. Some 10% of group-A streptococci have inhibitory activity against all nine strains (eight of them streptococci) in a set of indicators in an inhibitor-production typing (P-typing) scheme. This activity was associated with the concurrent synthesis of cell-associated proteinase by the streptococcal strain. Inhibitor production was prevented either by incubation of the test strain in conditions inimical to proeteinase production, e.g., at low temperature and alkaline H, or by addition to the medium of substances, such as glucose, iodoacetic acid, lincomycin, Congo red or trypan blue, that had an anti-proteinase effect. Inhibitory activity was not detectable in liquid cultures, but freeze-thaw extracts of cultures of group-A streptococcus strain A1013 on Gibco Columbia Agar Base (Gibco Diagnostics, Madison, WI, USA) had some inhibitory activity. The inhibitor was concentrated and partially purified, and the active agent was shown to be a high-mol.-wt cationic protein which was bactericidal for various bacteria in the logarithmic growth phase, including the homologous producer strain.


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