Mechanism of Action of the Enteropathogenic Factor of Clostridium perfringens Type A

Analysis of the complete genome sequences of Clostridium perfringens strains harbouring the binary enterotoxin BEC gene and comparative genomics of pCP13-like family plasmids

Background

BEC-producing Clostridium perfringens is a causative agent of foodborne gastroenteritis. It was first reported in 2014, and since then, several isolates have been identified in Japan and the United Kingdom. The novel binary ADP-ribosylating toxin BEC, which consists of two components (BECa and BECb), is encoded on a plasmid that is similar to pCP13 and harbours a conjugation locus, called Pcp, encoding homologous proteins of the type 4 secretion system. Despite the high in vitro conjugation frequency of pCP13, its dissemination and that of related plasmids, including bec-harbouring plasmids, in the natural environment have not been characterised. This lack of knowledge has limited our understanding of the genomic epidemiology of bec-harbouring C. perfringens strains.

Results

In this study, we determined the complete genome sequences of five bec-harbouring C. perfringens strains isolated from 2009 to 2019. Each isolate contains a ~ 3.36 Mbp chromosome and 1–3 plasmids of either the pCW3-like family, pCP13-like family, or an unknown family, and the bec-encoding region in all five isolates was located on a ~ 54 kbp pCP13-like plasmid. Phylogenetic and SNP analyses of these complete genome sequences and the 211 assembled C. perfringens genomes in GenBank showed that although these bec-harbouring strains were split into two phylogenetic clades, the sequences of the bec-encoding plasmids were nearly identical (>99.81%), with a significantly smaller SNP accumulation rate than that of their chromosomes. Given that the Pcp locus is conserved in these pCP13-like plasmids, we propose a mechanism in which the plasmids were disseminated by horizontal gene transfer. Data mining showed that strains carrying pCP13-like family plasmids were unexpectedly common (58/216 strains) and widely disseminated among the various C. perfringens clades. Although these plasmids possess a conserved Pcp locus, their ‘accessory regions’ can accommodate a wide variety of genes, including virulence-associated genes, such as becA/becB and cbp2. These results suggest that this family of plasmids can integrate various foreign genes and is transmissible among C. perfringens strains.

Conclusion

This study demonstrates the potential significance of pCP13-like plasmids, including bec-encoding plasmids, for the characterisation and monitoring of the dissemination of pathogenic C. perfringens strains.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08453-4.

The Comparative Pathogenesis of Some Enteric Diseases. Based on Cases Presented at the 22nd Annual Seminar of the American College of Veterinary Pathologists

Basic reactions of the intestinal tract to injury are discussed using cases presented at the American College of Veterinary Pathologists' Seminar on Intestinal Pathology. Reports of the individual cases are cited in the text. Material reported during discussions is presented to preserve something of the tenor of the Seminar. First, the morphogenesis of the lesions in each case will be discussed, followed by the resultant functional changes related to clinical signs, and comparisons to other similar diseases.

Development and application of a multiplex PCR assay for detection of the Clostridium perfringens enterotoxin-encoding genes cpe and becAB

Clostridium perfringens causes food-borne gastroenteritis following the consumption of contaminated food by producing C. perfringens enterotoxin (CPE) in the intestines. Recently, we reported a novel enterotoxin, binary enterotoxin of C. perfringens (BEC) in C. perfringens isolates, which caused two disease outbreaks in Japan. Consequently, in the event of food poisoning outbreaks caused by C. perfringens, it is now necessary to screen for both the cpe and becAB genes by diagnostic PCR. Here, we present a simple multiplex PCR method for simultaneous detection of cpe, becAB and a C. perfringens control locus, phospholipase C (plc). Applying this method, we investigated the prevalence of cpe- or becAB-carrying C. perfringens strains in human stool and bovine rectum swab samples. Using a total of 169 isolates, we found that the percentage of becAB-carrying strains was very small (0.59%), one-tenth that of cpe-carrying strains. The simple method presented in this study with high specificity and sensitivity to C. perfringens will be a useful tool to survey the global prevalence of becAB-carrying C. perfringens strains.

