Introduction

Herb is an immeasurable wealth of nature not only from the global environmental perspective but also from the medicinal point of view. It plays a significant role ameliorating the disease resistant ability and combating against various unfavourable metabolic activities within the living system. Numerous infectious diseases have been known to be controlled by herbal remedies that have been proved variously since primitive to present history of the mankind. Since time immemorial, man has used various parts of plants in treatment and prevention of various ailments ( ₁ ). Unimaginably unrevealed and unmatched varieties of compounds are present in the diversified herbs on earth. From these points of view, it is obvious that natural products, either in the form of pure compounds or as standardized plant extracts, provide unlimited opportunities to develop a variety of new drugs.

Antibiotic resistance has become a global concern ( ₂ ). The clinical efficacy of many existing antibiotics is being threatened by the emergence of multidrug-resistant pathogens ( ₃ ). There is a continuous and urgent need to discover new antimicrobial compounds with diverse chemical structures and novel mechanisms of action for new and re-emerging infectious diseases ( ₄ ). Therefore, researchers are increasingly turning their attention to folk medicine, looking for new leads to develop better drugs against microbial infections ( ₅ ). The increasing failure of chemotherapeutics and antibiotic resistance exhibited by pathogenic microbial infectious agents has led to the screening of several medicinal plants for their potential antimicrobial activity ( ₆₇ ). Recent, studies have suggested that several plants species exhibit promising antimicrobial effects ( ₈ ). Plant-based antimicrobials have enormous therapeutic potential as they can serve the purpose with lesser side effects that are often associated with synthetic antimicrobials ( ₇ ). In recent years, it has been proposed that the herbal extracts may be used as natural antifungal agents to inhibit the growth of foodbrone pathogen ( ₉ ) and as a source of various medicinal agents ( ₁₀ ).

From the above understanding, the present study has been focused on three wild herbs, Asteracantha longifolia (Fam: Acanthaceae English name: Hygrophila, Local name: kulekhara), Ipomoea aquatica (Fam: Convolvulaceae, English name: water spinach, Local name: Kalmi) and Enhydra fluctuans (Fam: Convolvulaceae, English name: Enhydra, Local name: Helencha), usually found in moist places on the banks of tanks, ditches, paddy fields, etc., throughout India and commonly used as green vegetable. Asteracantha longifolia is a source of the Ayurvedic drug Kokilaaksha and the Unani drug Talimakhana and its seeds are acrid, bitter, aphrodisiac, tonic, sedative, and useful in diseases of the blood ( ₁₁ ). Enhydra fluctuans has been used in Indian medicine in treatment of nervous ailments, skin diseases and as a laxative ( ₁₂ ).

However, from the above account, it is obvious that there is no information available about the antimicrobial activity of these herbs. The present investigation was designated to explore the antibacterial activity of methanol extract of the above mentioned herbs.

Materials and methods

Collection and identification of plant materials

Preparation of plant extract

Bacterial strains

Preparation of bacterial culture

Antimicrobial activity assay

Statistical analysis

Results

Antimicrobial activity of

Antimicrobial activity of

Antimicrobial activity of

There was also a clear variation of antimicrobial activity of E. fluctuans extract in all strains of bacteria tested (P < 0.05, ANOVA). Likewise the response of A. longifolia extract, no clear zone was created in P. aeruginosa and a very small clear zone (0 – 8 mm) was also found in the remaining bacterial strains (Figure 1c). Mean value of the clear zone was maximum in S. aureus and followed by E. coli and M. luteu. In E. coli and S. aureus, the clear zone was started from concentration of extract 30 mg/ml, whereas the clear zone appeared in the highest concentration (60 mg/ml) in M. luteu.

Figure 1

Figure 1. Antimicrobial activity of (a), (b) and (c) on four pathogenic bacterial species examined.

Discussion

Agar well diffusion assay of extract activity showed a variable clear zones, 0 to 10.7 mm, 0 to 10 mm and 0 to 8 mm in different extract concentrations of A. longifolia, I. aquatica and E. fluctuans, respectively. Above obtained results of the present study clearly demonstrated that though there were variations but methanol extract of A. longifolia, I. aquatica and E. fluctuans have an antimicrobial activity against pathogenic bacteria, S. aureus, P. aeruginosa, E. coli and M. luteu. According to Pawar, A. longifolia is variously used in ayurvedic drug (Kokilaaksha), Unani drug (Talimakhana), tonic and sedative preparation as well as it is also used for the treatment of the blood disease ( ₁₁ ).

The mean values of the clear zone in S. aureus were1.17 to 3.85, 1.02 to 1.45 and 1.14 to 2.58 times greater compared to that of the remaining bacteria in A. longifolia, I. aquatica and E. fluctuans, respectively (Figure 2). Present results obviously implied that the methanol extract of three types of herbs have a higher antimicrobial efficacy against the S. aureus over P. aeruginosa, E. coli and M. luteu.

Figure 2

Figure 2. Mean of clear zone for antimicrobial activity of three herbs against four bacterial species tested.

Though no clear zone was found in the methanol extract of the A. longifolia and E. fluctuans against P. aeruginosa, but the mean values of the clear zone of the I. aquatica extract exhibited 7.4 mm in P. aeruginosa. I. aquatica showed 28 to 118% (in E. coli), 12 to 96% (in S. aureus) and 200 to 250% (in M. luteu) higher antimicrobial efficacy than that of the remaining two herb extracts. Therefore, it may be concluded that I. aquatica exerted a higher magnitude of antimicrobial activity against the tested four types of bacterial species compared to that of the rest two herb extracts. In this context, furthermore it is obvious that A. longifolia and E. fluctuans herbs have no activity against the P. aeruginosa as no clear zone was found.

On account of the above critical appraisal of data, therefore, it could be concluded that (i) I. aquatica has potentially higher antimicrobial efficacy when three herbs species is considered and all tested herbs have a promising antimicrobial efficacy against S. aureus than that of the remaining bacteria examined, (ii) Differential antimicrobial activity of one herb against different bacteria only due to present of different active phytocompounds of an herbs and (iii) Compositional variation of herb active biomolecules in different plants is responsible for exertion of differential antimicrobial activity. It is anticipated that phytochemicals with adequate antibacterial efficacy will be used for the treatment of bacterial infections ( ₁₄ ). Secondary plant metabolites (phytochemicals compounds have been extensively investigated as a source of medicinal agents ( ₁₀ ). Among those antimicrobial compounds, phenolic compounds, terpenoids, and alkaloids’ are very important compounds in antimicrobial or antioxidant effects ( _151617181920 ). Further research is necessary to determine the different antibacterial compounds from these herbs and their full spectrum of efficacy. However, the present study of in vitro antimicrobial evaluation of these herbs forms a primary platform for further phytochemical and pharmacological studies. These promissory extracts open the possibility of finding new clinically effective antimicrobial compounds.

Acknowledgements