Bactericidal activity of M protein conserved region antibodies against group A streptococcal isolates from the Northern Thai population

The emm genes of GAS isolates were sequenced and grouped as 14 different J14-types. The most diversity of J14-types was found in the C1-repeat. The J14.1 type was the major sequence in the C2 and C3-repeats. We have shown that antisera raised against the M protein conserved C-repeat region peptides, J14, J14.1, J14-R1 and J14-R2, commonly found in GAS isolates from the Northern Thai population, are able to kill GAS of multiple different emm types derived from an endemic area. The mean percent of bactericidal activities for all J14 and J14-like peptide antisera against GAS isolates were more than 70%. The mean percent of bactericidal activity was highest for J14 antisera followed by J14-R2, J14.1 and J14-R1 antisera.Our study demonstrated that antisera raised against the M protein conserved C-repeat region are able to kill multiple different strains of GAS isolated from the Northern Thai population. Therefore, the four conserved "J14" peptides have the potential to be used as GAS vaccine candidates to prevent streptococcal infections in an endemic area.Streptococcus pyogenes or group A streptococcus (GAS) is a human bacterial pathogen that colonizes the throat or skin surfaces of the host. GAS infection can lead to a number of diseases including pharyngitis, impetigo and necrotising fasciitis. In a small percentage of individuals that are left untreated or are treated ineffectively with antibiotics, streptococcal infections can lead to more serious illnesses such as rheumatic fever (RF) and rheumatic heart disease (RHD) which are a significant health concern in developing countries [1].Most GAS vaccine strategies have focused on the M protein, a major virulence factor of GAS. The M protein has an alpha helical coiled-coil structure comprised of a variable amino terminal domain followed by a set of three repeat regions called A, B and C-repeats, a cell wall anchor motif and a stretch of hydrophobic amino acids which are embedded in the cell membrane. Antibodies to the