A third staphylococcal enterotoxin C (C3) has been identified, purified, and characterized. Staphylococcal enterotoxin C3 was identified from a Staphylococcus aureus isolate received from England. The purified toxin was determined by gel permeation chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be a simple protein with a molecular weight of 26,900. The isoelectric point of the major band was determined by isoelectric focusing in polyacrylamide gels to be 8.15. The reaction of enterotoxin C3 with its specific antibody was not affected by tryptic digestion at pH 8.0 or peptic digestion at pH 4.5. The enterotoxin C3 consisted of 236 amino acid residues. Serine was shown to be the NH2-terminal amino acid residue by end group analysis. The protein was highly emetic in cynomolgus monkeys both per os and intravenously.

Staphylococcus aureus is a major bacterial pathogen involved in a wide range of diseases varying from infections to toxaemia. Staphylococcal food-poisoning syndrome is caused by ingestion of bacterial enterotoxins. These toxins are microbial superantigens and may also be virulence factors involved in staphylococcal infection. This study determined the enterotoxin types and pulsed-field gel patterns found among S. aureus isolates obtained from food handlers in community or hospital-located kitchens. Staphylococcal enterotoxin C was the most frequent enterotoxin produced. The data also suggested horizontal spread of ent genes among isolates belonging to the Brazilian epidemic MRSA clone 1II::B:A. A subclone of MRSA clone 1II::B:A was isolated from two hospital kitchen workers. This was the first report of this clone from a hospital in Teresina, Piaui State, although the presence of this MRSA clone has already been reported in six other Brazilian cities.

Enterotoxigenic Staphylococcus aureus strains were grown with a non-enterotoxigenic strain in laboratory medium, in milk, and in ham. Differences in pigmentation were used to differentiate the enterotoxigenic strains from the non-enterotoxigenic ones. Enterotoxin was detectable in milk when the colony counts of the non-enterotoxigenic strain were 15 to 20 times greater than those of the enterotoxigenic ones and in ham when the ratio was 60 to 77:1. Enterotoxin was detectable in milk when the enterotoxigenic strains reached counts of 10(7) colony-forming units per ml and in ham when the counts reached 10(8) colony-forming units per ml. It may be necessary in some food poisoning outbreaks to examine many isolates (up to 50 or 60) for enterotoxin production to be able to detect the enterotoxigenic staphylococci.

Thirty-seven (16.9%) of 219 raw milk samples and 38 (13.7%) of 280 pasteurized milk samples were positive for Yersinia sp. The isolates from raw milk samples include Yersinia enterocolitica (32.4%) comprising biotype 1 (0:5, 10.8%), and biotype 2 (0:10 K1, 1.6%); Yersinia intermedia (64.9%) comprising 0:18 (40.5%), 0:7,8 (8.1%), 0:16 (2,7%) and non-typable (13.5%) and Yersinia frederiksenii (0:22, 2.7%). The isolates from pasteurized milk samples include Y. enterocolitica (41.5%) comprising 0:5 (31.7%), 0:13 (2.4%), 0:7,8 (2.4%) and 0:16 (4.8%); Y. frederiksenii (56.1%) comprising 0:27 (7.3%), 0:25,35 (12.2%), non-typable (36.6%) and Y. intermedia (non-typable, 2.4%). Most Y. enterocolitica and about one third of non-Y. enterocolitica strains produce heat-stable toxin (ST). Antibiotic susceptibility, autoagglutination capacity and calcium-dependency of strains also were investigated.

Two Staphylococcus aureus strains were grown in brain-heart infusion (BHI) broth and a meat medium with Bacillus cereus, Streptococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa. Both S. aureus strains grew well and produced enterotoxin in the presence of S. faecalis in BHI broth; however, enterotoxin production was observable in the meat medium only when the S. aureus inoculum was greater than the S. faecalis inoculum. S. aureus FRI-100 grown with B. cereus produced enterotoxin in both media only when the S. aureus inoculum was much higher than the B. cereus inoculum (10 versus 104 CFU), whereas S. aureus FRI-196E produced enterotoxin in both media at all inoculum combinations except in the meat medium, when the inocula of the two organisms were the same. S. aureus grown with E. coli in BHI broth produced enterotoxin at all inoculum combinations except when the E. coli inoculum was greater than the S. aureus inoculum; however, in the meat medium, enterotoxin was produced only when the S. aureus inoculum was much greater than the E. coli inoculum (10 versus 104 CFU), S. aureus FRI-100 grown with P. aeruginosa in either medium produced enterotoxin only when the S. aureus inoculum was much greater than the P. aeruginosa inoculum (10 versus 103 or 104 CFU). It can be concluded from these results that enterotoxin production is unlikely in mixed cultures unless the staphylococci outnumber the other contaminating organisms.