Effect of lytSR gene knocking out on S. epidermidis biofilm formation. The biofilm formation of S. epidermidis ΔlytSR and its parent strain was detected by semi-quantitative microtiter plate assay. Briefly, the overnight bacterial were diluted by 1:200 and cultured in 96-well plate (200 μl/well) at 37 °C for 24 h. The well was washed by PBS for 3 times, fixed by 99% methanol and stained with crystal violet. Data are means ± SD of 3 independent experiments. *P < 0.05; ΔlytSR vs. WT; ΔlytSR(pNS-lytSR) vs. ΔlytSR(pNS-lytSR).