Inhibitor production by group-G streptococci of human and of animal origin.

Strains of group-G streptococci were tested by a "fingerprinting" method for the production of (P typing) and sensitivity to (S typing) inhibitory agents, and were biotyped. In the standard P-typing test, 28 of 50 strains of human origin, but none of 30 strains of animal origin, showed inhibitory activity. Of the human strains, 12 formed a bacteriocin that was active on group-A streptococci, including three (strains I2, I5 and I8) of the four streptococci of this group among the indicator strains. Sixteen other human strains inhibited the fourth group-A indicator (strain I7), and to a lesser extent strain I2, by lowering the pH of the typing medium. This acid-mediated inhibition was eliminated by testing on a medium containing calcium carbonate 0.5%; the 16 strains were then completely non-inhibitory, and the bacteriocin-forming strains, the typing pattern of which had originally been I2, I5, I7, I8, showed only inhibition attributable to the action of the bacteriocin. Nearly all group-A streptococci were sensitive to the group-G bacteriocin. The indicator strain I7 and several other members of M-type 28 were exceptions, but their resistance was not associated with the presence of R-antigen 28. Fifteen inhibitor-sensitivity patterns and 12 biotypes were identified among the strains; some of these tended to be associated with either a human or an animal origin. Neither S type nor biotype appeared to correlate with inhibitor production.