Project description:A new variant of group A Streptococcus (GAS) serotype M1 (designated ‘M1UK’) has been reported in the United Kingdom, linked with seasonal scarlet fever surges, marked increase in invasive infections, and exhibiting enhanced expression of the superantigen SpeA. The progenitor GAS ‘M1global’ and M1UK clones can be differentiated by 27 SNPs and 4 indels, yet the mechanism for speA upregulation is unknown. Here we investigate the previously unappreciated expansion of M1UK in Australia, now isolated from the majority of serious infections caused by serotype M1 GAS. M1UK sub-lineages circulating in Australia also contain a novel toxin repertoire associated with epidemic scarlet fever causing GAS in Asia. A single SNP in the M1UK tmRNA gene ssrA drives enhanced SpeA superantigen expression as a result of ssrA terminator readthrough in the M1UK lineage. This represents a new paradigm of toxin expression and urges enhanced international surveillance.
