Evaluation of ELISA, RPLA, and Vero cell assays for detecting Clostridium perfringens enterotoxin in faecal specimens

Proteomic identification and quantification of Clostridium perfringens enterotoxin using a stable isotope-labelled peptide via liquid chromatography-tandem mass spectrometry

PURPOSE

Detection of Clostridium perfringens enterotoxin (CPE) in human stool is critical evidence of food poisoning. However, processing patient-derived samples is difficult and very few methods exist to confirm the presence of CPE. In this study, a technique was developed using proteomic analysis to identify and quantify CPE in artificial gut fluid as an alternative.

METHODS

The standard CPE was spiked into artificial gut fluids, and effective methods were developed by employing both a stable isotope-labelled internal standard peptide and liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Proteotypic peptide EILDLAAATER formed by tryptic digestion was selected for quantitation of CPE. The peptide was identified using product ion spectra. Although the nontoxic peptides originating from CPE showed very low detectability in extraction and tryptic digestion, they could be detected with sufficient sensitivity using the method we developed. Based on a spiked recovery test at two concentrations (50 and 200 µg/kg), the recovery values were 85 and 78%, respectively. The relative standard deviations of repeatability and within-laboratory reproducibility were less than 8 and 11%, respectively. These standard deviations satisfied the criteria of the Japanese validation guidelines for residues (MHLW 2010, Director Notice, Syoku-An No. 1224-1). The limit of quantification (LOQ) was estimated to be 50 µg/kg. The combination of the product ion spectra and relative ion ratio supported CPE identification at the LOQ level.

CONCLUSIONS

To the best of our knowledge, this is the first report of proteomic analysis of CPE using LC-MS/MS. The method would greatly help in assessing CPE reliably.

Innovative and Highly Sensitive Detection of Clostridium perfringens Enterotoxin Based on Receptor Interaction and Monoclonal Antibodies

Clostridium perfringens enterotoxin (CPE) regularly causes food poisoning and antibiotic-associated diarrhea; therefore, reliable toxin detection is crucial. To this aim, we explored stationary and mobile strategies to detect CPE either exclusively by monoclonal antibodies (mAbs) or, alternatively, by toxin-enrichment via the cellular receptor of CPE, claudin-4, and mAb detection. Among the newly generated mAbs, we identified nine CPE-specific mAbs targeting five distinct epitopes, among them mAbs recognizing CPE bound to claudin-4 or neutralizing CPE activity in vitro. In surface plasmon resonance experiments, all mAbs and claudin-4 revealed excellent affinities towards CPE, ranging from 0.05 to 2.3 nM. Integrated into sandwich enzyme-linked immunosorbent assays (ELISAs), the most sensitive mAb/mAb and claudin-4/mAb combinations achieved similar detection limits of 0.3 pg/mL and 1.0 pg/mL, respectively, specifically detecting recombinant CPE from spiked feces and native CPE from 30 different C. perfringens culture supernatants. The implementation of mAb- and receptor-based ELISAs into a mobile detection platform enabled the fast detection of CPE, which will be helpful in clinical laboratories to diagnose diarrhea of assumed bacterial origin. In conclusion, we successfully employed an endogenous receptor and novel high affinity mAbs for highly sensitive and specific CPE-detection. These tools will be useful for both basic and applied research.

Diagnostic Accuracy of Nucleic Acid Amplification-Based Assays for Clostridium perfringens-Associated Diseases: a Systematic Review and Meta-analysis

Timely and accurate methods for detecting Clostridium perfringens-associated diseases (CPAD) are crucial to improve patient care. A number of studies have evaluated the accuracy of nucleic acid amplification tests (NAAT) in detecting CPAD, but decisive results about their effectiveness have not been reported. We conducted a meta-analysis to evaluate the diagnostic performance of NAAT for detecting C. perfringens in clinical diarrheal samples. Five databases including PubMed, Embase, Scopus, Web of Science, and the Cochrane library were systematically probed for studies published before 6 December 2019. From 2,632 citations, we identified five eligible studies comprising 817 samples. Three studies (n = 695 samples) compared NAAT with a microbiological culture while the other three studies (n = 322 samples) compared NAAT with an immunoassay. NAAT revealed higher diagnostic accuracy against immunoassay (sensitivity, 0.53 [95% confidence interval [CI], 0.35 to 0.7]; specificity, 0.97 [95% CI, 0.95 to 0.99]; positive likelihood ratio [PLR], 23.2 [95% CI, 3.49 to 153.98]; negative likelihood ratio [NLR], 0.25 [95% CI, 0 to 245.28]; diagnostic odds ratio [DOR], 74.11 [95% CI, 2.11 to 2,593.7]) than microbiological culture (sensitivity, 0.31 [95% CI, 0.22 to 0.41]; specificity, 0.95 [95% CI, 0.93 to 0.97]; PLR, 11.56 [95% CI, 3.87 to 34.6]; NLR, 0.57 [95% CI, 0.27 to 1.21]; DOR, 18.1 [95% CI, 4.83 to 67.8]). NAAT pooled specificity was consistently ≥95% against that of applied reference standards. A meta-regression and subgroup analysis of sample condition, gene target, study design, and reference standards could not explain the heterogeneity (P > 0.05) in the diagnostic efficiency. The analysis has demonstrated that the diagnostic accuracy of NAAT is relatively insufficient to replace traditional reference standards as a single diagnostic test. NAAT can be applied in combination with microbiological culture because of the advantage of time to result and in scenarios where traditional tests are not feasible. Further investigations in this direction with larger sample sizes are still warranted to support our findings.

