Three additional libraries that were used are unique at the HZI: iv) the NCH collection consisting

of 154 secondary metabolites from myxobacteria [33]; v) the library Various Sources (VAR) contained at the time of this study 1,936 synthetic organic molecules that were provided by various collaborators; and vi) the Peptide library contained 1,045 short linear or cyclic peptide sequences synthesized at the HZI [6]. All test compounds were utilized CH5183284 as stock solutions in DMSO. Growth assay 50 μl or 25 μl of LB-Km medium were inoculated in clear flat-bottom 96-well or 384-well MTP, respectively. Test compounds were added from DMSO stocks in amounts that resulted in assay concentrations between 20 and 50 μM. 50 μl or 25 μl of bacterial culture in LB-Km medium with an absorbance of 0.2 at 600 nm (OD600) (Ultraspec 2100 selleck chemicals llc Pro photometer, Pharmacia, GE Healthcare, Chalfont St Giles, UK) were added to the 96-well or 384-well MTP, respectively. The seeding of bacteria and addition of the compounds was carried

out with the pipetting system Evolution P3 (PerkinElmer, Waltham, USA). Stationary incubation of the plates for 24 h at 37°C under moist conditions was carried out, followed by determination of absorbance at 600 nm and fluorescence at 485/535 nm (Fusion Universal Microplate Analyzer, PerkinElmer, Waltham, USA). As negative and positive controls DMSO (1%) and Cip (100 μM)

were used, respectively. During the initial screening, approximately 28,300 compounds were investigated with single determinations. Compounds that reduced bacterial growth by at least 50% were retested in a second campaign and the most active substances were reevaluated at different concentrations between 0.1 and 100 μM. MIC and MBC values determination The determination of MIC and MBC values was carried out with V. cholerae wild type strains and several Gram-negative and Gram-positive bacteria (Table  3) following standardized protocol [34] in broth dilution assays. Starting inocula of 2-8×105 colony forming units/ml (CFU/ml) in MH medium at 37°C were used and serial dilutions crotamiton were carried out in 96-well MTP in duplicate. At 2, 6 and 24 h of incubation, 10 μl of the cultures were see more plated on LB agar plates. After an incubation of the plates for 24 h at 37°C, CFU/ml were determined and used for the determination of MBC, which is defined as minimum concentration of the substance required for 99.9% reduction of CFU after an incubation period of 6 h. The 2 h and 24 h measurements were used for additional correlation. MIC values were determined after 24 h of incubation. Cytotoxicity assay The mammalian cell line L929 was utilized to investigate the cytotoxicity of the active compounds in a MTT assay according to a modified protocol of Mosmann [11, 12].