Study of antibacterial activity and cytotoxicity of the bioactive compound of Bacillus megaterium L2 strains isolated from the oral cavity of hospital workers and visitors at Dental Health Centre, Babylon, Iraq

Abstract

Because of the resistance of pathogenic bacteria to antibiotics, there is an urgent necessity to search for new antibiotics produced by Bacillus spp., which are characterized by their capability to produce secondary metabolites with high efficacy against numerous types of pathogenic bacteria. A total of 40 Bacillus isolates were isolated from the mouths of 150 volunteers from the Dental Health Center in Babylon and diagnosed based on phenotypic characteristics and biochemical and physiological reaction tests with a colorimetric reagent card using the VITEK2 analyzer. The active compounds were extracted from Bacillus megaterium L2 and their antibacterial activity was tested against a group of gram-negative and gram-positive bacteria. The Minimum inhibitory concentration (MIC) of the extract was estimated, whereas 16 isolates showed high effectiveness against pathogenic bacteria, with the zone of inhibition ranging from 8-22 mm and the MIC ranging from 0.25–6.25 mg/ml. The active compounds were extracted, purified, and detected by Thin-layer chromatography (TLC), Infrared (IR) spectroscopy, and Ultraviolet (UV) spectroscopy. The cytotoxic activity of the extracts was studied using the MCF7 cell line. This showed that cytotoxicity effects on valid object count, nuclear morphology, and total nuclear intensity ranged from 17.245-441.24 and the cytotoxic effect on cell membrane permeability, mitochondrial membrane potential, and cytochrome C ranged from 49.04-601.79 Among the isolates, Bacillus megaterium L2(B9) was the best isolated strain of bacteria that was the most effective against anti-pathogenic bacterial strains- Gram positive (Staphylococcus pyogenes NCTC 8198 and St. aureus ATCC 29213) and gram negative (Pseudomonas aeruginosa RW109, Escherichia coli O157, and Salmonella typhi Ty2) and was non-toxic to human cells (MCF7).