A paracrystalline inclusion formed during sporulation of enterotoxin-producing strains of Clostridium perfringens type A

Distribution of Enterotoxin- and Epsilon-Positive Clostridium perfringens Spores in U.S. Retail Spices

The role of spices as vehicles of foodborne illness prompted an examination of bacterial spores in these products. Here, we report on the levels and characteristics of spores of Clostridium perfringens associated with 247 U.S. retail spices. Forty-three confirmed isolates from 17% of samples were obtained, present at levels ranging from 3.6 to 2,400/g. Twenty-seven (63%) of C. perfringens isolates were positive for the enterotoxin gene ( cpe). Seven random spice isolates produced enterotoxin at levels of between 4 and 16 ng/mL, compared with three outbreak (control) strains that each produced enterotoxin levels of >1,024 ng/mL. D_95°C levels (1.0 to 3.3 min) of spores of four randomly selected spice isolates suggests a plasmid-localized cpe, while one had D_95°C (>45 min) consistent with chromosomally located cpe. Five of the 43 isolates possessed the epsilon toxin gene ( etx, as well as cpe). Foods could easily become contaminated with spores of cpe-positive C. perfringens by the addition of spices. Because of its spore-forming ability, its rapid generation times at elevated temperatures, improper heating, cooling, and holding conditions could lead to elevated levels of C. perfringens in foods, a requirement for its implication in foodborne outbreaks.

Sporulation and enterotoxin (CPE) synthesis are controlled by the sporulation-specific sigma factors SigE and SigK in Clostridium perfringens

Clostridium perfringens is the third most frequent cause of bacterial food poisoning annually in the United States. Ingested C. perfringens vegetative cells sporulate in the intestinal tract and produce an enterotoxin (CPE) that is responsible for the symptoms of acute food poisoning. Studies of Bacillus subtilis have shown that gene expression during sporulation is compartmentalized, with different genes expressed in the mother cell and the forespore. The cell-specific RNA polymerase sigma factors sigma(F), sigma(E), sigma(G), and sigma(K) coordinate much of the developmental process. The C. perfringens cpe gene, encoding CPE, is transcribed from three promoters, where P1 was proposed to be sigma(K) dependent, while P2 and P3 were proposed to be sigma(E) dependent based on consensus promoter recognition sequences. In this study, mutations were introduced into the sigE and sigK genes of C. perfringens. With the sigE and sigK mutants, gusA fusion assays indicated that there was no expression of cpe in either mutant. Results from gusA fusion assays and immunoblotting experiments indicate that sigma(E)-associated RNA polymerase and sigma(K)-associated RNA polymerase coregulate each other's expression. Transcription and translation of the spoIIID gene in C. perfringens were not affected by mutations in sigE and sigK, which differs from B. subtilis, in which spoIIID transcription requires sigma(E)-associated RNA polymerase. The results presented here show that the regulation of developmental events in the mother cell compartment of C. perfringens is not the same as that in B. subtilis and Clostridium acetobutylicum.

Typing of Clostridium perfringens by in vitro amplification of toxin genes

The strains of Clostridium perfringens are classified according to major toxins produced. Classically, this determination involves the seroneutralization of their lethal effect in mice. However, this method requires specific antisera and a large number of mice. In this work, a new typing method was developed based on the amplification of toxin genes by polymerase chain reaction (PCR). By combination of several pairs of primers, the toxinotype of a Cl. perfringens strain was determined by looking at the pattern of bands on an agarose gel electrophoresis. This mixture contained primers amplifying simultaneously a part of alpha-toxin, beta-toxin, epsilon-toxin and enterotoxin genes. In order to distinguish between toxinotype A and E, the l-toxin gene fragment must be amplified in a separate PCR reaction. Moreover, with the primers combination, in most cases, a PCR product corresponding to the alpha-toxin gene was obtained from direct enrichments of animal intestinal contents.

Sporulation and enterotoxin production by Clostridium perfringens type A at 37 and 43 degrees C

Enterotoxin-positive strains of Clostridium perfringens were grown in Duncan-Strong sporulation medium in the presence of 0.4% (7.9 mM) raffinose at 37 and 43 degrees C. Enterotoxin- and heat-resistant spores were produced at similar concentrations but sooner at 43 degrees C than at 37 degrees C. There was a direct relationship between spore heat resistance and sporulation temperature (32, 37, and 43 degrees C).

Characterization of a parasporal inclusion body from sporulating, enterotoxin-positive Clostridium perfringens type A

Inclusion bodies (IB) synthesized during sporulation and enterotoxin formation by Clostridium perfringens NCTC 8239 and 8798 were isolated and characterized. IB were isolated by disruption of sporangia by sonication in the presence of tetrasodium EDTA and phenylmethylsulfonyl fluoride. Fractionation was carried out in a linear gradient of sodium bromide, sucrose, or diatrizoate sodium. Denaturing and reducing agents were necessary to solubilize the IB. An alkylating agent was required to prevent reaggregation of the subunits. Molecular weight, compositional, and serological analyses and peptide mapping revealed strong similarities between the IB subunits and the enterotoxin synthesized during sporulation by C. perfringens. IB appear to represent the structural component where overproduced enterotoxin accumulates intracellularly. Enterotoxin-like subunits in the IB appeared to be held together by noncovalent and disulfide bonds, which were generally resistant to the action of intracellular proteases of C. perfringens, trypsin, or trypsin plus bile salts.

