Abstract
The aim of this study was to characterise an oral bacterial isolate possessing extracellular bacteriolytic activity and to determine the basic properties of this activity. The lytic strain L1 was a gram-positive pleomorphic rod that grew only under anaerobic conditions. Glucose and raffinose were fermented whereas catalase and urease were not produced. The activity spectrum of a crude lytic fraction was restricted to strains of Actinomyces naeslundii and Actinomyces viscosus. On the basis of its molecular weight (>30 kDa) as well as sensitivity to heat and trypsin, the factor(s) has a proteinaceous component. The activity was highly sensitive to EDTA suggesting that cations may be essential for optimal activity. Sulfhydryl groups are also of major importance in the lytic process as activity was highly stimulated by dithiothreitol and inhibited by p-chloromercuriphenylsulfonic acid. Strain L1 was found to grow on a solid basal medium containing heat-killed A. naeslundii cells, and suggests a physiological role for the bacteriolytic activity. The bacteriolytic activity demonstrated in the present study may constitute a selective advantage for establishment of the bacteria in a complex ecosystem like the oral cavity.