The effects of antimicrobial peptides WAM-1 and LL-37 on multidrug-resistant Acinetobacter baumannii

Increasing multidrug resistance (MDR) in Acinetobacter baumannii warrants therapeutic alternatives, and the bactericidal nature of antimicrobial peptides (AMPs) offers a possible approach. In this study, we examined the interaction of cathelicidin AMPs WAM-1, a marsupial AMP, and LL-37, a human AMP, with A. baumannii clinical isolates. We characterized the antibiotic resistance of the isolates, the bacteriostatic and bactericidal effects of these AMPs, synergistic activity with antibiotics, and their effects on biofilm formation and dispersal. All clinical isolates were resistant to commonly prescribed antibiotics, with four of seven isolates showing MDR. WAM-1 and LL-37 showed variable activity in clinical isolates, with WAM-1 having a stronger bacteriostatic effect than LL-37 and showing rapid bactericidal activity against clinical isolates. Furthermore, synergistic bactericidal activity was observed with WAM-1 and commonly prescribed antibiotics. Both peptides were able to inhibit biofilm formation in all clinical isolates at some concentrations, and WAM-1 dispersed mature biofilm in most isolates. LL-37 was unable to disperse mature biofilms in any strains. Further studies must be done to elucidate the true value of these alternative treatments, but these results suggest that MDR A. baumannii's susceptibility to AMPs may result in innovative therapeutics to prevent or treat these infections.