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Effects of garlic on the susceptibility of MRSA to beta-lactam antibiotics

Wood, Jonathan 2009. Effects of garlic on the susceptibility of MRSA to beta-lactam antibiotics. PhD Thesis, Cardiff University.

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It is well recognised that resistance to antibiotics is a major global health problem which is increasing in significance year on year. Many authorities believe it to be the biggest healthcare issue of the 21st century. In particular, methicillin-resistant Staphylococcus aureus (MRSA) is a major clinical problem, particularly in the UK. Plant-derived products, and particularly garlic, have been recognised as having antimicrobial activity for centuries. This traditional use has now been substantiated by credible science. Recent studies have begun to investigate whether there is any synergism between clinically-employed antimicrobials and plant-derived products, which could, in theory, make use of our currently redundant antibiotics In this study sub-MIC concentrations of garlic (MICs 1-2 mg mL-1) were shown to potentiate oxacillin susceptibility (MIC < 4 ug mL-1) against MRSA, and increase the sensitivity of MRSA to penicillin. Results suggest that increasing antibiotic susceptibility was as a result of the cumulative effects of the garlic and antibiotic rather than interaction between the two. It therefore appears that garlic does not exhibit the same mechanism of action as oxacillin or penicillin. Low concentrations of garlic (<0.5 mg mL-1), however, decreased the susceptibilities of MRSA and S. aureus to oxacillin or penicillin. Garlic caused thickening of the primary Staphylococcal cell wall, but did not damage the cell wall integrity. This is the first study to show in vitro decreasing sensitivity to garlic through repeated sub-culture in sub-inhibitory concentrations (0.5x MIC). Such isolates exhibited morphological changes but did not differ from control cultures in terms of growth dynamics. Acquired resistance to garlic has not previously been reported, suggesting these data are worthy of further investigation. The present study lends further support to the continued investigation into potentiation of antibiotic susceptibility in antibiotic-resistant organisms by phytochemicals. The results presented here do however suggest that these interactions may be more complex than anticipated and that low concentrations of phytochemicals could potentially exacerbate the problem of antibiotic-resistance.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Biosciences
ISBN: 9781303190070
Date of First Compliant Deposit: 30 March 2016
Last Modified: 10 Oct 2014 14:27

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