C. difficile Toxin A; bioMérieux, Marcy l'Etoile, France) and one for toxins A and B (Cytoclone A + B EIA; Cambridge Biotech Corp., Codiapharm, Evian, France), with a cytotoxicity assay and toxigenic culture for the diagnosis of C. difficile-associated diarrhea (CDAD). The study was performed with 285 fresh stools from 285 patients with suspected CDAD. In case of disagreement, the tests were repeated on a frozen aliquot of the same stool sample, and the patient's chart was reviewed. CDAD diagnosis was established in 55 cases (incidence, 19.3%). The sensitivities and specificities of the methods were, respectively, 92.7 and 100% for the cytotoxicity assay, 96.4 and 99.1% for toxigenic culture, 75.5 and 97.8% for Cytoclone, 65.4 and 99.6% for Premier, and 65.4 and 100% for Vidas. The results were uninterpretable in 3.2% of cases with Cytoclone, 0.3% with Premier, and 2.5% with Vidas. We conclude that the cytotoxicity assay and toxigenic culture remain the best methods for the diagnosis of CDAD even though they lack standardization and require 48 to 96 h to obtain the result. Despite their rapidity and simplicity, EIAs are not sensitive enough to be relied on as the sole laboratory test.

Heterogeneity of Clostridium difficile isolates from infants

In order to improve our understanding of the role of Clostridium difficile in infants we characterised the strains isolated from this population. The production of toxin A and toxin B was studied. The toxin A, playing a major role in the disease, was searched for in faecal samples. The serogroup of the isolates was determined because some serogroups have been shown to be more pathogenic than others. Over a 9-month period, 102 faecal samples from 102 hospitalised infants (0-12 months) were analysed and 26% of the children were colonised with C. difficile. Fifteen isolates secreted neither toxin A nor B (62.5%). Nine isolates were toxigenic and secreted both toxins (37.5%). Of the eight toxigenic strains tested, six were from serogroup H and two serogroup K. Of the 13 nontoxigenic strains tested, 8 belonged to serogroup D, 2 to serogroup X, and 1 each to serogroup A, serogroup B and serogroup C. Three infants out of 102 studied had toxin A in their faeces. In summary, the infants can be colonised by (1) nontoxigenic strains, most of them from nonpathogenic serogroup D, without toxin A in the faeces; (2) toxigenic strains of virulent serogroups H and K, with or without toxin A in the faeces. Although some infants had diarrhoea, none needed a specific treatment for C. difficile. No specific C. difficile pathology could be retained and different mechanisms are advanced to explain this absence of pathogenicity.

Saccharomyces boulardii inhibits Clostridium difficile toxin A binding and enterotoxicity in rat ileum

BACKGROUND

Saccharomyces boulardii is a nonpathogenic yeast used for the prevention and treatment of Clostridium difficile-associated diarrhea and colitis. However, the mechanism by which S. boulardii exerts its protective effects remains unclear.

METHODS

The binding of [3H]toxin A to its brush border receptor preincubated with S. boulardii-cultured suspension or filtered conditioned medium was measured in vitro. The effect of toxin A on secretion, epithelial permeability, and morphology in rat ileal loops in vivo was also examined in rats pretreated with S. boulardii.

RESULTS

S. boulardii reduced [3H]toxin A-receptor binding in a dose-dependent fashion. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of ileal brush border exposed to S. boulardii-conditioned medium revealed a diminution of all brush border proteins. Treatment of rats with S. boulardii suspension reduced fluid secretion and mannitol permeability caused by toxin A.

CONCLUSIONS

S. boulardii may reduce some of the enterotoxic effects of toxin A by inhibiting toxin A-receptor binding. This effect appears to be manifested by a secreted product of the yeast, possibly a protease.

