Staphylococcal enterotoxin production in the presence of non-enterotoxigenic staphylococci

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.