Survival of Group A Streptococcus (GAS) is Enhanced Under Desiccated Culture Conditions.

Streptococcus pyogenes or Group A Streptococcus (GAS) infections are the leading cause of bacterial tonsillopharyngitis. The bacterium can survive and persist within the human host for a long time as it is observed in up to 40% of the population who are considered as carriers. Recurrent tonsillopharyngitis is a particular problem in children which is caused either by relapses due to failed bacterial clearance or by reinfection. A prolonged survival in tonsillar crypts or on inanimate surfaces might be sources for reinfection. We therefore examined 64 clinical GAS isolates from children with tonsillopharyngitis for their long-term survival under either liquid or desiccated culture conditions. After 6 weeks, the overall GAS survival rate was 400-fold increased under desiccated culture conditions compared to liquid culture conditions, but varied depending on the emm-type between 20-fold (emm4) and 14000-fold (emm3). The survival rates of isolates from emm75 were significantly lower which is probably due to their production of hydrogen peroxide up to fatal doses. No hydrogen peroxide production could be detected for other emm-types. Furthermore, 11 isolates from patients with recurrent tonsillopharyngitis were compared to isolates of the same emm-type from patients with single episodes of tonsillopharyngitis. A significant elevated pH value and an increased survival rate for isolates from patients with recurrent infections were observed. In conclusion, significant differences in long-term survival of different GAS isolates as well as survival under desiccated culture conditions might contribute to both failed bacterial clearance and reinfection in patients with recurrent tonsillopharyngitis.

Hydrogen Peroxide Production of Group A Streptococci (GAS) is emm-Type Dependent and Increased at Low Temperatures.

Group A streptococcus (GAS) is an important human pathogen whose clinical isolates differ in their ability to produce hydrogen peroxide (H2O2). H2O2 is primarily produced by the enzyme lactate oxidase (LctO), an in depth in silico research revealed that all genome-sequenced GAS possess the required gene lctO. The importance of lctO for GAS is underlined by its highly conserved catabolite control element (cre box) as well as its perfect promotor sequence in comparison to the known consensus sequences of the Gram-positive model organism Bacillus subtilis. In this study, we provide further insight in the function and regulation of lactate oxidase by analyzing a large group of clinical GAS isolates. We found that H2O2 production increased over time in the late stationary phase; after 4 days of incubation, 5.4% of the isolates showed a positive result at 37 °C, while the rate increased to 16.4% at 20 °C. This correlation between H2O2 production and low temperatures suggests additional regulatory mechanisms for lctO besides catabolite control protein A (CcpA) and indicates that lctO might play a role for GAS energy metabolism at sub-body temperatures. Furthermore, we could identify that H2O2 production was different among clinical isolates; we could correlate H2O2 production to emm-types, indicating that emm-types 6 and 75 had the highest rate of H2O2 production. The emm-type- and temperature-dependent H2O2 production of clinical GAS isolates might contribute to their different survival strategies.

A standardized microdilution susceptibility test to determine the resistance capacity of human pathogenic bacteria towards hydrogen peroxide.

The susceptibility protocol established in this study takes into account that complex media are capable to buffer H2O2 which otherwise may adulterate test results. Furthermore, we demonstrate that clinical isolates of Staphylococcus aureus showed a higher resistance against H2O2 than Streptococcus pyogenes after 30 mins of incubation but not after 24 h.