The suitability of Tórtora's medium for the production of enterotoxin in Clostridium perfringens strains

Examination of 200 samples from soil and the same number of samples from healthy human feces yielded 49 (24.5%) and 105 (52.5%) strains of heat-resistant Clostridium perfringens respectively. Fourteen (7.0%) strains isolated from soil and 37 (18.5%) from feces synthesized enterotoxin, as demonstrated by Tórtora's method, at sufficient levels to permit its detection by mouse lethality, microslide double gel diffusion or counterimmunoelectrophoresis tests. By using the Duncan-Strong (DS) method, only four (2%) enterotoxigenic strains from soil and 14 (7.0%) from feces were obtained. The supernatant fluid from two enterotoxigenic-negative strains grown in DS medium gave a false-positive reaction when they were injected intravenously into mice. Tórtora's medium was preferable because a larger number of isolated strains produced spores and enterotoxin to permit their recognition as enterotoxigenic strains.

Alternative medium for Clostridium perfringens sporulation

A medium containing 0.50 g of thiotone peptone, 0.30 g of soluble starch, 0.02 g of MgSO4 X 7H2O, 0.90 g of Na2HPO4 X 2H2O, 100.00 ml of distilled water, and optionally , 166 micrograms of dichloridric thiamine supported sporulation of 138 out of 141 Clostridium perfringens strains. Comparatively this medium gave a greater percentage of sporulation than five other media described previously.

Enterotoxin formation by Clostridium perfringens type A in a defined medium

Enterotoxin was produced by 9 of 10 strains of Clostridium perfringens type A when grown in a defined medium. Additional dextrin increased the amount of enterotoxin in extracts of sporulating cells of strain NCTC 10239.

Clostridium perfringens type A: in vitro system for sporulation and enterotoxin synthesis

Polysomes were isolated from an enterotoxigenic strain of Clostridium perfringens during vegetative growth and at 1-h intervals after transfer into Duncan-Strong sporulation medium. During vegetative growth, about 67% of the ribosomes were in polysomal complexes. This proportion decreased to about 20% during the first 2 h in sporulation medium and then gradually increased to a maximum of 45% at 6 h. Ribosomes isolated from cells in vegetative or in sporulation phase could equally translate vegetative, sporulation, and natural viral R17 messenger ribonucleic acid with either vegetative or sporulation initiation factors. When polysomes were allowed to complete their nascent chains with labeled amino acids in vitro, most of the polypeptides synthesized by the vegetative phase and by the sporulation phase polysomes appeared to be identical. There were, however, notable differences upon further investigation. Specifically, when antiserum against the enterotoxin was reacted with the completed polypeptides, no counts were precipitated from the vegetative products. On the other hand, up to 12% of the total labeled protein was precipitated from the products obtained with the sporulation phase polysomes. Upon electrophoresis on sodium dodecyl sulfate, the putative enterotoxin synthesized in vitro ran as a major band with a molecular weight of 35,000, and as two minor bands with molecular weights of 17,000 and 52,000, respectively.

Evidence for stable messenger ribonucleic acid during sporulation and enterotoxin synthesis by Clostridium perfringens type A

Stable messenger ribonucleic acid (mRNA) was shown to be involved in both enterotoxin synthesis and synthesis of other spore coat proteins in Clostridium perfringens. When used at a concentration that inhibited [14C]uracil incorporation, rifampin, a specific inhibitor of deoxyribonucleic acid-dependent RNA polymerase, prevented incorporation of a mixture of labeled amnoo acids by 3-h sporulating cells. At that time, enterotoxin protein was first detectable and cells were primarily at stage II or III of sporulation. When rifampin or streptolydigin was added to 5-h sporulating cells, which were primarily at stage IV or V and had significant toxin levels, incorporation of labeled amino acids continued through 30 min despite its presence. Rifampin also failed to prevent the specific synthesis of enterotoxin, a structural protein of the spore coat. The half-life of enterotoxin RNA was estimated to be at least 58 min. When cell extracts from 5-h sporulating cells that had been exposed to 3H-labeled amino acids for 10 min were subjected to electrophoresis on polyacrylamide gels and the gels were subsequently analyzed for radioactivity, two major peaks of radioactivity were obtained. The two peaks corresponded to enterotoxin and another spore coat protein(s). Similar results were obtained when the cells had been preincubated for 60 min with rifampin before label addition, indicating the functioning of stable mRNA.

Structure and morphogenesis of the bacterial spore coat

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Enterotoxin formation by different toxigenic types of Clostridium perfringens

Sixty-nine strains of Clostridium perfringens of different toxigenic types were investigated for enterotoxin production. Enterotoxin was definitively detected only in strains of types A and C. This is the first report where enterotoxin production has been demonstrated in a toxigenic type other than type A. The exterotoxin-positive type C strains were isolated from cases of enteritis necroticans ("pig bel+) in New Guinea. The major enterotoxin from type C showed a reaction of complete identity with enterotoxin from type A in immunodiffusion using anti-enterotoxin serum prepared against the latter; it induced erythema when injected intradermally into depilated guinea pigs and caused fluid accumulation in the rabbit ileal loop. The results indicate that the major enterotoxin from type C was serologically and biologically similar to enterotoxin from type A. In some C was serologically and biologically similar to enterotoxin from type A. In some type C strains, an enterotoxin was detected that showed a reaction of partial serological identity. Spore coat proteins were extracted from 14-strains by alkaline dithiothreitol, and the extracts were assayed for enterotoxin-like spore protein. Enterotoxin could be extracted from type A and type C spores, and all positive strains showed a reaction of complete identity in immunodiffusion with enterotoxin obtained from cell extracts of type A. Disc immunoelectrophoresis demonstrated that two distinct components that reacted serologically with anti-enterotoxin serum were present in both the cell extract and in extracted spore protein from one type C strain. These distinct components differed in molecular weight.