ROLE OF M-PROTEIN IN PHARYNGEAL COLONIZATION BY GROUP-A STREPTOCOCCI IN RATS

As the initial step in infection, group A streptococci (GAS) colonize either the nasopharyngeal mucosa or the skin Of humans. A number of vi rulence factors have been implicated in the colonization phase of path ogenesis based upon their in vitro activities, but the in vivo data su pporting their role in colonization of the host tissues is lacking. In this investigation, the potential requirement for M protein in pharyn geal colonization by GAS was explored by using near-isogenic strains i n experimental animal studies. Fischer rats were infected by intranasa l and oral inoculation with both M-positive and M-negative Streptococc us pyogenes strains. Colonization of the pharyngeal area by the strept ococci was monitored at various time intervals. Both M-positive and M- negative strains colonized during the first week following infection, indicating that M protein was not necessary for this initial colonizat ion. Two M-positive strains of S. pyogenes were recovered from the rat s up to 23 weeks following inoculation, while the colonization levels for M-negative strains decreased rapidly in the second and third weeks , becoming negligible by the fourth week. This indicates a potential r ole for M protein in the persistence of colonization at this mucosal s urface. Colonization of rats with either M-positive strain of S. pyoge nes also resulted in the appearance of salivary and serum antibody res ponses. This in vivo model should allow further investigation into fac tors required for GAS disease, including the examination of the potent ial role of the host immune response both in modulation of the pharyng eal surface and in modulation of antigenic changes in M protein or oth er surface factors.