Abstract

Acinetobacter baumannii has been identified by the WHO as a high priority pathogen. It can be resistant to
multiple antibiotics and colistin sulphate is often used as a last-resort treatment. However, the potentially severe
side-effects of colistin are well documented and this study compared the bactericidal and anti-biofilm
activity of two synthetic nature-inspired antimicrobial peptides, bicarinalin and BP100, with colistin. The minimum
bactericidal concentration (MBC) against planktonic A. baumannii was approximately 0.5 μg/ml for
colistin sulphate and ∼4 μg/ml for bicarinalin and BP100. A. baumannii commonly occurs as a biofilm and
biofilm removal assay results highlighted that both bicarinalin and BP100 had significantly greater potential
than colistin. Atomic force microscopy (AFM) showed dramatic changes in A. baumannii cell size and
surface conformity when treated with peptide concentrations at and above the MBC. Scanning electron microscopy
(SEM) visualised the reduction of biofilm coverage and cell surface changes as peptide concentration
increased. Liposome assays revealed that these peptides most likely act as pore-forming agents in the
membrane. Bicarinalin and BP100 may be effective therapeutic alternatives to colistin against A. baumannii
infections but further research is required to assess if they elicit cytotoxicity issues in patients.