JAC Advance Access published online on January 3, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkm479
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Analysis of in vitro activities and modes of action of synthetic antimicrobial peptides derived from an 
-helical ‘sequence template’
1 Institute for Medical Microbiology, Immunology and Parasitology—Pharmaceutical Microbiology Section, University of Bonn, 53105 Bonn, Germany 2 Department of Biological Chemistry, The Weizmann Institute of Science, 76100 Rehovot, Israel 3 Institute for Experimental Medicine of the Russian Academy of Medical Sciences, 197376 St Petersburg, Russian Federation 4 Department of Biochemistry, Biophysics and Macromolecular Chemistry, University of Trieste, 34127 Trieste, Italy
Received 16 August 2007; returned 10 October 2007; revised 16 November 2007; accepted 18 November 2007
* Corresponding author. Tel: +49-228-73-5272; Fax: +49-228-73-5267; E-mail: sahl{at}mibi03.meb.uni-bonn.de
Objectives: Cationic antimicrobial peptides (AMPs) are indispensable components of innate immune systems and promising candidates for novel anti-infective strategies. We rationally designed a series of peptides based on a template derived from known 
-helical AMPs, which were then analysed regarding efficacy against clinical isolates and antibiotic mechanisms.
Methods: Efficacy tests included standard MIC and synergy assays. Whole cell assays with staphylococcal strains included killing kinetics, efflux experiments and determination of membrane depolarization. The transcriptional response of AMP-treated Staphylococcus aureus SG511 was analysed using a Scienion genomic microarray covering (
90% of) the S. aureus N315 genome and AMP P16(6|E).
Results: The AMPs showed remarkable broad-spectrum activity against bacteria and fungi regardless of any pre-existing antibiotic resistance mechanism. Whole cell assays indicated that the AMPs target the cytoplasmic membrane; however, significant membrane leakage and depolarization was only observed with a standard laboratory test strain. Transcriptional profiling identified up-regulation of putative efflux pumps and of aerobic energy generation mechanisms as major counter activities. Important components of the staphylococcal cell wall stress stimulon were up-regulated and the lipid metabolism was also affected.
Conclusions: The broad spectrum activity of amphiphilic helical AMPs is based on multiple stresses resulting from interactions with microbial membranes; however, rather than killing through formation of pores, the AMPs appear to interfere with the coordinated and highly dynamic functioning of membrane bound multienzyme complexes such as electron transport chains and cell wall or lipid biosynthesis machineries.
Key Words: membrane permeabilization , intracellular targets , transcriptional profiling , microarray
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