Trends in antimicrobial resistance patterns of Group A streptococci, molecular basis and implications

Group A streptococcus (GAS) causes a wide variety of diseases ranging from mild skin and soft-tissue infections to severe, life-threatening conditions. A fluctuating trend has been observed in the antibiotic resistance pattern from different parts of the world. The present study was undertaken to determine the prevalence of antibiotic resistance among GAS isolates and the underlying genetic mechanisms.

Two hundred and six GAS isolates were characterised by antimicrobial susceptibility pattern, macrolide resistance phenotype (double-disc test) and resistance determinants by multiplex polymerase chain reaction.

All the isolates were susceptible to penicillin, vancomycin and linezolid. Erythromycin resistance was found in 53% of isolates with inducible macrolide, lincosamide and streptogramin B the predominant phenotype (63%) with ermB the major genetic determinant. Clindamycin resistance was observed in 33% of isolates with all being inducible resistant. Tetracycline resistance was found in 58% of isolates with tetM as the major genetic determinant (97%). Erythromycin and tetracycline co-resistance was found in 39% of tested GAS isolates.

The erythromycin and tetracycline resistance in GAS continues to exist at high levels and may be attributed to the over-prescription and use of these antibiotics. Our findings indicate that the use of these antibiotics especially macrolides as empiric therapy in penicillin-allergic patients may not be appropriate.