Animal models to study the pathogenesis of human and animal Clostridium perfringens infections

The most common animal models used to study Clostridium perfringens infections in humans and animals are reviewed here. The classical C. perfringens-mediated histotoxic disease of humans is clostridial myonecrosis or gas gangrene and the use of a mouse myonecrosis model coupled with genetic studies has contributed greatly to our understanding of disease pathogenesis. Similarly, the use of a chicken model has enhanced our understanding of type A-mediated necrotic enteritis in poultry and has led to the identification of NetB as the primary toxin involved in disease. C. perfringens type A food poisoning is a highly prevalent bacterial illness in the USA and elsewhere. Rabbits and mice are the species most commonly used to study the action of enterotoxin, the causative toxin. Other animal models used to study the effect of this toxin are rats, non-human primates, sheep and cattle. In rabbits and mice, CPE produces severe necrosis of the small intestinal epithelium along with fluid accumulation. C. perfringens type D infection has been studied by inoculating epsilon toxin (ETX) intravenously into mice, rats, sheep, goats and cattle, and by intraduodenal inoculation of whole cultures of this microorganism in mice, sheep, goats and cattle. Molecular Koch's postulates have been fulfilled for enterotoxigenic C. perfringens type A in rabbits and mice, for C. perfringens type A necrotic enteritis and gas gangrene in chickens and mice, respectively, for C. perfringens type C in mice, rabbits and goats, and for C. perfringens type D in mice, sheep and goats.

BEC, a novel enterotoxin of Clostridium perfringens found in human clinical isolates from acute gastroenteritis outbreaks

Clostridium perfringens is a causative agent of food-borne gastroenteritis for which C. perfringens enterotoxin (CPE) has been considered an essential factor. Recently, we experienced two outbreaks of food-borne gastroenteritis in which non-CPE producers of C. perfringens were strongly suspected to be the cause. Here, we report a novel enterotoxin produced by C. perfringens isolates, BEC (binary enterotoxin of C. perfringens). Culture supernatants of the C. perfringens strains showed fluid-accumulating activity in rabbit ileal loop and suckling mouse assays. Purification of the enterotoxic substance in the supernatants and high-throughput sequencing of genomic DNA of the strains revealed BEC, composed of BECa and BECb. BECa and BECb displayed limited amino acid sequence similarity to other binary toxin family members, such as the C. perfringens iota toxin. The becAB genes were located on 54.5-kb pCP13-like plasmids. Recombinant BECb (rBECb) alone had fluid-accumulating activity in the suckling mouse assay. Although rBECa alone did not show enterotoxic activity, rBECa enhanced the enterotoxicity of rBECb when simultaneously administered in suckling mice. The entertoxicity of the mutant in which the becB gene was disrupted was dramatically decreased compared to that of the parental strain. rBECa showed an ADP-ribosylating activity on purified actin. Although we have not directly evaluated whether BECb delivers BECa into cells, rounding of Vero cells occurred only when cells were treated with both rBECa and rBECb. These results suggest that BEC is a novel enterotoxin of C. perfringens distinct from CPE, and that BEC-producing C. perfringens strains can be causative agents of acute gastroenteritis in humans. Additionally, the presence of becAB on nearly identical plasmids in distinct lineages of C. perfringens isolates suggests the involvement of horizontal gene transfer in the acquisition of the toxin genes.

Animal models to study the pathogenesis of enterotoxigenic Clostridium perfringens infections

Rabbits, mice, rats, non-human primates, sheep and cattle have been used to study the effect of Clostridium perfringens enterotoxin (CPE). CPE produces mostly necrosis of the small intestinal epithelium along with fluid accumulation in rabbits and mice. In the latter, CPE can bind to internal organs such as the liver, which induces lethal potassium levels in blood.

Inactivation of the gene (cpe) encoding Clostridium perfringens enterotoxin eliminates the ability of two cpe-positive C. perfringens type A human gastrointestinal disease isolates to affect rabbit ileal loops

Previous epidemiological studies have implicated Clostridium perfringens enterotoxin (CPE) as a virulence factor in the pathogenesis of several gastrointestinal (GI) illnesses caused by C. perfringens type A isolates, including C. perfringens type A food poisoning and non-food-borne GI illnesses, such as antibiotic-associated diarrhoea and sporadic diarrhoea. To further evaluate the importance of CPE in the pathogenesis of these GI diseases, allelic exchange was used to construct cpe knock-out mutants in both SM101 (a derivative of a C. perfringens type A food poisoning isolate carrying a chromosomal cpe gene) and F4969 (a C. perfringens type A non-food-borne GI disease isolate carrying a plasmid-borne cpe gene). Western blot analyses confirmed that neither cpe knock-out mutant could express CPE during either sporulation or vegetative growth, and that this lack of CPE expression could be complemented by transforming these mutants with a recombinant plasmid carrying the wild-type cpe gene. When the virulence of the wild-type, mutant and complementing strains were compared in a rabbit ileal loop model, sporulating (but not vegetative) culture lysates of the wild-type isolates induced significant ileal loop fluid accumulation and intestinal histopathological damage, but neither sporulating nor vegetative culture lysates of the cpe knock-out mutants induced these intestinal effects. However, full sporulation-associated virulence could be restored by complementing these cpe knock-out mutants with a recombinant plasmid carrying the wild-type cpe gene, which confirms that the observed loss of virulence for the cpe knock-out mutants results from the specific inactivation of the cpe gene and the resultant loss of CPE expression. Therefore, in vivo analysis of our isogenic cpe mutants indicates that CPE expression is necessary for these two cpe-positive C. perfringens type A human disease isolates to cause GI effects in the culture lysate:ileal loop model system, a finding that supports CPE as an important virulence factor in GI diseases involving cpe-positive C. perfringens type A isolates.

