Medicinal Plants with Anti-mycobacterial Activity!
Over the past decade there has been a proliferation of literature on the antibacterial, anti-tuberculosis, antifungal and antiviral properties of plant extracts. Screening plant extracts for anti-mycobacterial activity is usually carried out using mycobacteria cultured in various types of broth and agar based media.
There are several reports on in vitro inhibition of mycobacterium species by medicinal plants and the bioassay-guided research for anti-mycobacterial properties from plants has shown signs of success. Major review articles have appeared on anti-mycobacterial natural products in the last eight years.
Although no marketable products for the treatment of tuberculosis have been isolated from plants, some lead compounds have been identified.
Mitscher and Baker discussed plant-derived compounds (berberine, lichoisoflavone, erygibisoflavone, phaseollidin, erythrabyssin II and tryptanthrin) as potential anti-tuberculosis agents. Newton et al., 2000 reviewed plant-derived anti-mycobacterial natural products, describing the activity of extracts and compounds from 123 plants species.
Reports of 88 naturally occurring compounds and synthetic analogues from plants, fungi and marine organisms, that demonstrated significant activity in the in vitro bioassays against M. tuberculosis and other mycobacterial species, have been described.
Recent developments in myco-bacteriology and innovative natural products chemistry tools and their potential to impact on the early steps of the TB drug discovery process have been reviewed. Gautam et al., 2007 described 70% of Indian medicinal plant species, from a wide range of families, which have shown anti-mycobacterial activity.
Interestingly, when tested preliminary in the in vitro screening, 149 species have shown positive ethno medicinal uses in correlation with the traditional knowledge for TB or related diseases.
Ten of the 408 ethanolic extracts of plants such as Actaea spicata, Angustura vera, Cinnamonium camphora, Piper cubeba, Cuauacum officinale, Ipomea purga, Rhamnus cathartica inhibited growth of M. tuberculosis H37Rv at dilutions of 1 in 160 to 1280 and a high proportion of the other extracts inhibited growth at lower dilutions.
It was found that M. tuberculosis was also sensitive towards Pentas longifolia, Tetradenia riparia and Bidens pilosa, medicinal plants used in Rwanda. The active compound isolated from the leaves of T. riparia was tested against M. tuberculosis which showed activity at 100 µg/ml.
Hydrocotyle asiaticum inhibited growth of M. tuberculosis at a dilution of 1:20. Organic extracts of Helichrysum crispum inhibited the growth of M. tuberculosis.
Lall and Meyer (2001) demonstrated the inhibition of drug-sensitive and drug-resistant strains of M. tuberculosis by diospyrin isolated from the roots of Euclea natalensis AD. The phytochemical and biological studies of E. natalensis and isolated compounds from this plant indicated in vitro activity against M. tuberculosis.
In structure-activity related studies against M. tuberculosis different research groups have found activity using a variety of natural products with no definite trend towards a specific group of compounds.
In South Africa, it has been reported that people smoke dried flower and seed of Helichrysum krausii in a pipe for the relief of coughs and as a remedy for pulmonary tuberculosis. Chelerythrine isolated from methanolic root extracts of Sanguinaria canadensis was found to be the most active isolated compound against M. smegmatis at 29.0 µg/ml.
Plants have been endowed with therapeutic virtues both in legend and in scientific literature and are being used in treating various ailments such as coughs, colds, other pathogenic bacterial and viral infections.
The use of antimicrobials from the natural vegetation has a great impact in human health care in undeveloped countries. Herbal medicine has been used for centuries in rural areas by local healers and has been improved in industrialized countries.