Abstract
BackgroundAcinetobacter 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.MethodsGenotyping 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.ResultsThe 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.ConclusionsElevated 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.
Highlights
Acinetobacter baumannii is responsible for large epidemics in hospitals, where it can persist for long time on abiotic surfaces
Biofilm formation Twenty-three A. baumannii strains isolated during outbreaks that occurred in several hospitals in France, Greece, Italy, Lebanon, Netherlands and Turkey [4,28,29,30,31], and A. baumannii ATCC19606T and ATCC1 7978 reference strains [32,33] were investigated
Results demonstrate that epidemic A. baumannii genotypes differ in the ability to form biofilm on abiotic surfaces
Summary
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. The ability of A. baumannii strains to survive for a long time on dry surfaces is likely to contribute to their persistence in hospitals [18]. In this respect, it has been recently reported that RecA protein is involved in general stress response and resistance to heat shock and desiccation in A. baumannii [19]. Among the virulence factors that may contribute to these processes, the Bap protein has been demonstrated to play a role during adherence to epithelial cells [21], and OmpA and phospholipase D have been shown to contribute to invasion of epithelial cells [15,22]
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