Antibiotic Activity of Herbal Plants
M. S. Wani
Antibiotics Study of Medicinal Plants
Long before mankind discovered the existence of microbes, the idea that certain plants had healing potential, indeed, that they contained what we would currently characterize as antimicrobial principles, was well accepted. Since antiquity, man has used plants to treat common infectious diseases and some of these traditional medicines are still included as part of the habitual treatment of various maladies. For example,
the use of cranberry juice (Vaccinium macrocarpon) to treat urinary tract infections is reported in different manuals of phytotherapy, while species such as lemon balm (Melissa ofﬁcinalis), garlic (Allium sativum) and tea tree (Melaleuca alternifolia) are described as broad-spectrum antimicrobial agents. That being said, it has generally been the essential oils of these plants rather than their extracts that has been the greatest use in the treatment of infectious pathologies in the respiratory system, urinary tract, gastrointestinal and biliary systems, as well as on the skin. For example, the use of the essential oil (tea tree oil) is a common therapeutic tool to treat acne and other infectious troubles of the skin rather than their extracts.1 In the present work, we analyze the past, present and future of medicinal plants, both as potential antimicrobial crude drugs as well as a source for natural compounds that act as new anti-infection agents.
In the past few decades, the search for new anti-infection agents has occupied many research groups in the field of ethnopharmacology.2 Reviewed the most relevant articles on this subject published between 1978 and 1988, compiling a list of 75 species in which the authors had established the activity of the extract along with both the spectrum and the principles responsible for this activity. In general, it showed that phenolic compounds are the predominant active chemical in plants, with Gram positive bacteria being the most sensible germs. The major problem with plants research, namely the lack of uniformity in the criteria selected to study the activity. This has in the past lead to relevant contradictions between the results obtained by different groups and even for the same authors studying the same sample with different methods.3 The solid dilution method was recommended for studying polar and non-polar substances as well as all types of complex extracts. This method is especially good for determining the relative potency of extracts or essential oils and for establishing their antimicrobial spectrum as it facilitates the use of different strains against the extract on the same plate. Finally, the liquid dilution method is the best way to establish the real potency of a pure compound, but solubility is an obvious requisite.4
To examine the problems i.e. lack of unified criteria more in depth, we can look particularly at the study of the antimicrobial activity of medicinal plants.5 The characteristics of these kinds of complex mixtures as well as the techniques used for studying them and concluded that the results are difficult to compare as the test methods differed so widely. They thus proposed that in future the strain number of the tested microorganism, the composition of the medicinal plants and the conditions under which it was obtained be included as an integral part of the report. Recently reviewed the classical methods commonly used for the evaluation of the antibacterial and antifungal activities of medicinal plants, including the agar diffusion method (paper disc and well), the dilution method (agar and liquid broth), the turbidimetric and impedimetric methods.6 Monitoring of microorganism growth in the presence of tested medicinal plants material to draw conclusions about the factors that influence the in vitro antimicrobial activity of plant extracts and their mechanisms of action. Moreover, they include an overview of the susceptibility of bacteria and fungi towards different extracts and their constituents.
The number of articles published on the antimicrobial activity of medicinal plants in PubMed during the period between 1966 and 1994, this number on the antimicrobial activity of plant extracts 187 references appeared in PubMed between 1971 and 2005; however, in a search processed by the ISI web of knowledge, the number of references for natural plants was much higher (323 between 1986 and 2005). These figures demonstrate the increased interest for this type of research among that portion of the scientific community dedicated to the investigation of the medicinal properties of plants. Many focus on determining the antimicrobial activity of plant extracts found in bulk medicine,7 essential oils,8 isolated compounds such as alkaloids,9 flavonoids,10 sesquiterpene lactones,11 diterpenes,12 triterpenes13 and naphtoquinones.14 Some of these compounds were isolated or obtained by isolation after previously detecting antimicrobial activity on the part of plant. Although this type of research is the most common, the selection of microorganisms is not well established, the assayed doses are extremely high, the positive control is not clearly defined or the methods are inadequate.
The study of medicinal plants as antimicrobial agents should be focused in part on ascertaining specific information about the plants antimicrobial activity, avoiding studies in which researchers use this criterion merely as a complement to a phytochemicals study. The isolation of active compounds should be undertaken in light of the known activity of the plant and likewise flora guided isolation of potential principles. Thus, when the activity of fractions and compounds is inferior to the total extract or fraction, rather than invalidating the results, this should confirm the known anti-infection properties of the plant. In the last 25 years, there was a predominant tendency to publish the activity of plants or natural products in isolation, but we think that the next 25 years should be spent in part on probing this activity more in depth. The fact that plant extracts exhibits activity is of interest, but it is only a preliminary piece of data and should be followed by the identification of the active compounds. The research should be kept up in order to uncover as much potentially interesting data as possible, including toxicity against animal or human cells, mechanisms of action, effects in vivo, positive and negative interactions with common antibiotics.
