ROLE OF EMM AND MRP GENES IN THE VIRULENCE OF GROUP-A STREPTOCOCCAL ISOLATE-64 14 IN A MOUSE MODEL OF SKIN INFECTION/

The virulence of group A streptococcal isolate 64/14 and paired isogen ic mutants in which either the emm or mrp gene had been insertionally inactivated was compared in mice. Loss of expression of the emm gene p roduct resulted in a significant loss of virulence when the isolate wa s injected into the skin but had no significant difference when inject ed intraperitoneally. By contrast, inactivation of the mrp gene caused the organism to be more virulent in the skin, while having no signifi cant effect intraperitoneally. An isogenic mutant, in which the mga ge ne was inactivated and neither the emm gene nor the mrp gene was expre ssed, demonstrated no significant difference in virulence from the wil d type organism. Organisms recovered from the spleen of mice lethally infected with the mga mutant expressed all Mga-regulated IgG-binding g ene products despite the presence of the spectinomycin-resistance cass ette, which was used to inactivate the mga gene, in its original posit ion.