Is cardiorespiratory failure induced by bacterial toxins the cause of sudden infant death syndrome? Studies with an animal model (the rabbit)

Recent studies have implicated various toxigenic bacteria and their toxins in the aetiology of sudden infant death syndrome (SIDS). Therefore the effect of six bacterial toxins on the cardiorespiratory system of the rabbit was studied as a model for SIDS. The toxins' effect on the heart rate, arterial blood pressure, and breathing of anaesthetized rabbits was determined and their action compared to that of endotoxin. Intravenous injection of Clostridium perfringens enterotoxin and alpha-toxin, Staphylococcus enterotoxin B, Escherichia coli heat-stable toxin (STa), Clostridium difficile toxin A and B reduced heart rate, blood pressure, respiration and increased, slowed and prolonged thorax expansion, and at higher concentrations caused sudden death without visible stress or trauma. A combination of a low concentration of enterotoxins caused a greater reduction of these activities and sudden death. These effects were generally similar to those produced by endotoxin. In non-anaesthetized rabbits, the toxins slowed metabolism until death occurred without agitation, spasms, visible distress or prolonged illness. Intestinal production of these toxins by toxigenic strains, when conditions are suitable, and their systemic absorption, could therefore cause SIDS by an endotoxin-like shock mechanism.

Tetanus toxin and Clostridium perfringens enterotoxin as tools for the study of exocytosis

The role of calmodulin in exocytotic secretion was studied using digitonin-permeabilized bovine adrenal chromaffin cells to examine the effect of calmodulin directly introduced into the cells and using tetanus toxin as a specific inhibitor of exocytotic secretion. Addition of calmodulin to the permeabilized cells increased Ca(2+)-dependent norepinephrine release in a dose-dependent manner. The enhancement of release by calmodulin was specific to calmodulin: bovine serum albumin, actin, and caldesmon had no such effect. Enhancement of release by calmodulin occurred at Ca2+ concentrations of more than 10(-6) M and increased with an increase of Mg2+ concentration. The release of norepinephrine enhanced by calmodulin was inhibited by tetanus toxin. These results indicate directly that calmodulin plays an important role in exocytotic secretion from chromaffin cells. Exocytosis is known to occur by fusion of plasma membrane with limiting membranes of secretory vesicles following an increase in intracellular Ca2+. We used the enterotoxin of Clostridium perfringens type A as a specific tool to modify plasma membrane permeability to induce calcium influx. Multigranular exocytosis was recognized electron-microscopically in addition to the single-granular exocytosis in rat anterior pituitary cells and pancreatic acinar cells treated with the enterotoxin in the presence of extracellular Ca2+. The treatment with the enterotoxin did not induce any drastic change in the fine membrane structures of both types of cells. The enterotoxin-treated anterior pituitary cells and pancreatic acinar cells should provide a useful system for studying the molecular mechanism of fusion of membranes in exocytosis.

Pathodynamics of intoxication in rats and mice by enterotoxin of Clostridium perfringens type A

