Tracing the recent evolution of Group A Streptococcus M1 serotype.

The twenty-first century has seen global surges in scarlet fever and invasive Group A Streptococcus (GAS) infections, partly driven by the emergence of the toxigenic M1UK lineage. Characterized by increased SpeA superantigen expression and the stepwise accumulation of 27 single nucleotide polymorphisms (SNPs), M1UK has become the dominant GAS emm1 lineage in Europe, Australia and Canada, representing a notable shift in GAS molecular epidemiology. Interestingly, other distinct emm1 variants have emerged in China and Denmark but are yet to expand globally in the same manner. This review examines the recent evolution of the GAS emm1 lineage, with emphasis on genomic and molecular drivers, highlighting the ongoing diversification of this pathogen and the need for continued surveillance and research.