Streptococcus invasive locus (sil) in Group A Streptococcus causing non-invasive infections in Chennai, South India

Introduction

Group A Streptococcus (GAS) causes diseases ranging from superficial skin & throat infections to severe life-threatening diseases. Streptococcus invasive locus (sil) is a virulence gene responsible for pathogenesis of GAS. This study intends to detect the presence of sil gene among the non-invasive GAS and its association with toxin genes, erythromycin resistance genes, and emm types.

Methods

A total of 85 GAS isolates (43 pyoderma, 18 pharyngotonsilitis, 24 carrier) were screened for presence of sil C&D gene, toxin genes (speA, speB, speC, speG, smeZ, speH, speJ, ssa, speF), and erm genes by PCR. emm typing was done by emm gene amplification and sequencing.

Results

Among 85 isolates, 20/85 (23.5%) were positive for sil C and 27/85 (31.8%) isolates were positive for sil D. Both sil C&D were present in 20/85 (23.5%) isolates, whereas 58/85 (68.2%) isolates were negative for both sil C&D. Comparing the presence of sil C&D among the isolates from different sources, no significant difference (p>0.05) was found. There was no significant differences between the toxin gene profile and presence of erm genes between sil-positive/negative isolates (p>0.05). Thirty nine different emm types were observed among the 85 GAS, reflecting a diversity of 45.88%. emm types harbouring sil were emm89.0b(5), emm82.1(3), emm74.0(2), emm80.0(1), emm95.0(1), emm105.0(1), emm11.0(1), emm44.0(1), emm55.0(1), emm66.0(1), st2460.1(1), st6735.0(1), stG652.0(1). Many of these emm types were also found among the sil-negative strains.

Conclusion

23.5% of the non-invasive GAS harboured sil. There was no specific association of sil genes with toxin genes erm genes, emm types or source of isolation.