Distribution of macrolide-resistant genes among isolates of macrolideresistant Streptococcus pyogenes and Streptococcus pneumoniae in Serbia

Macrolide resistance in Streptococcus pneumoniae and in group A streptococci (GAS) is a significant problem worldwide. In Serbia, data on the mechanisms of resistance and the corresponding resistance genes in streptococci are largely lacking. Therefore, we analyzed the distribution of macrolide resistance phenotypes and genotypes in 44 macrolideresistant GAS (MRGAS) and 50 macrolide-resistant S. pneumoniae (MRSP) isolates collected in the same period. The double disk diffusion test and PCR were used to analyze resistance phenotypes and resistance genes, respectively. Among MRSP, the MLSB phenotype dominated, whereas the M phenotype was the most prevalent among MRGAS isolates. Consequently, in MRSP, the ermB gene was the most common (n=40, 80%), followed by the mefA gene (n=7,14%). In MRGAS strains, mefA dominated (n=27,61%), followed by ermA (n=15, 33%) and ermB (n=3, 7%). In 3 MRSP isolates no resistance genes were detected, while one MRGAS strain with iMLSB phenotype harbored both ermA and mefA genes