Abstract
BackgroundAcinetobacter baumannii is a significant hospital pathogen, particularly due to the dissemination of highly multidrug resistant isolates. Genome data have revealed that A. baumannii is highly genetically diverse, which correlates with major variations seen at the phenotypic level. Thus far, comparative genomic studies have been aimed at identifying resistance determinants in A. baumannii. In this study, we extend and expand on these analyses to gain greater insight into the virulence factors across eight A. baumannii strains which are clonally, temporally and geographically distinct, and includes an isolate considered non-pathogenic and a community-acquired A. baumannii.ResultsWe have identified a large number of genes in the A. baumannii genomes that are known to play a role in virulence in other pathogens, such as the recently studied proline-alanine-alanine-arginine (PAAR)-repeat domains of the type VI secretion systems. Not surprising, many virulence candidates appear to be part of the A. baumannii core genome of virulent isolates but were often found to be insertionally disrupted in the avirulent A. baumannii strain SDF. Our study also reveals that many known or putative virulence determinants are restricted to specific clonal lineages, which suggests that these virulence determinants may be crucial for the success of these widespread common clones. It has previously been suggested that the high level of intrinsic and adaptive resistance has enabled the widespread presence of A. baumannii in the hospital environment. This appears to have facilitated the expansion of its repertoire of virulence traits, as in general, the nosocomial strains in this study possess more virulence genes compared to the community-acquired isolate.ConclusionsMajor genetic variation in known or putative virulence factors was seen across the eight strains included in this study, suggesting that virulence mechanisms are complex and multifaceted in A. baumannii. Overall, these analyses increase our understanding of A. baumannii pathogenicity and will assist in future studies determining the significance of virulence factors within clonal lineages and/or across the species.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-1020) contains supplementary material, which is available to authorized users.
Highlights
Acinetobacter baumannii is a significant hospital pathogen, due to the dissemination of highly multidrug resistant isolates
Strains selected for comparative analyses The genomic data made available over the last decade have significantly advanced our knowledge of A. baumannii
The A. baumannii strain D1279779 was isolated from an outpatient from a remote area in tropical Australia and represents the first fully sequenced community-acquired A. baumannii isolate [26], whereas SDF is the only fully sequenced representative of a non-pathogenic isolate
Summary
Acinetobacter baumannii is a significant hospital pathogen, due to the dissemination of highly multidrug resistant isolates. Comparative genomic studies have been aimed at identifying resistance determinants in A. baumannii. Acinetobacter baumannii is a formidable Gram-negative human pathogen that is prominent in hospitals where it is a common cause of infections in critically ill patients in intensive care units and in particular with using respiratory assistance [1]. Clinical A. baumannii isolates display major phenotypic differences in virulence-associated phenotypes such as, biofilm formation, adherence to human epithelial cells, invasion, motility and cytotoxicity [2,3,4,5,6]. It has been shown that classical biofilms at the solid/liquid interface and pellicle formation are not directly correlated when examining different strains [2]
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