In the screening campaigns of the six different substance collections

with 28,300 compounds in total, Z’-values between 0.5 and 0.9 with a mean of 0.8 were obtained, which is an indication of a reliable performance of the assay [3]. Figure 1 HTS assay. Growth of V. cholerae MO10 pG13 strain in 96- (A) and 384-well MTP (B) in the presence of test compounds and controls. (A): 12 A-B: 1% DMSO, 12C-D: 100 μM ciprofloxacin, 12 E-F: no addition of compounds, 12 G-H: sterile medium. (B): 23 A-D and 24 A-D: 1% DMSO, 23 E-H and 24 E-H: 100 μM ciprofloxacin, 23 J-M and 24 J-M: no addition of compounds, 23 M-P and 24 M-P: sterile medium. Upper panels: absorbance at 600 nm; lower panels: fluorescence (485/535 nm). Wells framed in red indicate active compounds. The six groups of screening compounds consisted of: i) the commercially available LOPAC library (a collection of pharmaceutically active Copanlisib ic50 compounds); ii) and iii) the EMC (Echaz Microcollection) and CDI collections (Chemical Diversity Lab), which contain small

organic molecules that were mainly generated by combinatorial synthesis; iv) the VAR collection (various sources), which is unique at the HZI and consists of small organic molecules that were synthesized by cooperating chemists; v) the NCH collection (natural compounds), which is also unique at the HZI and consists of purified secondary metabolites from myxobacteria. It included potent agents with already known antimicrobial or antiproliferative activity, e.g. epothilon, which has been developed only into a therapeutic agent against breast cancer [4, 5]; and finally vi) collections of linear and cyclic peptides with a length of seven STA-9090 clinical trial or eight D- or L-amino acids were investigated [6]. The compounds were used in one defined concentration between 20 to 50 μM in the initial screening. An overview of the growth-reducing activities of the six different substance collections is shown in Figure  2 and in Table  1. The threshold for active

compounds was defined at a minimum growth reduction of 50% in comparison to the DMSO control, which resulted in a suitable initial hit rate. The smallest of the six collections, the NCH collection of 154 compounds, showed the most active molecules with 32.5 hits per 1,000 substances. Several of these molecules displayed antibacterial activities that have been known before [7]. The VAR library consists of molecules with predominantly unexplored activities and contained 8.8 antibacterial compounds per 1,000 molecules. With 17 hits this collection contained the highest number of antibacterial molecules in total. Figure 2 Screening results. Summary of the initial screening results for novel antibacterial compounds. The tested compounds came from the NCH, Peptide, LOPAC, VAR, EMC and CDI collections. The shaded area highlights the activities that were defined as initial hits. The most active compound, vz0825, stemming from the VAR collection, is highlighted in red.