Cell-bound and extracellular autolytic activity of a tolerant and a nontolerant Staphylococcus aureus strain exposed to methicillin.

Cell-bound and extracellular autolytic activity was studied in a tolerant and a non-tolerant Staphylococcus aureus strain after exposure to low (10 mg/l) and high (80 mg/l) concentrations of methicillin. Tolerance was defined as survival after 24 h of over 2% of the inoculum after exposure to high concentrations of methicillin (greater than or equal to 64 mg/l). The nontolerant strain showed an increased cell-bound autolytic activity after exposure to both low and high concentrations of methicillin. The tolerant strain on the other hand selectively showed a reduced cell-bound autolytic activity after exposure to 80 mg/l of methicillin. In both types of strains extracellular activity was less after exposure to a high concentration of methicillin than after exposure to a low concentration. This phenomenon was caused by the release of an inhibitor of the autolysins under the influence of the high concentration of methicillin.