S. epidermidis attachment to polystyrene surfaces in the presence or absence of DNase I. (A) Attached SE1457ΔatlE, SE1457ΔsaeRS, SE1457 and SE1457saec cells were observed by microscopy. Briefly, cell suspensions from the mid-exponential phase were diluted to OD600 = 0.1 in PBS and then incubated in wells (1 mL per well) of cell-culture polystyrene chambers (Nunc, Roskilde, Denmark) with DNase I (140 U/mL) for 2 h at 37°C. S. epidermidis cells attached to the polystyrene surface were counted under microscope (400× magnification). (B) The number of attached bacteria per field was then counted. Results represent the mean ± SD of three independent experiments. *, P < 0.05; WT, SE1457; SAE, SE1457ΔsaeRS; SAEC, SE1457 saec; ATLE, SE1457ΔatlE.