Using More Than 1 (Path)Way to Kill a Host Cell: Lessons From Clostridium perfringens Enterotoxin

Clostridium perfringens enterotoxin (CPE) is responsible for the symptoms of common intestinal infections due to C. perfringens type F isolates. CPE is a pore-forming toxin that uses certain claudins as a receptor. Previous studies showed that, in enterocyte-like Caco-2 cells, low CPE concentrations cause caspase 3-mediated apoptosis but high CPE concentrations cause necrosis. The recent work published in mBio by Shrestha, Mehdizadeh Gohari, and McClane determined that RIP1 and RIP3 are involved in both CPE-mediated apoptosis and necrosis in Caco-2 cells. Furthermore, mixed lineage kinase-domain (MLKL) oligomerization was shown to be important for necrosis caused by CPE, identifying this necrosis as programmed necroptosis. In addition, calpain activation due to Ca²⁺ influx through the CPE pore was identified as a critical intermediate step for MLKL oligomerization and, thus, CPE-induced necroptosis. These findings may have applicability to understand the action of some other pore-forming toxins that induce necroptosis and may also be important for understanding CPE action in vivo.

A sandwich duplex immuno PCR for rapid and sensitive identification of Clostridium perfringens alpha and enterotoxin

The prevalence and lethality associated with C. perfringens alpha (CPA) and enterotoxin (CPE) toxaemia necessitate the need for rapid and definitive detection systems to initiate management measures. In the present study, a sandwich duplex immuno-capture PCR (SD-IPCR) was developed by employing IgY antibodies against a bivalent protein r-Cpae derived from CPA and CPE for antigen capture and reporter antibodies against truncated CPA or CPE conjugated to oligomers of distinguishable size for antigen revealing and signal amplification. The avian immunoglobulin's (IgY) were devoid of reactivity with S. aureus protein A (SpA), a commensal that often co-exists with C. perfringens. The assay was specific, had a detection limit (LOD) of 1 pg/ml for both CPA and CPE in PBS and improved the LOD by 10⁴ folds compared to an analogous sandwich ELISA with same set of antibodies. In spiking studies, a ten-fold reduction in LOD was observed in case of intestinal tissue samples (10 pg/ml) however, no change in LOD was observed when SD-IPCR was applied on to faecal, serum or muscle tissue samples. Of the 136 natural samples examined, the SD-IPCR could detect CPA and CPE in 29.4% and 35.3% samples, while the sandwich ELISAs could detect the same in 25.7% and 25% samples respectively owing to the relatively lesser sensitivity. The LOD and specificity of the SD-IPCR demonstrates its applicability as an efficient and rapid platform for direct detection CPA and CPE from diverse samples matrices in clinical microbiological and meat testing laboratories.

Potential Therapeutic Effects of Mepacrine against Clostridium perfringens Enterotoxin in a Mouse Model of Enterotoxemia

Clostridium perfringens enterotoxin (CPE) is a pore-forming toxin that causes the symptoms of common bacterial food poisoning and several non-foodborne human gastrointestinal diseases, including antibiotic-associated diarrhea and sporadic diarrhea. In some cases, CPE-mediated disease can be very severe or fatal due to the involvement of enterotoxemia. Therefore, the development of potential therapeutics against CPE action during enterotoxemia is warranted. Mepacrine, an acridine derivative drug with broad-spectrum effects on pores and channels in mammalian membranes, has been used to treat protozoal intestinal infections in human patients. A previous study showed that the presence of mepacrine inhibits CPE-induced pore formation and activity in enterocyte-like Caco-2 cells, reducing the cytotoxicity caused by this toxin in vitro Whether mepacrine is similarly protective against CPE action in vivo has not been tested. When the current study evaluated whether mepacrine protects against CPE-induced death and intestinal damage using a murine ligated intestinal loop model, mepacrine protected mice from the enterotoxemic lethality caused by CPE. This protection was accompanied by a reduction in the severity of intestinal lesions induced by the toxin. Mepacrine did not reduce CPE pore formation in the intestine but inhibited absorption of the toxin into the blood of some mice. Protection from enterotoxemic death correlated with the ability of this drug to reduce CPE-induced hyperpotassemia. These in vivo findings, coupled with previous in vitro studies, support mepacrine as a potential therapeutic against CPE-mediated enterotoxemic disease.

Evidence that Clostridium perfringens Enterotoxin-Induced Intestinal Damage and Enterotoxemic Death in Mice Can Occur Independently of Intestinal Caspase-3 Activation

Clostridium perfringens enterotoxin (CPE) is responsible for the gastrointestinal symptoms of C. perfringens type A food poisoning and some cases of nonfoodborne gastrointestinal diseases, such as antibiotic-associated diarrhea. In the presence of certain predisposing medical conditions, this toxin can also be absorbed from the intestines to cause enterotoxemic death. CPE action in vivo involves intestinal damage, which begins at the villus tips. The cause of this CPE-induced intestinal damage is unknown, but CPE can induce caspase-3-mediated apoptosis in cultured enterocyte-like Caco-2 cells. Therefore, the current study evaluated whether CPE activates caspase-3 in the intestines and, if so, whether this effect is required for the development of intestinal tissue damage or enterotoxemic lethality. Using a mouse ligated small intestinal loop model, CPE was shown to cause intestinal caspase-3 activation in a dose- and time-dependent manner. Most of this caspase-3 activation occurred in epithelial cells shed from villus tips. However, CPE-induced caspase-3 activation occurred after the onset of tissue damage. Furthermore, inhibition of intestinal caspase-3 activity did not affect the onset of intestinal tissue damage. Similarly, inhibition of intestinal caspase-3 activity did not reduce CPE-induced enterotoxemic lethality in these mice. Collectively, these results demonstrate that caspase-3 activation occurs in the CPE-treated intestine but that this effect is not necessary for the development of CPE-induced intestinal tissue damage or enterotoxemic lethality.

