Molecular characterisation of csgA gene among ESBL strains of A. baumannii and targeting with essential oil compounds from Azadirachta indica

Objectives: A. baumannii is considered as a "red alert" nosocomial human pathogen and exhibits an exten-sive antibiotic resistance spectrum. The biofilm formation mediated by the csgA is a potent virulence factor in A. baumannii and targeting the same would be of a novel strategy to control A. baumannii infections. The aim of the present study is thus to evaluate the anti-biofilm activity of essential bio-compounds from Azadirachta indica against the ESBL producing strains of A. baumannii by in-vitro and in-silico studies. Methods: Biofilm formation by Semi-quantitative adherence assay was performed for the 73 strains of ESBL producing A. baumannii. Genomic DNA was extracted and molecular characterization of csgA gene was done by PCR amplification with further sequencing. In-vitro anti biofilm assay from crude extract of A.indica was performed which was then followed by the in-silico docking involving retrieval of csgA protein and ligand optimisation, molinspiration assessment on drug likeliness, docking simulations and visualisations. Results: Biofilm assay showed 58.9%, 31.5% and 0.09% as high grade, low grade and non-biofilm formers respectively. 20.54% (15/73) of the screened genomes showed positive amplicons for the csgA gene associated with biofilm formation among the ESBL producing strains of A. baumannii. All the ceftazidime, cefipime and cefotaxime resistant strains showed the presence of csgA gene (100%; 15/15), followed by 46.6% (7/15) resistant isolates for ceftriaxone. In-vitro crystal violet viability assay showed MBEC50 and MBEC90 at a concentration of 20 ml and 40 ml respectively. In-silico assessments on the essential oil compounds from neem showed imidazole to exhibit the highest interaction with least docking energy and high number of hydrogen bonds. Conclusion: The current study emphasises that imidazole from A.indica to be a promising candidate for targeting the csgA mediated biofilm formation in ESBL strains of A. baumannii. However, further in-vivo studies have to be implemented for the experimental validation of the same. (C) 2020 The Authors. Published by Elsevier B.V.