Investigation of aminoglycoside modifying enzyme genes in methicillin-resistant staphylococci

Methicillin-resistant staphylococci may also be resistant to some other antibiotics as well as β-lactams. In this study, co-existence of resistance to methicillin and aminoglycosides was genetically investigated in staphylococci. A total of 50 staphylococci from in-patients, 17 Staphylococcus aureus and 33 coagulase negative staphylococci (CNS) that contained mecA (gene encoding PBP 2a, an altered penicillin-binding protein) determined by polymerase chain reaction (PCR) were included in the study. Aminoglycoside modifying enzyme (AME) genes were investigated using multiplex-PCR. Aminocyclitol-6′-acetyltransferase-aminocyclitol-2″-phosphotransferase [ aac(6′)/aph(2″)] gene (encoding bifunctional acetyltransferases/phosphotransferases) was determined in 66% of the isolates, aminocyclitol-4′-adenylytransferase ( ant(4′)-Ia) gene (encoding phosphotransferases) in 24%, and aminocyclitol-3′-phosphotransferase ( aph(3′)-IIIa) gene (encoding nucleotidyltransferases) in 8%. Two isolates contained all these three genes. Thirty-six (72%) isolates had at least one of these genes. Three CNS and one S. aureus isolates sensitive to oxacillin had the mecA gene. In conclusion, a high rate of aminoglycoside resistance was determined in methicillin-resistant staphylococci. The aac(6′)/aph(2″) was the most frequently detected.