Effects of Clostridium difficile toxin B on human monocytes and macrophages: possible relationship with cytoskeletal rearrangement

Toxin B from Clostridium difficile is cytopathic in vitro for various types of cells, including polymorphonuclear cells, lymphocytes, and monocytes. Since intestine lamina propria is rich in macrophages, we studied the effect of toxin B on human monocytes and on human macrophages generated in vitro by long-term culture of purified circulating blood monocytes. Upon addition of toxin B, human monocytes exhibited few modifications whereas macrophages adopted a stellate morphology, with rounding up of the perikaryon. Toxin B made microfilaments of actin disappear and induced an important reorganization of vimentin and a redistribution of tubulin. Membrane area increased by approximately 16%. Toxin B did not affect the viability of human mononuclear phagocytes and did not exert any significant lytic effect. It profoundly altered the phagocytic function of macrophages. When activated by gamma interferon in the presence of toxin B, monocytes were more cytotoxic for U-937 target cells than control monocytes activated in absence of toxin. Finally, the combined treatment of monocytes with gamma interferon and toxin B increased significantly the secretion of tumor necrosis factor alpha, whereas toxin B alone was unable to induce tumor necrosis factor production. These results suggest that morphological and functional alterations induced in human mononuclear phagocytes by toxin B from C. difficile are due to the disorganization of the cytoskeleton and the resulting impairment of the membrane traffic equilibrium.

Specific detection of toxigenic strains of Clostridium difficile in stool specimens

Clostridium difficile is the infectious agent responsible for antibiotic-associated colitis. We report the use of the polymerase chain reaction technique to identify toxigenic strains of C. difficile in human stool specimens. A set of primers based on the nucleotide sequence of the toxin B gene, which amplified a 399-bp fragment from isolates producing toxin B, was designed. We examined 28 known toxigenic strains, which were all positive by this assay. DNAs from the nontoxigenic strains examined and from strains of Clostridium sordellii and C. bifermentans were not amplified with these primers. The sensitivity of this assay allowed us to identify as little as 10% toxigenic C. difficile cells in the presence of 90% nontoxigenic cells and to detect the toxin B gene in 1 pg of DNA from a toxigenic strain. DNAs extracted from 18 clinical stool specimens that were positive for toxin B by the tissue culture cytotoxicity assay were also positive by this assay. In addition, we detected toxin B sequences in DNA from 2 of 18 stool specimens that were negative for toxin B by the cytotoxicity assay. These two stool specimens were from patients who had a clinical pattern of colitis that was compatible with C. difficile causation. This rapid, sensitive assay will be useful for specific identification of toxigenic C. difficile and for revealing cases that are undetected by analysis of fecal samples for toxin B alone.

Comparison of enterotoxin production, cytotoxin production, serogrouping, and antimicrobial susceptibilities of Clostridium difficile strains isolated from AIDS and human immunodeficiency virus-negative patients

We analyzed and compared Clostridium difficile strains isolated from diarrheic stools of 49 human immunodeficiency virus (HIV)-negative and 50 AIDS patients. Our results suggest that distribution patterns of serogroups are different in these two populations. Serogroup C (which has been previously reported to be very resistant to antimicrobial agents) represents 66.0 and 18.4% of the isolates from AIDS and HIV-negative patients, respectively (P < 0.001); the selection of serogroup C could be explained by multiple antibiotic pressure to which AIDS patients have been subjected.

Identification and characterization of adhesive factors of Clostridium difficile involved in adhesion to human colonic enterocyte-like Caco-2 and mucus-secreting HT29 cells in culture

Experiments reported in this communication showed that the highly toxinogenic Cd 79685, Cd 4784, and Wilkins Clostridium difficile strains and the moderately toxinogenic FD strain grown in the presence of blood adhere to polarized monolayers of two cultured human intestinal cell lines: the human colonic epithelial Caco-2 cells and the human mucus-secreting HT29-MTX cells. Scanning electron microscopy revealed that the bacteria interacted with well-defined apical microvilli of differentiated Caco-2 cells and that the bacteria strongly bind to the mucus layer that entirely covers the surface of the HT29-MTX cells. The binding of C. difficile to Caco-2 cells developed in parallel with the differentiation features of the Caco-2 cells, suggesting that the protein(s) which constitute C. difficile-binding sites are differentiation-related brush border protein(s). To better define this interaction, we tentatively characterized the mechanism(s) of adhesion of C. difficile with adherence assays. It was shown that heating of C. difficile grown in the presence of blood enhanced the bacterial interaction with the brush border of the enterocyte-like Caco-2 cells and the human mucus-secreting HT29-MTX cells. A labile surface-associated component was involved in C. difficile adhesion since washes of C. difficile grown in the presence of blood without heat shock decreased adhesion. After heating, washes of C. difficile grown in the presence of blood did not modify adhesion. Analysis of surface-associated proteins of C. difficile subjected to different culture conditions was conducted. After growth of C. difficile Cd 79685, Cd 4784, FD and Wilkins strains in the presence of blood and heating, two predominant SDS-extractable proteins with molecular masses of 12 and 27 kDa were observed and two other proteins with masses of 48 and 31 kDa disappeared. Direct involvement of the 12 and 27 kDa surface-associated proteins in the adhesion of C. difficile strains was demonstrated by using rat polycolonal antibodies pAb 12 and pAb 27 directed against the 12 and 27 kDa proteins. Indeed, adhesion to Caco-2 cell monolayers of C. difficile strains grown in the presence of blood, without or with heat-shock, was blocked. Taken together, our results suggest that C. difficile may utilize blood components as adhesins to adhere to human intestinal cultured cells.

