Variability in carbapenemase activity of intrinsic OxaAb (OXA-51-like) β-lactamase enzymes inAcinetobacter baumannii

Abstract

Objectives To measure the variability in carbapenem susceptibility conferred by different OxaAb variants, characterize the molecular evolution of oxaAb and elucidate the contribution of OxaAb and other possible carbapenem resistance factors in the clinical isolates using WGS and LC–MS/MS. Methods Antimicrobial susceptibility tests were performed on 10 clinical Acinetobacter baumannii isolates. Carbapenem MICs were evaluated for all oxaAb variants cloned into A. baumannii CIP70.10 and BM4547, with and without their natural promoters. Molecular evolution analysis of the oxaAb variants was performed using FastTree and SplitsTree4. Resistance determinants were studied in the clinical isolates using WGS and LC–MS/MS. Results Only the OxaAb variants with I129L and L167V substitutions, OxaAb(82), OxaAb(83), OxaAb(107) and OxaAb(110) increased carbapenem MICs when expressed in susceptible A. baumannii backgrounds without an upstream IS element. Carbapenem resistance was conferred with the addition of their natural upstream ISAba1 promoter. LC–MS/MS analysis on the original clinical isolates confirmed overexpression of the four I129L and L167V variants. No other differences in expression levels of proteins commonly associated with carbapenem resistance were detected. Conclusions Elevated carbapenem MICs were observed by expression of OxaAb variants carrying clinically prevalent substitutions I129L and L167V. To drive carbapenem resistance, these variants required overexpression by their upstream ISAba1 promoter. This study clearly demonstrates that a combination of IS-driven overexpression of oxaAb and the presence of particular amino acid substitutions in the active site to improve carbapenem capture is key in conferring carbapenem resistance in A. baumannii and other mechanisms are not required.

Analysis of β-lactone formation by clinically observed carbapenemases informs on a novel antibiotic resistance mechanism

“…oxazolone formation from penicillins/cephalosporins with a nucleophilic acetamido side chain) is an open question. Evidence of the in vivo /clinical relevance of β-lactone formation is of interest, and this is something that we are pursuing in ongoing work including with clinically relevant strains, harboring relevant OXA variants ( 21 , 33 , 39 ).…”

Diversity of carbapenem-resistant Acinetobacter baumannii and bacteriophage-mediated spread of the Oxa23 carbapenemase

“…In addition, all A. baumannii carry an intrinsic OXA β-lactamase gene called oxaAb (or bla OXA-51-like ), certain alleles of which, when highly expressed due to the presence of an IS Aba1 insertion sequence upstream, can confer carbapenem resistance [12–14]. The most common of these resistance mechanisms globally is oxa23 [15].…”

“…The acquired OXA-type β-lactamases in A. baumannii are encoded by genes belonging to five main groups -oxa23 (or bla OXA-23-like ), oxa40 (or bla OXA-40-like ), oxa58 (or bla OXA-58-like ), oxa134 (or bla OXA-134-like ) and oxa143 (or bla OXA-143-like ) [10,11]. In addition, all A. baumannii carry an intrinsic OXA β-lactamase gene called oxaAb (or bla OXA-51-like ), certain alleles of which, when highly expressed due to the presence of an ISAba1 insertion sequence upstream, can confer carbapenem resistance [12][13][14]. The most common of these resistance mechanisms globally is oxa23 [15].…”

Molecular Characterization of Carbapenem-Resistant Acinetobacter baumannii Isolated from the Intensive Care Unit in a Tertiary Teaching Hospital in Malaysia

“…The CRAB isolates from UMMC expressed mainly OXA carbapenemase-mediated resistance, with 100% of the isolates harbouring at least one OXA-carbapenemase genes. The bla OXA-51-like gene is present in all isolates, supporting the understanding that this gene is intrinsic to A. baumannii species and can be used as a marker for identification [ 22 ]. Furthermore, 99% of the isolates coharboured bla OXA-23-like gene.…”