The use of and search for drugs and dietary supplements derived from plants have accelerated in recent years. Ethnopharmacologists, botanists, microbiologists, and natural-products chemists are combing the Earth for phytochemicals and “leads” which could be developed for treatment of infectious diseases. While 25 to 50% of current pharmaceuticals are derived from plants, none are used as antimicrobials. Traditional healers have long used plants to prevent or cure infectious conditions; Western medicine is trying to duplicate their successes. Plants are rich in a wide variety of secondary metabolites, such as tannins, terpenoids, alkaloids, and flavonoids, which have been found in vitro to have antimicrobial properties. This review attempts to summarize the current status of botanical screening efforts, as well as in vivo studies of their effectiveness and toxicity. The structure and antimicrobial properties of phytochemicals are also addressed. Since many of these compounds are currently available as unregulated botanical preparations and their use by the public is increasing rapidly, clinicians need to consider the consequences of patients self-medicating with these preparations.

Plant Products as Antimicrobial Agents

Screening of some Palestinian medicinal plants for antibacterial activity.

Antimicrobial activities of the crude ethanolic extracts of five plants were screened against multidrug resistant (MDR) strains of Escherichia coli, Klebsiella pneumoniae and Candida albicans. ATCC strains of Streptococcus mutans, Staphylococcus aureus, Enterococcus faecalis, Streptococcus bovis, Pseudimonas aeruginosa, Salmonella typhimurium, Escherichia coli, Klebsiella pneumoniae and Candida albicans were also tested. The strains that showed resistance against the maximum number of antibiotics tested were selected for an antibacterial assay. The MDR strains were sensitive to the antimicrobial activity of Acacia nilotica, Syzygium aromaticum and Cinnamum zeylanicum, whereas they exhibited strong resistance to the extracts of Terminalia arjuna and Eucalyptus globulus. Community-acquired infections showed higher sensitivity than the nosocomial infections against these extracts. The most potent antimicrobial plant was A. nilotica (MIC range 9.75-313µg/ml), whereas other

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Antimicrobial activity of five herbal extracts against multi drug resistant (MDR) strains of bacteria and fungus of clinical origin.

Antibacterial activity of some folklore medicinal plants used by tribals in Western Ghats of India.

The increasing recognition and importance of fungal infections, the difficulties encountered in their treatment and the increase in resistance to antifungals have stimulated the search for therapeutic alternatives. Essential oils have been used empirically. The essential oils of Thymus (Thymus vulgaris, T. zygis subspecies zygis and T. mastichina subspecies mastichina) have often been used in folk medicine. The aim of the present study was to evaluate objectively the antifungal activity of Thymus oils according to classical bacteriological methodologies - determination of the minimal inhibitory concentration (MIC) and the minimal lethal concentration (MLC) - as well as flow cytometric evaluation. The effect of essential oils upon germ tube formation, an important virulence factor, was also studied. The mechanism of action was studied by flow cytometry, after staining with propidium iodide. The chemical composition of the essential oils was investigated by gas chromatography (GC) and gas chromatography/mass spectroscopy (GC/MS). The antifungal activity of the major components (carvacrol, thymol, p-cymene and 1,8-cineole) and also possible interactions between them were also investigated. The essential oils of T. vulgaris and T. zygis showed similar antifungal activity, which was greater than T. mastichina. MIC and MLC values were similar for all the compounds tested. At MIC values of the essential oils, propidium iodide rapidly penetrated the majority of the yeast cells, indicating that the fungicidal effect resulted primarily from an extensive lesion of the cell membrane. Concentrations below the MIC values significantly inhibited germ tube formation. This study describes the potent antifungal activity of the essential oils of Thymus on Candida spp., warranting future therapeutical trials on mucocutaneous candidosis.

Edith Grein

Papers

Antibacterial activity of plant extracts used externally in traditional medicine