Mammalian epithelial cell line kit for detection of Clostridium difficile toxin

The performance characteristics of a mammalian epithelial (MEP) cell line kit (Cytotoxi Test; Advanced Clinical Diagnostics, Toledo, Ohio) for the detection of Clostridium difficile toxin was compared with that of conventional tissue culture assays with human embryonic lung (HEL) cells in shell vials and human foreskin fibroblasts (HFFs) in test tubes. One hundred forty-nine stool samples were tested. The MEP cells were at least as sensitive as the HEL cells for use in C. difficile toxin detection. Results for the MEP cells were also obtained considerably more rapidly than those for HEL cells when the cells were examined at 4 and 24 h and then every 24 h for up to 5 days. Approximately one-third of all positive MEP cells were detected at 4 h and 95% were detected by 48 h. In comparison, in the HEL shell vial monolayers, only 6% of the positive cells were detectable at 4 h and 76% were detectable at 48 h. The times for C. difficile toxin-induced cytotoxicity in HFF cells were similar to those in HEL cells. Shell vials carrying HEL cell monolayers (ViroMed Laboratories Inc., Minnetonka, Minn.) are a sensitive and reliable commercial source for the detection of C. difficile toxin, although they cannot detect C. difficile as rapidly as the Cytotoxi test with the MEP cell monolayers.

Effect of okadaic acid on the cytotoxic activity of Clostridium difficile toxin B and Clostridium sordellii toxin L

Clostridium difficile toxin B and Clostridium sordellii toxin L, which are immunologically related toxins, possess a cytotoxic activity inducing depolymerization of microfilaments and cellular retraction of cell bodies that are different for toxin B- and toxin-L-treated cells. The biological mechanisms responsible for these effects are unknown, but a previous study revealed that both toxins induce modification of phosphorylation of cellular proteins extracted from toxin B- and toxin L-treated cells without changes in protein kinase C activity or cAMP concentration. In the present study, we have investigated the effect of okadaic acid, an inhibitor of protein phosphatases, on the cytotoxic activity of toxins B and L in MacCoy cells. Firstly, we reveal by cytotoxic assay and staining of F-actin that okadaic acid (1 microM or higher) induces depolymerization of microfilaments and cellular morphological modifications which are similar to that of cells treated with toxin L. Secondly, we show that 1 microM okadaic acid potentials the cytotoxic activity of toxin L but not of toxin B. These observations suggest that the cytotoxic mechanisms induced by okadaic acid and toxin treatment are partly common, indicating that an increase in phosphorylation favors the cytotoxicity of toxin L. Since okadaic acid had no influence on the cytotoxicity of toxin B, we suggest that toxin B and L, alter the cells by different cellular biological mechanisms.

Effect of oral Saccharomyces boulardii treatment on the activity of Clostridium difficile toxins in mouse digestive tract

Human antibiotic-associated diarrhoea and pseudomembranous colitis are partly due to toxin production by Clostridium difficile. It is now well documented that Saccharomyces boulardii protects against C. difficile induced diseases. In an attempt to understand better the mechanism of this protective effect, the action of S. boulardii on a crude toxin preparation was studied in vitro and in vivo. The results showed that the yeast had no effect on the toxins in vitro but was able to protect mice inoculated with these toxins. Furthermore, the observation by scanning electron microscopy that the mucosa of S. boulardii protected mice was not damaged suggest that the yeast mainly acts on the intestinal mucosa.

