ROLE OF PUTATIVE VIRULENCE FACTORS OF STREPTOCOCCUS-PYOGENES IN MOUSEMODELS OF LONG-TERM THROAT COLONIZATION AND PNEUMONIA

To investigate the role of putative virulence factors of Streptococcus pyogenes (group A streptococcus; GAS) in causing disease, we introduc ed specific mutations in GAS strain B514, a natural mouse pathogen, an d tested the mutant strains in two models of infection. To study late stages of disease, we used our previously described mouse model (C3HeB /FeJ mice) in which pneumonia and systemic spread of the streptococcus follow intratracheal inoculation. To study the early stages of diseas e, we report here a model of long-term (at least 21 days) throat colon ization Following intranasal inoculation of C57BL/10SnJ mice. When the three emm family genes of GAS strain B514-Sm were deleted, the mutant showed no significant difference from the wild type in induction of l ong-term throat colonization or pneumonia. We inactivated the scpA gen e, which encodes a complement C5a peptidase, by insertion of a nonrepl icative plasmid and found no significant difference from the wild type in the incidence of throat colonization. However, there was a small b ut statistically significant decrease in the incidence of pneumonia ca used bg the scpA mutant. Finally, we demonstrated a very important eff ect of the hyaluronic acid capsule in both models. Following intranasa l inoculation or mice with a mutant in which a nonreplicative plasmid was inserted into the hasA gene, which encodes hyaluronate synthase, w e found that all bacteria recovered from the throats of the mice were encapsulated revertants. Following intratracheal inoculation with the hasA mutant, the incidence of pneumonia within 72 h mas significantly reduced from that of the control strain (P = 0.006). These results ind icate that the hyaluronic acid capsule of S. pyogenes B514 confers an important selective advantage for survival of the bacteria in the uppe r respiratory tract and is also an important determinant in induction of pneumonia in our model system.