Chemical composition, antioxidant and antimicrobial activities of basil (Ocimum basilicum) essential oils depends on seasonal variations

The Vegetation of South Africa, Lesotho and Swaziland

Essential oils (EOs) have been long recognized for their antibacterial, antifungal, antiviral, insecticidal and antioxidant properties. They are widely used in medicine and the food industry for these purposes. The increased interest in alternative natural substances is driving the research community to find new uses and applications of these substances. EOs and their components show promising activities against many food-borne pathogens and spoilage microorganisms when tested in vitro. In food systems, higher concentrations of EOs are needed to exert similar antibacterial effects as those obtained in in vitro assays. The use of combinations of EOs and their isolated components are thus new approaches to increase the efficacy of EOs in foods, taking advantage of their synergistic and additive effects. The purpose of this review is to provide an overview on the antimicrobial efficacy of these combinations. A survey of the methods used for the determination of the interactions and mechanisms involved in the antimicrobial activities of these combinations are also reported.

Essential oils in combination and their antimicrobial properties.

Essential oils are complex mixtures isolated from aromatic plants which may possess antioxidant and anti-inflammatory activities of interest in thye food and cosmetic industries as well as in the human health field. In this work, a review was done on the most recent publications concerning their antioxidant and anti-inflammatory activities. At the same time a survey of the methods generally used for the evaluation of antioxidant activity and some of the mechanisms involved in the anti-inflammatory activities of essential oils are also reported.

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Antioxidant and anti-inflammatory activities of essential oils: a short review.

Certain plants products widely used in the traditional medicine system of India were studied for immunostimulant activity. In the present study, strong stimulation of antigen specific and non specific immunity was evidenced by increase in haemagglutinating antibody (HA) titre, plaque forming cells (PFC) and in macrophage migration index (MMI), in mice fed with 50% ethanolic extract of these plants. The observation provides scientific basis for wide spread use of these plant products which are likely to play a role in Indian traditional medicine as tonic for rejuvenation therapy and chronic ailments.

	Key words: Macrophage migration index, haemagglutinating antibody, immunostimulant.

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Techniques for evaluation of medicinal plant products as antimicrobial agents: Current methods and future trends

Antimicrobial activity of South African medicinal plants.

Two common essential oil constituents, 1,8-cineole and limonene, were assessed for antimicrobial activity, using the minimum inhibitory concentration (MIC) microtitre plate method against eight organisms. The limonene enantiomers, i.e. (+), (−) and the racemate, singularly and in combination (1:1) with 1,8-cineole, were investigated to establish possible interactions. The MIC values were in the ranges 3–27 mg/ml for (+)-limonene; 2–27 mg/ml for (−)-limonene and 23 mg/ml for 1,8-cineole, depending on the pathogen studied. The combinations, when investigated in a 1:1 ratio, mostly indicated reduced activity. Using various ratios of limonene and 1,8-cineole, the specific interaction was further investigated against Staphylococcus aureus (Gram-positive), Pseudomonas aeruginosa (Gram-negative) and a yeast, Cryptococcus neoformans. A figurative representation of the results using isobologram construction indicated that, depending on the ratio and specific enantiomer, an additive, synergistic or antagonistic interaction may be observed. Copyright © 2007 John Wiley & Sons, Ltd.

Antimicrobial activity of limonene enantiomers and 1,8-cineole alone and in combination

Aims: Due to the emergence of multi-drug resistance, alternatives to conventional antimicrobial therapy are needed. This study aims to investigate the in vitro pharmacological interactions between essential oils (considered valuable as natural therapeutic treatments) and conventional antimicrobials (ciprofloxacin/amphotericin B) when used in combination.



Methods and Results:  Interactions of the essential oils (Melaleuca alternifolia, Thymus vulgaris, Mentha piperita and Rosmarinus officinalis) when combined with ciprofloxacin against Staphylococcus aureus indicate mainly antagonistic profiles. When tested against Klebsiella pneumoniae the isobolograms show antagonistic, synergistic and additive interactions depending on the combined ratio. The R. officinalis/ciprofloxacin combination against K. pneumoniae displayed the most favourable synergistic pattern. The interactions of M. alternifolia (tea tree), T. vulgaris (thyme), M. piperita (peppermint) and R. officinalis (rosemary) essential oils with amphotericin B indicate mainly antagonistic profiles when tested against Candida albicans.



Conclusion:  While a number of interactions show complete antagonism, others show varied (synergistic, additive and/or antagonistic) interactions, thus the efficacy is dependent on the ratio in which the two components co-exist.



Significance and Impact of the Study:  The predominant antagonistic interactions noted here, suggests that some natural therapies containing essential oils should be used with caution when combined with antibiotics.

S.F. Van Vuuren

Papers

Antimicrobial activity of South African medicinal plants.

Antimicrobial activity of limonene enantiomers and 1,8-cineole alone and in combination

The antimicrobial activity of four commercial essential oils in combination with conventional antimicrobials.

In vitro biological activity and essential oil composition of four indigenous South African Helichrysum species.

The in vitro pharmacological activities and a chemical investigation of three South African Salvia species