Streptococcus pyogenes isolated in a Tunisian pediatric population: Emm types, T types, virulence factors and genes of resistance to macrolide and tetracycline

Aims: The aims of our study were to determine epidemiological markers of S. pyogenes isolates as well as the antimicrobial activities against these strains and we determined the macrolide and tetracycline resistance genes. Methodology and Results: We studied the epidemiological markers of 148 Streptococcus pyogenes isolates collected from children in Tunisia between October 2000 and December 2006. Antimicrobial susceptibility was performed according to the CA-SFM guidelines. T-serotypes were determined by slide agglutination. Virulence factor genes (pyrogenic exotoxin gene and superantigen gene) and macrolide and tetracycline resistance genes were revealed by PCR method. The emm types were determined by sequencing the variable 5’ end of the emm gene. The predominant markers were T3/12/13/B3264, emm22 and speB. All isolates were susceptible to β-lactam antibiotics (penicillin and amoxicillin). Resistance to tetracycline was observed in 65 isolates (43.9%), and strains harboured the tet(M) gene alone in 95.4% (62/65) or both tet(M) and tet(L) genes in 4.6% (3/65). Six strains (4%) were resistant to erythromycin among these; five were also resistant to clindamycin. Five strains of genotypes emm11, emm22, emm28, and emm76 expressed the constitutive MLSB phenotype with the presence of the ermB gene alone (3 strains) or in association with the mefA gene (2 strains). One emm4 strain expressed the M phenotype and harboured the mefA gene alone. Conclusion, Significance and Impact of Study: This work provided the molecular characteristics of paediatric S. pyogenes isolates in Tunisia. Our study affirmed that this micro-organism still susceptible to β-lactam antibiotics but showed an increase in macrolide resistance. We concluded that the epidemiology and the molecular characteristics of S. pyogenes strains were different around the world.