Abstract
Release of extracellular DNA (eDNA) was observed during in vitro growth of a clinical strain of Acinetobacter baumannii. Membrane vesicles (MV) of varying diameter (20–200 nm) containing DNA were found to be released by transmission electron microscopy (TEM) and atomic force microscopy (AFM). An assessment of the characteristics of the eDNA with respect to size, digestion pattern by DNase I/restriction enzymes, and PCR-sequencing, indicates a high similarity with genomic DNA. Role of eDNA in static biofilm formed on polystyrene surface was evaluated by biofilm augmentation assay using eDNA available in different preparations, for example, whole cell lysate, cell-free supernatant, MV suspension, and purified eDNA. Biofilm augmentation was seen up to 224.64%, whereas biofilm inhibition was 59.41% after DNase I treatment: confirming that eDNA facilitates biofilm formation in A. baumannii. This is the first paper elucidating the characteristics and role of eDNA in A. baumannii biofilm, which may provide new insights into its pathogenesis.
Highlights
Pathogenesis and multidrug resistance of Acinetobacter baumannii has been a serious concern in the management of infections caused by the organism worldwide
To check the presence of DNA in the extracellular growth medium of A. baumannii AIIMS 7, extracellular DNA (eDNA) was purified by isopropanol precipitation at ice-cold temperature. eDNA was found to be present along the temporal scale of A. baumannii AIIMS 7 growth up to 96 hours and showed a pattern as shown in graph (Figure 1(b))
Concentrations of eDNA were comparable to earlier findings in Pseudomonas aeruginosa [15]
Summary
Pathogenesis and multidrug resistance of Acinetobacter baumannii has been a serious concern in the management of infections caused by the organism worldwide It contributes to 2–10% of all Gram negative infections and 9% of total nosocomial infections [1, 2]. Biofilm formation is considered as a factor contributing to the pathogenicity of A. baumannii, and it imparts high levels of drug resistance that lead to treatment failure. The capacity of this bacterium to adhere to epithelial cells is due to a positive correlation of biofilm formation with adherence [9] and probably explains the clinical success of A. baumannii [10]. In A. baumannii ATCC 19606, a two-component regulatory system bfmRS is found to play an important role in biofilm formation and cellular morphology [11]
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