Isolation, identification, and In Vitro antibacterial activity of Bacillus subtilis strain AzF1 against human pathogenic bacteria

Abstract

The prevalence of dangerous microorganisms poses a significant threat to global public health. A viable alternative to searching for new antimicrobials is biological control, which uses beneficial microbes to reduce disease-causing populations. The current study aimed to identify and characterise novel bacterial antagonists isolated from various environmental sources, including soil, wastewater, fruit peels, and olive leaves. The antibacterial activity of the isolates and their cell-free culture filtrates was evaluated against Staphylococcus aureus (ATCC6633), Escherichia coli (ATCC29213), Klebsiella pneumoniae (CIPA22), and Proteus mirabilis (ATCC29906) using standardized microbiological assays. A highly potent isolate was identified using conventional phenotypic and molecular methods. Results identified the antagonist as Bacillus subtilis strain AzF1, and its nucleotide sequence was deposited in the NCBI database under the accession number OP861484.1. The strain exhibited significant antibacterial activity against S. aureus , E. coli , K. pneumoniae , and P. mirabilis , with inhibition zones of 21.67 ± 0.29 mm, 16.13 ± 1.03 mm, 17.67 ± 1.15 mm, and 17.33 ± 1.15 mm, respectively. Additionally, the culture filtrate exhibited significant inhibitory activity, producing zone diameters of 18.40 ± 0.66 mm, 15.17 ± 0.76 mm, 15.67 ± 0.58 mm, and 13.33 ± 0.58 mm, respectively. The filtrate's minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC) values varied from 6.25% to 25.00% (v/v), indicating a purely bactericidal mode of action against all strains tested (MBC/MIC ratio = 1). The results demonstrate the promise of B. subtilis strain AzF1 as a significant source of bioactive compounds that can combat human pathogens.