One of the biggest threats in health care settings is the Gram negative opportunistic pathogen Acinetobacter baumannii which causes a variety of infections in immunosuppressed patients. Its ability to persist in clinical environment and multidrug resistance profile makes A. baumannii one of the most challenging nocosomial pathogens [1]. Therefore, identification of the virulent features is for understanding of the pathogenesis mechanisms displayed by A. baumannii.
Frequently virulence genes are acquired during horizontal gene transfer, e.g. plasmids or transposable elements [2]. spl gene is located in A. baumannii plasmid pAB120 [3] and possibly could be described as one of the putative virulence genes, since the product of this gene -septicolysin- has homology to the pore-forming toxins in other pathogenic bacteria [4]. The aim of this work was to assess the importance of septicolysin in A. baumannii pathogenesis.
In order to determine, whether septicolysin could be a pore-forming virulence factor, spl gene from plasmid pAB120 was cloned into pUC_gm_AcORI and pUC_gm_AcORI_Ptac vectors. These constructs were further transformed into septicolysin-lacking A. baumannii strain. Resulting strains were tested for the hemolytic activity. Cytotoxicity on the mice lung epithelial cells LLC1 was determined by measuring cell viability by trypan blue uptake. C. elegans fertility assay was performed to identify if septicolysin increases A. baumannii virulence in vivo.
According to our results, we did not observe any differences in hemolysis and cytotoxicity comparing A. baumannii wild type strain and the strain with introduced spl gene. Also, spl gene did not have an impact on nematodes fertility.
In conclusion, septicolysin didn't demonstrate the expected properties of pore-forming toxins in the tested models. However, further investigations using purified septicolysin are needed in order to determine its virulence.