Antibacterial and Antibiofilm Activity of Ethanolic and Methanolic Nigella sativa L. Seed Extracts Against Pseudomonas aeruginosa ATCC 27853

Abstract

Biofilm associated infection is responsible for majority of chronic bacterial diseases. The conventional antimicrobial has not been able to cope with the increasing level of resistance. Nigella sativa L. (commonly called black cumin or black seed) has demonstrated diverse pharmacological properties, but standardized quantitative phenotypic assessment of its crude solvent extracts against Pseudomonas aeruginosa biofilms at subinhibitory concentrations remains limited. This study evaluated the in vitro antibacterial and antibiofilm effects of ethanolic and methanolic N. sativa seed extracts against P. aeruginosa ATCC 27853. Antibacterial activity was determined by agar well diffusion, yielding inhibition zones of 26.50 ± 0.87 mm (ethanolic) and 28.00 ± 1.15 mm (methanolic). Broth microdilution established identical MIC and MBC values of 250 μg/mL and 500 μg/mL, respectively, for both extracts. Biofilm inhibition was assessed by the tissue culture plate method with crystal violet staining at sub-MIC concentrations (125.00 to 7.81 μg/mL). The untreated control exhibited strong adherence. Following treatment, biofilm categories decreased to weak or moderate adherence. Percentage inhibition ranged from 68.34% to 89.45%, with the methanolic extract achieving 89.45% inhibition at 125.00 μg/mL. These findings indicate that N. sativa seed extracts possess antibiofilm potential against P. aeruginosa at subinhibitory concentrations. However, as this was a purely phenotypic study, the mechanisms underlying the observed inhibition remain speculative and require direct experimental investigation.