Molecular Characteristics of Erythromycin-Resistant Streptococcus pyogenes Strains Isolated from Children Patients in Tunis, Tunisia.

Abstract

The aims of our study were to characterize phenotypically and genotypically erythromycin-resistant Streptococcus pyogenes or group A streptococci (ERGAS) isolates, to evaluate macrolide resistance and to analyze the association between emm types and virulence factors. Included in this study were all ERGAS strains isolated from 2000 to 2013 at the Children's hospital of Tunis. Antimicrobial susceptibility was performed according to the CA-SFM guidelines. Macrolide resistance genes were revealed by polymerase chain reaction (PCR) method. Virulence factor genes (pyrogenic exotoxin genes and superantigen gene) were detected by PCR, and the emm types were defined by the sequencing of the variable 5' end of the emm gene. Among the 289 GAS isolates collected, 15 (5.2%) were resistant to erythromycin; 7 of the strains were assigned to the cMLSB phenotype (46.6%); 5 harbored ermB gene alone (33.3%); and 2 strains coharbored ermB and mefA (13.3%). The remaining (53.4%) were assigned to the M phenotype and harbored the mefA gene. The frequency of detection of each toxin gene among ERGAS was 13.4% for speA (2 strains), 53.4% for speC (8 strains), and 13.4% for ssa (2 strains). Emm types 1, 58, 11, and 78 were the most frequent among ERGAS strains. The distribution of the cMLSB and M phenotypes changed over the period of investigation with a decrement of cMLSB phenotype and ermB gene that predominated between 2000 and 2006 and an increase of M phenotype and mefA gene between 2007 and 2013, but this difference was nonstatistically significant because of the low number of resistant strains. Emm types 1, 58, and 4 were only present among strains assigned to the M phenotype. However strains assigned to the cMLSB phenotype were associated to emm11, emm22, emm28, emm78, or emm76. There was diversity in emm distribution in ERGAS between the two study periods. There was diversity in emm distribution among ERGAS particularly in 2000-2006. Indeed, from 2000 to 2006, the 6 ERGAS belonged to 5 different emm types (22, 28, 76, 11, and 4), while between 2007 and 2013, seven among the nine ERGAS belonged to only 2 emm types 58 and 1. The speA gene was present only among emm1 isolates, and the ssa gene was associated with emm4 and emm78 types. All emm78, emm28, and emm11 strains harbored speC gene. Our study revealed a low frequency of ERGAS and few emm types were associated with these strains.