STUDIES ON VIRULENCE OF GROUP A β-HEMOLYTIC STREPTOCOCCI

Abstract

A strain of Streptococcus of low virulence for mice has been subjected to serial mouse passage and virulent, variant cultures recovered. There was reversion of colonial morphology from the smooth to the matt form on serial mouse passage. The virulence of the recovered organisms was markedly increased over the original culture. Studies on the fate in vivo of the 3 Q cultures showed quick disappearance of viable cocci of the Q496 culture when injected intraperitoneally into mice and rapid multiplication of cocci of the virulent cultures. The Q496 strain was readily phagocytized by human neutrophils, but cocci of the Q22X and Q43X strains were not ingested. The Q496 strain was found to be nonleukotoxic. In the absence of ingestion of the other 2 cultures by phagocytes, no statement as to leukotoxicity can be made. Study of the 3 cultures with human neutro-phils in the bacteriostatic test showed only slight inhibition of the Q496 culture by type 14 antibody and virtually complete inhibition of the Q22X and Q43X cultures. None of the 3 cultures were inhibited in the bacteriostatic test in the absence of type 14 antibody. M protein was not found in extracts of Q496 cell walls. M protein was present in extracts of the cell walls of the Q22X and Q43X variants. The glycolytic rate of the Q43X strain was significantly lower than that of the other 2 strains. Streptolysin S production decreased with increase in virulence. The Q22X culture produced less streptolysin O than the avirulent Q496 strain.