Potential problems in the use of oligonucleotide probes for staphylococcal enterotoxin genes

Oligonucleotide probes unique to the five major enterotoxin genes of Staphylococcus aureus were synthesized and used to detect DNA sequences homologous to these genes in 27 non-clinical isolates of Staph. aureus isolated from nasal swabs of 74 healthy human volunteers. Genomic DNA from all 27 isolates reacted with at least one of the probes. In a phenotypic assay for toxin production by a reverse passive latex agglutination test however, only 15 of the 27 isolates produced enterotoxin in culture. The results raise the possibility that a number of Staph. aureus isolates harbour DNA sequences that are apparently silent or mutant copies of the enterotoxin genes. This complicates the identification of enterotoxin producers by tests which depend on oligonucleotide or DNA hybridization.