Anti-Bacterial Properties And Gc-Ms Analysis Of Extracts And Essential Oils Of Selected Plant Products

ABSTRACT

Bacteria, as common microorganisms found in air, food, water and soil remain a major problem in developing countries where disease outbreaks frequently occur in congested areas. Antibiotics are used to treat common bacterial diseases such as respiratory, ear, gastrointestinal and skin infections but bacteria develop resistance to most of the drugs. The drugs also have serious side effects and the cost of medication is high. Plants are traditionally used for treatment of bacterial infections though they are not clinically regulated due to lack of awareness and enough data to support the reported therapeutic claims. Some plants used as food and vegetables are hardly considered in such studies. The aim of this study was to investigate the antibacterial properties associated with garlic, ginger, lemon, turmeric and onion. The bioactivities of juices, methanol extracts and essential oils of these materials were tested, individually and as blends, against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Salmonella typhi. Bioassay data obtained from the active extracts and oils were subjected to analysis of variance (ANOVA). Treatment means showing significant difference (p ≤ 0.05) were separated using Student-Newman-Keuls test (SNK). Identification of suspected antibacterial compounds was done by comparison of retention indices and the mass spectra with those in National Institute of Standards and Technology (NIST) libraries using GC-MS analysis. Garlic juice was bactericidal against Salmonella typhi (17.7±2.5), Staphylococcus aureus (14.7±2.5), Pseudomonas aeruginosa (10.0±0.0) and Escherichia coli (11.7±0.6). Lemon/garlic juice exhibited significantly higher activity against Escherichia coli (15.0±0.0) and Salmonella typhi (12.0±0.0). Turmeric/lemon/garlic methanol extracts blend was most active against S. aureus (12.0±1.0). Preliminary screening of the essential oils indicated significant antibacterial activity of lemon/garlic essential oil blend (10.0±0.0) against Pseudomonas aeruginosa. Garlic recorded time-course increasing activity against Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli from day 1 to day 5. GC-MS analysis of the active samples confirmed the presence of compounds containing -OOH, -OH, -N, -Cl, -F, -NH2 and –S groups which are associated with bacterial inhibition in conventional antibiotics. The 10 major constituents obtained from samples suspected to contain antibacterial activity include limonene (85.08%); 3-vinyl-1,2-dithiacyclohex-4-ene (21.43%); α-zingiberene (33.75%); diallyl disulphide (10.84%); 2-butanone,4-(-hydroxy-3-methoxyphenyl)- (14.14%); 3-chlorothiophene (8.93%); methanehydrazonic acid,N-[3-(methylthio)-1,-2,4-thiadiazol-5-yl]-,ethyl ester (8.87%); n-hexadecanoic acid (8.01%); γ-sitosterol (8.00) and propanamide,2-amino-3-phenyl (6.71%). Since juices of garlic, lemon and lemon/garlic blend were found to be active against one or more of the bacteria tested unlike methanol extracts and essential oils, they should be used in raw form as heating and drying is likely to render them inactive. Further studies on methanol extract and fresh juice of lemon/garlic blend need to be undertaken in order to elucidate the active principles in these extracts. These may provide novel antimicrobial agents and/or models for new generation of synthetic antibiotics.