Peptides 25 (2004) 2055–2061 Antimicrobial activity of Bac7 fragments against drug-resistant clinical isolates Monica Benincasa a , Marco Scocchi a , Elena Podda a , Barbara Skerlavaj b , Lucilla Dolzani c , Renato Gennaro a,∗ a Department of Biochemistry, Biophysics and Macromolecular Chemistry, University of Trieste, Via Giorgieri, 1, I-34127 Trieste, Italy b Department of Sciences and Medical Technologies, University of Udine, P.le Kolbe, 4, I-33100 Udine, Italy c Department of Biomedical Sciences, University of Trieste, Via Giorgieri, 7, I-34127 Trieste, Italy Received 9 June 2004; received in revised form 4 August 2004; accepted 4 August 2004 Available online 17 September 2004 Abstract Ten peptides from 13 to 35 residues in length and covering the whole sequence of the Pro-rich peptide Bac7 were synthesized to identify the domain responsible for its antimicrobial activity. At least 16 residues of the highly cationic N-terminal sequence were required to maintain the activity against Gram-negative bacteria. The fragments Bac7(1–35) and, to a lesser extent, Bac7(1–16) proved active against a panel of antibiotic-resistant clinical isolates of Gram-negative bacteria, with the notable exception of Burkholderia cepacia. In addition, when tested against fungi, the longer fragment was also active against collection strains and clinical isolates of Cryptococcus neoformans, but not towards clinical isolates of Candida albicans. © 2004 Elsevier Inc. All rights reserved. Keywords: Pro-rich peptide; Bactenecin 7; Cathelicidin peptide; Synthetic analog; Antimicrobial activity; Clinical isolate; Multidrug-resistance 1. Introduction The problem of the rapid and alarming spread of antibi- otic resistance among nosocomial Gram-negative strains of bacteria is worryingly increasing, with serious public health implications [23,24]. As a consequence, there is a pressing need to develop novel and effective classes of antimicrobial drugs with mechanisms of action based on cellular targets different from those of existing antibiotics. Cationic antimicrobial peptides (AMPs) are widespread in nature and constitute an effective component of natural immunity for host defense against microbial agents [15,20]. Thanks to their capacity to rapidly inactivate bacterial, fungal or viral pathogens [33], antimicrobial peptides furnish new opportunities for the design of more effective peptidic or pep- ∗ Corresponding author. Tel.: +39 040 558 3696; fax: +39 040 558 3691. E-mail address: gennaro@bbcm.units.it (R. Gennaro). tidomimetic derivatives, and thus for development into novel antibiotics. Most AMPs kill target microorganisms by direct disrup- tion of the integrity of their membranes [26]. However, AMPs belonging to the Pro-rich group, act without an initial dam- age to bacterial membranes [10,21]. Members of this group are characterized by a high content of proline residues, are mainly active against Gram-negative species, and appear to inactivate bacteria by inhibition of metabolic processes, such as protein synthesis [3] or chaperone-assisted protein folding [14]. Bac7, a cathelicidin-derived peptide from bovine neu- trophils, is a member of this distinctive group that also in- cludes the closely related Bac5 and PR-39 peptides, respec- tively from bovine and pig neutrophils [1,9,34], and several homologs from sheep and goat [2,27]. Bac7 has a peculiar primary structure composed of a highly cationic N-terminal region, which includes eight arginines in the first 16 residues, followed by three hydrophobic tandemly repeated sequences 0196-9781/$ – see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.peptides.2004.08.004