Seven temperature-sensitive penicillin-tolerant mutants of strain LD5 () were isolated and characterized. Treatment with β-lactams caused lysis of the mutants at 30 °C. Although growth of the mutants at 42 °C was inhibited by β-lactams, no lysis occurred. The mutants were also slightly tolerant to D-cycloserine at 42 °C but lysed readily when deprived of diaminopimelate or when treated with moenomycin. The minimum inhibitory concentrations of various antibiotics were the same for the mutants and their parent. The mutations conferring penicillin tolerance were phenotypically suppressed in the presence of a variety of compounds which may act as chaotropic or antichaotropic agents. No defects in penicillin-binding proteins and peptidoglycan hydrolases were detected. Temperature-resistant revertants of the mutants were no longer tolerant to penicillin-induced autolysis at 42 °C. The mutations in five isolates were localized to the 56 to 61 min region of the linkage map and to the 44 to 51 min region in the case of two other isolates.


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