New rapid identification test for Clostridium difficile

AIMS

A set of five tests were developed and tested for their ability to confirm the identity of C difficile colonies within 30 minutes.

METHODS

The relevant substrates were incorporated into four filter paper squares attached to a plastic carrier (Diffstrip), five enzymes/products (prolyl aminopeptidase, galactosidase, leucine aminopeptidase, acid phosphatase and indole). The strips were inoculated, incubated for 20 minutes, and reagents added.

RESULTS

96.4% (212 of 220) strains of C difficile were immediately differentiated from 51 other Clostridium spp tested. The remaining 3.6% (eight of 220) of C difficile isolates produced a reaction pattern similar to some of the Clostridium sporogenes tested and required additional tests. None of the other Clostridium spp tested produced reaction patterns similar to C difficile.

CONCLUSION

The Diffstrip allowed colonies of C difficile to be confirmed within 30 minutes for 96.4% of isolates, with less than 4% requiring any additional tests. No strains of C difficile were misidentified and no strains of other Clostridium spp tested were misidentified as C difficile.

Characterization of a toxin A-negative, toxin B-positive strain of Clostridium difficile

This study was undertaken to examine toxin production by Clostridium difficile 8864, a naturally occurring isolate that has been reported to produce toxin B in the absence of toxin A. To date, this is the only strain of C. difficile reported to produce only one of the toxins. The results of our initial studies with antibodies against toxins A and B confirmed these observations. Toxin B from strain 8864 and from VPI strain 10463, a strain that produces high levels of both toxin A and toxin B, was purified to homogeneity by sequential anion-exchange chromatography on DEAE-Sepharose CL-6B, gel filtration on Ultrogel AcA22, and immunoadsorption chromatography, and their toxic activities were compared. Our results showed that toxin B from strain 8864 and toxin B from C. difficile VPI strain 10463 were comparable in their cytotoxic activities and that the 8864 toxin B was more lethal. In addition, we observed that toxin B from strain 8864 was weakly enterotoxic, which may explain the ability of this strain to cause intestinal disease in hamsters treated with antibiotics. Analysis with specific antibodies showed that the toxin B molecules from these strains were highly related but contained distinct epitopes. The results of hybridization studies with probes specific for the toxin B gene of VPI strain 10463 demonstrated differences between the toxin B genes of the two strains. In addition, probes specific for the toxin A gene of VPI strain 10463 showed that strain 8864 contains a region which shows identity with the 5' end of the toxin A gene but not the region of the gene which encodes a hydrophobic region and the repeating units.

Role of human microflora in health and disease

The human host and its microbial flora constitute a complex ecosystem whose equilibrium serves as a remarkable example of reciprocal adaptation. Intestinal bacteria play an important role in the development of the immune system. The normal intestinal flora is responsible for resistance to colonization by exogenous pathogenic microorganisms. Nevertheless, it also constitutes a reservoir of potentially pathogenic bacteria in close contact with the host. These bacteria are responsible for opportunistic infections in immunocompromised hosts. The equilibrium of the flora can be upset by antibiotics, leading to infections as a result of proliferation of antibiotic-resistant pathogenic bacteria.

Prospective study of oral teicoplanin versus oral vancomycin for therapy of pseudomembranous colitis and Clostridium difficile-associated diarrhea

