Erythromycin resistance genes in group A streptococci in Finland

Streptococcus pyogenes isolates (group A streptococcus) of different erythr omycin resistance phenotypes were collected from all over Finland in 1994 a nd 1995 and studied; they were evaluated for their susceptibilities to 14 a ntimicrobial agents (396 isolates) and the presence of different erythromyc in resistance genes (45 isolates). The erythromycin-resistant isolates with the macrolide-resistant but lincosamide- and streptogramin B-susceptible p henotype (M phenotype) were further studied for their plasmid contents and the transferability of resistance genes. Resistance to antimicrobial agents other than macrolides, clindamycin, tetracycline, and chloramphenicol was not found. When compared to our previous study performed in 1990, the rate of resistance to tetracycline increased from 10 to 93% among isolates with the inducible resistance (IR) phenotype of macrolide, lincosamide, and stre ptogramin B (MLSB) resistance. Tetracycline resistance was also found among 75% of the MLSB-resistant isolates with the constitutive resistance (CR) p henotype. Resistance to chloramphenicol was found for the first time in S. pyogenes in Finland; 3% of the isolates with the LR phenotype were resistan t. All the chloramphenicol-resistant isolates were also resistant to tetrac ycline. Detection of erythromycin resistance genes by PCR indicated that, w ith the exception of one isolate with the CR phenotype, all M-phenotype iso lates had the macrolide efflux (mefA) gene and all the MLSB-resistant isola tes had the erythromycin resistance methylase (ermTR) gene; the isolate wit h the CR phenotype contained the ermB gene. No plasmid DNA could be isolate d from the M-phenotype isolates, but the mefA gene was transferred by conju gation.