The Potential Therapeutic Agent Mepacrine Protects Caco-2 Cells against Clostridium perfringens Enterotoxin Action

Clostridium perfringens enterotoxin (CPE) causes the gastrointestinal (GI) symptoms of a common bacterial food poisoning and several nonfoodborne human GI diseases. A previous study showed that, via an undetermined mechanism, the presence of mepacrine blocks CPE-induced electrophysiologic activity in artificial membranes. The current study now demonstrates that mepacrine also inhibits CPE-induced cytotoxicity in human enterocyte-like Caco-2 cells and that mepacrine does not directly inactivate CPE. Instead, this drug reduces both CPE pore formation and CPE pore activity in Caco-2 cells. These results suggest mepacrine as a therapeutic candidate for treating CPE-mediated GI diseases.

Clostridium perfringens enterotoxin (CPE) causes the diarrhea associated with a common bacterial food poisoning and many antibiotic-associated diarrhea cases. The severity of some CPE-mediated disease cases warrants the development of potential therapeutics. A previous study showed that the presence of mepacrine inhibited CPE-induced electrophysiology effects in artificial lipid bilayers lacking CPE receptors. However, that study did not assess whether mepacrine inactivates CPE or, instead, inhibits a step in CPE action. Furthermore, CPE action in host cells is complex, involving the toxin binding to receptors, receptor-bound CPE oligomerizing into a prepore on the membrane surface, and β-hairpins in the CPE prepore inserting into the membrane to form a pore that induces cell death. Therefore, the current study evaluated the ability of mepacrine to protect cells from CPE. This drug was found to reduce CPE-induced cytotoxicity in Caco-2 cells. This protection did not involve mepacrine inactivation of CPE, indicating that mepacrine affects one or more steps in CPE action. Western blotting then demonstrated that mepacrine decreases CPE pore levels in Caco-2 cells. This mepacrine-induced reduction in CPE pore levels did not involve CPE binding inhibition but rather an increase in CPE monomer dissociation due to mepacrine interactions with Caco-2 membranes. In addition, mepacrine was also shown to inhibit CPE pores when already present in Caco-2 cells. These in vitro studies, which identified two mepacrine-sensitive steps in CPE-induced cytotoxicity, add support to further testing of the therapeutic potential of mepacrine against CPE-mediated disease.

IMPORTANCEClostridium perfringens enterotoxin (CPE) causes the gastrointestinal (GI) symptoms of a common bacterial food poisoning and several nonfoodborne human GI diseases. A previous study showed that, via an undetermined mechanism, the presence of mepacrine blocks CPE-induced electrophysiologic activity in artificial membranes. The current study now demonstrates that mepacrine also inhibits CPE-induced cytotoxicity in human enterocyte-like Caco-2 cells and that mepacrine does not directly inactivate CPE. Instead, this drug reduces both CPE pore formation and CPE pore activity in Caco-2 cells. These results suggest mepacrine as a therapeutic candidate for treating CPE-mediated GI diseases.

A Five Site Clostridium Perfringens Food-Borne Outbreak: A Retrospective Cohort Study

Introduction

In May of 2012, we investigated a food-borne Clostridium perfringens outbreak in Slovenia involving a single kitchen and five venues, with 477 exposed persons.

Methods

In order to identify the causative agent, vehicle of infection and source of contamination, we conducted microbiological and environmental investigations and an analytical cohort study (n = 138).

Results

The case definition in the outbreak was met by 104 persons. Predominant symptoms were diarrhoea, nausea and abdominal cramps. Median incubation time and duration of illness were 12 and 22.5 hours respectively. Stool samples were collected from 18 persons and in 13 C. perfringens spores were present; enterotoxin was detected in 9 persons. PCR and PFGE analysis of isolates from a cook with earlier onset time, who did not consume the implicated food, and cases from four venues showed the same strain of C. perfringens type A (with cpe-gene), indistinguishable by PFGE analysis. No food samples could be obtained. An analytical study showed that one food item (French salad) was the most likely vehicle of infection (RR: 6.35; 95% CI: 1.62–24.90).

Conclusions

This was the largest C. perfringens outbreak in Slovenia to date. Proper analytical study in combination with detailed laboratory investigation with genotypisation enabled us to identify a causative agent, vehicle of infection and possible source of contamination. Fast response and interdisciplinary collaboration led to timely implementation of control measures. These have led to the kitchen acquiring new equipment and improving staff knowledge of risks and processes, thus reducing the likelihood of future reoccurrences.

