FIG 1.

Effects of bacterial growth phases on invasion. (A) Growth curves of wild-type S. aureus USA300, the Δlpl mutant, and the complemented mutant USA300 Δlpl(pTX30::lpl). The bacteria were precultivated aerobically in TSB overnight at 37°C, inoculated into fresh TSB at an OD₅₇₈ of 0.1, and cultivated at 37°C for 24 h under constant shaking at 160 rpm. The OD₅₇₈ of the cultures was monitored over time and was measured every hour during the first 8 h and after 24 h. (B) Effect of the S. aureus growth phase on the invasion of HaCaT cells. A total of 10⁶ HaCaT cells were infected with USA300, its Δlpl mutant, or the complemented mutant USA300Δlpl(pTX30::lpl) at an MOI of 30. The host cells were infected for 1.5 h, followed by lysostaphin treatment for another 1.5 h to kill adherent S. aureus cells. All experiments were performed at least in triplicate in three independent replications. Error bars indicate standard deviations. Statistical significance was calculated by using Student's t test (ns, no statistical difference; *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001).