A prospective, randomized study comparing oral teicoplanin with oral vancomycin in the treatment of pseudomembranous colitis (PMC) and Clostridium difficile-associated diarrhea (CDAD) was performed. Teicoplanin was administered at a dosage of 100 mg twice a day for 10 days, and vancomycin was administered at a dosage of 500 mg four times a day for 10 days. CDAD was diagnosed by demonstrating both C. difficile and cytotoxin in the feces of symptomatic patients (more than three loose stools per day). The diagnosis of PMC was also based on colonoscopy. Cytotoxin assay and cultures were checked in all patients 7 to 10 days after discontinuation of therapy and 25 to 30 days thereafter. Of the 51 patients enrolled, 46 were judged to be assessable. Among these, 26 received teicoplanin and 20 received vancomycin. At enrollment, both groups were comparable in terms of age, sex, occurrence of PMC or CDAD, and previous antibiotic treatment. Eighteen of the 20 patients in the vancomycin group and 10 of the 26 patients in the teicoplanin group had previously undergone surgery (P = 0.0004). Treatment resulted in the clinical cure of 20 (100%) vancomycin and 25 (96.2%) teicoplanin patients (P = 0.56). After discontinuation of therapy, clinical symptoms recurred in four (20%) vancomycin patients and two (7.7%) teicoplanin patients (P = 0.21). Posttherapy asymptomatic C. difficile carriage (positive follow-up cultures without any clinical symptoms) occurred in five (25%) vancomycin patients and two (7.7%) teicoplanin patients (P = 0.11).Overall, 9 of 20 (45%) vancomycin patients and 5 of 26 (19.2%) teicoplanin patients (P=0.059) appeared not to be cleared of C. difficile after treatment. No adverse effects related to vancomycin or teicoplanin therapy were observed.

Evidence for a modular structure of the homologous repetitive C-terminal carbohydrate-binding sites of Clostridium difficile toxins and Streptococcus mutans glucosyltransferases

The homologous C-terminal repeats of Clostridium difficile toxins (ToxA and ToxB) and streptococcal glucosyltransferases appear to mediate protein-carbohydrate interactions at cellular binding sites with sugar moieties as substrates. A consensus sequence of 134 repeating units from gram-positive bacteria indicates that these repeats have a modular design with (i) a stretch of aromatic amino acids proposed to be involved in the primary carbohydrate-protein interaction, (ii) an amplification of this interaction by repetition of the respective sequences, and (iii) a second domain, not characterized, that is responsible for carbohydrate specificity.

Molecular, immunological, and biological characterization of a toxin A-negative, toxin B-positive strain of Clostridium difficile

A cytotoxigenic Clostridium difficile strain that fails to produce toxin A but causes hemorrhage and bloody fluid accumulation in ligated ileal loops of rabbits and hemorrhage and diarrhea in hamsters is described. The lack of reaction of DNA from this strain in hybridization studies with a toxin A gene-specific 4.5-kb probe and polymerase chain reaction studies with six toxin A-specific primers indicate the absence of the toxin A gene. The cytotoxin produced by this strain was not responsible for the enterotoxic or hemorrhagic activity and shared characteristics with toxin B, i.e., its cytotoxicity was neutralized by antibodies to toxigenic strains of C. difficile and Clostridium sordellii. Polymerase chain reaction studies with toxin B-specific primers showed that the DNA from this strain produced a 690-bp product in addition to the expected 591-bp product.

Impaired detection of faecal verocytotoxin in the presence of Clostridium difficile cytotoxin in patients with haemolytic uraemic syndrome

Three cases of haemolytic uraemic syndrome associated with infection with verocytotoxin producing Escherichia coli are described. The concomitant presence of Clostridium difficile cytotoxin in the patients' stool impaired the detection of free faecal verocytotoxin. Stool specimens containing Clostridium difficile cytotoxin should thus be considered negative for verocytotoxin only after neutralisation of the Clostridium difficile cytotoxin with antitoxin.

Antibiotic-associated colitis and cystic fibrosis

The use of antibiotics in patients with cystic fibrosis is widespread, and fecal carriage of Clostridium difficile occurs in up to 50% of these patients; however, antibiotic-associated colitis appears to be a rare occurrence. The reasons why this is so remain unknown. A case of antibiotic-associated colitis occurring in a patient with cystic fibrosis is described. Possible mechanisms for the rarity of antibiotic-associated colitis are reviewed and implications for prompt diagnosis and therapy are discussed.

New selective medium for isolating Clostridium difficile from faeces

AIMS

To compare CCFA (cycloserine, cefoxitin fructose agar) with a new selective medium CDMN (containing cysteine hydrochloride, norfloxacin, and moxalactam) for the isolation of Clostridium difficile after direct faecal culture.

METHODS

The minimum inhibitory concentration (MIC) of norfloxacin was determined for 64 strains of C difficile, 17 strains of other Clostridium sp, and 66 various isolates of faecal origin, together with MIC determinations of moxalactam against the 81 strains of Clostridium sp and 15 isolates of Bacteroides sp. Using C difficile agar base with 0.5 g/l of cysteine hydrochloride, norfloxacin and moxalactam were incorporated into the medium and compared with CCFA for the isolation of C difficile after direct faecal culture.

