Bacteriocin-like Inhibitory Activity Associated with Beta-hemolytic Strains of Streptococcus salivarius

Abstract

Seven beta-hemolytic Streptococcus salivarius isolates produced bacteriocin-like inhibitory activity in deferred antagonism tests using a set of nine indicator bacteria (I1-I 9). Five of these S. salivarius strains (KWF, TOVE-R, K17, K21, and K26) were inhibitory to indicators I2, I5, I6, and I7. Mutated non-hemolytic derivatives showed concomitant loss of inhibitory activity against I2, I5, and 16, but retained activity against I7. Inhibitory activity against I2, I5, and I6 was restored in beta-hemolytic revertants of such mutants. Strain 3638 was inhibitory to all of the indicator organisms except I3, and this pattern of inhibitory activity was retained by non-hemolytic derivatives. It appeared that strain 3638 produced an additional broadly-active inhibitory agent, since a mutant (strain 3638A), which was apparently defective in the production of this inhibitor, retained both the beta-hemolytic and I2-, I5-, 16-, and I7-inhibitory activities. Non-hemolytic derivatives of strain 3638A were inhibitory only to I7. Strain 3638, therefore, appeared to produce at least three inhibitory agents: one active only on I7; another acting on I 2, 15, and 16 (and associated with beta-hemolytic activity); and a third apparently active on all of the indicators other than I3. S. salivarius strain JH inhibited all nine indicator strains and possessed a beta-hemolytic character which differed from that of the other strains in being readily eliminated on treatment with the plasmid-curing agent novobiocin. Non-hemolytic derivatives of JH retained inhibitory activity against the complete set of indicators. The results of this study suggest that hemolysin production by some S. salivarius strains may be intimately associated with a distinctive type of bacteriocin-like activity.