Deciphering the Multifactorial Nature of Acinetobacter baumannii Pathogenicity

Background: Acinetobacter baumannii is an emerging bacterial pathogen that causes a broad array of infections, particularly in hospitalized patients. Many studies have focused on the epidemiology and antibiotic resistance of A. baumannii, but little is currently known with respect to its virulence potential. Methodology/Principal Findings: The aim of this work was to analyze a number of virulence-related traits of four A. baumannii strains of different origin and clinical impact for which complete genome sequences were available, in order to tentatively identify novel determinants of A. baumannii pathogenicity. Clinical strains showed comparable virulence in the Galleria mellonella model of infection, irrespective of their status as outbreak or sporadic strains, whereas a non-human isolate was avirulent. A combined approach of genomic and phenotypic analyses led to the identification of several virulence factors, including exoproducts with hemolytic, phospholipase, protease and iron-chelating activities, as well as a number of multifactorial phenotypes, such as biofilm formation, surface motility and stress resistance, which were differentially expressed and could play a role in A. baumannii pathogenicity. Conclusion/Significance: This work provides evidence of the multifactorial nature of A. baumannii virulence. While A. baumannii clinical isolates could represent a selected population of strains adapted to infect the human host, subpopulations of highly genotypically and phenotypically diverse A. baumannii strains may exist outside the hospita

Comparison of the Virulence Potential of Acinetobacter Strains from Clinical and Environmental Sources

Several Acinetobacter strains have utility for biotechnology applications, yet some are opportunistic pathogens. We compared strains of seven Acinetobacter species (baumannii, Ab; calcoaceticus, Ac; guillouiae, Ag; haemolyticus, Ah; lwoffii, Al; junii, Aj; and venetianus, Av-RAG-1) for their potential virulence attributes, including proliferation in mammalian cell conditions, haemolytic/cytolytic activity, ability to elicit inflammatory signals, and antibiotic susceptibility. Only Ah grew at 102 and 104 bacteria/well in mammalian cell culture medium at 37°C. However, co-culture with colonic epithelial cells (HT29) improved growth of all bacterial strains, except Av-RAG-1. Cytotoxicity of Ab and Ah toward HT29 was at least double that of other test bacteria. These effects included bacterial adherence, loss of metabolism, substrate detachment, and cytolysis. Only Ab and Ah exhibited resistance to killing by macrophage-like J774A.1 cells. Haemolytic activity of Ah and Av-RAG-1 was strong, but undetectable for other strains. When killed with an antibiotic, Ab, Ah, Aj and Av-RAG-1 induced 3 to 9-fold elevated HT29 interleukin (IL)-8 levels. However, none of the strains altered levels of J774A.1 pro-inflammatory cytokines (IL-1β, IL-6 and tumor necrosis factor-α). Antibiotic susceptibility profiling showed that Ab, Ag and Aj were viable at low concentrations of some antibiotics. All strains were positive for virulence factor genes ompA and epsA, and negative for mutations in gyrA and parC genes that convey fluoroquinolone resistance. The data demonstrate that Av-RAG-1, Ag and Al lack some potentially harmful characteristics compared to other Acinetobacter strains tested, but the biotechnology candidate Av-RAG-1 should be scrutinized further prior to widespread use

Genome-assisted identification of putative iron-utilization genes in Acinetobacter baumannii and their distribution among a genotypically diverse collection of clinical isolates

New putative iron-uptake genes were identified in published genomes of the opportunistic human pathogen Acinetobacter baumannii, and their occurrence was determined in a genotypically distinct collection of 50 clinical isolates by PCR and Southern blot assays. The results demonstrated that all A. baumannii isolates tested share the coding potential for two endogenous siderophores, a heme-acquisition and a ferrous iron-uptake system. A second heme-uptake cluster was detected in almost two thirds of isolates, without any apparent correlation with the clonal lineage of the strains. The wide distribution of multiple iron-acquisition systems among diverse A. baumannii clinical isolates argues for a contribution of iron uptake to the pathogenicity of this species. (C) 2010 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved

Virulence-related traits of epidemic Acinetobacter baumannii strains belonging to the international clonal lineages I-III and to the emerging genotypes ST25 and ST78.

Background: Acinetobacter baumannii is responsible for large epidemics in hospitals, where it can persist for long time on abiotic surfaces. This study investigated some virulence-related traits of epidemic A. baumannii strains assigned to distinct MLST genotypes, including those corresponding to the international clones I-III as well as emerging genotypes responsible for recent epidemics. Methods: Genotyping of bacteria was performed by PFGE analysis and MLST according to the Pasteur’s scheme. Biofilm formation on polystyrene plates was assessed by crystal violet staining; resistance to desiccation was evaluated on glass cover-slips when kept at room-temperature and 31% relative humidity; adherence to and invasion of A549 human alveolar epithelial cells were determined by the analysis of viable bacteria associated with or internalized by A549 human alveolar epithelial cells; Galleria mellonella killing assays were used to analyze the virulence of A. baumannii in vivo. Results: The ability to form biofilm was significantly higher for A. baumannnii strains assigned to ST2 (international clone II), ST25 and ST78 compared to other STs. All A. baumannii strains survived on dry surfaces for over 16 days, and strains assigned to ST1 (international clone I) and ST78 survived for up to 89 and 96 days, respectively. Adherence to A549 pneumocytes was higher for strains assigned to ST2, ST25 and ST78 than other genotypes; a positive correlation exists between adherence and biofilm formation. Strains assigned to ST78 also showed significantly higher ability to invade A549 cells. No significant differences in the killing of G. mellonella worms were found among strains. Conclusions: Elevated resistance to desiccation, high biofilm-forming capacity on abiotic surfaces and adherence to A549 cells might have favoured the spread and persistence in the hospital environment of A. baumannii strains assigned to the international clones I and II and to the emerging genotypes ST25 and ST78