The pathodynamics of lethal intoxication in rats and mice by i.v. administration of enterotoxin of Clostridium perfringens type A was studied using whole animals and isolated organs. A lethal i.v. dose (50 micrograms/kg) of enterotoxin killed anesthetized rats and mice within 4-15 min. Rapid changes of ECG pattern suggestive of hyperpotassemia, rapid fall of blood pressure and transient hyperpnea followed by respiratory depression were observed. Analysis of plasma levels of cations revealed hyperpotassemia in both animal species. On the other hand, enterotoxin (up to 100 micrograms) showed little direct cardiotoxicity on the isolated heart. ECG changes produced by i.v. injection of KCl (0.5 ml of 50 mM) mimicked the ECG changes observed in the intoxicated rats injected with a lethal dose of enterotoxin. Perfusion of rat isolated organs showed that potassium concentration in the eluent from the liver (but not lungs or lower extremities) increased markedly within 1-2 min after the administration of enterotoxin. The amount of potassium liberated from a rat liver was about 133 mumoles, which is sufficient to increase the plasma level of potassium to more than 10 mM. In addition to potassium, cytoplasmic enzymes, such as glutamate oxalacetate transaminase, glutamate pyruvate transaminase and lactate dehydrogenase, were also liberated from the intoxicated liver, indicating that potassium was liberated from hepatocytes by the change in membrane permeability produced by enterotoxin. It is concluded that hyperpotassemia elicited by the cytotoxic action of enterotoxin on hepatocytes caused cardiac failure leading to the death of the intoxicated animals.

Indomethacin induced hepatic alterations in mono-oxygenase system and faecal Clostridium perfringens enterotoxin in the rat

The administration of indomethacin to rats, at the dose of 10 mg/kg once daily for three days, caused a loss of microsomal cytochrome P-450 and cytochrome b5 in the liver, and a fall in drug-metabolizing enzyme activities (i.e. aminopyrine N-demethylase, NADP cyt. c. reductase). Indomethacin also induced intestinal lesions and a significant increase in Clostridium perfringens enterotoxin levels in the feces at 24 hours after both the second and third day of treatment. The above findings suggest that the development of intestinal lesion and the accompanying release of Clostridium perfringens enterotoxin, as well as hepatic enzyme alterations in the rat, result from indomethacin administration. Some of the data in this paper were presented at the Meeting of British Pharmacological Society in Ireland, July 6th-8th, 1988.

Response of ligated rabbit ileal loop to Clostridium perfringens type C strains and their toxic filtrates

The vegetative cells and toxic filtrates of Clostridium perfringens type C strains were injected into ligated rabbit ileal loops and the responses were observed. Out of 12 strains examined, 2 strains showed positive reaction in this test, when the vegetative cells were injected. One of these 2 strains was an enterotoxigenic and beta-toxigenic and the other was beta- and delta-toxigenic but not enterotoxigenic. Culture filtrates containing beta or delta toxin also showed fluid accumulation in the rabbit ileal loop. Histological findings of loops injected with culture filtrates containing beta toxin showed separated and effaced villi, hemorrhage in the mucosa, engorged vessels, inflammatory cell infiltration, and hyperplasia of the lymphoid tissue.

Clostridium perfringens type A enterotoxin induces release of noradrenaline from the neurosecretory PC12 cell line

Clostridium perfringens type A enterotoxin(500 ng/ml) induced extensive release of noradrenaline (1/3-2/3 of the total cell content) from PC12 cells in 2-4 min in the presence, but not the absence of extracellular Ca2+. Cells treated with toxin in the absence of Ca2+ released noradrenaline promptly on subsequent addition of Ca2+ to the medium. The amount of noradrenaline released depended on the concentrations of both Ca2+ and toxin in the medium (ED50, 0.3 mM and 420 ng/ml respectively). Ca2+ could be replaced by Ba2+ or Sr2+, and Mn2+ or Co2+, which are Ca2+ channel blockers, did not inhibit the release of the transmitter. These findings are discussed in relation to the systemic effects of enterotoxin.

A hypothesis concerning Clostridium perfringens type A enterotoxin (CPE) and sudden infant death syndrome (SIDS)

This study identifies the presence of Clostridium perfringens type A enterotoxin (CPE) in some gastrointestinal and serum samples from babies who had died of the Sudden Infant Death Syndrome (SIDS) and other causes. On occasion antibodies to this toxin were identified in sera. CPE is parasympathomimetic in its action. In the adult food poisoning model it is produced when the organism sporulates in vivo. This leads to speculation as to whether this toxin may play an ante-mortem role in the dying process of infants, either in the agonal stages or as a causative factor in SIDS.

