Characterization and Antibacterial Activity of Bacillus subtilis MK-4 Isolated from Southern Area of Pakistan

Abstract

Antibacterial molecules are generally considered as secondary metabolites produced by bacteria during the stationary phase of their growth, which can kill or inhibit the growth of other bacteria. Nowadays, the unsystematic use of antibiotics has resulted in resistant bacteria. Investigation of new antibacterial metabolites and the identification of unexplored antibacterial exhibiting bacteria are necessary. In this study, the bacterial isolate MK-4 was obtained from the soil of the local habitat (Karak, Pakistan). The isolate MK-4 was preliminarily screened for antibacterial activity against a set of Gram-positive as well as Gram-negative bacterial isolates. Antibacterial activity was evaluated against 9 ATCC bacterial strains including Staphylococcus aureus (29213), Staphylococcus epidermidis (12228), Escherichia coli (25922), Salmonella typhimurium (14028), Shigella flexneri (12022), Streptoccocus pneumonia (6305), Pseudomonas aeruginosa (27853), Klebsiella pneumoniae (13889) and Vibrio cholerae (9459) and 4 clinical multidrug-resistant (A. buemannii, S. aureus, E. coli and P. aeruginosa). Antibacterial activity was measured as zone of inhibition (ZOI) in mm. Identification of bacterial isolate B. subtilis MK-4 was based on 16S rRNA gene sequencing apart from biochemical and morphological characteristics. The isolate was further optimized for growth as well as for antibacterial metabolites production at different pH, temperature and incubation time. The isolate MK-4 showed maximum growth at 30°C, maximum antibacterial activity at 37°C. MK-4 exhibited maximum growth and antibacterial activity at pH 8 after 48 hours incubation time.