International Journal of Antimicrobial Agents 37 (2011) 480–484 Contents lists available at ScienceDirect International Journal of Antimicrobial Agents journal homepage: http://www.elsevier.com/locate/ijantimicag Short communication Broad-spectrum antimicrobial efficacy of peptide A3-APO in mouse models of multidrug-resistant wound and lung infections cannot be explained by in vitro activity against the pathogens involved Eszter Ostorhazi a,1 , Marianna Csilla Holub b,1 , Ferenc Rozgonyi a , Ferenc Harmos a , Marco Cassone c , John D. Wade d,e , Laszlo Otvos Jr c,∗ a Microbiology Laboratory, Department of Dermatology, Venereology and Dermato-oncology, Semmelweis University, Budapest, Hungary b Department of Genetics, Cell- and Immunobiology, Semmelweis University, Budapest, Hungary c Department of Biology, Temple University, Philadelphia, PA 19122, USA d Florey Neuroscience Institutes, University of Melbourne, Victoria 3010, Australia e School of Chemistry, University of Melbourne, Victoria 3010, Australia article info Article history: Received 12 November 2010 Accepted 16 January 2011 Keywords: Aerosol Anti-inflammatory Bacterial counts Enterobacteriaceae Intramuscular MRSA Peptide antibiotic Survival rate abstract Although the designer proline-rich antimicrobial peptide A3-APO has only modest activity against Escherichia coli and Acinetobacter baumannii in vitro, in mouse models of systemic and wound infec- tions it shows superior efficacy compared with conventional antibiotics. In this study, the efficacy of A3-APO in several additional mouse models was investigated, including Staphylococcus aureus wound infection, mixed Klebsiella pneumoniae–A. baumannii–Proteus mirabilis wound infection and K. pneumo- niae lung infection, mimicking blast wound infections, foot ulcers and ventilator-induced nosocomial infections, respectively. Whilst the peptide practically did not kill the strains in vitro, when adminis- tered intramuscularly or as an aerosol it significantly improved mouse survival and reduced bacterial counts at the infection site and in blood. In the lung infection study, the blood bacterial counts following A3-APO treatment were as low as after treatment with colistin and were lower than after treatment with imipenem or amikacin. The wounds of treated animals, unlike their untreated counterparts, lacked pus and signs of inflammation. In human peripheral blood mononuclear cells, A3-APO upregulated the expression of the anti-inflammatory cytokines interleukin-4 and interleukin-10 by four- to six-fold. One of the mechanisms mediating the in vivo protective effects might be the prevention of inflammation around bacterial infiltration. © 2011 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. 1. Introduction Although the minimum inhibitory concentration (MIC) of the designer proline-rich antibacterial peptide A3-APO is as high as 16–64 mg/L against most clinical Escherichia coli and Acinetobac- ter baumannii strains, the in vivo therapeutic dose is 10 mg/kg when administered intraperitoneally and 5 mg/kg when adminis- tered intramuscularly [1,2]. A3-APO protects mice better against a multidrug-resistant A. baumannii strain at a 5 mg/kg intramus- cular (i.m.) dose than imipenem at 40 mg/kg [3] and improves the ∗ Corresponding author. Present address: 801 Mockingbird Lane, Audubon, PA 19403, USA. Tel.: +1 610 666 7110; fax: +1 215 204 6646. E-mail address: lotvos@comcast.net (L. Otvos Jr). 1 These two authors contributed equally to this study. soft tissue and skin conditions around artificial burn wounds even without inoculation of bacteria into the lesions [3]. Cationic antimi- crobial peptides (other than A3-APO) were shown to protect mice from bacterial invasion by upregulating cellular immune responses [4]. Here we extend the investigations of the in vivo antimicrobial efficacy of peptide A3-APO into three mouse models of burn/soft tissue and lung-originated systemic infections where the peptide had practically no in vitro bacterial killing properties against the invading pathogens. In the first model the skin wound infection assay was repeated using a clinical meticillin-resistant Staphylo- coccus aureus (MRSA) strain. In the second model, the pathogen in the soft tissue injury model was a mixture of A. baumannii, Klebsiella pneumoniae and Proteus mirabilis, all freshly isolated from a patient suffering from foot ulcer. To ultimately show that A3-APO protects animals from a wide range of experimental infections, in the third 0924-8579/$ – see front matter © 2011 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. doi:10.1016/j.ijantimicag.2011.01.003