Morphological alterations and changes in cellular cations induced by Clostridium perfringens type A enterotoxin in tissue culture cells

The morphological alterations (bleb-balloon formation) induced by Clostridium perfringens type A enterotoxin in HeLa and Vero cells were studied under defined extracellular conditions. The action of enterotoxin was found to depend on the temperature but not on energy metabolism. The morphological alterations by the enterotoxin occurred in phosphate buffered saline containing Ca2+ and Mg2+. Of the constituents of the buffered saline, Ca2+ was essential for the morphological alterations and other ions were interchangeable. The morphological alterations by the enterotoxin occurred also in 10 mM Hepes-Na buffer, pH 7.2 containing NaCl, KCl or choline chloride at a concentration of over ca. 50 mM and in 10 mM Hepes-Ca buffer, pH 7.2 containing CaCl2 at a concentration of over ca. 50 mM. Addition of sucrose to the medium prevented induction of the morphological alterations. The amount of sucrose necessary to protect the cells increased with increase in NaCl, KCl or CaCl2 concentration in the medium. A calcium ionophore A23187 mimicked the action of enterotoxin. Examination of the cation contents of the cells by atomic absorption spectrophotometry showed early and rapid increase of Ca2+ during intoxication with concomitant changes in Na+, K+ and Mg2+ that reduced the ion concentration gradients between inside and outside of the cell present before toxin treatment. The mechanism of action of C. perfringens type A enterotoxin is discussed on the basis of these findings.

Isolation and some properties of an enterotoxin produced by Bacillus cereus

Extracellular proteins produced by Bacillus cereus B-4ac were separated by chromatography on Amberlite CG-400, QAE-Sephadex, Sephadex G-75, and hydroxylapatite. A fraction, containing three detectable antigens, obtained from chromatography on hydroxylapatite caused fluid accumulation in ligated rabbit ileal loops, was dermonecrotic to rabbit skin, was cytotoxic to cultured cells, and was lethal to mice after intravenous injection. Two other fractions obtained from chromatography on hydroxylapatite showed essentially no toxic activity when tested individually. Each nontoxic fraction contained two of the three proteins present in the toxic material. When the two nontoxic fractions were combined, activity in all of the biological assays was observed. Antiserum against either of the nontoxic fractions neutralized the dermonecrotic response of the combined material. These results suggest that all of these biological activities probably are due to a single entity and that more than one component probably comprise the toxic entity.

Quantitation of binding and subcellular distribution of Clostridium perfringens enterotoxin in rat liver cells

Binding of enterotoxin from Clostridium perfringens type A was studied in suspensions of parenchymal and nonparenchymal cells from rat liver. In hepatocytes, 1.5 X 10(6) specific binding sites per cell with an association constant of 3.2 X 10(6) M-1 were found. About 1% of the added toxin was nonspecifically bound to the hepatocytes. At concentrations of toxin below 0.1 micrograms/ml, 80% of the toxin density of 7 X 10(6) cells per ml. Binding did not increase after the cells became permeable to the toxin. Subcellular fractionation in a sucrose gradient produced no evidence for binding to parts of the cell other than the plasma membrane. The degree of binding to nonparenchymal cells was less than 10% of the binding to hepatocytes.

Clostridium perfringens in animal disease: a review of current knowledge

The diseases caused by various types of Clostridium perfringens are critically reviewed in the light of current knowledge. Particular emphasis is placed on information concerning these diseases in Canadian livestock. There are two etiologically clearly-defined acute C. perfringens diseases recognized in Canada: hemorrhagic enteritis of the new born calf, caused by C. perfringens type C, and enterotoxemia of sheep, caused by type D. Clostridium perfringens type A may play a role as a secondary pathological agent in various disease conditions, such as necrotic enteritis of chickens. It may also cause wound infections and may provide a source for human food poisoning outbreaks. There appears to be a considerable lack of knowledge regarding the distribution of C. perfringens types, their pathogenesis, diagnosis and the incidence of diseases caused by this organism.

Binding of enterotoxin from Clostridium perfringens type A to liver cells in vivo and in vitro. The enterotoxin causes membrane leakage

Enterotoxin from Clostridium perfringens was shown to retain its biological activity after labelling with 125I. When injected intravenously into mice and rats, most of the radioactivity in the organs was present in the form of intact toxin. Studies of the tissue distribution of labelled enterotoxin showed the largest amounts in the liver, where the activity reached a maximum 10--15 min after administration. The highest concentration per g tissue was found in liver and kidneys. The radioactivity was excreted in the urine as a mixture of intact labelled toxin and low molecular weight degradation products. In vitro studies with purified parenchymal liver cells showed rapid release of lactate dehydrogenase (LDH) during treatment with enterotoxin, thus indicating severe membrane damage.

