The main purpose was to examine how the type of cationic amino acid and sequence length affected the antibacterial activity and to
correlate this to a potential membrane-related mode of action in viable bacteria. Part of this work was presented at the 50th InterScience Conference on Antimicrobial Agents and Chemotherapy in Boston 12-15th of September 2010. Methods Bacterial strains and culture conditions Initial activity experiments were carried out with twelve strains from seven bacterial species representing common laboratory strains and clinical strains derived from both food-borne and nosocomial infections (Table 1). Stock cultures were stored at -80°C in 4% (w/v) glycerol, 0.5% (w/v) glucose, 2% (w/v) skimmed milk MK5108 in vivo powder and 3% (w/v) tryptone soy powder. All experiments were carried out with bacteria incubated for one night (i.e. approximately 18 hours) at 37°C. buy Givinostat Experiments were performed in cation-adjusted Mueller Hinton II broth (MHB) (Becton Dickinson 212322) adjusted to pH 7.4 or Tryptone Soy Broth (TSB) (Oxoid CM0129) for the ATP leakage assays. Brain Heart Infusion (BHI) (CM1135) with agar (VWR 20768.292) 1.5% as gelling
agent was used throughout for colony plating. Table 1 Origin and reference of bacterial strains used in the present study Origin Ref S. aureus 8325-4 Wildtype  K. pneumoniae ATCC 13883 Human, clinical – S. marcescens ATCC 8100 Human, clinical – E. coli ATCC 25922 Wildtype – E. coli MG1655 K-12 F- lambda-  E. coli AAS-EC-009 Human, clinical a E.coli AAS-EC-010 Human, clinical a L. monocytogenes 4446 Human, clinical  L. monocytogenes N53-1 Food processing  L. monocytogenes EGD Wildtype b V. vulnificus ATCCT Human, clinical – V. parahaemolyticus ATCCT Human, clinical – Susceptibility testing were carried out with a selection of twelve different bacterial strains comprising common laboratory strains and clinical strains derived from food-borne pathogens as well as pathogens
responsible for nosocomial infections. a ESBL-producing clinical samples from Danish patients in 2007; b This strain was kindly provided by Werner PAK6 Goebel, University of Würzburg. Peptide synthesis and selection α-Peptide/β-peptoid chimeras consisting of alternating repeats of natural cationic α-amino acids and synthetic lipophilic β-peptoid residues were prepared by solid-phase synthesis as previously described [21, 22]. Six chimeras were investigated in this study. The possible differences in sensitivity of different bacterial species were evaluated by testing the analogues 1, 2 and 3, distinguished by different degrees of chirality and type of cationic amino acid. Additionally, the mixed series 4a, 4b and 4c, differing only in the chain length, was used for evaluating the effect of this on antimicrobial activity (Figure 1).