Novel Oligonucleotide probes for identification of enterotoxigenic Staphylococcus aureus

Based on the DNA sequences coded for Staphylococcus aureus enterotoxins (SE) A, B, C, D and E, oligonucleotides unique to each enterotoxin were synthesized and used as probes for the identification of types A, B, C, D and E enterotoxigenic S. aureus. Probes A1, C1, D1 and E1 encode amino acid 124 (Lys) to 131 (Leu) of SEA, 52 (Asn) to 59 (Lys) of SEC, 26 (Ala) to 33 (Gly) of SED and 15 (Leu) to 21 (Ser) of SEE, respectively. Probes A2, B2, C2 and E2 are the complementary sequences for genes encoding amino acid 189 (Ser) to 196 (Tyr) of SEA, amino acid 232 (Val) to 239 (Lys) of SEB, amino acid 122 (His) to 129 (Glu) of SEC and amino acid 161 (His) to 166 (Leu) of SEE, respectively. The hybridization specificities for these oligonucleotide probes were confirmed by colony hybridization with standard isolates of enterotoxigenic S. aureus and some other bacterial strains. Despite the high degree of homology among these S. aureus enterotoxin genes, each probe allows specific identification with total discrimination from other types of enterotoxin genes. DNA from non-enterotoxigenic S. aureus or from non- S. aureus isolates does not interfere with the hybridization result. In addition, probes designed for SEE gene detection allow discrimination of SEE strains that, when assayed with a staphylococcal enterotoxin A, B, C, D detection kit by reversed passive latex agglutination (SET-RPLA), would be grouped together with enterotoxin A producing strains. When these oligonucleotide probes were used for a survey of enterotoxigenic types of S. aureus isolated from frozen foods, the results showed that SEA, SEB, and SEAB were the major enteroxigenic types.