Purification and partial characterization of heat-stable enterotoxin of enterotoxigenic Escherichia coli

Heat-stable enterotoxin was purified from a strain of enterotoxigenic Escherichia coli 53402 A-1 from human intestine. The cells were cultured in Casamino Acids-yeast extract-salts medium, and the purification procedure consisted of protamine sulfate treatment of the culture supernatant, ultrafiltration with an Amicon PM-10 membrane, diethylaminoethyl-cellulose column chromatography, hydroxyapatite column chromatography, Bio-Gel P-10 gel filtration, 90% ethanol extraction, and preparative polyacrylamide gel disc electrophoresis. About 300-fold purification was achieved, with a yield of about 12%. However, the homogeneity of the purified heat-stable enterotoxin was not rigorously demonstrated. The purified heat-stable enterotoxin had an absorption maximum at about 275 nm, and its isoelectric point was about 3.90. The molecular weight of the purified heat-stable enterotoxin was ca. 4,000 by Sephadex G-100 gel filtration. The minimum effective dose of purified heat-stable enterotoxin was about 2.5 ng in the suckling mouse assay. The purified heat-stable enterotoxin gave a positive reaction in not only the suckling mouse assay but also the mouse intestinal loop test and the guinea pig skin permeability test.

Fluid accumulation in mouse ligated intestine inoculated with Clostridium perfringens enterotoxin

Clostridium perfringens enterotoxin, when inoculated into the ligated intestinal loop of mice, caused marked distension due to fluid accumulation. The increase in weight of the intestinal loop was proportional to the log dose of enterotoxin within a range from 1 to 16 micrograms. The fluid accumulation was arrested by washing the loop with saline or by injection of the specific anti-enterotoxin serum into the loop 5 or even 30 min after inoculation of the enterotoxin. A significant increase in weight of the loop was found as early as 10 min after inoculation of the toxin. These results may suggest that entergotoxin is neither bound firmly to the mucosal membrane nor permeates into the cells of the intestinal wall. The mouse intestinal loop test is economical, simple to perform, and applicable for quantitative determination of the enteropathogenic activity of C. perfringens enterotoxin.

Enterotoxigenic Clostridium perfringens type A isolated from intestinal contents of cattle, sheep and chickens

One hundred and fourteen strains of Clostridium perfringens, isolated from the intestinal contents of cattle, sheep, and chickens with enteritis or other disease conditions were studied for their ability to produce enterotoxin. Reversed passive hemagglutination, fluorescent antibody and immunodiffusion tests were used. On the basis of the reversed passive hemagglutination titres, supported by the other two tests, enterotoxigenicity of the strains was arbitrarily classified into two categories: highly enterotoxigenic and potentially enterotoxigenic, with 12% falling into each category. All the highly enterotoxigenic strains originated from cases of enteritis and included all three animal species. Apart from enterotoxigenicity, one C. perfringens strain produced beta toxin (type C) and 21 strains produced large amounts of alpha-toxin. The latter strains were predominantly associated with necrotic enteritis in chickens.

Histopathological effect of Clostridium perfringens enterotoxin in the rabbit ileum

Highly purified enterotoxin from Clostridium perfringens was found to have histopathological activity in the rabbit ileum. Unlike the action of cholera, Escherichia coli, and Shigella enterotoxins, epithelium was denuded from the tips of ileal villi at concentrations of the enterotoxin necessary to induce fluid accumulation in the rabbit. Whether or not this observed histopathology is essential for the diarrheal syndrome associated with Clostridium perfringens food poisoning remains unclear.

Effects of Clostridium perfringens enterotoxin on metabolic indexes of everted rat ileal sacs

Everted sacs of rat ileum were incubated in Ringer phosphate solution while oxygen uptake, glucose uptake, and lactate production were determined. Sacs treated with Clostridium perfringens enterotoxin, in the form of crude cell-free extract and purified protein, consumed significantly less oxygen than untreated sacs. However, the toxin-treated sacs took up glucose and produced lactate at levels that were not significantly different than those observed in controls. We conclude that oxidative metabolism is inhibited by the action of the toxin, whereas conversion of glucose to lactate via glycolysis seems unaffected

Measurement of biological activities of purified and crude enterotoxin of Clostridium perfringens

Enterotoxin of Clostridium perfringens was assayed and compared with toxicity in mice and erythemal activity in guinea pigs. Conversion factors were used to express these biological activities of crude enterotoxin in terms of weight of pure enterotoxin protein. One microgram of enterotoxin was equivalent to 3.41 erythema units and to 0.68 mouse median lethal dose.

