[Phenotypical curing of Streptococcus pneumoniae treated with amidase induced by the Dp-1 bacteriophage].

A phage-associated murein hydrolase activity (PAL) induced in an autolysis-defective mutant of Streptococcus pneumoniae infected with the bacteriophage Dp-1 has been recently isolated and purified to electrophoretic homogeneity as well as biochemically characterized as an endo-N-acetyl-muramyl-L-alanine amidase (1, 3, 4). The PAL and the inactive form (E-form) of the host cell autolysin show a remarkable biochemical similarity, although they differ in their immunological characteristics. The PAL was adsorbed onto a live, defective mutant of pneumococcus (cwl) and such cells reverted to the wild type phenotype ("cured" cells) in some important characteristics present in the wild type strain (R6), as: i) lysis of the culture in the stationary phase, ii) protoplast formation by hypertonic sucrose, and iii) bacteriolytic response against the penicillin in contrast with the bacteriostatic response of the "non-cured" cwl. The adsorbed enzyme segregates during growth of the "cured" cells. Our results demonstrate that PAL acts in the phenotypically "cured" cells in a similar way to that previously described for the host enzyme, and also confirm the finding that the autolysins play a direct role in the irreversible effects produced in S. pneumoniae by the betalactamic antibiotics.