For example, the transcriptional response to ciprofloxacin [11], an inhibitor of bacterial DNA gyrase, is clearly find more different from that of fosfomycin, because the cell wall stress stimulon genes were not activated. Similarly, the transcriptional profile of the antiseptic compound triclosan, that targets fatty acid biosynthesis [12], confirms the specificity of the cell wall stress response. The effects of fosfomycin on S. aureus metabolism, supported by our transcription data, are schematized in Figure 6. The inhibition of MurA causes accumulation

of its substrate phosphoenolpyruvate (PEP) which is known to act as a carbon starvation signal. PEP accumulation was shown to be responsible for downregulation of several central metabolism genes and nucleic acid biosynthesis genes in different organisms including bacteria [13]. A downregulation of pur and pyr operons was observed at the latest time point. Downregulation of both operons has also been reported in the SOS response [8], acid-shock response [7],

ciprofloxacin response [11] and in the S. aureus MurF underexpression mutant [6]. Figure 6 Fosfomycin effects on S. aureus metabolism supported by transcriptional data in this study. Processes in red ovals were induced and those in green ovals were repressed by fosfomycin treatment. In order CYC202 in vivo to reach target enzymes MurA and MurZ, fosfomycin has to cross the cell membrane. Because of its hydrophilic

Branched chain aminotransferase nature it uses the active transport MK-2206 concentration systems (ABC transport proteins), specifically the L-α-glycerophosphate and the glucose-6-phosphate uptake systems [1]. The PEP phosphotransferase system (PTS) mediates the uptake and phosphorylation of carbohydrates and controls metabolism in response to carbohydrate availability, and can therefore affect the whole cell metabolic rate [14]. GSEA shows that PTS was downregulated by fosfomycin 20 and 40 minutes after treatment. This downregulation could be a defense mechanism against the influx of fosfomycin. It has been reported that PTS mutant bacteria are highly resistant to fosfomycin [15] and that some fosfomycin-resistant E. coli isolates have altered glpT and/or uhp transport systems [16]. The downregulation of PTS genes can also contribute to PEP accumulation [13]. As shown in Figure 3 and Table 1, transport processes in general were significantly downregulated. The majority of differentially expressed genes in this group encode proteins that transport oligopeptides (opp genes), amino acids, sugars, polyamines (potABCD) and cations into the cell. Genes encoding iron transport and binding proteins, belonging to the Isd system, were also downregulated similarly as in a MurF underexpression mutant study [6]. However, a small proportion of transport genes were upregulated, including some amino acid and oligopeptide carrier genes and the sodium/hydrogen exchanger genes mnhBCDEG.