The human antimicrobial peptide LL-37 and its fragments possess both antimicrobial and antibiofilm activities against multidrug-resistant Acinetobacter baumannii

Acinetobacter baumannii infections are difficult to treat due to multidrug resistance. Biofilm formation by A. baumannii is an additional factor in its ability to resist antimicrobial therapy. The antibacterial and antibiofilm activities of the human antimicrobial peptide LL-37 and its fragments KS-30, KR-20 and KR-12 against clinical isolates of multidrug-resistant (MDR) A. baumannii were evaluated. The minimal inhibitory concentration (MIC) of LL-37 against MDR A. baumannii isolates ranged from 16 to 32 mu g/mL. The MIC of KS-30 fragment varied from 8.0 to16 mu g/mL and the KR-20 fragment MIC ranged from 16 to 64 mu g/mL. LL-37 and KS-30 fragment exhibited 100% bactericidal activity against five A. baumannii strains, including four MDR clinical isolates, within 30 min at concentrations of 0.25-1 mu g/mL. By 0.5h, the fragments KR-20 and KR-12 eliminated all tested strains at 8 and 64 mu g/mL respectively. LL-37 and its fragments displayed anti-adherence activities between 32-128 mu g/mL. A minimum biofilm eradication concentration (MBEC) biofilm assay demonstrated that LL-37 inhibited and dispersed A. baumannii biofilms at 32 mu g/mL respectively. Truncated fragments of LL-37 inhibited biofilms at concentrations of 64-128 mu g/mL. KS-30, the truncated variant of LL-37, effectively dispersed biofilms at 64 mu g/mL. At 24 h, no detectable toxicity was observed at the efficacious doses when cytotoxicity assays were performed. Thus, LL-37, KS-30 and KR-20 exhibit significant antimicrobial activity against MDR A. baumannii. The prevention of biofilm formation in vitro by LL-37, KS-30 and KR-20 adds significance to their efficacy. These peptides can be potential therapeutics against MDR A. baumannii infections. (C) 2013 Elsevier Inc. All rights reserved.