Cell envelope structural and functional contributions to antibiotic resistance inBurkholderia cenocepacia

Abstract

Antibiotic activity is limited by the physical construction of the Gram-negative cell envelope. Species of theBurkholderia cepaciacomplex (Bcc) are known as intrinsically multidrug-resistant opportunistic pathogens with low permeability cell envelopes. Here, we re-examined a previously performed chemical-genetic screen of barcoded transposon mutants inB. cenocepaciaK56-2 with a focus on cell envelope structural and functional processes. We identified structures mechanistically important for resistance to singular and multiple antibiotic classes. For example, the polymeric O-antigen was specifically important for resistance to cationic antibiotics, while defects in peptidoglycan precursor synthesis specifically increased susceptibility to cycloserine and revealed a new putative amino acid racemase. Susceptibility to novobiocin, avibactam, and the LpxC inhibitor, PF-04753299, was linked to the BpeAB-OprB efflux pump, suggesting these drugs are substrates for this pump inB. cenocepacia. Additionally, disruption of the periplasmic disulfide bond formation system caused pleiotropic defects on outer membrane integrity and β-lactamase activity. Our findings highlight the layering of resistance mechanisms in the structure and function of the cell envelope. Consequently, we point out processes which can be targeted for the development of antibiotic potentiators.