Experimental diarrhea in cynomolgus monkeys by oral administration with Clostridium perfringens type A viable cells or enterotoxin

Purified C. perfringens type A enterotoxin fed orally in an amount of 5 mg caused both vomiting and diarrhea in the monkey only when the gastric juice had been neutralized. Exposure of enterotoxin to pH 4.0 or below rapidly destroyed the activity. All three monkeys receiving sodium bicarbonate and 2.4 X 10(10) viable cells grown in DS medium developed diarrhea, and only one of them vomited once. The diarrhea lasted for 13, 18 and 19 hr. The symptoms were similar to those reported in human cases of C. perfringens food poisoning. These results have verified the general notion that C. perfringens food poisoning should be categorized as a true "intravital intoxication". The reversed passive hemagglutination test detected enterotoxin directly in most fecal samples. This method may be applicable for diagnosis of human cases of C. perfringens food poisoning. Neither enterotoxin nor anti-enterotoxin was detected in serum samples taken from any monkey up to 21 days after the challenge. We are tempted to conclude, therefore, that no significant amount of C. perfringens enterotoxin is absorbed from the intestine.

Response of ligated intestinal loops in chickens to the enterotoxin of Clostridium perfringens

Approximately 45-cm length of jejunoileum of 7-week-old chickens was found to be responsive and suitable for testing the enterotoxin of Clostridium perfringens by the ligated intestinal loop technique. Injections of 20 to 30 mug of enterotoxin per loop caused positive response of fluid accumulation. Chickens were found to be more convenient and economical for this purpose than other laboratory and domestic animals.

Clostridium welchii and Bacillus cereus infection and intoxication

Clostridium welchii type A is a common agent of food poisoning when allowed to proliferate to large numbers in cooked foods, usually meat and poultry. The main factors of importance are survival of the spores, frequently found on raw products, through the cooking process, and possible contamination of cooked meats transferred to unclean containers; subsequent germination of spores and rapid multiplication of the vegetative cells during long slow cooling and non-refrigerated storage lead to heavy contamination. The toxin responsible is different from the soluble antigens, and its formation in the intestine is associated with sporulation.

Large numbers of Cl. welchii of the same serological types in food and faeces is the main diagnostic factor. Important preventive measures are rapid cooling and cold storage to prevent growth.

Bacillus cereus is an aerobic sporulating organism commonly found in cereals. Outbreaks described from Europe have a different aetiology with regard to food vehicles, incubation period and symptoms from those that have been reported recently in the U.K. from fried and boiled rice. The spores survive through cooking procedures and grow out to cells which sporulate readily in the cooked food and which are assumed to produce toxin in the food. Large numbers of B. cereus are found in foods causing illness and, as with Cl. welchii, the main preventive measure is inhibition of growth by quick cooling and cold storage of foods cooked ahead of requirements. A comparative table of the characteristics and clinical symptoms of Cl. welchii and B. cereus is given.

Assay methods for Clostridium perfringens type A enterotoxin

Enterotoxin produced by a sporulating culture of Clostridium perfringens type A NCTC 8798 was purified to a level of 3,500 mouse mean lethal doses per mg of nitrogen. High-titer sera were obtained from rabbits injected with enterotoxin and used to compare the sensitivity of serological tests and bioassays for C. perfringens enterotoxin. Reversed passive hemagglutination was by far the most sensitive test, followed by microslide diffusion, single gel diffusion and electroimmunodiffusion, guinea pig skin test, mouse test, and rabbit ileal loop test.

Extracellular factor synthesized by Bacillus cereus which evokes a dermal reaction in guinea pigs

A guinea pig skin assay was developed as a measure of ileal loop fluid-inducing factor in the rabbit and possibly of the causative principle of Bacillus cereus food poisoning. A green or bloody necrotic reaction was produced in the guinea pig skin by injection of culture filtrates from 21 of 24 B. cereus strains tested, and by no other Bacillus species tested except for the closely related B. thuringiensis. The skin factor was synthesized and excreted by logarithmically growing cells, inactivated by heating at 56 C for 5 min, precipitable by ammonium sulfate, and was nondialyzable. The skin activity was not related to the lecithinolytic or hemolytic activities of B. cereus. Production of the skin factor depended on the medium in which the culture was growing. The factor was an antigenically active substance. There are indications that at least two antigenically distinct species of skin factors exist.