Comparison of procedures for the extraction of supernatants and cytotoxicity tests in Vero cells, applied to assess the toxigenic potential of Bacillus spp. and Lactobacillus spp., intended for use as probiotic strains

Interest in using Bacillus strains as probiotic components of animal feeds has grown in recent years. However, some of these strains, especially those taxonomically related to the Bacillus cereus group, may have enterotoxigenic activity. Assessment of their toxigenic potential by well-established and robust protocols is required before authorizing their use in animal nutrition. Three methods of extraction and concentration of supernatants of Bacillus and Lactobacillus strains (methanol extraction, ammonium sulphate and ultrafiltration concentration) and three cytotoxic tests in Vero cells (WST-1, LDH and protein synthesis inhibition assays) for the assessment of the cytotoxicity activity of Lactobacillus strains (as probiotic strains in human and animal nutrition) and Bacillus toyonensis BCT-7112(T) (as animal probiotic strain in animal nutrition-Toyocerin®-) were evaluated in this study. Methanol extraction was not useful under any circumstances. The other two concentration methods (ammonium sulphate and ultrafiltration) were feasible, with slightly greater sensitivity achieved by ultrafiltration. The probiotic strain B. toyonensis BCT-7112(T) proved to be a non-cytotoxic strain in all the protocols tested. However, some Lactobacillus strains showed cytotoxicity activity, regardless of the protocols applied.

Clostridium perfringens type A enterotoxin damages the rabbit colon

Clostridium perfringens enterotoxin causes the gastrointestinal (GI) symptoms of C. perfringens type A food poisoning and CPE-associated non-food-borne human GI diseases. It is well established that CPE induces fluid accumulation and severe tissue damage in ligated small intestinal loops of rabbits and other animals. However, a previous study had also reported that CPE binds to rabbit colonic cells yet does not significantly affect rabbit colonic loops. To the contrary, the current study determined that treatment with 50 or 100 μg/ml of CPE causes significant histologic lesions and luminal fluid accumulation in rabbit colonic loops. Interestingly, a CPE-neutralizing monoclonal antibody blocked the development of CPE-induced histologic damage but not luminal fluid accumulation in these loops. Similar luminal fluid accumulation, without significant histologic damage, also occurred after treatment of colonic loops with heat-inactivated CPE, antibody alone, or bovine serum albumin (BSA), indicating that increased osmolarity was causing or contributing to fluid accumulation in CPE-treated colonic loops. Comparative studies revealed the similar development of histologic damage and luminal fluid accumulation in both small intestinal loops and colonic loops after as little as a 1-h treatment with 50 μg/ml of CPE. Consistent with the CPE sensitivity of the small intestine and colon, Western blotting detected CPE binding and large-complex formation in both organs. In addition, Western blotting demonstrated the presence of the high-affinity CPE receptors claudin-3 and -4 in both organs of rabbits, consistent with the observed toxin binding. Collectively, these results offer support for the possible involvement of the colon in CPE-mediated GI disease.

Enteropathogenic bacteria in dogs and cats: diagnosis, epidemiology, treatment, and control

This report offers a consensus opinion on the diagnosis, epidemiology, treatment, and control of the primary enteropathogenic bacteria in dogs and cats, with an emphasis on Clostridium difficile, Clostridium perfringens, Campylobacter spp., Salmonella spp., and Escherichia coli associated with granulomatous colitis in Boxers. Veterinarians are challenged when attempting to diagnose animals with suspected bacterial-associated diarrhea because well-scrutinized practice guidelines that provide objective recommendations for implementing fecal testing are lacking. This problem is compounded by similar isolation rates for putative bacterial enteropathogens in animals with and without diarrhea, and by the lack of consensus among veterinary diagnostic laboratories as to which diagnostic assays should be utilized. Most bacterial enteropathogens are associated with self-limiting diarrhea, and injudicious administration of antimicrobials could be more harmful than beneficial. Salmonella and Campylobacter are well-documented zoonoses, but antimicrobial administration is not routinely advocated in uncomplicated cases and supportive therapy is recommended. Basic practices of isolation, use of appropriate protective equipment, and proper cleaning and disinfection are the mainstays of control. Handwashing with soap and water is preferred over use of alcohol-based hand sanitizers because spores of C. difficile and C. perfringens are alcohol-resistant, but susceptible to bleach (1:10 to 1:20 dilution of regular household bleach) and accelerated hydrogen peroxide. The implementation of practice guidelines in combination with the integration of validated molecular-based testing and conventional testing is pivotal if we are to optimize the identification and management of enteropathogenic bacteria in dogs and cats.

Clostridium perfringens toxin genotypes in the feces of healthy North Americans

We investigated the frequency of Clostridium perfringens in the normal fecal flora of healthy North Americans. About half of 43 subjects were colonized with C. perfringens at levels of approximately 10(6)cfu/g feces. Only type A strains were recovered. Spores sometimes outnumbered vegetative cells. Several genotypes were found. Some donors carried two genotypes, some only one. We found no alpha, beta2 or enterotoxin in the stools of any donors. Though some isolates carried toxin genes (e.g. cpe and cpb2) on plasmids, we saw no indication that healthy humans are the reservoir for the chromosomally-borne cpe recovered from cases of C. perfringens food poisoning.

Laboratory diagnosis of antibiotic-associated diarrhea: a Polish pilot study into the clinical relevance of Clostridium difficile and Clostridium perfringens toxins

In the present study, we investigated the prevalence of the Clostridium perfringens enterotoxin (CPEnt) in stool samples originally submitted for detection of Clostridium difficile toxins. Fifty-two fecal samples from inpatients were screened simultaneously for C. difficile and C. perfringens toxins: 75% of the specimens were positive for TcdA/TcdB toxins, 40% were positive for CPEnt, and 31% gave positive test results for both. It is interesting to note that only a relatively small number of C. perfringens isolates were positive for the cpe gene. All C. difficile strains were susceptible to metronidazole, but intermediate metronidazole resistance was documented for the C. perfringens isolates, which decreased upon in vitro passaging in the absence of metronidazole. We recommend that CPEnt detection should be included when diagnosing patients with presumed antibiotic-associated diarrhea.

