Multiplex PCR for the detection of genes encoding aminoglycoside modifying enzymes and methicillin resistance among staphylococcus species

We developed multiplex polymerase chain reaction (PCR) to detect aac(6')/aph(2"), aph(3)-IIIa, and ant(4')-Ia, the genes encoding the most clinically relevant aminoglycoside modifying enzymes (AME), and simultaneously, the methicillin resistant gene, mecA, in Staphylococcus species. Clinical isolates of 45 S. aureus and 47 coagulase negative staphylococci (CNS) from tertiary university hospitals were tested by conventional susceptibility testing, using the agar dilution method and by multiplex PCR. Of a total of 92 isolates, 61 isolates were found to be methicillin-resistant. Of these, 54 isolates (89%) were found to be harboring mecA. Seventy-five percent of the 92 isolates demonstrated resistance to at least one of the aminoglycosides tested. Moreover, resistance to aminoglycosides was closely associated with methicillin-resistance (p<0.05). The most prevalent AME gene was aac(6')/aph(2") which was found in 65% of the isolates, and ant(4)-Ia and aph(3)-IIIa were present in 41% and 9% of the isolates, respectively. The concordance between methicillin-resistance and the presence of mecA gene was 98% in S. aureus and 81% in CNS. The concordance between gentamicin resistance and the presence of aac(6')/aph(2") gene was 100% in S. aureus and 85% in CNS. The multiplex PCR method that we developed appears to be both a more rapid and reliable than conventional method.