0±1.2 mm, while that for the control strain was 18.5±0.4 mm. This indicates that BMS-777607 the overexpression of Spx has little effect on

the adaptation of S. epidermidis to diamide. To further confirm this, we extracted the RNA from WT and the spx-overexpressing strain, and determined the transcription level of trxB (encoding thioredoxin reductase and associated with thiol homeostasis). The transcription level of trxB was induced remarkably through the overexpression of Spx in B. subtilis, and decreased in both B. subtilis and S. aureus spx mutants. Consistent with our phenotypic observation, no significant difference of the trxB transcriptional level was found between the spx-overexpressing strain and WT. In addition, we found that the overexpression of Spx has little effect on the stress response of S. epidermidis to ethanol or hydrogen peroxide (data not shown). Spx is a conserved protein in low-G+C-content find more gram-positive bacteria. Its cellular level is controlled by ClpP protease. In both B. subtilis and S. aureus, Spx functions as a novel type of transcriptional regulator, and was proved as a substrate of ClpP protease (Nakano et al., 2002, 2003b; Pamp et al., 2006). Many bacterial functions are regulated by

Spx, such as competence, thiol homeostasis and biofilm formation (Zuber, 2004; Pamp et al., 2006). We found a much higher level of Spx in the clpP mutant strain, suggesting that Spx is likely a substrate of ClpP protease in S. epidermidis. The spx-overexpressing plasmid was constructed by modification of the C-terminal of spx gene, which also supports this view. In S. aureus, Spx negatively regulates biofilm formation (Pamp et al., 2006). In our study, decreased biofilm formation was found in the S. epidermidis Spx-overexpressing heptaminol strain. The primary attachment and the PIA production were severely reduced in the Spx-overexpressing strain compared with WT, and the biofilm by the strain carrying the antisense spx plasmid was decreased compared with WT. The transcription of atlE was similar to WT in the Spx-overexpressing strain, indicating that Spx does not affect the primary attachment through inhibiting the transcription of atlE.

Olson et al. (2006) have previously found that PIA enhanced the adherence of S. epidermidis to several orthopedic prosthetic biomaterials, including zirconia, ultra-high-molecular-weight polyethylene and cobalt chromium, but had no impact on the primary attachment to polymethylmethacrylate and titanium. In our study, there was no notable difference in the level of the initial adherence between WT and the isogenic PIA-negative strain under the selected experimental conditions. Thus, the mechanism behind the decreased initial attachment of the Spx-overexpressing strain needs further investigation. Decreased icaADBC transcription was found in the Spx-overexpressing strain of S. epidermidis, indicating that Spx affects PIA production by regulating the transcription of icaADBC. In S.