Background: Antibiotic resistance of group A streptococci (GAS) is increasing nationwide. Pulsed-field gel electrophoresis (PFGE) is useful for investigating genetic relationship among outbreaks of bacterial infection. Erythromycin (EM) resistance is mediated by either ermB, ermTR,or mefA gene. The emm gene encodes M protein which is the most important virulence factor of GAS.

Methods: The clonal relationship among 56 EM resistant GAS isolated from the children with acute pharyngitis in Jinju was investigated by analysis of chromosomal DNA restriction pattern with SmaI enzyme. The ermB and mefA genes were amplified and emm genotype was identified with PCR and sequencing. Their relationship with PFGE pattern was investigated.

Results: The emm genotyes were identified as 2, 3, 12, 18, and 75. Mostly emm 12 had ermB gene, while emm 3, 18 and 75 had mefA resistance gene. All strains with mefA gene were not restricted with SmaI. The emm12 strains showed 5 different PFGE patterns.

Conclusions: The emm genotypes were closely related with resistance genes. Analysis of macrorestriction fragment patterns by PFGE showed that EM resistant GAS were polyclonal at least in Jinju. GAS strains with mefAgene were not restricted with SmaI suggesting mefA gene might inhibit chromosomal digestion with SmaI. (Korean J Clin Microbiol 2004;7(1):27-30)