Heterogeneity of aminoglycoside resistance genes profile in clinical Staphylococcus aureus isolates

One hundred clinical Staphylococcus aureus including 57 methicillin-resistant (MRSA) and 43 methicllin-sensitive (MSSA) isolates were analyzed for susceptibility to three aminoglycosides and for the presence of genes encoding aminoglycoside modifying enzymes (AMEs). 52% of these isolates were resistant to 1-3 aminoglycosides, which included 65% MRSA and 35% MSSA isolates. The aminoglycoside resistance genes were more frequently identified in MRSA than in MSSA isolates. The most frequent gene was aac(6')/aph(2") and it was detected in 45% S. aureus isolates which included 52.6% MRSA and 34.8% MSSA isolates. The second prevalent gene was ant(4',4") and it was detected in 31% S. aureus which included 40.3% MRSA and 18.6% MSSA isolates. 21% of S. aureus isolates including 29.8% MRSA and 9.3% MSSA isolates, carried the aph(3') III gene. The most frequent combination of genes was aac(6 ′)/aph(2 ′′ ) with ant(4',4") in 22.8% MRSA and in 16.2% MSSA isolates. The second dominant gene combination was aac(6')/aph(2") with aph(3')III in 17.5% MRSA and in 6.9% MSSA isolates. The ant(4',4") and aph(3 ′)III combination existed only in 7% MRSA isolates. The 3 genes coexisted in 5.3% MRSA and in 2.3% MSSA isolates. The concordance between the presence of genes and aminoglycoside resistance phenotype was observed in most MRSA and MSSA isolates. Emerging of isolates harboring these genes must not be ignored because it limits the choices in the number of antibiotics available to clinicians to treat staphylococcal infections in risk patients.