Polymorphism of the virulence regulon and allelic variations of the sic gene among the emm1 isolates of group A Streptococcus from western Norway

With the objective of finding genetic markers of invasiveness, 43 isolates of group A streptococcus, isolated in western Norway and from both severe invasive disease and superficial infections, were studied initially by restriction fragment length polymorphism of the virulence regulon (virR -RFLP). Polymorphism that seemed to be related to the severity of infection was observed within the emm1 sequence type, which included 11 invasive and seven non-invasive isolates. These emm1 isolates were further investigated by restriction mapping of the virR and sequence analysis of a polymorphic region, which revealed the presence of a hypervariable sic gene. Of the nine distinct sic alleles, seven were found in single isolates, of which only two were from patients with invasive disease. The other two alleles were shared among nine invasive and two non-invasive isolates. The presence of only two sic allotypes in nine of the 11 invasive isolates, as compared to a different allele in each of the five non-invasive, contemporary isolates supports the hypothesis that selection of the sic variants occurs at mucosal surfaces and implicates mainly two clones among the invasive emm1 isolates.