Previous studies in our laboratory have shown that the Staphylococcus aureus LytSR two-component regulatory system affects
murein hydrolase activity and
autolysis. A LytSR-regulated dicistronic operon has also been identified and shown to encode two potential membrane-associated
proteins, designated LrgA and LrgB, hypothesized to be involved in the control of
murein hydrolase activity. In the present study, a lrgAB mutant strain was generated and analyzed to test this hypothesis. Zymographic and quantitative analysis of
murein hydrolase activity revealed that the lrgAB mutant produced increased extracellular
murein hydrolase activity compared to that of the wild-type strain. Complementation of the lrgAB defect by providing the lrgAB genes in trans restored the wild-type phenotype, indicating that these genes confer negative control on extracellular
murein hydrolase activity. In addition to these effects, the influence of the lrgAB mutation on
penicillin-induced lysis and killing was examined. These studies demonstrated that the lrgAB mutation enhanced
penicillin-induced killing of cells approaching the stationary phase of growth, the time at which the lrgAB operon was shown to be maximally expressed. This effect of the lrgAB mutation on
penicillin-induced killing was shown to be independent of cell lysis. In contrast, the lrgAB mutation did not affect
penicillin-induced killing of cells growing in early-exponential phase, a time in which lrgAB expression was shown to be minimal. However, expression of the lrgAB operon in early-exponential-phase cells inhibited
penicillin-induced killing, again independent of cell lysis. The data generated by this study suggest that
penicillin-induced killing of S. aureus involves a novel regulator of
murein hydrolase activity.