Database of Plants with Antimicrobial Activity

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Parasites predate their hosts in evolution and then co-evolved with their hosts. Parasites bypass the hosts’ internal and external defences and provide templates and direction for the hosts immune system. These points have an important role in our decisions on the choice of plants against specific pathogens.

Most diseases are caused by micro-organisms and several of these are contagious. Particularly devastating are the gastro-intestinal infections and diseases like tuberculosis and malaria.

The following are the common tropical diseases caused by microbial parasites:

MICROBIAL PARASITIC DISEASES

VIRAL: Smallpox; Chickenpox; Measles; Rubella; Mumps;Influenza; Rabies; Encephalitis;

Poliomyelitis; Hepatitis; Yellow fever; Dengue.

MYCOPLASMAL: Pneumonia.

RICKETTSIAL: Typhus.

SPIROCHAETAL: Syphilis.

BACTERIAL: Cholera; Typhoid; Paratyphoid; Tuberculosis; Leprosy; Plague; Anthrax; several types of dysentery and diarrhoea.

FUNGAL: Aspergillosis; Candidiosis; Mycoses of the lungs, skin, eye, nose, mouth, intestines, rectum, and vagina.

PROTOZOAL: Malaria; Amoebiosis; Meningitis; Encephalitis; Leshmaniasis; Trypanosomiasis; Giardiasis; Toxoplasmiasis; Balantidiasis.

In the ancient Ayurvedic literature, pathogens and pathogenesis were not known the same way as we understand them today. Nevertheless, over 300 species of plants were recorded by Charaka and Sushrutha, against diseases which we now recognise as infectious (Sathyanarayana Bhat, 1993).

Initially sulphonamides and later a battery of antibiotics have brought immense relief from microbial infections, but yet there is a great need for more antimicrobial agents, directed against specific pathogens. The phenomenon of acquired resistance reduces the effectiveness of drugs over a time and perpetuates the need for new drugs. This is true of all microbial diseases. Today, antimicrobial agents are one of the prime concerns of medicine and there is an ever increasing demand for these. Consequently, plants with antimicrobial activity were one our priorities. We recorded separately, plants with antibacterial, antiviral, antifungal and antiprotozoal activity. Several species appear in more than one category.

PLANTS WITH ANTIBACTERIAL ACTIVITY

Our survey of literature, old and recent, resulted in a staggering number of 771 species mentioned directly or indirectly, as antibacterial (Appendix 1). Several of these species have been tested for in vitro antibacterial activity, by different workers. Some were also tested by us (Appendix 37). There is a lot of scope for work in this area, in identifying pathogen-specific activity.

In recent times there has been a realisation that certain bacterial diseases, such as tuberculosis and leprosy, have again become a serious threat, as the pathogens became resistant to antibiotics, that were considered very effective till recently. More disturbing is the finding that the much trusted BCG vaccination against tuberculosis has not been that effective. There is a need to identify plants effective against such diseases. Species known for antituberculosis activity are listed separately in Appendix 1.

PLANTS WITH ANTIVIRAL ACTIVITY

Viral infections are much more difficult to handle than bacterial infections. In the case of bacteria, disruption of the synthesis of the bacterial cell wall or replication of DNA or protein synthesis are the basis of action of the controlling agents. In bacteria, these aspects operate on the basis of molecular parameters that are different from those of the human system. As a consequence, a drug that affects the pathogen’s biosynthetic pathways does not very adversely affect those of the human system. Viruses utilise the host’s biochemical and molecular machinery for nucleic acid replication and protein synthesis and hence, a drug that affects the biosynthetic pathways needed for viral multiplication equally affects the host’s system too.

There are hardly any effective antiviral drugs. Interferon therapy, which costs US$ 14,000 to 20,000 a treatment cycle, does not seem to work in over 50 per cent of the cases. Only for a few viral pathogens there are vaccines, whose effectiveness is neither uniform nor always without adverse reactions. There have been reports of polio vaccine causing the ailment. Hence, antiviral agents, from biological sources, are of great interest.

A number of species of plants seem to have antiviral activity which does not very adversely affect the host. This was also reflected in traditional medicine, as for example the successful treatment of jaundice. A list of 96 species with antiviral activity is given in Appendix 2. Thirty six species used against jaundice are separately listed.

PLANTS WITH ANTIFUNGAL ACTIVITY

Fungi affect the external and internal surfaces of our body, causing particularly, the dermatoses, while a few, like Candida albicans affect the mucous membrane of the mouth, throat, vagina or the gut. While there are some antifungal drugs, there are fewer antifungal antibiotics. There is also the belief that plants with antifungal activity are too few. That this impression is erroneous is refcted by the list of 263 species of plants with antifungal activity (Appendix 3).

PLANTS WITH ANTIPROTOZOAL ACTIVITY

The most devastating protozoal pathogens belongs to the genus Plasmodium, four species of which cause malaria, a disease that has altered the course of human history many a time. The most effective drug against the malarial parasite, the alkaloid quinine, came from the species of Cinchona. A number of synthetic substitutes have been developed to treat malaria which gave a false hope of a total control of the disease. Of late, strains of Plasmodium, resistant to drugs, due to acquired resistance, have appeared. The severity of the situation has made the WHO issue global warnings calling for new effective control measures, before the disease goes totally out of control once again. Coupled with a reversion to the native alkaloid quinine, there is a renewed search for antimalarial drugs of plant origin.

The gene (Pgh1) that imparts resistance in Plasmodium falciparum to mefloquine, quinine, nalofantsrine, chloroquine and artemisinin, has been identified recently (Reed et al., 2000). An effective antimalarial drug should be outside the influence of this gene.

Amoebic dysentery caused by Entamoeba hystolytica is a common protozoal infection. Another common protozoal infection is caused in the vagina by Trichomonas vaginalis. As with malaria, for amoebic dysentery too, the earlier most effective drug was plant based, the alkaloid emetin from Cephaelis ipecacuanha (Rubiaceae).

A list of 55 species with antiprotozoal activity is given in Appendix 4. Sixteen species with antimalarial and three with antiamoebic activity are separately listed. Several species with anti-amoebic activity also seem to be good emetics (discussed later on).

Two hundred and twenty species were selected (Appendix 5), from Appendices 1 to 4, for a detailed treatment in the ‘Database of plants with antimicrobial activity’ (Sathyanarayana Bhat, 1993). Information on the botany, vernacular names (in Bengali, Hindi, Marathi, Samskrit, Kannada, Tamil, Telugu and Tulu), habit, ethnopharmacology, ethonotherapeutics, uses as food, phytochemistry, pharmacognosy, cultivation, marketing aspects, etc., has been provided for each species. The profiles of Costus speciosus and Piper nigrum are presented in Appendix 6, as specimens from this database. Discussion on the concepts of infection in ancient literature, taxonomical and nomenclatural specialities of ancient literature, law of signatures, extensive literature citations and a glossary of terms, are included in this database.