Streptococcus pyogenes (group A streptococcus, GAS) is related to various clinical presentations in humans, from benign to severe invasive infections. GAS possesses a wide range of virulence factors and displays great genomic diversity. It is suggested that invasive disease is associated with virulent elements. Understanding the dynamics of GAS could inform vaccine development and disease control strategies.
Seventeen GAS isolates, 8 invasive and 9 non-invasive were identified through a prospective passive surveillance study in Cape Town. S. pyogenes strains were cultured, genomic DNA was extracted, and the samples were sequenced. The WGS-analysis pipeline screened for the presence of surface structure, exotoxin, virulence related gene targets and streptococcal antimicrobial resistance determinants. The antimicrobial susceptibility was confirmed using the Sensititre® STP6F platform of a panel of 20 antibiotics.
All isolates were confirmed to be GAS positive and characterized by WGS. There were two unrelated Cape Town emm92 clones, one of which corresponds to the common US emm92 (ST82). All isolates contained the hyaluronic acid capsule, SOF and SFB1 surface proteins. The isolates showed the presence of various exotoxins; spe_G (100%), spe_Z (100%), spe_C (72%), spe_J (78%) and spe_A (44%). There were no antimicrobial resistance genes detected among all isolates. This was confirmed by the antimicrobial susceptibility test.
This pilot study demonstrated the presence of various streptococcal pyrogenic exotoxins and surface proteins in isolates from Cape Town. No differences were apparent between invasive and non-invasive isolates. Overall, this study contributes to further knowledge to GAS vaccine development efforts and the identification of virulence factors that may be associated with invasive GAS infection.