The last two decades have witnessed the growth of a new interdisciplinary field, termed ethnobotany, biochemistry ecological, phytochemistry, ethnopharmacognosy or ethnopharmacology which is basically concerned with the biochemistry of plant and microbe interactions in correlation to their pharmacological effect. It has also been due to the awareness of plant physiologist, we realise today that chemical substances and particularly secondary metabolites for example, alkaloids, tannins and saponins have a significant role in the complex interaction occurring between microbes, man, animal and plant in the natural environment. These developments have enormously expanded our knowledge of plant, animal and man interactions in the field of ethnopharmacology.15
Screening of Antimicrobial Plants
Plants are oldest source of pharmacologically active compounds, and have provided human kind with many medically useful compounds from centuries.16 Today it is estimated that more than two thirds of the world’s population relays on plant derived drugs.17 7000 medicinal compounds used in the Pharmacopoeia are derived from plants 18 In the USA approximately 25 % of all prescription drugs used contain one or more bioactive compounds derived from plants.19 Thus phytochemicals screening of plants species, especially of ethnopharmaceutical use, will provide valuable baseline information in the search for new pharmaceuticals. Yet fewer than 10 % of the plant species have been examined for the presence of bioactive compound.20 Hence screenings of antimicrobial plants for new agent possess an enormous challenge and are important especially with the emergence of drug resistant disease strains. During past 10 years has been a substantial resurgence of interest and pursuit of natural products discovery and development, both in the public and private sectors. This is possibly due to transient and increasingly sophisticated science that can be brought to bear on the discovery and development process.21 It has only been in the past two decades higher plant antimicrobial agent has been reawakened world wide and the literature in this area is becoming substantial.22
Antimicrobial Compounds and Plant Defense
Plant produced a diverse array of secondary metabolites, many of which have antimicrobial activity. Some of these compounds are constitutive, existing in healthy plants in their biologically active forms. Others such as cyanogenic glycoside and glucosinolates, occur as inactive precursor and are activated in response to tissue damage or pathogen attack. This activation often involves plant enzyme, which are released as a results of breakdown in cell integrity.23
Efficacy of Traditionally used Plants
The research for natural products to cure diseases represents an area of great interest in which plants have been the most important source. In Indian traditional medicine, the use of plants is a widespread practice and the persistence in the use of medicinal plants among people of urban and rural communities in Indian could be considered as evidence of their efficacy.24 Although there is an important local ethnobotanical bibliography describing the most frequently used plants in the treatment of conditions consistent with diseases, there are very few experimental studies, which validate the therapeutic properties of these plants.
Fungi differ from bacteria in possessing a number of chromosomes within a well defined nuclear membrane, mitochondria and reticulum. Like plants they have definite cell walls but these are usually composed of cellulose. They lack chlorophyll so they living either on dead organic material as saprophytes or on living organic matter as a parasites. The cell may live separately (yeasts) or more commonly, they form long multicellular filaments which may contain cross well or septa. A mass of filaments is a mycelium. Many species have both yeast and mycelial form which are dependent on the cultural conditions, a process known as dimorphism.25 The classification of fungi is based on the form of their sexual reproductive apparatus but there is a large group containing most of the human parasites, which have never been known to undergo sexual reproduction.
Antimicrobial Activity as Per WHO
The most important development with an international impact was initiated in 1979 by the World Health Organisation (WHO), which set up a Working Group within a special programme on safety measures in microbiology26. This group formulated a set of minimum standards for laboratory safety (Laboratory Biosafety Manual). This Manual has been revised periodically. The Manual includes the definition of four risk groups based on the relative hazard of infective micro-organisms to the laboratory workers, the community, the livestock and the environment. Although no list of infective agents is supplied, WHO recommends to each country to draw up their own classification by risk group of the agents encountered in that country based on the following factors27
- Pathogenicity of the agent.
- Mode of transmission and host range of the agent28.
These may be influenced by existing levels of immunity, density and movement of the host population, presence of appropriate vectors and standards of environmental hygiene. WHO also points out the necessity, when assessing the various criteria for classification, to take into account conditions prevailing in the geographical area in which the micro-organisms are handled. Individual governments should also decide to prohibit certain pathogens from being imported other than for urgent diagnostic purposes (quarantine organisms).29
Alternative (traditional) health care service
In Indian country, when modern medical services are insufficient to provide the population with basic curative attention. Traditional medical treatment, supported mainly by the use of medical plants, represents the main alternative methods which has its mainly undocumented scientifically and is still communicated verbally from one generation to the next. Many leads for further investigation could be discovered. So far few species of belongs to Cappariadacea family have been recorded with antimicrobial activity, of which a small percentage represents ethnomedical contribution from different parts of the country. However, similar studies particularly on Capparis species in other regions have not been conducted. Such information is expanded to be useful in maintaining the equilibrium between utilization and conservation of plant resources, as well as help development activities, which will provide local benefits.30
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- Recio, M. C., Rios, J. L. and Villar, A., 1989. Antimicrobial activity of selected Plants employed in the Spanish Mediterranean area. Part II. Phytotherapy Research, 3, 77–80.
- Otshudi, A. L., Foriers, A., Vercruysse, A., Van Zeebroeck, A. and Lauw-ers, S., 2000. In vitro antimicrobial activity of six Medicinal Plants Traditionally used for the treatment of dysentery and diarrhoea in Democratic Republic of Congo (DRC), Phytomedicine, 7, 167–172.