Rapid detection of enterotoxigenic clostridium perfringens by real-time fluorescence resonance energy transfer PCR

Clostridium perfringens is one of the etiologic agents of gas gangrene that can occur when a wound is contaminated with soil. Type A C. perfringens can cause foodborne and nonfoodborne gastrointestinal illnesses due to an enterotoxin (CPE) produced by some strains during sporulation. We developed a quantitative real-time PCR assay based on fluorescence resonance energy transfer hybridization chemistry that targets the C. perfringens-specific phospholipase C (plc) gene and the enterotoxigenic gene (cpe) with the LightCycler and the Ruggedized Advanced Pathogen Identification Device (R.A.P.I.D.). The assay can detect as few as 20 copies of target sequences per PCR. The total assay time, from extraction to PCR analysis, is 90 min. This assay is rapid, sensitive, and specific and will allow direct detection of C. perfringens in water, food, and stool samples. It should prove helpful in investigating foodborne illnesses due to C. perfringens and can be used as a tool to ensure the safety of food and water supplies.

Incidence and characterization of Clostridium perfringens isolated from antibiotic-associated diarrhoeal patients: a prospective study in an Indian hospital

Clostridium perfringens has been reported as causing between 2-15% of all cases of antibiotic-associated diarrhoea (AAD), and may be diagnosed by detection of enterotoxin in faeces. A prospective study comprising 150 diarrhoeal patients and 100 non-diarrhoeal controls was undertaken to assess the incidence of C. perfringens-associated diarrhoea in an Indian hospital. Methods used included C. perfringens culture, reverse passive latex agglutination (RPLA) and enzyme-linked immunosorbent assay (ELISA) for detection of enterotoxin, and polymerase chain reaction (PCR) assay for the presence of enterotoxin gene. Attempts were made to type the isolates by multiplex PCR. Of the 150 diarrhoeal stool samples tested, 13 were culture positive. Of these, four were positive for C. perfringens enterotoxin by RPLA, two were positive by PCR and two were positive by RPLA and ELISA. Twenty-seven samples were positive for culture of C. perfringens in non-diarrhoeal controls but none were positive for enterotoxin either by RPLA or by PCR. The average incidence of C. perfringens AAD using these methods was 2.6%. Toxin typing showed that all the isolates belonged to type A. To conclude, the relatively low incidence of toxigenic C. perfringens suggests that enterotoxigenic C. perfringens is not a major cause of AAD in this population.

Detection of Viral, Bacterial, and Parasitological RNA or DNA of Nine Intestinal Pathogens in Fecal Samples Archived as Part of the English Infectious Intestinal Disease Study

Fecal samples were collected from cases and controls as part of the Infectious Intestinal Disease (IID) study in England and were stored as frozen suspensions for 8 to 12 years. The purpose of this study was to apply PCR-based procedures to assess the stability of pathogen-specific nucleic acid sequences present in this archive. Samples from which Cryptosporidium, Giardia, Salmonella, Campylobacter, enteroaggregative Escherichia coli (EAggEC), enterotoxigenic Clostridium perfringens, rotaviruses, noroviruses, or sapoviruses had been previously detected during the IID study using conventional methods were selected from the archive. A generic nucleic acid extraction method to recover RNA or DNA was used. Complementary DNA was generated from RNA by reverse transcription with random priming. Block-based and real-time PCR assays were used to amplify and detect gene fragments from each of these pathogens. The percentage reconfirmation of target was as follows: Giardia duodenalis 68%, Cryptosporidium 96%, Campylobacter 98%, Salmonella 98%, enterotoxigenic C perfringens 34%, EAggEC 93.3%, rotavirus 95%, norovirus 73%, and sapovirus 85%. This study has shown that nucleic acid can be extracted and specific sequences amplified and detected from archived fecal samples. The IID archive therefore represents a valuable resource for further studies, especially the investigation of the samples from which no pathogens had previously been detected.

Bacterial-associated diarrhea in the dog: a critical appraisal

The clinical documentation of enteropathogenic bacteria causing diarrhea in dogs is clouded by the presence of many of these organisms existing as normal constituents of the indigenous intestinal flora. The diagnosis of a putative bacterial enteropathogen(s) in dogs should be made based on a combination of parameters, including signalment and predisposing factors, clinical signs, serologic assays for toxins, fecal culture, and PCR. Relying on results of fecal culture alone is problematic, because C perfringens, C difficile, Campylobacter spp, and pathogenic and non-pathogenic E coli are commonly isolated from apparently healthy dogs [10,13,33]. Nevertheless, culture may be useful in procuring isolates for the application of molecular techniques, such as PCR, for detection of specific toxin genes or molecular typing of isolated strains to establish clonality in suspected outbreaks. The oversimplistic attempt to characterize bacterially associated diarrhea by anatomic localization of clinical signs should be discouraged, because most of the previously mentioned bacteria have been associated with small and large intestinal diarrhea. Accurate diagnosis of infections may require diagnostic laboratories to incorporate PCR-based assays using genus- and species-specific primers to facilitate detection of toxin genes and differentiation of species that appear phenotypically and biochemically similar. There has been tremendous interest in the application of microarray technology for the simultaneous detection of thousands of genes or target DNA sequences on one glass slide. This powerful tool could be used for detection of specific pathogenic bacterial strains in fecal specimens obtained from dogs in the future.

