anti-microbial plant extract

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Brief Description In initial trials, redbush (Aspalathus linearis) and honeybush (Cyclopia sp.) extracts showed potential for inhibiting bacterial and yeast growth as determined by viable cell counts when applied at five mg/ml (0.5% m/v). Both the redbush and honeybush tea extracts have a bacteriostatic effect on the bacterial strains Escherichia coli, Propionibacterium acnes, Pseudomonas aeruginosa and Staphylococcus aureus, while a fungistatic effect was shown against C. albicans growth. The growth of Candida albicans was only inhibited in the first six hours and the yeast recovered from the effect relatively quickly. Furthermore, the antimicrobial sensitivity was shown to be highly strain-specific. An inhibitory effect on cell growth of all the test organisms was visible after six hours, but this inhibitory effect was diminished after 48 hours for most of the test organisms. This suggests that the antimicrobial components in the tea extracts have a short half-life and therefore result in a bacteriostatic effect on both the bacterial and yeast strains. Using a spectrophotometric method based on cell density, growth inhibition of 50% -100% was observed after 6-24 hours in the presence of 10-50 mg/ml redbush or honeybush extracts for Escherichia coli, Staphylococcus aureus, Propionibacterium acnes, Enterococcus feacalis, Streptococcus mutans, Salmonella enterica, Listeria monocytogenes and a Vibrio sp. Further investigation showed that a combination of redbush and honeybush extracts had a similar effect, i.e. there is a synergistic effect. Redbush and honeybush tea extracts stimulated biomass production in Aspergillus niger and Botrytis cinerea strains by more than threefold.. Biomass production was also induced in Mucor hiemales, Mucor circinelloides and Penicillium expansum strains in the presence of either redbush or honeybush extracts. However, the ability of B. cinerea to cause necrosis in white grape berries was inhibited by 55% and 21% in the presence of honeybush and redbush tea extracts respectively. The results suggest that micro-nutrients in the tea extracts stimulated fungal growth, whereas the antioxidants in the extracts may inhibit the oxidative burst associated with the plant’s response to infection that normally results in plant necrosis. Technical Description Water or solvent-based extracts in the range of 10 mg/ml to 50 mg/ml of Cyclopia subternata and Cyclopia genistoides (and possibly also other Cyclopia sp.) leaves can be used alone or in combination with extracts from Aspalathus linearis (redbush) to inhibit the growth of selected micro-organisms.  Sensitive organisms include Escherichia coli; Salmonella enterica; Vibrio spp.; Staphylococcus aureus; Pseudomonas aeruginosa; Propionibacterium acnes; Enterococcus feacalis; Streptococcus mutans; Listeria monocytogenes and Candida albicans.   Extracts used for the evaluation were prepared by the ARC (C. genistoides) or provided by Raps GmbH (A. linearis and C. subternata). Innovation Status Proof of concept has been shown in lab trials, but need to be evaluated in commercial products.  Since it contains natural antioxidants, the extract must be stabilised and standardised to ensure consistency.  The preparation of the extract(s) needs further development in terms of selective extraction/fractionation for enrichment of potent antimicrobial compounds.