RESULTS

Norfloxacin (12 mg/l) inhibited the growth of enterobacteriaceae and faecal streptococci; moxalactam (32 mg/l) inhibited the growth of most strains of Bacteroides sp tested, together with Clostridium sp other than C difficile. Using the antibiotics in combination (CDMN), the growth and colonial morphology of 64 strains of C difficile were unaffected. When CDMN medium was compared with CCFA for the isolation of C difficile from 832 faeces from inpatients with diarrhoea, the CDMN agar isolated 20% more strains and reduced the number of contaminating colonies by 30%.

CONCLUSIONS

CDMN both improves the isolation rate of C difficile from faecal specimens and reduces the growth of other organisms compared with CCFA.

Presence of Clostridium difficile and antibiotic and beta-lactamase activities in feces of volunteers treated with oral cefixime, oral cefpodoxime proxetil, or placebo

Three groups of six healthy adult volunteers were randomly assigned to a treatment with 400 mg of oral cefpodoxime proxetil, oral cefixime, or placebo per day for 10 days. Informed consent was obtained from all volunteers. Clostridium difficile was not detected in the feces of any subject before treatment or at any time in the subjects in the placebo group. C. difficile was, however, detected in all subjects treated with cefpodoxime proxetil and in five of six treated with cefixime. Genomic DNA restriction patterns showed that the strains of C. difficile differed from one volunteer to another. Two subjects both shed different strains at different times during the 25-day surveillance period. All isolates were resistant to cefixime and cefpodoxime (MIC for 90% of strains, 256 and 512 mg/liter, respectively). Antibiotic activity was found in the feces of one volunteer treated with cefpodoxime proxetil and of four volunteers treated with cefixime. It was inversely correlated with the presence of fecal beta-lactamase activity. Intestinal side effects were limited to modifications of stool consistency, which occurred in only 3 of the 12 treated volunteers and did not lead to cessation of treatment. These modifications were significantly associated with the presence of fecal antibiotic activity (P less than 0.05) but not with the shedding of toxigenic or nontoxigenic strains of C. difficile or with the presence of toxin A in feces, which was detected only in one perfectly healthy treated volunteer.

Evaluation of C. diff.-CUBE test for detection of Clostridium difficile-associated diarrhea

The toxin B assay was used to evaluate C. diff.-CUBE, a new dot-immunobinding assay (DIA) for the laboratory diagnosis of Clostridium difficile-associated diarrhea. The widely used latex agglutination test was also included for comparison. Stools from 100 patients suspected of having C. difficile-associated diarrhea were tested. The toxin B assay, latex agglutination, and DIA tests were positive for 12%, 9%, and 22% of the specimens, respectively. The sensitivity, specificity, and positive and negative predictive values of the DIA test were 67%, 84%, 36%, and 95%, respectively, compared with the toxin B assay. The specificity (98%) and positive predictive value (78%) for the latex agglutination test were significantly higher than those of the DIA test. Of 13 specimens solely positive by the DIA test, 11 were cultured and none were positive. Clinical assessment supported only two of the 13 positive DIA results. When clinical assessment was included in the analysis, the DIA positive predictive value rose to 45%. Although the sensitivity and negative predictive values of the DIA test are comparable to the latex agglutination test, the low specificity and positive predictive values of the DIA test make it an inappropriate method to use for screening in a population with a low prevalence of true positives.

Laboratory diagnosis of Clostridium difficile-associated gastrointestinal disease: comparison of a monoclonal antibody enzyme immunoassay for toxins A and B with a monoclonal antibody enzyme immunoassay for toxin A only and two cytotoxicity assays

