Erythromycin resistance associated to mefA gene and emm75 allele in Streptococcus pyogenes from uncomplicated pharyngitis in Mexico

Erythromycin-resistant Streptococcus pyogenes strains have been reported in many parts of the world; however, few reports have shown the prevalence of the erythromycin-resistant genes and their relationship to M-serotype of the bacteria. A total of 391 S. pyogenes isolates collected from different hospitals in Mexico City between 2001 and 2004 were analyzed. Erythromycin resistance was evaluated by susceptibility discs and resistance phenotype by double-disc test with erythromycin and clindamycin discs. Identification of mefA, ermTR and ermB resistance genes was performed by PCR. Resistance genotype was associated with the emm allele (M protein gene) of each strain, which was performed previously by emm typing. Thirty isolates (7.7%) were resistant to erythromycin. Virtually, all (28/30, 93%) showed the resistance phenotype designated as “M” and had the mefA gene (efflux-mediated mechanism). Twenty-seven mefA positive isolates had the emm75 allele. The other three erythromycin-resistant organisms were emm77(mefA), emm4(ermTR) and emm41 (undetermined resistance mechanism). The prevalence of erythromycin-resistant isolates was of 7.7%; however, the 50% of emm75 organisms evaluated were resistant to erythromycin. This study emphasizes the need to establish an epidemiological surveillance in order to follow the distribution of erythromycin-resistant clones in this population.