Investigating the Interaction of Octapeptin A3 with Model Bacterial Membranes

Abstract

Octapeptins are cyclic lipopeptides that do not exhibit cross-resistance with polymyxins and have a broader spectrum of activity that includes fungi and Gram-positive bacteria. In the present study we investigated the interaction of octapeptin A3 with asymmetric outer membrane models of the Gram-negative pathogen Pseudomonas aeruginosa, using neutron reflectometry, together with fluorimetric and calorimetry methods. For the first time our neutron reflectometry results reveal that the interaction of octapeptin A3 with the Gram-negative outer membrane involves an initial transient polar interaction with the phospholipid and lipid A head groups, followed by the penetration of the entire octapeptin molecule into the fatty acyl core of the outer membrane. This mechanism contrasts that of polymyxin B which specifically targets lipid A, whereas octapeptins appear to target both lipid A and phospholipids. Furthermore, the mechanism of octapeptins does not appear to be highly dependent on an initial complimentary electrostatic interaction with lipid A, which accounts for their ability to bind to the lipid A of polymyxin-resistant Gram-negative bacteria which is modified with cationic moieties that act to electrostatically repel the cationic polymyxin molecule. The presented findings shed new light on the mechanism whereby octapeptins penetrate the outer membrane of polymyxin-resistant Gram-negative pathogens and highlight their potential as candidates for development as new antibiotics against problematic multi-drug resistant pathogens.

Comparative Metabolomics and Transcriptomics Reveal Multiple Pathways Associated with Polymyxin Killing in Pseudomonas aeruginosa

“…Lipid A was isolated by mild acid hydrolysis as previously described (59, 60). Briefly, P. aeruginosa PAK and PAK pmrB6 were treated by polymyxin B at 4 mg/liter and 8× MIC for 1 h. The bacterial cell pellets were harvested from 100 ml of normalized culture (OD 600 = 0.50 ± 0.02) via centrifugation at 3,220 × g for 20 min and washed twice with 5 ml PBS.…”

Octapeptin C4 and polymyxin resistance occur via distinct pathways in an epidemic XDRKlebsiella pneumoniaeST258 isolate

“…11,20,21 Interestingly, several octapeptin in vivo mouse studies have shown activity against Pmx-R infections and less toxicity compared with polymyxins. 13,[22][23][24] We have recently reported the first syntheses of octapeptin C4 11 and A3, 22 followed by detailed biological characterization of octapeptin C4 that demonstrates its potential as a new 'last-resort' antibiotic. 23 In view of the limited understanding of the mechanism by which octapeptins target bacteria, and to help advance their preclinical development, we sought to investigate the differences driving development of octapeptin C4 and polymyxin resistance at a genetic level.…”

Reversing resistance to counter antimicrobial resistance in the World Health Organisation’s critical priority of most dangerous pathogens

“…Importantly though, octapeptin retains efficacy against polymyxin-resistant bacteria due to their interaction with both lipid A and phospholipids. Octapeptins also have a broader spectrum of activity that include Gram-positives and yeasts and displays a superior preclinical safety profile compared with the polymyxins [86,100,101]. Hence, in addition to their antibiotic activity octapeptin could also be ideal resistance breakers to be used as adjuvants to reverse resistance in the most critically important multidrug-resistant organisms.…”