Structure and Evolution of Acinetobacter baumannii Plasmids

Abstract

Acinetobacter baumannii is an emergent bacterial pathogen that provokes many types of infections in hospitals around the world. The genome of this organism consists of a chromosome and plasmids. These plasmids vary over a wide size range and many of them have been linked to the acquisition of antibiotic-resistance genes. Our bioinformatic analyses indicate that A. baumannii plasmids belong to a small number of plasmid lineages. The general structure of these lineages seems to be very stable and consists not only of genes involved in plasmid maintenance functions but of gene sets encoding poorly characterized proteins, not obviously linked to survival in the hospital setting, and opening the possibility that they improve the parasitic properties of plasmids. An analysis of genes involved in replication, suggests that members of the same plasmid lineage are part of the same plasmid incompatibility group. The same analysis showed the necessity of classifying the Rep proteins in ten new groups, under the scheme proposed by Bertini et al. (2010). Also, we show that some plasmid lineages have the potential capacity to replicate in many bacterial genera including those embracing human pathogen species, while others seem to replicate only within the limits of the Acinetobacter genus. Moreover, some plasmid lineages are widely distributed along the A. baumannii phylogenetic tree. Despite this, a number of them lack genes involved in conjugation or mobilization functions. Interestingly, only 34.6% of the plasmids analyzed here possess antibiotic resistance genes and most of them belong to fourteen plasmid lineages of the twenty one described here. Gene flux between plasmid lineages appears primarily limited to transposable elements, which sometimes carry antibiotic resistance genes. In most plasmid lineages transposable elements and antibiotic resistance genes are secondary acquisitions. Finally, broad host-range plasmids appear to have played a crucial role.

Mechanisms Protecting Acinetobacter baumannii against Multiple Stresses Triggered by the Host Immune Response, Antibiotics and Outside-Host Environment

“…They constitute a reservoir of genes important not only for the dissemination of antibiotic resistance but also essential for bacteria adaptation and evolution. Recent analysis of 173 complete plasmid sequences from A. baumannii isolates originated from 17 countries revealed that 34.6% of the plasmids pose antibiotic resistance genes [ 199 ]. Bertini et al constructed a classification system for the A. baumannii plasmids based on the sequence of replicase genes, and they identified 19 homology groups (GR1–GR19) [ 200 ].…”

“…Bertini et al constructed a classification system for the A. baumannii plasmids based on the sequence of replicase genes, and they identified 19 homology groups (GR1–GR19) [ 200 ]. Fourteen additional groups of plasmids were recently proposed [ 199 , 201 , 202 ]. GR6 was the most prevalent group detected in antibiotic-resistant A .…”

“…baumannii isolates from Europe [ 203 ]. The GR6 plasmids harbor class D β-lactamase genes, including bla OXA-23 , bla OXA-58 , and bla OXA-40 , aminoglycoside-resistant genes ( aph (3’)-Via, aadB , aadA2 , strA , strB , aacA4, aph (3’)-Via), and sulfonamide ( sul2 ) and streptomycin ( strAB ) resistance genes [ 199 , 200 , 203 ].…”

Complete genome sequencing ofAcinetobacter baumanniiAC1633 andAcinetobacter nosocomialisAC1530 unveils a large multidrug resistant plasmid encoding the NDM-1 and OXA-58 carbapenemases

“…Acinetobacter GR8/GR23 group that was preceded by four 22-bp iterons characteristic of Rep3 family plasmids (43,44). pAC1633-2 also encodes a tetA(39) tetracycline resistance gene which was adjacent to and divergently transcribed from a tetR (39) regulatory gene (Fig.…”

“…Both plasmids do not encode any antimicrobial, metal resistance or any genes that could confer a specific phenotype to their host and are thus, cryptic plasmids. Both plasmids contain RepB replicases of the Rep3 superfamily that are common in Acinetobacter plasmids(43,44). Comparative analysis of the RepB protein sequences indicate that pAC1633-3 belonged to the recently categorized GR28 group of Acinetobacter plasmids (43) whereas pAC1633-4…”