Genomic comparison of multi-drug resistant invasive and colonizing Acinetobacter baumannii isolated from diverse human body sites reveals genomic plasticity

Jason W Sahl,J Kristie Johnson,Adam M Phillippy,William W Hsiao,Anthony D Harris,David A Rasko,Kerri A Thom

doi:10.1186/1471-2164-12-291

Abstract

BackgroundAcinetobacter baumannii has recently emerged as a significant global pathogen, with a surprisingly rapid acquisition of antibiotic resistance and spread within hospitals and health care institutions. This study examines the genomic content of three A. baumannii strains isolated from distinct body sites. Isolates from blood, peri-anal, and wound sources were examined in an attempt to identify genetic features that could be correlated to each isolation source.ResultsPulsed-field gel electrophoresis, multi-locus sequence typing and antibiotic resistance profiles demonstrated genotypic and phenotypic variation. Each isolate was sequenced to high-quality draft status, which allowed for comparative genomic analyses with existing A. baumannii genomes. A high resolution, whole genome alignment method detailed the phylogenetic relationships of sequenced A. baumannii and found no correlation between phylogeny and body site of isolation. This method identified genomic regions unique to both those isolates found on the surface of the skin or in wounds, termed colonization isolates, and those identified from body fluids, termed invasive isolates; these regions may play a role in the pathogenesis and spread of this important pathogen. A PCR-based screen of 74 A. baumanii isolates demonstrated that these unique genes are not exclusive to either phenotype or isolation source; however, a conserved genomic region exclusive to all sequenced A. baumannii was identified and verified.ConclusionsThe results of the comparative genome analysis and PCR assay show that A. baumannii is a diverse and genomically variable pathogen that appears to have the potential to cause a range of human disease regardless of the isolation source.

Highlights

Acinetobacter baumannii has recently emerged as a significant global pathogen, with a surprisingly rapid acquisition of antibiotic resistance and spread within hospitals and health care institutions
Cohort Description The University of Maryland Medical Center (UMMC) is a 656-bed tertiary-care hospital located in Baltimore, Maryland, with a 19 bed surgical intensive care unit (SICU) and a 29 bed medical intensive care unit (MICU) that provides care to adult patients who have acute or potentially life-threatening medical conditions
The comparison of these sequence types to the previously sequenced genomes identified that there is not a consistent multilocus sequence typing (MLST) pattern associated with the isolates from invasive or colonization sources

Summary

Introduction

Acinetobacter baumannii has recently emerged as a significant global pathogen, with a surprisingly rapid acquisition of antibiotic resistance and spread within hospitals and health care institutions. Russo et al [12] identified a carbohydrate biosynthesis pathway, as well as a protein tyrosine kinase, as virulence factors by using a transposon screen and survival in a rat soft tissue model. This complements the findings by Choi et al that complex carbohydrates were required in the formation of a complex biofilm [14] that is required for full virulence [13]. Mutation of the phospholipase D gene resulted in a decreased ability to invade epithelial cells in vitro but did not affect the lung bacterial load in vivo [16] These initial studies have provided limited, but significant insight into the virulence factors of A. baumannii. Further detailed studies will be required to more completely understand the pathogenesis and regulatory networks of A. baumannii

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