The antimicrobial properties of Ocimum gratissimum extracts on some selected bacterial gastrointestinal isolates

The antimicrobial efficacy of cold and hot water, hexane and methanolic extracts of fresh and dried leaf of Ocimum gratissimum against Salmonella typhimurium, E. coli, Yersinia enterocolitica, Bacillus cereus, and Aeromonas hydrophila were determined using the Agar gel diffusion method. The zones of inhibition, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and Phytochemistry of the extracts were also determined. Results obtained revealed that the cold water extracts of the fresh leaf was most potent, inhibiting all isolates with diameter zones of inhibition ranging from 5 mm to 18 mm, followed by hexane extract of the fresh leaf with zone range of 6 mm to 14 mm, but E. coli showed no resistance to the hexane extract, methanol extract of the fresh leaf showed no inhibitory effect on all isolates. The extracts inhibited the growth of the bacterial isolates in a concentration dependent manner with MICs ranging between (12.5 - 150) mg/ml, while MBCs gave a range of (3.13 - 100) mg/ml. Phytochemical analysis of fresh and dried leaf extracts revealed the presence of antimicrobial principles such as resins, tannins, glycosides, alkaloids, flavonoids saponin, anthraquinone, cardiac glycoside, steroidal ring, steroidal terpens and carbohydrates at different concentrations. The findings from this study seem to provide the in vitro evidence that might justify O. gratissimum as a good candidate medicinal plant for further investigations, and that the active principles of the plant may be more polar in nature.