Production of bacteriolytic activity in the oral cavity by nutritionally variant streptococci

Microorganisms from the oral flora were examined for the production of bacteriolytic substances. Among human viridans group streptococci, only one group of strains with thiol-dependent properties was shown to secrete enzymes with bacteriolytic activity on heat-killed cells of Micrococcus luteus on double-layer nutrient agar plates. By morphology, culture requirements, and biochemical properties, they were found to conform to descriptions of nutritionally variant streptococci (NVS). Bacteriolytic activity was shown to be a constant property of all of the human oral NVS isolated and a property of some reference strains of NVS from clinical sources. No other known species of viridans group streptococci demonstrated bacteriolytic activity. Analysis of bacteriolytic activity could be a useful tool for both the isolation and identification of this fastidious group of microorganisms.