Lysis of Streptococcus mutans BHT by salivary lysozyme

The aim of this work was to study the bacteriolytic ability of human salivary lysozyme (HSL) on Streptococcus mutans BHT. The cells were grown in a synthetic medium containing 3H-thymidine to monitor DNA release after incubation with either HSL, purified by ion exchange chromatography, or hen egg white lysozyme (HEWL). The experiments demonstrated that HSL as well as HEWL could liberate DNA from cells. The lysis was dependent on enzyme concentration as well as incubation-time. Approximately 80% of the 3H-thymidine was released at final concentrations of 4.5 micrograms/ml and incubation-times exceeding 16 hr. Additional treatment of the suspensions with DNase increased the levels of released radioisotopes. The lytic ability of HSL and HEWL was similar at low concentrations. HSL inactivated with goat antiserum to human lysozyme decreased the liberation of DNA by about 70%. This study suggests that HSL can lyse S. mutans BHT without presence of inorganic ions.