Detection of Clostridium difficile cytotoxin and Clostridium perfringens enterotoxin in cases of diarrhoea in the community

Faecal specimens from 843 cases of diarrhoea in the community were tested for the presence of Clostridium difficile cytotoxin and Clostridium perfringens enterotoxin. C. difficile cytotoxin was detected in faecal specimens from 0.6 % of cases aged at least 2 years by using a Vero cell assay. Factors associated with detection of C. difficile cytotoxin were antibiotic therapy, age over 60 years and living in a home with other elderly people. Three methods were used for the detection of C. perfringens enterotoxin: a Vero cell assay, a commercial (TechLab) enzyme immunoassay (EIA) and an in-house EIA. The lower level of detection of pure C. perfringens enterotoxin in buffer was 0.01 micro g ml(-1) by the TechLab EIA and 1.0 micro g ml(-1) by the Vero cell assay. C. perfringens enterotoxin was detected by using the TechLab EIA in faecal specimens from 2.5 % of cases. This commercial EIA was less sensitive than the in-house EIA, detecting only 31 % of positive cases, but was specific and could be used for outbreak investigation by routine diagnostic laboratories. Age over 60 years was a factor associated with C. perfringens enterotoxin detection; this age group may be targeted for testing.

Laboratory diagnosis of Clostridium perfringens antibiotic-associated diarrhoea

Clostridium perfringens has been reported as the cause of up to 15% of cases of antibiotic-associated diarrhoea (AAD) and may be diagnosed by detection of enterotoxin (CPEnt) in faeces. The performance of a commercial ELISA method for CPEnt, with culture and PCR methods to confirm the presence of enterotoxigenic C. perfringens, was evaluated in 200 consecutive specimens from patients with clinical details suggestive of AAD: 8% of the specimens were positive for CPEnt, 16% were positive for C. difficile cytotoxin and 2% gave positive test results for both C. perfringens and C. difficile toxins. Culture and PCR results confirmed the majority of ELISA results, although 2 (12.5%) reactive specimens were only weakly positive. C. perfringens is a potentially important cause of infective AAD and can be detected with the C. perfringens enterotoxin ELISA kit, although weak positive results should be considered with caution.

Evaluation of a routine diagnostic fecal panel for dogs with diarrhea

OBJECTIVES

To assess the diagnostic yield of a routine fecal panel and determine whether Clostridium perfringens or C difficile toxin production is associated with acute hemorrhagic diarrheal syndrome (AHDS) in dogs.

DESIGN

Case-control study.

ANIMALS

260 dogs with diarrhea and 177 dogs with normal feces.

PROCEDURE

Medical records were reviewed for results of culture for C difficile, Campylobacterspp, and Salmonella spp; C perfringens fecal enterotoxin (CPE) assay via ELISA or reverse passive latex agglutination (RPLA) assay; fecal endospore enumeration; C difficile toxin A assay; and parasite evaluation.

RESULTS

Prevalence of CPE in dogs with diarrhea was 22/154 (14.3%) via ELISA and 47/104 (45.2%) via RPLA assay, versus 9/74 (12%) via ELISA and 26/103 (25%) via RPLA assay in control dogs. Prevalence of C difficile was 47/260 (18%) in dogs with diarrhea and 41/74 (55%) in control dogs. Prevalence of C difficile toxin A was 26/254 (10.2%) in dogs with diarrhea and 0/74 in control dogs. Diagnosis of AHDS was made in 27 dogs; 8 had positive results for CPE, 7 had positive results for toxin A, and 1 had positive results for both toxins. Campylobacter spp were isolated from 13 of 260 (5%) dogs with diarrhea and 21 of 74 (28.4%) control dogs. Salmonella spp were isolated from 3 (1.2%) dogs with diarrhea.

CONCLUSIONS AND CLINICAL RELEVANCE

Diagnostic value of a fecal panel in dogs with diarrhea appears to be low.

In vitro culture and interferon-tau secretion by ovine blastocysts

Embryos were collected surgically from superovulated ewes on days 7, 8, 9 and 10 (oestrus=day 0) to evaluate the long-term culture and interferon-tau (IFN-tau) secretion of ovine blastocysts. Embryos were cultured in 2 ml Dulbecco's modification of Eagle's medium (DMEM) supplemented with 15 mg/ml BSA in 5% CO(2) in air or DMEM without BSA in 5% CO(2), 7% O(2), and 88% N(2) at 39 degrees C, examined daily for morphological features and diameter and each day placed into fresh culture medium to enable daily measurement of IFN-tau secretion. Nine day-7 and two day-9 embryos were cultured in DMEM with BSA and nine continued to develop. The day-7 embryos reached a mean maximum diameter of 370.0+/-50.25 microm after 4 days in culture. Nineteen day-7, 12 day-8 and five day-10 embryos were cultured in DMEM without BSA but only six of the day-7 and one day-8 embryos survived for at least 7 days with the former reaching a mean maximum diameter on day 7 of 357+/-43.75 microm whereas all five day-10 embryos survived for at least 7 days reaching a mean maximum diameter on day 6 of 1038+/-155.8 microm. An anti-viral assay and a ELISA for IFN-tau were developed. There was a considerable variation in the time of onset and amount of IFN-tau secreted that did not seem to be related to embryo morphology. Of 28 day-7 embryos cultured, 60.7% were secreting IFN-tau after 1 day of culture whereas 87.5% of day-8 embryos were secreting IFN-tau after 1 day in culture. The mean concentration of IFN-tau secreted by day-8 embryos after 1 day in culture (10.99+/-2.55 ng/ml) was not significantly different to day-7 embryos after 2 days in culture (8.8+/-1.75 ng/ml).

