The dual M protein systems have diverse biological characteristics, but both contribute to M18-type Group A Streptococcus pathogenicity.

M protein is a key surface virulence factor in Group A Streptococcus (GAS), Group C Streptococcus (GCS), and other streptococcal species. GAS encodes M protein using the emm gene, while GCS employs the szm (or sem) gene. In M18-type GAS, dual M protein systems exist, comprising both GAS and GCS M proteins (encoded separately by emm18 and spa18).

Protection Efficacy of Monoclonal Antibodies Targeting Different Regions of Specific SzM Protein from Swine-Isolated Streptococcus equi ssp. Strains.

Streptococcus equi subsp. (SEZ) has a wide host spectrum, including humans and domestic animals. The SEZ-caused swine streptococcicosis outbreak has occurred in several countries, and the swine-isolated strains usually have specific M-like () gene types.