Autolysis assay of S. epidermidis 1457 ΔlytSR. Bacterial cells were collected from early exponentially growing cultures (OD600 = 0.7) containing 1 M NaCl, washed twice with ice-cold water and resuspended in an equal volume of Tris-HCl(pH 7.2) containing 0.05%(vol/vol) Triton X-100. The rate of autolysis was measured as the decline in optical density. The atlE knockout mutant was used as a negative control. Data are means ± SD of 3 independent experiments.