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

Abstract

The menace of drug resistant pathogens is increasing and their level of evading conventional antimicrobials is rising. It is therefore important to discover new antimicrobials to counter the current challenges. 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 current study screened for the antimicrobial activity of the extract and fractions of the isolate by broth microdilution method. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and the ratio of the MBC/MIC were determined. All the tested pathogens were susceptible to the ethyl-acetate extract (MIC between 28.70 mg/ml and 57.40 mg/ml). The extract displayed bactericidal activity against all tested pathogens (MBC/MIC between 1.00 and 2.00) while Proteus mirabilis was least susceptible. The extract was purified by vacuum liquid chromatography and the fractions challenged with pathogenic strains.  The fraction E was the most potent (MIC between 0.09 mg/ml and 0.75 mg/ml) and also bactericidal against all the test microbes (MBC/MIC between 2.00 and 2.11).  GC-MS analysis of the purified sub fraction obtained from fraction E identified 13 compounds with different Retention time and peak areas.  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.)-.  Our findings suggest that Bacillus subtilis subsp. subtilis 168 isolated locally could serve as a valuable source of lead compounds for pharmaceutical and biotechnological purposes.