Objectives The β-barrel assembly machinery (BAM) complex plays a critical role in outer membrane protein (OMP) biogenesis. The outer membrane (OM) of Pseudomonas aeruginosa is centrally involved in mechanisms of antibiotic resistance. This study aimed to identify effects of a synthetic peptide based on conserved sequences in the putative BamA-binding region of BamD, focusing on antibiotic susceptibility and OMP characteristics in P. aeruginosa. Methods We synthesized a peptide FIRL (Phe-Ile-Arg-Leu-CONH₂) with a sequence related to that of the BamD protein. We assessed antibiotic susceptibility of P. aeruginosa PAO1 using the chequerboard method and a time–kill assay. Changes in OMPs and in OM permeability were examined using SDS-PAGE, western blot analysis and nitrocefin assays. The combined effects of the peptide and antibiotics were investigated using a mouse pneumonia model. Results Although the peptide alone exerted no antimicrobial effect, it reduced the MICs of colistin, levofloxacin, erythromycin, vancomycin and rifampicin for P. aeruginosa PAO1 by 4-fold or more. Time–kill tests revealed bacterial numbers were significantly reduced after 2 h of incubation with the peptide plus colistin or levofloxacin. Moreover, in the presence of the peptide, expression of OprM was reduced by a third, and OM permeability was increased. The combination of the peptide (2.08 mg/kg) and colistin (1.25 mg/kg) significantly reduced P. aeruginosa by more than 1 log cfu/mL in a mouse pneumonia model. Conclusions We show, for the first time, that a synthetic peptide based on homologous sequences of BamD can potentiate antibiotic susceptibility of P. aeruginosa.

Mori N, et al. Ann Lab Med. 2018 May;38(3):189-195. https://doi.org/10.3343/alm.2018.38.3.189