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 i nvasive disease and superficial infections, were studied initially by restr iction fragment length polymorphism of the virulence regulon (virR-RFLP). P olymorphism that seemed to be related to the severity of infection was obse rved within the emm1 sequence type, which included 11 invasive and seven no n-invasive isolates. These emm1 isolates were further investigated by restr iction mapping of the virR and sequence analysis of a polymorphic region, w hich revealed the presence of a hypervariable sic gene. Of the nine distinc t sic alleles, seven were found in single isolates, of which only two were from patients with invasive disease. The other two alleles were shared amon g 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 a nd implicates mainly two clones among the invasive emm1 isolates. (C) 2001 Academic Press.