Antimicrobial Activity and GC-MS Based Analysis of the Extract of Bacillus subtilis subsp. subtilis 168 Isolated from a River Bank

Abstract

Drug-resistant pathogens are becoming a greater threat, and they are becoming more adept at dodging traditional antibiotics. Therefore, it's crucial to find new antimicrobials to combat the problems we currently face. Our preliminary investigation identified Bacillus subtilis subsp. subtilis 168 isolated from soil sample sourced from a river bank in Abuja, Nigeria, as the most potent antibiotic-producing bacteria among the other identified producers. The objectives of the current study were to: (i) screen for the antimicrobial activity of the extract, and fractions of the candidate isolate by broth microdilution method (ii) identify the bioactive compounds by Gas Chromatography-Mass spectrometry (GC-MS) method. We calculated the minimum bactericidal concentration (MBC), minimum inhibitory concentration (MIC), and the MBC/MIC ratio. All the tested pathogens were susceptible to the ethyl-acetate extract (MIC between 28.70 mg/ml and 57.40 mg/ml). Proteus mirabilis was the least susceptible pathogen, and the extract demonstrated bactericidal efficacy against all tested pathogens (MBC/MIC between 1.00 and 2.00). Vacuum liquid chromatography was used to separate the extract, and pathogenic strains were challenged with the fractions after purification. The most effective fraction was fraction E, which was also the most bactericidal (MBC/MIC between 2.00 and 2.11) against all of the test microorganisms (MIC between 0.09 mg/ml and 0.75 mg/ml). 13 compounds with various retention times and peak regions were found by GC-MS analysis of the purified subfraction produced from fraction E. Among these were three major compounds which include: (i) bis(2-ethylhexyl) phthalate (ii) 1,4-epoxynaphthalene-1(2H)-methanol, 4,5,7-tris(1,1-dimethylethyl)-3,4-dihydro- (iii) D:B-Friedo-B':A'-neogammacer-5-en-3-ol, (3.beta.)-. According to our research, the locally isolated Bacillus subtilis subsp. subtilis 168 could be a rich source of lead compounds for use in biotechnology and medicine.