Fluid secretory response of bovine Thiry jejunal fistula to enterotoxin of Clostridium perfringens

The effect of enterotoxin of Clostridium perfringens type A was studied in Thiry fistula of the bovine jejunum. Accumulation of fluid as a pathological response was demonstrable within 30 min after introduction of enterotoxin into the fistula; the fluid volume increased rapidly within the first 2 hr and reached maximum in 7 hr. The enterotoxin was not destroyed by the jejunal fluid; 52% of it was absorbed in 2 to 3 hr, and all of the enterotoxin was taken up within 8 hr postinoculation. The accumulation of fluid by the fistula after 0.5 to 2 hr of exposure to enterotoxin ceased completely within 5 hr.

Purification and biochemical properties of Clostridium perfringens type A enterotoxin

The sporulation-specific enterotoxin of Clostridium perfringens type A, which is the toxin active in human food poisoning, has been purified from extracts of sporulating cells. Highly purified enterotoxin was obtained by treatment of crude cell extract with ribonuclease for 30 min, followed by sequential chromatography on Sephadex G-100, Cellex T cellulose, and hydroxylapatite. Recovery was 65 to 75% of the initial activity. Enterotoxin purity was > 99% as indicated by sedimentation velocity, sedimentation equilibrium, disc electrophoresis, and serological methods. Purified enterotoxin focused at pH 4.3 during isoelectric focusing. Molecular weights of 34,000 and 35,000 were obtained by Sephadex G-100 chromatography and sedimentation equilibrium, respectively. An S(20,w) of 3.08 was obtained for the purified enterotoxin. The enterotoxin precipitated heavily at its isoelectric point and at concentrations greater than 4 mg/ml.

Sporulation and enterotoxin production by mutants of Clostridium perfringens

The ability of Clostridium perfringens type A to produce an enterotoxin active in human food poisoning has been shown to be directly related to the ability of the organism to sporulate. Enterotoxin was produced only in a sporulation medium and not in a growth medium in which sporulation was repressed. Mutants with an altered ability to sporulate were isolated from an sp(+) ent(+) strain either as spontaneous mutants or after mutagenesis with acridine orange or nitrosoguanidine. All sp(0) (-) mutants were ent(-). Except for one isolate, these mutants were not disturbed in other toxic functions characteristic of the wild type and unrelated to sporulation. A total of four of seven osp(0) mutants retained the ability to produce detectable levels of enterotoxin. None of the ent(-) mutants produced gene products serologically homologous to enterotoxin. A total of three sp(-) mutants, blocked at intermediate stages of sporulation, produced enterotoxin. Of these mutants, one was blocked at stage III, one probably at late stage IV, and one probably at stage V. A total of three sp(+) revertants isolated from an sp(-) ent(-) mutant regained not only the ability to sporulate but also the ability to produce enterotoxin. The enterotoxin appears to be a sporulation-specific gene product; however, the function of the enterotoxin in sporulation is unknown.

Transient increase in capillary permeability induced by Clostridium perfringens type A enterotoxin

A transient increase in capillary permeability was induced in the skin of guinea pigs by Clostridium perfringens type A enterotoxin. Maximum intensity and maximum diameter of the area of increased capillary permeability were obtained with injection of enterotoxin 10 to 20 min before dye injection.

Biological characteristics of Clostridium perfringens type A enterotoxin

An enterotoxin with the ability to induce fluid accumulation in rabbit ileal loops, erythema in the skin of guinea pigs, and lethality in mice appears in cell extracts (CE) and culture filtrates (CF) of sporulating cells of some Clostridium perfringens type A strains. All activities in CE and CF were eluted simultaneously from a Sephadex G-200 column. Different elution patterns were obtained for these activities present in CE and CF. Rabbit immune serum against CF and the active CE fractions eliminated the three biological activities in CE and CF. These activities present in CF and CE were not eliminated by any of the known antitoxins present in diagnostic serum against C. perfringens types A, B, C, D, and E. Immunodiffusion studies with immune serum against active CE fractions and CF indicated a precipitin line of identity between CF and CE of NCTC 8798 and other enterotoxin-positive strains but not enterotoxin-negative strains. Disc electrophoresis of active G-200 fractions on 7.0% polyacrylamide gels revealed a single area containing erythemal activity and mouse lethality. Immunodiffusion with acrylamide gels, containing crude fractionated enterotoxin, and immune serum against partially purified enterotoxin revealed a single precipitin band in the same area as the biological activities. Immunoelectrophoresis of CE of enterotoxin-positive and enterotoxin-negative strains also showed one precipitin band which occurred only with enterotoxin-positive strains. These findings suggest that one component is responsible for the biological activities attributed to the enterotoxin.