Acronym for M protein gene. The M protein gene (emm) encodes the cell surface M virulence protein(M protein) responsible for at least 100 Streptococcus pyogenes M serotypes. The emm typing is based on the sequence analysis of the section of the emm gene that specifies the M serotype. The hypervariable sequence associated with M serospecificity is located adjacent to an amplifying primer sequence, allowing direct sequencing.
The method of sequence analysis of the section of the emm gene was replaced in the late 1990s by the typing system based on sequencing of the 5' end of the emm gene and is referred to as emm typing.
Although there were significant differences in emm type distribution depending on geographic areas or clinical disease states, the most common emm types found in a large systematic review were emm1 (18.3%), emm12 (11.1%), emm28 (8.5%), emm3 (6.9%), and emm4 (6.9%).