Investigating group A Streptococcus antibiotic tolerance in necrotizing fasciitis

Group A Streptococcus (GAS) necrotizing fasciitis (NF) is a difficult-to-treat bacterial infection associated with high morbidity and mortality despite extensive surgery and targeted antibiotic treatment. Difficult-to-treat infections are often characterized by the presence of bacteria surviving prolonged antibiotic exposure without displaying genetic resistance, referred to as persisters. In the present study, we investigated the presence of GAS persisters in tissue freshly debrided from patients as well as in an in vivo mouse model of NF and examined the phenomenon of antibiotic tolerance. Time-lapse imaging of GAS plated directly upon isolation from NF debrided tissue and an antibiotic challenge-based persisters assay were used to assess the presence of persisters. We show for the first time that GAS recovered directly from freshly debrided NF tissue is characterized by heterogeneous and overall delayed colony appearance time, suggesting the presence of persisters. Acidic pH or nutrient stress exposure, mimicking the NF-like environment in vitro, led to a similar phenotypic heterogeneity and resulted in enhanced survival upon antibiotic challenge, confirming the presence of GAS persisters. GAS persisters might contribute to NF treatment failure, despite extensive surgery and adequate antibiotic treatment.