The Evolution of Multidrug Resistance in a Hospital Pathogen

Abstract

The recent emergence of multidrug resistance(MDR) in Acinetobacter baumannii has raised concern inhealthcare settings worldwide. In order to understand therepertoire of resistance determinants and their organizationand origins, we compared the genome sequences of threeMDR and three drug-susceptible A. baumannii isolates. Theentire MDR phenotype can be explained by the acquisitionof discrete resistance determinants distributed throughoutthe genome. A resistance island (RI) with a variablecomposition of resistance determinants interspersed withtransposons, integrons, and other mobile genetic elements isa significant, but not universal, contributor to the MDRphenotype. Variable resistance gene composition amongidentical clone types from a single outbreak suggestsdynamic and active horizontal transfer. 475 genes areshared among all six clinical isolates, but absent from therelated environmental species Acinetobacter baylyi ADP1.These genes are enriched for transcription factors andtransporters and suggest physiological features of A.baumannii that are related to adaptation for growth inassociation with humans.