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Title: Investigation into the antibacterial effects of Allium sativum (garlic)
Author: Cottrell, Simon
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2004
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This study set out to compare and contrast the antimicrobial effects of freeze-dried garlic powder against the commonly occurring pathogens specifically Escherichia coli, and the probiotic bacterium Lactobacillus casei. Also to identify possible active components and sites of action of garlic, and study the reactive nature of allicin. Freeze dried garlic proved more inhibitory to E. coli than L. casei (24 h MIC values of 1.9 mg ml-1 and 16.9 mg ml-1 respectively) This was manifested against E. coli as a dose-dependent extension in lag phase (no effect on specific growth rate (SGR)). Inhibitory effects of garlic powder extract against L. casei were manifested as a dose- dependent decrease in specific growth rate. No bacteriocidal activity was observed on treatment of E. coli cultures with garlic concentrations of 20 mg ml-1 or less over 24 hours. Bacteriocidal activity was seen against E. coli when using concentrations in excess of 20 mg ml-1 over 48 h and 72 h. Garlic powder extract proved inhibitory to MRS A strains (EMRSA 15), and displayed synergism with penicillin and methicillin. GC-MS analysis proved garlic powder extract to be a dynamic mixture of sulphur containing compounds, including allicin and allicin reaction products. Half-life of allicin in nutrient broth (37° C) was approximately 11 h, this was reduced to 30 min on addition of E. coli cells. The inhibitory effect of allicin was observed as a dose-dependent increase in lag phase (no effect on SGR). Inhibitory activity of diallyl sulphides was observed as a dose-dependent decrease in SGR and small extensions in lag phase duration. Allyl alcohol brought about a substantial decrease in SGR and culture density at 24 h (concentration independent). Garlic powder extract caused membrane damage and abnormal morphology in E. coli (<2.0 mg ml-1) and L. casei (>10 mg ml-1). A reduction in glucose metabolism was observed in E. coli and L. casei on addition of garlic, also ethanol production and oxygen uptake were stimulated in E. coli cultures. This investigation has highlighted differences in the nature of garlic powder extract inhibition in a susceptible and non-susceptible organism, and identified possible mechanisms of action against E. coli to be cell structure damage, oxidative damage, and metabolic inhibition.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available