Background: Macrolide resistance in β-hemolytic streptococci has increased during the 1990s, and the proportion of MLS (Macrolide-lincosamide-streptogramin) resistance phenotypes and genotypes of β-hemolytic streptococci are quite different by geographical variation and study period. The aim of the present study was to determine the distribution of MLS resistance phenotypes and genotypes in β-hemolytic streptococci isolated from Wonju Christian Hospital.

Methods : The minimal inhibitory concentrations of erythromycin and clindamycin of 426 β-hemolytic streptococci isolated from clinical specimens between 1990 to 1999 were determined by agar dilution method. MLS resistance phenotypes were determined by double disk diffusion method using erythromycin and clindamycin disk, and genotypes were determined by polymerase chain reaction (PCR). The PCR primers for erm(A), erm(B), erm(C), erm(TR), and mef(A) were used in these study.

Results: The proportion of MLS resistance phenotypes of 80 erythromycin-resistant β-hemolytic streptococci were 60.0% for constitutive phenotype, 23.8% for M phenotype, and 16.2% for inducible phenotype. The proportion of three MLS resistance phenotypes of group A streptococci were nearly equal. About three-fourths of group B streptococci had the constitutive phenotypes, whereas three-fourths (75%) of group G streptococci had the M phenotypes. All MLS resistant strains carried the erm(B) genes in constitutive phenotypes, erm(TR)genes in inducible phenotypes, and mef(A) genes in M phenotypes, respectively.

Conclusions : Mechanisms and phenotype proportions of MLS resistance are different by species in β-hemolytic streptococci. It is possible that MLS resistance genes have transferred among β-hemolytic streptococci because the erythromycin resistance genes are the same in β-hemolytic streptococci. (Korean J Clin Microbiol 2001;4:16-21)