Distribution of emm types and superantigens among group A Streptococcus isolates recovered from northern Tshwane, South Africa

Abstract

Background: Group A Streptococcus (GAS) is a human pathogen that causes various diseases ranging from localised infections to toxin- and immune-mediated conditions.
Objectives: We aimed to describe the prevalence of GAS pharyngitis in northwestern Tshwane and to characterise GAS isolates from this region.
Method: GAS isolates were obtained from throat swabs of patients presenting with symptoms of pharyngitis. Clinical isolates were also collected from the DGM Laboratory. Minimum inhibitory concentrations for penicillin, erythromycin and clindamycin were determined using the E-test method. M-protein (emm) typing and superantigens (SAgs) profiles were determined using conventional PCR and sequencing.
Results: Among the 400 throat swabs collected, 33 (8%) tested positive for GAS on culture. Additionally, 72 clinical isolates were obtained. Overall, 105 isolates were available, of which 8 (7.6%) were invasive and 97 (92.4%) were non-invasive. All the isolates were susceptible to the tested antibiotics. Twenty-seven emm types were identified, with emm82 being the most prevalent (15%). The potential vaccine coverage among the isolates was 11%. The SAg profiles identified were K and Q.
Conclusion: The prevalence of GAS pharyngitis was 8%. No antimicrobial resistance detected. Emm typing showed significant diversity, with more than half of the isolates not covered by the 30-valent M-protein vaccine. The most prevalent was emm82, with speH and speI SAgs equally prevalent in these isolates. The main SAg profiles identified were K and Q. The diversity of these virulence factors suggests that it would be a challenge to consider them as potential vaccine candidates in this region.
Contribution: These epidemiological findings offer significant data on the emm types and SAgs in GAS isolates circulating in the region, which may inform the development of an effective vaccine.