The genetic control of virulence in group A streptococci. II. Trigger effect by plasmids on anti-phagocytic activity, opacity factor and IgG and IgA Fc-receptors.

The erythromycin-resistance marker of two plasmids, pSM19035 and pERL1, could be transferred by conjugation in matings within group A streptococci and between group H and group A streptococci, with a frequency of 10(-5) to 8 X 10(-7). Two of the recipient strains used, 22v-1 and 22v-2, showed traces of opacity factor (OF) activity. This activity increased markedly upon transfer of both plasmids to the strains, whereas a number of other recipients, viz. 22h-21, 12Teiko-1 and Challis 6-1, remained OF-negative after conjugation. Furthermore, the transconjugants resulting from matings using strains 22v-1 and 22v-2 as recipients expressed anti-phagocytic activity. Attempts were made to type the transconjugants but they did not belong to type M12, M22 (the types from which the parents were derived) M3 or M1. Concomitant with the expression of anti-phagocytic activity, IgG and IgA Fc-receptor activity occurred in the transconjugants of 22v-1 and 22v-2, whereas the donor and recipient cells were without receptors. It was not possible to demonstrate extrachromosomal DNA in transconjugants possessing anti-phagocytic, OF or Fc-receptor activity, although they retained their ability to serve as donors of the Emr marker. It is suggested that the triggering by plasmids of anti-phagocytic activity, OF and IgG and IgA Fc-receptors is due to insertion of plasmid DNA into the chromosome.