Recovery of culturable Streptococcus pyogenes from swabs stored at different temperatures

Abstract

Improving our understanding of superficial Streptococcus pyogenes (Strep A) carriage and transmission necessitates robust sampling methods. Here, we compared the effect of storing swab samples in fridge (+4°C) and freezer (−20°C) conditions on the recovery of laboratory-cultured S. pyogenes. Streptococcus pyogenes colony-forming units progressively declined at +4°C, but not at −20°C, over 2 weeks. Results demonstrate that freezing is preferable over refrigeration for storage and transport of skin and throat swabs to ensure that culturing accurately reflects the true results of sampling. This is particularly important in remote community research and practice when immediate incubation is not possible or batch processing is most practical, increasing the elapsed time between collection and laboratory analysis. The study suggests that temperature negatively affects S. pyogenes viability and provides a method to further investigate the role of other environmental factors affecting S. pyogenes transmission.