Association of group A streptococcal emm types with virulence traits and macrolide resistance

Objectives: Aim of this study was to determine M (emm) subtypes of Streptococcus pyogenes strainsisolated from asymptomatic carriers and children with pharyngitis, and to investigate the correlationbetween emm types, the presence of fibronectin binding protein genes, and phenotypes of antibioticresistance.Methods: We detected and characterized emm subtypes in 59 strains of S. pyogenes isolated in Sicily(Italy) from asymptomatic carriers (29) and children with pharyngitis (30) previously characterized for thepresence of prtF1 and pfbpI genes and erythromycin resistance phenotypes (Musumeci et al., Clin. Infect.Dis. 2003; 37:173-179). emm gene specific PCR and emm sequence typing were performed as describedby Beall et al. (J. Med. Microbiol. 1998; 47:893-898). In addition, to confirm the relationship between emmpattern type and SOF (serum opacity factor), sof gene was detected and sequenced basing upon PCRand sequence analysis of a variable length 450-650-base PCR fragment.Results: The most frequent emm subtypes detected in isolates from pharyngitis were: emm1.0 (30.0%),emm89.0 (23.3%), emm2.0 (13.3%) and emm28.0 (10.0%). One new emm12 subtype (emm12.40) wasdetected. In isolates from asymptomatic carriers (enrolled from different classes of many primary schools)the most frequent emm subtypes were: emm12.0 (51.7%) and emm94.0 (10.3%); while there were noemm1.0 strains. The most significant differences between the two groups concerned the presence of thetwo more common emm subtypes, 1.0 (P = 0.001) and 12.0 (P < 0.001). The prtF1 and prtF2 genes weresimultaneously present in 14 of 16 (87.5%) emm12.0 and 8 of 9 (88.9%) emm89.0 isolates. Correlationwith phenotypes of resistance showed that 9 of 11 (81.0%) M phenotype strains belonged to emm12.0subtype and all 3 iMLS-A phenotype strains to emm89.0.Conclusion: This study suggests that S. pyogenes emm12 and emm89 isolates, mainly positive for prtF1and prtF2 genes, are more virulent than the others, and that emm12 isolates may have a role in theasymptomatic carrier status.