Genotypic diversity of imipenem resistant isolates of Acinetobacter baumannii in Spain

Horizontal Gene Transfer and Assortative Recombination within the Acinetobacter baumannii Clinical Population Provide Genetic Diversity at the Single carO Gene, Encoding a Major Outer Membrane Protein Channel

“…1). This observation most probably reflects not only the existence in A. baumannii of an OM channel(s) other than CarO, allowing also an efficient carbapenem permeation (see above), but also the workings of different mechanisms (or combination of mechanisms) leading to carbapenem-resistant phenotypes, similar to the acquisition of MDR (1,12,13,18,34,35,38,47,49,51). Still, A. baumannii clinical strains bearing IS-mediated carO interruptions have so far been detected only among carbapenem-resistant isolates (21,26,29).…”

“…Still, A. baumannii clinical strains bearing IS-mediated carO interruptions have so far been detected only among carbapenem-resistant isolates (21,26,29). Thus, the IS-mediated inactivation of carO, or the HGT-mediated exchange of particular carO variants, by reducing carbapenem influx through the OM may act synergistically with other mechanisms present in some genetic backgrounds (1,12,13,18,20,21,34,35,38,39,47,49,51), therefore resulting in an increased fitness phenotype under carbapenem pressure. The possible selected combinations are currently under study in our laboratory.…”

“…Yet, factors contributing to A. baumannii survival and spread in nosocomial environments, as well as in colonization, invasion, and evasion of host defenses, are unclear (13,28,35,38). The emergence of MDR A. baumannii strains has been attributed to the remarkable ability of this microorganism to rapidly evolve and accumulate resistance mechanisms as well as to being well suited for genetic exchange (1,12,13,18,29,34,35,38,39,49,51). The analysis of epidemic A. baumannii strains has in fact indicated that genetic relatedness is a poor predictor of the MDR phenotype, supporting the notion that individual strains can independently acquire different mechanisms of resistance (1,12,13,18,34,35,39,49).…”

“…The emergence of MDR A. baumannii strains has been attributed to the remarkable ability of this microorganism to rapidly evolve and accumulate resistance mechanisms as well as to being well suited for genetic exchange (1,12,13,18,29,34,35,38,39,49,51). The analysis of epidemic A. baumannii strains has in fact indicated that genetic relatedness is a poor predictor of the MDR phenotype, supporting the notion that individual strains can independently acquire different mechanisms of resistance (1,12,13,18,34,35,39,49). In this context, localized DNA changes and gene mutations due to mobile genetic elements, resulting in loss, enhancement, or gain of novel functions, as well as remnants of horizontal gene transfer (HGT) from different proteobacterial species, are all represented in the genomes of the A. baumannii clinical strains presently analyzed (1,12,18,35,39,49).…”

Extensively drug-resistant Acinetobacter baumannii: risk factors for acquisition and prevalent OXA-type carbapenemases—a multicentre study

“…Antimicrobial resistance and ubiquity of the organism may contribute to these outbreaks [1], and one or more epidemic clones often coexist with endemic strains [26,27]. This pathogen appears to be spreading from hospital to hospital and has become endemic in various geographical areas through multiple hospital outbreaks [28].…”