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- Janssen, A. M., Scheffer, J. J. C., Baerheim Svendsen, A., 1976. Antimicrobial activity of essential oils, Planta Medica, 53, 395–398.
- Kalemba, D., Kunicka, A., 2003. Antibacterial and antifungal properties of essential oils. Current Medicinal Chemistry, 10, 813–829.
- Ngwendson, J. N., Bedir, E., Efange, S. M., Okunji, C. O., Iwu, M. M., Schuster, B. G. and Khan, I. A., 2003. Constituents of Peucedanum zenkeri seeds and their antimicrobial effects, Pharmazie, 58, 587–589.
- Alma, M. H., Malvi, A., Yildirim, A., Digrak, M. and Hirata, T., 2003. Screening chemical composition and in vitro antioxidant and antimicrobial activities of the essential oils from Origanum syriacum L. Bioplogical and Pharmaceutical Bulletin, 26, 1725-1729.
- Klausmeyer, P., Chmurny, G. N., McCloud, T. G., Tucker, K. D. and Shoe-maker, R. H., 2004. A novel antimicrobial Indolizinium alkaloid from Aniba panurensis, J. of Nat. Products, 67, 1732– 1735.
- Sohn, H Y., Son, K. H., Kwon, C. S., Kwon, G. S. and Kang, S. S., 2004. Antimicrobial and cytotoxic activity of 18 prenylated flavonoids isolated from Medicinal Plants: Morus alba L., Morus mongolica Schneider, Broussnetia papyrifera (L.) Vent Sophora. avescens Ait and Echinosophora koreensis Nakai, Phytomedicine, 11, 666–672.
- Lin, F., Hasegawa, M. and Kodama, O., 2003. Purification and identifications of antimicrobial sesquiterpene lactones from yacon (Smallanthus sonchifolius) leaves, Biotechnology and Biochemistry, 67, 2154–2159.
- El-Seedi, H. R., Sata, N., Torssell, K. B. and Nishiyama, S., 2002. New Labdene Diterpenes from Eupatorium glutinosum, J. of Nat. Products, 65, 728–729.
- Otshudi, A. L., Foriers, A., Vercruysse, A., Van Zeebroeck, A. and Lauw-ers, S., 2000. In vitro antimicrobial activity of six medicinal plants traditionally used for the treatment of dysentery and diarrhea in Democratic Republic of Congo (DRC), Phytomedicine, 7, 167–172.
- Machado, T. B., Pinto, A.V., Pinto, M. C., Leal, I. C., Silva, M. G., Amaral, A. C., Kuster, R. M. and Netto-dos Santos, K. R., 2003. In vitro activity of Brazilian Medicinal Plants, naturally occurring naphthoquinones and their analogues, against methicillin-resistant Staphylococcus aureus, Int. J. of Antimicrobial Agents, 21, 279–284.
- Barbour, E. K., Sharif, M., Sagherian, V. K., Habre, A. N., Talhouk, R. S. and Talhouk, S. N., 2004. Screening of selected indigenous Plants of Lebanon for antimicrobial activity, J. of Ethnopharmacology, 93, 1–7.
- Cordell, G. A., 1981. Introduction to the Alkaloids Biogenetic approach. John Wiley and Sons Publication, New York. P p. 892.
- Anon, J. W. 1987. The research for new drugs from natural sources. Pharmacy Times, 50, 32-39.
- Caufield, C., 1991. In; The Rain Forest. The Oxford University Press. Chicago, 58-67.
- Farnsworth, N. R., and Morris, R. W., 1976. Higher Plants the sleeping giant of drug development, American J. of Pharmacy, 148, 46-50.
- Meyer, J. J. M., Afolayan, A. J., Taylor, M. B. and Engelbrecht, L., 1996. Inhibition of herbs simplex virus Type- I by aueous extracts from shoots of Helichrysum aureonitens, J. of Ethnopharmacology, 52, 41-43.
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- Van Etten, H. D., Mansfield, J. W., Bailey, J. A., and Farmer, F. E., 1994. Letters to editor. Two class of plant antibiotics: Phytoalexins versus phytoanticipins, Plant cell, 6, 1191-1192.
- Hammond-Kosack, K. E. and Jones, J. G., 1996. Resistance gene- dependent Plant defense response, Plant cell, 8, 1773-1791.
- Meyer, J. J. M., and Marion, M. H., 2000. Antimicrobial properties from Helichrysum caespititium, Phytochemistry, 53, 93-96.
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- Lake, S. and Pruner, M. S., 1989. Flavonoid structure and activity relation of flavonoid phytoalexin analogue, Phytochemistry, 28(1), 87-91.
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Prof.Manish S. Wani
Working as Lecturer at MAEER’s Maharashtra Institute of Pharmacy, MIT campus, Pune. He has done his M.Pharm in Pharmaceutics from Pune University. He has also done his MBA from Pune University
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Working as Principal and Professor in Pharmaceutics at MAEER’s, Maharastra Institute of Pharmacy, MIT Campus, Pune-411038
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