Statistical analysis Experimental data were analyzed with the SPSS software and compared

using the Student’s t-test. Differences with a P value of < 0.05 were considered statistically significant. Results Effect of saeRS deletion on S. epidermidis biofilm formation In order to explore the influence of saeR and saeS on S. epidermidis biofilm formation, an S. epidermidis 1457ΔsaeRS mutant (SE1457ΔsaeRS) and a complemented strain (SE1457saec) were constructed using the shuttle plasmids pMAD and pBT2, respectively. The biofilm-forming ability of SE1457ΔsaeRS on polystyrene plates was higher compared to the parental strain. Although it did not reach the level of the wild-type Quisinostat strain, complementation of saeRS resulted in decreased biofilm formation (Student’s t-test,

P < 0.05) (Figure 1). The growth curves of SE1457ΔsaeRS and the parental strain were similar in either aerobic or anaerobic growth conditions (Additional file 1: Fig. S1). Figure 1 Effect of DNaseI on SE1457 ΔsaeRS , SE1457, and SE1457 saec biofilm formation. SE1457ΔsaeRS, SE1457, and SE1457saec biofilms were washed and then stained with crystal violet. Their retained biomass was quantified by measuring the absorbance of each well at 570 nm. Biofilms were formed GS-1101 in vivo in the absence (black bars) or presence of DNase I (28 U/200 μL/well) (white bars). Mean values and standard deviations from three independent experiments are shown. (*), P < 0.05. WT, SE1457; SAE, SE1457ΔsaeRS; SAEC, SE1457saec. Scanning electron microscopy (SEM) of biofilms on catheters showed that SE1457ΔsaeRS biofilms contained more extracellular matrix compared to SE1457 and SE1457saec

biofilms (Figure 2A). In planktonic cultures, intercellular adhesion of the SE1457ΔsaeRS and the wild-type strain was observed using transmission electron microscopy (TEM). While thread-like material between SE1457ΔsaeRS cells was observed, such material was rarely found between parental strain cells (Figure 2B). Figure 2 SEM and TEM observations of SE1457 ΔsaeRS and wild-type strain. (A) Biofilms of SE1457ΔsaeRS, SE1457, Megestrol Acetate and SE1457saec after 24 h of growth on hydroxyapatite disks were observed by SEM. Arrows show the extracellular polymeric substances (EPSs) (10,000× magnification). (B) Planktonic cells of SE1457ΔsaeRS and SE1457 cultured for 24 h were observed by TEM. Cell-cell accumulations in SE1457ΔsaeRS are Roscovitine circled; arrow indicates the thread-like material linking neighboring cells. WT, SE1457; SAE, SE1457ΔsaeRS; SAEC, SE1457saec. Effect of saeRS deletion on the autolysis of S. epidermidis To examine the effect of saeRS deletion on autolysis, Triton X-100-induced autolysis of SE1457ΔsaeRS, SE1457, and SE1457saec was analyzed. Bacterial cells were harvested at the mid-exponential phase grown in TSB medium containing 1 M NaCl. Following the addition of 0.