Identification of a Chimeric M4 Protein and Novel Emm Pattern in Currently Circulating Strains of Emm4 Group A Streptococcus

Group A Streptococcus (GAS) is classified by sequence of the gene encoding the M protein (emm) and the patterns into which emm types are grouped. We discovered a novel emm pattern in emm4 GAS, historically considered pattern E, arising from a fusion event between emm and the adjacent enn gene. We identified the emm/enn fusion event in 51/52 emm4 GAS strains isolated by national surveillance in 2015. GAS isolates with an emm/enn fusion event completely replaced pattern E emm4 strains over a 4-year span in Houston (2013-2017). The novel emm/enn gene fusion and new emm pattern has potential vaccine implications.