Comparison of the antibacterial effects of a short cationic peptide and 1% silver bioactive glass against extensively drug-resistant bacteria, Pseudomonas aeruginosa and Acinetobacter baumannii, isolated from burn patients.

We have already established that a short cationic peptide (CM11) has high antimicrobial activity against a number of bacterial pathogens. Considering the untreatable problem of burn infections caused by Pseudomonas aeruginosa and Acinetobacter baumannii, this study evaluated and compared antibacterial effects of the CM11 peptide and 1% silver-doped bioactive glass (AgBG) against extensively drug-resistant strains of these bacteria which were isolated from burn patients. Accordingly, the bacteria were isolated from burn patients and their antibiotic resistance patterns and mechanisms were fully determined. The isolated bacterial from patients were resistant to almost all commonly used antibiotics and silver treatment. The isolates acquired their resistance through inactivation of their porin, the overexpression of efflux pump, and beta-lactamase. CM11 peptide and 1% AgBG had minimum inhibitory concentration (MIC) of ≥ 16 μg ml and ≥ 4 mg ml for clinical isolates, respectively. The minimum bactericidal concentration (MBC) of peptide and 1% AgBG for resistant bacteria was ≥ 32 μg ml and ≥ 4 mg ml, respectively. Among the clinical isolates, two P. aeruginosa isolates and one A. baumannii isolate were resistant to 1% AgBG disk. The CM11 peptide also showed high biocompatibility in vivo and no cytotoxicity against fibroblasts and adipose-derived mesenchymal stem cells in concentrations ≤ 64 μg ml and ≤ 32 μg ml, respectively, while the safe concentration of 1% AgBG for these cells was ≤ 16 μg ml. In conclusion, these findings indicated that the 1% silver is not safe and effective for treatment of such infections. The data suggest that CM11 peptide therapy is a reliable and safe strategy that can be used for the treatment of burn infections caused by antimicrobial-resistant isolates. The next stage of the study will be a multicenter clinical trial.