Carbapenem Resistance Genes in Acinetobacter baumannii From Intensive Care Units

Abstract

Carbapenems have long been the dependable last line against multidrug-resistant Acinetobacter baumannii, the Gram-negative bacterium that has settled into intensive care units (ICUs) around the world. That reliability is eroding, and the genes behind the erosion are the subject of this narrative review. It draws on published work on the oxacillinase families, the metallo-beta-lactamases, the insertion sequences that switch resistance genes on, the contribution of efflux and permeability changes, and the clonal lineages that carry all of this between hospitals. No new data are reported, and the title is treated as a topic in the literature, not as a local survey. The evidence shows that resistance rarely rests on a single gene: an intrinsic OXA-51-like enzyme becomes clinically relevant only when an upstream insertion sequence drives it, acquired OXA-23, OXA-24/40 and OXA-58 enzymes add to it, and NDM-1 now threatens to remove the remaining options. Detection is uneven, because phenotypic susceptibility results and gene-based assays answer different questions, and published surveillance is dominated by a few regions and by outbreak reports, which limits how far any pattern can be generalised. The review sets out what a laboratory report should state, what an ICU can reasonably infer from it, and which gaps in the literature matter most.