Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2024

Unravelling the molecular mechanisms underlying scarlet fever: insights from Streptococcus pyogenes   (#100)

Phoebe K Shaw 1 , Stephan Brouwer 1 , Mark J Walker 1
  1. The University of Queensland, Saint Lucia, QLD, Australia

Streptococcus pyogenes (Group A Streptococcus, GAS) is a human-restricted pathogen that causes a wide range of diseases from pharyngitis and scarlet fever to more severe, invasive infections such as necrotising fasciitis and streptococcal toxic shock syndrome. Once considered a fatal disease during the 19th and early 20th centuries, scarlet fever has largely disappeared in developed countries during the 20th century. However, there has been a global re-emergence of this toxin-mediated disease since 2011, with case numbers markedly increasing during the COVID-19 post-pandemic period. The cause(s) for disease resurgence are still largely unknown, but the acquisition of novel prophages harbouring new combinations of toxin genes has been linked with epidemic scarlet fever-causing GAS isolates. In Australia, scarlet fever is not notifiable, however the establishment of a sentinel hospital surveillance system in South East Queensland allowed us to monitor scarlet fever case numbers which also show an upward trend. The aim of this study was the molecular characterisation of seventeen scarlet fever GAS isolates from the Gold Coast University hospital collected in 2022. Whole genome sequencing revealed that the most prevalent GAS emm types were emm22 (3/17, 18%), emm12 (3/17, 18%), and emm3 (3/17, 18%), which is similar to other geographical regions (e.g. China and the UK). Using PCR and western blotting, we confirmed that the majority of the isolates (10/17, 59%) carried at least one superantigen gene associated with scarlet fever, and carriage of these toxin genes was non-emm type specific. Alarmingly, phylogenetic analysis and phenotypic characterisation of these isolates further revealed the presence of a novel, hypervirulent acapsular emm4 GAS clone in Australia which is now the dominant emm type in the US. Future work will explore the specific role of superantigens in different emm types during host-pathogen interactions to better understand the pathogenesis of scarlet fever-causing GAS.