Genetic diversity of Group A Streptococcus M protein: Implications for typing and vaccine development

Group A Streptococci (GAS) are classified into 180 emm-types based on the sequence of the amino-terminal hyper-variable region of the M surface protein. The genetic relatedness of the whole surface-exposed part of M was investigated in well-characterized Belgian and Brazilian GAS isolates which belong to different epidemiological and clinical landscapes. Despite a small number of different emm-types and an apparent low diversity in the Belgian isolates (as revealed by the emm-typing method), our data showed that the overall genetic diversity of the M proteins was higher than expected. On the contrary, the M proteins from the Brazilian isolates were genetically highly related. Since M is a multi-functional protein, an analysis of the whole surface-exposed sequence that takes into account the different functional domains may provide tools for typing as well as for analyzing the molecular mechanisms of M virulence or defining vaccine strategies.