A total of 320 stool specimens obtained from 262 patients suspected of having Clostridium difficile-associated gastrointestinal disease were examined with two cytotoxicity assays (CTAs) and two commercially available enzyme immunoassays (EIAs). The CTAs were an in-house-developed procedure (University of Massachusetts Medical Center [UMMC], Worcester, Mass.) and a commercial test (Bartels CTA; Baxter Healthcare Corp., West Sacramento, Calif.). One EIA was a monoclonal antibody-based assay for C. difficile toxins A and B (Cambridge Biotech Corp. [CBC], Worcester, Mass.). The other EIA employed monoclonal antibodies directed against only toxin A (Meridian Diagnostics, Cincinnati, Ohio). True-positive and true-negative results were defined on the basis of the results of the four assays, clinical assessments of patients, and the results of other laboratory tests. The sensitivities of the four assays were as follows: Bartels CTA, 100%; UMMC CTA, 97.2%; CBC EIA, 84.5%; and Meridian EIA, 69.0%. The Bartels CTA demonstrated a specificity of 99.2%. The other three assays had a specificity of 100%.

Comparison of the VIDAS Clostridium difficile toxin A immunoassay with C. difficile culture and cytotoxin and latex tests

The VIDAS Clostridium difficile toxin A immunoassay (CDA) is a new, automated, enzyme-linked fluorescent-antibody assay for detection of C. difficile toxin A antigen in stool specimens. Simultaneous, parallel testing was performed by using the VIDAS CDA, the Culturette brand CDT latex test for C. difficile antigens, and conventional laboratory cell culture tests for C. difficile, cytotoxicity and C. difficile culture. One hundred ninety-four consecutive fresh soft or liquid stool samples submitted for C. difficile testing between July and September 1990 were evaluated. Of the 194 samples tested, 19 (10%) were from 16 patients who met our case definition for C. difficile-associated disease. The in vitro tests were evaluated in relation to two forms of a clinical case definition. In one form, a positive culture for toxin-producing C. difficile or a positive cytotoxin result obtained directly from the stool specimen was required as laboratory evidence of C. difficile. In the other, a positive result of any of the four laboratory tests was accepted for the laboratory portion of the case definition. No significant difference between the sensitivity of the VIDAS CDA and that of the Culturette brand CDT latex test was found (48 to 58% sensitivity for the CDT latex test and 52 to 63% sensitivity for the VIDAS CDA compared with 93 to 100% sensitivity for culture and 70 to 100% sensitivity for cytotoxin testing). The performance of the VIDAS CDA, however, was hampered by a high percentage of tests (19%) which gave an uninterpretable result.

Monoclonal antibodies specific for Clostridium difficile toxin B and their use in immunoassays

Five mouse monoclonal antibodies (MAbs) against Clostridium difficile toxin B have been raised and characterized. Three of them were immunoglobulin M (IgM) antibodies (6B10, 6G3, and 10B9), and the other two were of the IgG1 isotype (9E5 and 17G2), recognizing specifically two distinct epitopes on the toxin B molecule. No MAb was able to neutralize cytotoxic activity significantly. The two IgG1 MAbs were purified and applied to various immunodiagnostic assays. MAbs coupled to latex beads were used for specific removal of toxin B from cytotoxic samples and for agglutination assay. An indirect sandwich enzyme-linked immunosorbent assay with MAb 9E5 or 17G2 as the capture antibody was established for identification of toxin B with a lower detection limit of 5 ng/ml.

Localization of two epitopes recognized by monoclonal antibody PCG-4 on Clostridium difficile toxin A

The toxin A gene of Clostridium difficile contains a 2.5-kb region encoding a series of contiguous repeating units located at the COOH terminus of the molecule. We previously showed that the monoclonal antibody (MAb) PCG-4, which neutralizes the enterotoxic activity of toxin A, binds to epitopes located within these repeating units. In the present study, we subcloned a series of fragments from this portion of the gene. The recombinant peptides expressed from the gene fragments were examined for reactivity with MAb PCG-4 to identify the epitopes involved in binding. Our results showed that MAb PCG-4 recognizes epitopes in amino acid residues 2097 through 2141 and amino acid residues 2355 through 2398.

Effects of antibiotics and other drugs on toxin production in Clostridium difficile in vitro and in vivo

In an attempt to understand more completely why patients treated with phenothiazines (chlorpromazine and cyamemazine), methotrexate, and certain antibiotics such as clindamycin have an increased risk of developing pseudomembranous colitis, the production of toxins A and B by Clostridium difficile in the presence of these drugs was measured in vitro as well as in vivo by using axenic mice. None of the drugs tested increased the production of toxins either in vitro or in vivo.