CHAPTER ONE

1.0 INTRODUCTION

Allium cepa. (Onion) belongs to the family Alliaceae, is also known as ‘garden onion or ‘bulb’onion. It is one of the oldest cultivated vegetables in history. It is thought that bulbs from the onion family have been utilized as a food source for millennia. Above ground, the onion shows only a single vertical shoot, the bulb grows underground, and is used for energy storage, leading to the possibility of confusion with a tuber which it is not (Wikipedia, 2013). The leaves are bluish-green and hollow, the bulbs are large, fleshy and firm (Azu et al., 2007). Three main varieties of onion are available viz; red, white and purple skinned (Ying and Wang, 1996).

Onions are easily propagated, transported and stored. Onions are effective against common cold, heart disease, diabetes, osteoporosis, coughs and sore throat (Augusti, 1996). They also act as bacteristatic (Saulis et al.,2002). Certain chemical compounds believed to have anti-inflammatory, anti-cholesterol, anticancer and antioxidant properties such as quercetin are present in onions (Wilson and Demmings-Adams, 2007). They are high in flavonoids which is concentrated on the outer layer of the flesh (Nemeth and Piskula, 2007; Wang et al., 2009). Onions are also high in polyphenols than other allium vegetables (Wang et al., 2009).

Onions (Allium cepa) possess strong, characteristic aromas and flavours, which have made them important ingredients of food. Onions and onion flavours (essential oil) are important seasonings widely used in food processing. Recent research has demonstrated that onions possess several biological properties, such as antibacterial (Griffiths et. al., 2002), antimutagenic (Singh et al., 2009) and antioxidant activities (Dini et al., 2008). The medicinally most significant components of onion oil are the organosulfur-containing compounds (Dron et al.,1997; Sinha et al.,1992).These compounds are reactive, volatile, odour producing and lachrymatory (Block et al., 1992).

Onion is rich in proteins, carbohydrates, sodium, potassium and phosphorus (Lampe, 1999). Onion was consumed throughout Europe during the middle ages and was later thought to guard against evil spirits and the plague, probably because of their strong odor (Blumenthal, 1999). The plant is used as traditional remedy in the treatment of various disorders so it has particular medicinal importance (Grifiths et al., 2002).

It has been reported that Allium cepa has antibacterial, antiviral, anti-parasitic, antifungal properties. It is also antihypertensive, hypoglycemic, antithrombotic, anti-hyperlipidemic, anti-inflammatory, and antioxidant (Robertson and Heymann, 2006). Allium cepa extracts has been widely studied for its antimicrobial activity.( Kim et al.,1997) reported its antibacterial activity against Streptococcus mutans, Streptococcus sobrinus, Prevotella intermedia and Porphyromonas gingivalis. Benkeblia et al., (2004) investigated antimicrobial activity of different concentrations (50, 100, 200, 300, 500 ml/l) of essential oil extracts of three types of onions (green, yellow and red) and garlic against two bacteria, Staphylococcus aureus, Salmonella enteritidis, and three fungi, Aspergillus niger ,Penicillium cyclopium, and Usarium oxysporum. Green onion showed the lowest antimicrobial activity (Zohri et al.,1995). Maidment et al. (2001) examined a total of twelve Alliums for antibacterial activity against the tested microorganism. Allium cepa did not show antibacterial activity.

1.1 STATEMENT OF PROBLEM

There are various ophthalmic drugs and antibiotics that have been found in extensive application in the treatment of infections, which may be classified into two groups: therapeutic and diagnostic examples which include: atropine, hematropine, pilocarpine, etc for treating ocular injury and diseases (Davies, 2006). Antibiotics such as chloramphenicol, tetracycline, streptomycin (mostly in the form of drops and ointments) are also very useful as therapeutic agent infections. However, the increasing resistance of microorganism and other pathogenic microbes to conventional antibiotics resulted in a strong effort to develop antimicrobial compounds with new mechanisms of action. Hence, this research work of confirming the microbial properties of onion (Allium cepa) on some microorganisms implicated in ocular infections is of great relevance (Davies, 2006).

Staphylococcus aureus is a human pathogen that causes both nosocomial and community-acquired infections. The emergence of strains resistant to many antibiotics (methicillin-resistant S. aureus (MRSA) and of highly virulent community acquired  MRSA that can cause fatal infections such as necrotizing pneumonia is of considerable concern even in countries with well-developed health surveillance systems (Naimi et al., 2001; Torell et al., 2005).

Recently reports show high incidences of antibiotic resistance among staphylococcal strains obtained in the (Ako-Nai et al., 2002; Ako-Nai et al., 1999). Resistance to methicillin has also been documented and the phage types characterized (Parker, 1983; Ako-Nai et al., 1991). Non-pathogenic strains specifically coagulase negative staphylococci (CONS) often do not cause disease but occasionally, strains of S. saprophyticus have been associated with urinary tract infection (Khawaja et al., 1987; Ako-Nai et al., 1993).

1.2 JUSTIFICATION

The use of higher plants and their extracts to treat infection is an old age practice in traditional African medicine. Traditional medicinal practice has been known for centuries in many parts of the world. Numerous plants and herbs are used all over Nigeria by traditional medicine practitioners. It observed that these practices vary from one country to another (Sofowora, 1984). Extracts from the root, bark and leaves of various plants are used in herbal medicine production (Sofowora, 1983; 1984;1993). It is an established practice that plant extracts are given singly or as concoctions for various ailments. In fact more than 70% of the people living in Nigeria depend on these various forms of concoctions and herbal decoctions for the treatment of some diseases

1.3 AIM AND OBJECTIVES

1.3.1 Aim       

The aim of this research work is to determine the antibacterial activity of Allium cepa (onion) on clinical isolate of E. coli and S. aureus.

1.3.2 Objectives

The objectives of this research are to

1.      Determine the phytochemical constituents of the aqueous and methanolic extracts of onion.

2.      Determine antibacterial sensitivity test of the extracts of onions on clinical isolates of E. coli and S. aureus

3.      Determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of aqueous and methanolic extract of Allium cepa.

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