ANTIMICROBIAL ACTIVITY OF MORINDA LUCIDA AND DIALIUM GUINEENSE LEAVES ON SOME BACTERIAL PATHOGENS

ABSTRACT

The antimicrobial activity of the extracts of the leaves of Morinda lucida and Dialium guineense were investigated to ascertain their inhibitory activities against some bacterial pathogens. The aqueous and methanolic extracts of both plants were tested against Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Enterococcus faecalis and Staphylococcus aureus using the Agar well diffusion method. The methanolic crude leaf extracts of both plants, inhibited the growth of the organisms, but only the aqueous extract of Dialium guineense showed antimicrobial activity. The diameter zones of inhibition ranged from 7mm to 15mm. The Minimum inhibitory concentrations (MIC) of the extracts were determined using the broth dilution method and ranged from 25 to 50mg/ml. The phytochemical analysis carried out on both plant leaves showed that they contained Alkaloids, Flavonoids, Saponins and Terpenoids. The percentage phytochemical constituents of the leaves of Morinda lucida and Dialium guineense were as follows; Alkaloid (0.64-1.70%), Terpenoid (1.52-1.78%), Saponin (1.92-2.04%) and Flavonoid (0.84-1.58%). The results obtained indicated that the leaves of the plants have antimicrobial activities and can be utilized in the treatment of some ailments.

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CHAPTER ONE

1.1     INTRODUCTION

Plants, being a source of food to man over the years have been used for medicinal purposes as it is estimated that only about 1-10% of these plants are used as food but more, are used for medicinal purposes (Moermen, 1996). Right from biblical times, plants like frankincense and myrrh were of great importance and were used as antiseptics due to their medicinal properties (Majorie, 1999). Herbal medicine or Phytomedicine is the use of herbs, herbal, materials, herbal preparation and finished herbal products that contains parts of plants as active compounds. These plants parts includes seeds, leaves, fruits, barks or roots (WHO Media Center, 2013).

With the advent of conventional medicines over the past century, herbal medicines have been challenged by practitioners of mainstream medicine who have remained indifferent to the acceptance of herbal medicine because of lack of scientific evidence in the context of contemporary medicine despite its long history of effective use (Pan et al., 2010). Despite the popularity of modern medicines and the variety of drugs available for various ailments, it has been observed that 85% of patients combine herbal therapy with the drugs prescribed at hospitals and clinics. This shows that people show a level of confidence in herbal medicines (Amira et al., 2007). In Nigeria, there is a large market for herbal medicines, due to the fact that most of these western medicines are expensive to buy, there is continuous emergence of strange illnesses and there is also lack of good and affordable health facilities (Mafimisebi et al., 2013 ) but in recent years, there have been a resurgence of the use of herbs due to various reasons which ranges from; side effects of chemical drugs, lack of curative modern therapies for several chronic diseases, microbial resistance which is continuously occurring due to the short-life span of antibiotics gotten from microorganisms and the discovery by pharmaceutical companies and scientists that plant derived compounds have a potential for many biological activities which includes antimicrobial activity (Pan et al., 2010; Savoia, 2012) , discovery of bioactive compounds in plants which may serve as an alternative to existing antimicrobials, to the fact that they are comparatively cheap and since they are gotten from the environment, are in constant supply. Also, with the advent of diseases such as Human immunodeficiency virus (HIV) and Ebola which have defiled the efficiency of existing antibiotics, scientist have spurn into intensive investigation into plant derivatives for alternatives (Majorie, 1999). Therefore efforts should be made to preserve these medicinal plants from extinction.

Plants have limitless ability to produce aromatic substances, most of which are phenols or their oxygen substitute derivatives (Geissman, 1963). The derivatives are thought to impact toxicity to microorganisms by non-specific interactions with their proteins (Mason et al., 1987). The use of the plant parts which are termed medicinal is due to the presence of these secondary metabolites produced by these plants as defense[F1]  mechanism against predation by microorganisms, insects and herbivores (Majorie, 1999; Vaghasiya et al., 2011). The presence and quantity of these secondary metabolites is what determines the usefulness of a plant to herbal medicine (WHO Media Center, 2013). Just like frankincense and myrrh, another plant that have shown medicinal property is thyme whose medicinal property is due to the presence of Cafeic acid and is reported to have antibacterial (Brentner et al., 1997), antiviral (Wild, 1994) and antifungal capabilities (Duke, 1985).

These herbal medicines are either prepared as tinctures, are applied topically, or inhaled through steam, with water as the mostly used solvent. The preparation method of these medicinal plants into therapeutic use is important to retain its medicinal property, due to the fact that most active plant compounds are aromatics or saturated organic compounds; they are most often obtained using alcohol. Therefore it is expected that the alcoholic extracts, shows more broad spectrum of activity than other extracts prepared using other solvents or preparation methods (Majorie, 1999). Plants containing Phenolic derivatives which includes; Tannins and Flavonoids are used as healing agents for a number of diseases (Ololade et al., 2014). Terpenoids gives plants their odor and are inhibitory to both Fungi and Bacteria (Chaurasia et al., 1977), Quinones render substrates unavailable to the microorganisms. Tannins, Saponins and Flavonoids are thought to impact toxicity to microorganisms by non-specific interactions with their proteins (Majorie, 1999). Tannins have been known to display different biological activities including antifungal and antibacterial. (Savoia, 2012; Balls et al., 1942; Compean, 2014).

1.1       General aim

This study aims at assessing the extracts of the leaves of Morinda lucida and Dialium guineense for their antimicrobial activity on some selected bacterial pathogens.

1.2       Specific aim and objective

1. To investigate the scientific basis for the traditional use of the test plants Morinda lucida and Dialium guineense among people in Nigeria for treating ailments related to microbial infections with extracts from them .
2. To assess the capacity of the leaves extracts of the test plants to inhibit the growth of the test organisms. 

1.3       JUSTIFICATION OF THE STUDY

Traditional medicine is mostly dominated by herbalists who have used various herbs to produce concoctions which are believed to give cure to different ailments. This practice is usually passed on from generation to generation through oral tradition. These concoctions are not standardized and the bioactive ingredients are unknown to these herbalists. People increasingly patronize these herbal mixtures for cure, especially in areas where western medicine can’t be readily accessed. Scientists have now begun to look into these medicinal plants to discover their active ingredients that could be used as alternative to synthetic drugs. Therefore, the identification of these medicinal plants, the knowledge of the proper means of obtaining their extracts to produce antimicrobial drugs for treatment of ailments, the appropriate concentration for the treatment the knowledge of the mechanism of action of these bioactive compound present in the plant and the group of microorganisms it is active against, is important for the safety, control and acceptability of the general public. Therefore the identification of these medicinal plants and the knowledge of the proper means of obtaining their extracts to produce antimicrobial drugs for the treatment of ailments are necessary. This study emerged as a means to discover the bioactive components in the study plants gotten from our natural environment and the bacterial pathogens which it can effectively be used against. These bacterial pathogens have discovered new ways to evade the effect of existing antibiotics and are doing so by the day and as such, require that scientists go into research for the discovery of new substances can be used to improve the effect of the existing ones or to find replacements for them. Agencies and individuals to benefit from this study include; pharmaceutical companies, researchers who needs further information about these plants and their activities.

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