Evidence for antibiotic induced Clostridium perfringens diarrhoea

Clostridium difficile is a well documented cause of antibiotic associated diarrhoea in hospitalised patients, but may account for only approximately 20% of all cases. This leader reviews the current knowledge and understanding of the pathogenesis, epidemiology, and diagnosis of non-food borne Clostridium perfringens diarrhoea. Although enterotoxigenic C perfringens has been implicated in some C difficile negative cases of antibiotic associated diarrhoea, C perfringens enterotoxin detection methods are not part of the routine laboratory investigation of such cases. Testing for C perfringens enterotoxin in faecal samples from patients with antibiotic associated diarrhoea and sporadic diarrhoea on a routine basis would have considerable resource implications. Therefore, criteria for initiating investigations and optimum laboratory tests need to be established. In addition, establishing the true burden of C perfringens antibiotic associated diarrhoea is important before optimum control and treatment measures can be defined.

Recurrent diarrhea associated with enterotoxigenic Clostridium perfringens in 2 dogs

Two dogs were diagnosed with enterotoxigenic Clostridium perfringens-associated diarrhea. Diarrhea was responsive to antimicrobial therapy, but recurred after treatment was ceased. Clostridium perfringens enterotoxin was present in feces during diarrheic episodes but not when feces were normal. Both dogs responded to a prolonged course of oral cephalexin and dietary modification.

Molecular subtyping of Clostridium perfringens by pulsed-field gel electrophoresis to facilitate food-borne-disease outbreak investigations

Clostridium perfringens is a common cause of food-borne illness. The illness is characterized by profuse diarrhea and acute abdominal pain. Since the illness is usually self-limiting, many cases are undiagnosed and/or not reported. Investigations are often pursued after an outbreak involving large numbers of people in institutions, at restaurants, or at catered meals. Serotyping has been used in the past to assist epidemiologic investigations of C. perfringens outbreaks. However, serotyping reagents are not widely available, and many isolates are often untypeable with existing reagents. We developed a pulsed-field gel electrophoresis (PFGE) method for molecular subtyping of C. perfringens isolates to aid in epidemiologic investigations of food-borne outbreaks. Six restriction endonucleases (SmaI, ApaI, FspI, MluI, KspI, and XbaI) were evaluated with a select panel of C. perfringens strains. SmaI was chosen for further studies because it produced 11 to 13 well-distributed bands of 40 to approximately 1,100 kb which provided good discrimination between isolates. Seventeen distinct patterns were obtained with 62 isolates from seven outbreak investigations or control strains. In general, multiple isolates from a single individual had indistinguishable PFGE patterns. Epidemiologically unrelated isolates (outbreak or control strains) had unique patterns; isolates from different individuals within an outbreak had similar, if not identical, patterns. PFGE identifies clonal relationships of isolates which will assist epidemiologic investigations of food-borne-disease outbreaks caused by C. perfringens.

Direct detection of Clostridium perfringens enterotoxin in patients' stools during an outbreak of food poisoning

An outbreak of diarrhoea in a hotel affected 25 time keepers attending the 1997 Mediterranean Games. Epidemiological investigation implicated a 'pasta al ragù' consumed at the hotel's restaurant and Clostridium perfringens food poisoning was identified by direct detection of C. perfringens enterotoxin in patients' stools. This report confirms that a careful evaluation of epidemiological features, together with the availability of direct and rapid laboratory methods, may lead to a prompt identification of C. perfringens food poisoning.

Multiplex PCR assay for detection of Clostridium perfringens in feces and intestinal contents of pigs and in swine feed

A multiplex polymerase chain reaction (PCR) assay, developed to detect the alpha-toxin and enterotoxin genes (cpa and cpe, respectively) of Clostridium perfringens, was used to identify enterotoxigenic isolates of this organism from feces and intestinal contents of pigs and from feed samples from pig farms in Iowa. The organism was grown on tryptose-sulfite-cycloserine (TSC) agar, TSC agar without egg-yolk, sheep blood agar, or in brain heart infusion broth or cooked meat medium. DNA was extracted by boiling and the PCR assay was carried out using reagents from a commercial kit. The 319 bp amplification product of cpa and the 364 bp product of cpe were visualized under UV light after electrophoresis in a 2% agarose gel containing ethidium bromide. The average sensitivity of the assay, determined on artificially contaminated feces, was 9.2 x 10(4) colony forming units per gram. Assay of 97 isolates from feces and intestinal contents revealed cpa in 89, but all were negative for cpe. While 28% of the 442 total samples cultured yielded C. perfringens, only 5% of 298 fecal or intestinal contents samples were positive upon direct examination by the PCR assay. Ninety-one and eight-tenths % of isolates with the phenotype of C. perfringens were cpa positive by PCR. Forty-three percent of feed samples were culture positive, while 48.3% were PCR positive for cpa. None of these were cpe positive. We conclude that PCR is a useful assay for rapid detection of C. perfringens in feed, and for confirmation of the identity of isolates presumed to be C. perfringens.

