Mechanism of macrolide resistance in Malaysian isolates of group A streptococci

ABSTRACT

Hundred and forty four strains of group A Streptococci isolated from various clinical sources were tested for their susceptibility to antimicrobial agents by the disc diffusion technique in accordance with the National Committee for Clinical Laboratory Standards [NCCLS]. Erythromycin-resistant isolates were reconfirmed by E-test following the manufacturer's instructions. The phenotypes of the erythromycin-resistant strains were then determined by the triple disc test. Mulitplex polymerase chain reaction [PCR] was performed for the identification of resistance genes. The overall frequency for GAS erythromycin resistance was 4.86%, mostly from throat sources [p < 0.05]. All the erythromycin-resistant strains were susceptible to vancomycin, cefotaxime and cefuroxime. Tetracycline resistance was 59.72% while resistance to chloramphenicol was 0.69%. All 144 isolates were susceptible to penicillin, clindamycin and spiramycin. Minimum inhibition concentrations [MICs] of the 7 erythromycin-resistant strains ranged from 2 g/ml to 12 g/ml. All the erythromycin-resistant strains were found to be of the M phenotype possessing the mefA gene which is responsible for mediating the macrolide efflux mechanism