Detection by polymerase chain reaction of genes encoding aminoglycoside-modifying enzymes in methicillin-resistant Staphylococcus aureus isolates of epidemic phage types

Summary The polymerase chain reaction (PCR) was used to identify the aacA-aphD, aphA3 and aadC genes, encoding the aminoglycoside-modifying enzymes AAC(6′)-APH(2′), APH(3′)III and ANT(4′ 4"), respectively, and the methicillin resistance determinant mecA, in epidemic aminoglycoside and methicillin-resistant isolates of Staphylococcus aureus. In total, 37 isolates collected in the period 1980-1985 and 81 isolates from the period 1991-1992 were obtained from 10 different Belgian hospitals. Epidemic isolates from the earlier period were characterised by phage type C (6/47/54/75) of phage group III, whereas two other epidemic phage types of group III–types A (77) and B (47/54/75/77/84/85)–were commonest in isolates from the second period. The bifunctional AAC(6′)-APH(2′) was the enzyme encountered most frequently. The prevalence of APH(3′)III decreased significantly in the 1991-1992 period, while ANT(4′, 4") was found solely in isolates from this period. Resistance mechanisms were more complex in isolates from the 1991-1992 period and the mecA gene was detected in all isolates. The PCR results corresponded well with those obtained in the radiochemical phosphocellulose paper binding assay. Isolates from the 1991-1992 period were shown to express significantly higher levels of acetyltransferase activity than isolates from the 1980s.