Abstract
A unique, protective cell envelope contributes to the broad drug resistance of the nosocomial pathogen Acinetobacter baumannii. Here we use transposon insertion sequencing to identify A. baumannii mutants displaying altered susceptibility to a panel of diverse antibiotics. By examining mutants with antibiotic susceptibility profiles that parallel mutations in characterized genes, we infer the function of multiple uncharacterized envelope proteins, some of which have roles in cell division or cell elongation. Remarkably, mutations affecting a predicted cell wall hydrolase lead to alterations in lipooligosaccharide synthesis. In addition, the analysis of altered susceptibility signatures and antibiotic-induced morphology patterns allows us to predict drug synergies; for example, certain beta-lactams appear to work cooperatively due to their preferential targeting of specific cell wall assembly machineries. Our results indicate that the pathogen may be effectively inhibited by the combined targeting of multiple pathways critical for envelope growth.
Highlights
A unique, protective cell envelope contributes to the broad drug resistance of the nosocomial pathogen Acinetobacter baumannii
To examine the genome-wide molecular mechanisms that modulate antibiotic action in A. baumannii, we measured the effects of transposon insertion mutations on bacterial growth during challenge with a broad set of antimicrobial compounds by Tnseq[12]
We have systematically analyzed determinants of drug susceptibility in A. baumannii. Many of these determinants are encoded by nonessential genes that become essential during antibiotic therapy, allowing the identification of novel targets for potentiating antibiotics that have lost potency against the pathogen
Summary
A unique, protective cell envelope contributes to the broad drug resistance of the nosocomial pathogen Acinetobacter baumannii. The evolution of drug resistance in A. baumannii in large part is due to acquisition of inactivating enzymes or drug target mutations blocking antibiotic lethal action[7,8] These acquired alterations, which vary across isolates, act in concert with conserved mechanisms tightly linked to reduced drug penetration, including a low-permeability cell envelope and upregulation of efflux pumps[9,10]. By analyzing the patterns of altered antibiotic susceptibility caused by gene-inactivating mutations across the genome, we uncover functional relationships of conserved hypothetical proteins with key cell biological processes and expand the roles of annotated enzymes in envelope synthesis. This analysis informs a strategy to combine different β-lactam antibiotics for enhanced antimicrobial activity
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