Human disease associated with Clostridium perfringens enterotoxin

Clostridium perfringens continues to be a common cause of food-borne disease. Characteristics of this organism that contribute to its ability to cause food-borne illness include the formation of heat-resistant spores that survive normal cooking/heating temperatures, a rapid growth rate in warm food, and the production of enterotoxin (CPE) in the human gut. Time and temperature abuse associated with food preparation contributes to the majority of outbreaks of C. perfringens food-borne disease. CPE-induced diarrhea has been reported in the absence of a defined food vehicle. These cases have been typically associated with the elderly and following a course of antibiotic therapy. The incidence of CPE-induced diarrhea may be expected to increase with the growing population of immunocompromised (disease-, treatment-, or age-induced) individuals. Clostridium perfringens has been implicated as a possible contributor to the development of SIDS in susceptible individuals. Specifically, it has been hypothesized that CPE acts as a triggering agent, initiating the events associated with the development of SIDS. Continued refinement of both immunoassays and molecular methods for toxin and gene detection, respectively, will facilitate their eventual availability as commercial kits, providing rapid and simplified methods for the detection of C. perfringens isolates that produce or have the capacity to produce CPE as well as other toxins associated with this organism.

Comparison of Western immunoblots and gene detection assays for identification of potentially enterotoxigenic isolates of Clostridium perfringens

Clostridium perfringens enterotoxin (CPE) is an important sporulation-associated virulence factor in several illnesses of humans and domestic animals, including C. perfringens type A food poisoning. Therefore, the ability to determine the enterotoxigenicity of food or fecal C. perfringens isolates with simple, rapid assays should be helpful for epidemiologic investigations. In this study, Western immunoblotting (to detect CPE production in vitro) was compared with PCR assays and digoxigenin-labeled probe assays (to detect all or part of the cpe gene) as a method for determining the enterotoxigenicity of C. perfringens isolates. The cpe detection assays yielded reliable results with DNA purified from vegetative C. perfringens cultures, while Western immunoblots required in vitro sporulation of C. perfringens isolates to detect CPE production. Several cpe-positive C. perfringens isolates from diarrheic animals did not sporulate in vitro under commonly used sporulation-inducing conditions and consequently tested CPE negative. This result indicates that cpe gene detection and serologic CPE assays do not necessarily yield similar conclusions about the enterotoxigenicity of a C. perfringens isolate. Until further studies resolve whether these cpe-positive isolates which do not sporulate in vitro can or cannot sporulate and produce CPE in vivo, it may be preferable to use cpe detection assays for evaluating C. perfringens isolate enterotoxigenicity and thereby avoid potential false-negative conclusions which may occur with serologic assays.

Detection of Clostridium perfringens and its enterotoxin in cases of sporadic diarrhoea

AIMS

To determine the incidence of sporadic and apparently non-food related diarrhoea associated with Clostridium perfringens enterotoxin.

METHODS

Enzyme linked immunosorbent assay (ELISA) and reversed phase latex agglutination (RPLA) were used to detect C perfringens enterotoxin in faecal specimens from 818 sporadic cases of diarrhoea.

RESULTS

C perfringens enterotoxin was identified as a cause of sporadic diarrhoea in 56 of 818 (6.8%) cases. Diarrhoea was prolonged (three days or more) in most cases. Ages ranged from 3 months to 89 years, although most patients were over 60 years of age.

CONCLUSIONS

These results suggest that C perfringens may be a cause of sporadic cases of diarrhoea when causes such as food consumption or cross-infection are absent, particularly in the elderly.

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.

Analysis of plasmid profiling as a method for rapid differentiation of food-associated Clostridium perfringens strains

Plasmid analysis of over 120 strains of Clostridium perfringens, isolated during food-poisoning incidents and from animal carcasses and food constituents with no association with food poisoning, showed the potential of plasmid profiling as a means of differentiating epidemiologically related strains. On average 65% of freshly isolated strains contained one or more plasmids which could be used in the analysis. Comparison of profiles of strains from unrelated sources or unrelated strains from the same source showed a particularly wide variety of plasmid profiles. Thus the possibility that epidemiologically-unrelated strains might possess similar profiles appears to be very low in this organism. Analysis of serologically-related strains from the same source revealed similar plasmid profiles in all the plasmid-bearing strains examined. A high proportion (71%) of fresh and well-characterized food-poisoning strains possessed plasmids of 6.2 kb in size (compared with 19% of non-food-poisoning strains). The possible role of these plasmids is discussed, since the structural gene encoding the enterotoxin type A was not present on any of the plasmids in the food-poisoning strains tested.

Vero cell assay for rapid detection of Clostridium perfringens enterotoxin

A rapid assay which measured the biological activity of Clostridium perfringens enterotoxin was developed. The method involved the rapid killing of Vero cells by enterotoxin produced by C. perfringens grown in Duncan and Strong sporulation medium. Serial dilutions of toxin were added to Vero cells either in suspension or grown as monolayers in wells of a 96-well cell tissue culture cluster plate. Vital staining of Vero cells with neutral red, followed by extraction of the dye, allowed toxin levels to be determined either visually or by optical density measurements with a micro-ELISA M580 computer program. The toxin produced was confirmed as different from the Vero toxin of Escherichia coli and the alpha and theta toxins of C. perfringens.