Lytic and bactericidal activity of FCE 22101.

We have examined the lytic and cidal activities of FCE 22101 against bacteria exhibiting genetic tolerance (pneumococcal mutants) and bacteria phenotypically tolerant to penicillin (Escherichia coli, deprived of an essential amino acid). The pneumococcal strains included lyt- mutants in which the autolysin gene was inactivated or deleted and clinical isolates with penicillin MIC greater than 1.0 mg/l. The killing activity of FCE 22101 was superior to that of penicillin for all strains. FCE 22101 was also capable of inducing considerable lysis in all the lyt- strains in spite of the virtually complete inhibition (or actual absence) of the major autolysin. FCE 22101 also possessed bacteriolytic and cidal activity against a lysine-starved E. coli auxotroph (5 log kill in 24 h by 10 x MIC). Assays of the binding of FCE 22101 to the pneumococcal penicillin binding proteins (PBPs) suggest that the superior performance of FCE 22101 may be related to a uniquely high affinity for bacterial targets specifically involved with the bactericidal activity of beta-lactam antibiotics.