**5. References**

142 Antimicrobial Agents

as topical antiseptics, or have been reported to have antimicrobial properties (Hoffman 1987 and Lawless 1995). It is important to investigate scientifically those plants which have been used in traditional medicines as potential sources of novel antimicrobial compounds (Mitscher *et al.,* 1987). Also, the resurgence of interest in natural therapies and increasing consumer demand for effective, safe, natural products means that quantitative data on plant

Majority of studies conducted the search of compounds with antimicrobial properties have targeted plants with a history of ethno botanical uses (Janovska *et al.,* 2003), most of the medicinal plant species screened in this study were previously been surveyed for antimicrobial activities on human pathogens. And very few citations were reported on phytopathogens (Kaushik and Arora, 2003; Jaspal singh and Tripathi, 1993; Krishna kishore and Suresh pande, 2005; Meena and Goplakrishnan, 2005). The observed antimicrobial

The present study was designed to obtain information on the antimicrobial effect of 50 Indian medicinal plants on certain plant pathogenic microorganisms. The well diffusion/cup plate method was used in this study since it was found to be better than the disc diffusion method. All the medicinal plant extracts and isolated compounds showed

Hexane extracts never showed antimicrobial activity. The chloroform and water extracts showed very less antimicrobial activity compared with methanol extracts. This may be due to little diffusion properties of these extracts in the agar or because fresh plants contain active substances which may be affected or disappeared by the steps of extraction

The methanol extracts of all the medicinal plant screened (Table-1) exhibited grater antimicrobial activity. According to Darout *et al.,*(2000) the antimicrobial action of methanol extracts is due to the compounds such as thiocynate, nitrate, chloride and sulphates beside other high polarity soluble compounds which are naturally occurring in most plant

Methanolic extracts of *T. chebula, B. Montana, M. azadirach, W. somnifera, O santum* and *P. pterocarpum* showed greater antimicrobial activity. *Terminalia chebula* possessed 32-40% of tannin content and the antibacterial activity may be indicative of the presence of some metabolic toxins or broad-spectrum antibiotic compounds (Fundter *et al.,* 1992). *M. azadirach* was exhibited good antimicrobial activity against most of the tested pathogens in this study. According to Jacobson, (1995) this activity is due to Nimbidin, extracted from *M. azadirach* demonstrated several biological activities. From this crude principle some tetranortriterpenes, including nimbin, nimbinin, nimbidinin, nimbolide and nimbidic acid

The observations reveal that tested medicinal plant methanol extracts activity against all phytopathogenic species. As evidenced, the fungal strains that were sensitive are *M. phaseolina*, *R. solani* species, *C. graminicola* and *F. moniliforme* found to be resistant strains. Among the tested medicinal plants methanol extracts against the phytopathogenic species, *Terminalia chebula* extracts showed greater antimicrobial activity on all plant

activity of these plant extracts, and isolated compounds were of highly remarkable.

antimicrobial activity against selected pathogens of Sorghum.

have also been showing antimicrobial activities.

oils and extracts are required.

methods.

materials.

pathogens.


(http://www.apsnet.org/online/common/names/sorghum.asp).


**8** 

*Thailand* 

Aphichart Karnchanatat

*Chulalongkorn University, Bangkok,* 

*The Institute of Biotechnology and Genetic Engineering,* 

**Antimicrobial Activity of Lectins from Plants** 

There are at least three reasons for the need in finding out new alternative antimicrobial substances from natural sources. The first reason is that people nowadays concern about toxic of synthetic substances including daily contact chemicals or even drugs used in medical or healthcare purposes (Hafidh et al., 2009). Any synthetic drugs were avoided in order to keep physiological cleans as belief. Thus, natural substances were used increasingly instead as well as any substances used for antimicrobial purposes. The second reason is that new alternative drugs are human hope for better fighting with existed diseases and pathogens. They may replace currently used drugs in points of more efficiency, more abundant, lower side-effect or safer or even lower production cost. It is fact that most alive organisms should have some mechanisms or substances fight with all time contacting pathogens so that they can be survived in nature. Although a plenty of antibiotics were discovered after first time Fleming's declaration, but they were still relatively low amounts compared with overall real natural antimicrobial substances. This mean the natural sources still flourish with novel antimicrobial substances waiting for discovered. Additional small aspect may be raised here. The natural substances are usually good leading compound sources for mostly synthetic drug from the long past due to their diversities are far from human imagination. New chemical structures are always found in natural resources as higher frequency than artificial deducing structures. The final reason is that the mechanism used to synthesize natural substances are available and they are usually can be imitated in small, medium, and even large scale production with present biotechnological knowledge

Plants are of primary importance in the global ecosystem. They are, together with a small group of bacteria, the only living organisms which are capable of harvesting and storing solar energy by virtue of their photosynthetic apparatus which converts light energy into chemical energy through the reductive assimilation of carbon dioxide. Marine and terrestrial plants are the first link in the global food chain. Virtually all other life on earth depends on the organic molecules they synthesize. Evidently, the fact that the majority of heterotrophic organisms depends on them makes plants favorite targets of a whole variety of parasites and predators. Therefore, plants must defend themselves against their potential enemies. During the past 15 years, a large number of antimicrobial proteins (AMPs) have been identified in different plants (Broekaert et al., 1997). AMPs constitute a heterogenous class of low molecular mass proteins, which are recognized as important components of defense

**1. Introduction** 

which looks easier than newly designed plants.

