Deficient autolytic enzyme activity in antibiotic-tolerant lactobacilli

To define the mechanism(s) of penicillin tolerance in lactobacilli, one nontolerant and two tolerant strains were examined for autolytic enzyme activity. When incubated with ¹⁴C-labeled cell wall preparations, autolysin extracts of tolerant lactobacilli released significantly less radioactivity than did extracts of nontolerant lactobacillis (p < 0.02). These differences in the release of radioactivity by nontolerant and tolerant strains were maximal during the logarithmic growth phase. Moreover, this activity was greatest at pH 8, was heat labile, and was inhibited by the addition of magnesium, suggesting characteristics of an enzyme. This study illustrates that autolytic enzyme activity is deficient in strains of antibiotic-tolerant lactobacilli and suggests that this may be partially responsible for the delayed killing effect of penicillins against such strains.