Differences in virulence repertoire and cell invasive potential of Group A Streptococcus emm1-2 in comparison to emm1 genotype

Abstract Group A streptococcus (GAS, Streptococcus pyogenes ) type emm 1 is widely associated with streptococcal invasive disease. This type is prevalent worldwide but is rare in India. Instead, emm 1-2 type which is closely related to emm 1 but is a distinct type is more prevalent. Although emm 1 has been well characterized, information available on emm 1-2 is rare. In this study we present a comparative study of both types. DNA microarray analysis showed segregation of emm 1 and emm 1-2 isolates into two distinct clusters. Out of 229 arrayed genes, 83–87% were present, 6–9% absent and 4–8% genes were ambiguous in emm 1 isolates. emm 1-2 strains harboured only 68–77%, 11–13% were absent and 10–20% ambiguous genes. Fourteen genes, present in all emm 1, were completely absent in the emm 1-2 isolates. sfb 1 is a gene which encodes for Streptococcal fibronectin binding adhesin and invasin which has restricted distribution among different emm types of GAS. A variant of sfb 1 ( sfb 1-2) was the only gene which was present in all emm 1-2 isolates, but absent from all emm 1 strains. Sfb1 and Sfb1-2 differ in sequences in the aromatic domain and the proline rich repeat region, whereas the fibronectin binding region was conserved and exhibited similar fibronectin binding activity. The presence of Sfb1-2 in emm 1-2 strains was concomitant with significantly higher fibronectin-binding and invasion efficiency of HEp-2 cells when compared to emm 1 isolates. The role of Sfb1-2 in invasion was confirmed by latex bead assay. emm 1-2 isolates follow membrane ruffling mechanism during invasion and intracellularly follow classical endocytic pathway. Further studies are required to understand the correlation between the presence of emm 1-2 isolates and the disease pattern in North India.