Bacteriocin production and sensitivity among coaggregating and noncoaggregating oral streptococci

Twenty‐one oral Streptococcus isolates of known interbacterial coaggregation groups were tested against one another (as both producers and indicators) to detect bacteriocin‐like inhibitory activity. In agar‐based antagonism tests, seven strains produced small inhibitory zones (≤ 3 mm diameter) but in liquid medium, only strain Streptococcus gordonii DL1 (Challis) produced a detectable antibacterial action (bacteriocin STH1). Five strains were sensitive to bacteriocin STH1, but neither the production of nor the sensitivity to any of the antagonistic agents correlated with coaggregation groupings. Four strains (C219, 903, 118 and Wicky) developed stable resistance in response to the bacteriocin, whereas one isolate (strain 34) remained sensitive following repeated bacteriocin exposure. With one exception (strain 903), bacteriocin STH1‐sensitive strains were competent for genetic transformation, but not all competent strains were bacteriocin‐sensitive. Bacteriocin‐resistant derivatives of transformable strains exhibited decreased competence (80–90% reduction) compared with their parent strains.