A survey of antibiotic resistance patterns among Group A Streptococcus isolated from invasive and non-invasive infections in Cape Town, South Africa

Abstract

Background: There is concern regarding the increasing resistance of Group A streptococcus (GAS) to routinely used antibiotics. GAS is a common cause of bacterial pharyngitis and more severe invasive infections such as septicaemia. Furthermore, GAS pharyngitis is the antecedent for serious conditions such as rheumatic fever and rheumatic heart disease. The study aimed to determine the antimicrobial susceptibility patterns of GAS cultured from patients with invasive and non-invasive infections from Cape Town, as part of the AFROStrep Registry. Methods: Samples were provided by the AFROStrep Registry, a continental endeavour aiming to document Streptococcus pyogenes infection in Africa and create the first biorepository of its kind. Ninety-five GAS isolates (invasive, n = 40; non-invasive, n = 55) were evaluated for resistance to a panel of 20 antibiotics using the Sensititre® STP6F system with MICs interpreted by CLSI break points. Results: Amongst all isolates, highest levels of resistance were observed with respect to tetracycline (8.33 %), followed by azithromycin (1.04 %) and erythromycin (1.04 %). No resistance to the remaining antibiotics was detected amongst all isolates. No differences with regard to MIC values were observed between isolates from invasive and non-invasive infections (p-value >0.05 for all antibiotics). Conclusion: GAS remains susceptible to routine-antimicrobial agents used in our low-resourced setting. Eight percent of the GAS isolates were resistant to tetracycline, and we did not observe macrolide resistance as reported in high income countries. This is the first study to report on the antimicrobial patterns of GAS in South Africa. These results address a critical gap in the available data on GAS in Africa and specifically South Africa and, thus, aid in avoiding therapeutic failures.