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The antibacterial effect of aqueous and ethanolic extract of onion (Allium cepa) and Garlic (Allium sativum) applied singly as well as in combination on five intestinal bacteria (Escherichia coli, Salmonella, Shigella, Proteus and Enterobacter) was evaluated. The  paper disc diffusion method was adopted at different concentrations (10%, 25%, 75% and 100%). The result showed variable effect against the bacterial isolates. The extracts of these Allium plants (Garlic and Onion) exhibited marked antibacterial activity with the garlic extracts showing the highest inhibition. The highest inhibitory effect of the aqueous onion extract was seen against E. coli with a zone of inhibition of 6mm while the least was seen against Proteus which gave a zone of inhibition of 2mm. All isolates were resistant at concentrations below 100%. The ethanolic extract of the onion plant yielded a better antibacterial activity as the isolates showed resistance for the concentrations below 75%, Escherichia coli and Enterobacter showed more sensitivity as they gave an inhibition zone of 12mm respectively for the 100% concentration, the least was Proteus which gave a zone of inhibition of 6mm. E.coli and Enterobacter showed more sensitivity to the 75% concentration with 10mm each, while Proteus showed the least sensitivity of 2mm. The aqueous garlic extract gave a better inhibition than that of the onion extract. The isolates showed resistance for the concentrations below 75%, Escherichia coli and Salmonella showed a higher sensitivity for the 100% concentration with 13mm and 12mm zone of inhibition respectively, while both had 10mm respectively for the 75% concentration. Proteus showed less sensitivity as it gave the least inhibition zone of 6mm and 2mm at 100% and 75% concentration respectively. The ethanolic garlic extract showed the highest inhibition on the isolates. All isolates showed resistance for the concentration below 25%, except for Proteus which showed inhibition for the concentration below 75%, E. coli and Salmonella were inhibited most, as they showed inhibition zone of 14mm and 10mm at 100% respectively, 11mm and 8mm at 75% respectively and 4mm respectively for the 25% concentration. Proteus was less sensitive, it showed inhibition zone of 8mm and 7mm for 100% and 75% concentrations respectively. All isolates were resistant to gentamicin(the control) while the aqueous extracts of both plants combined showed greater antibacterial effect, with Escherichia coli being highly sensitive with 20mm inhibition zone and Proteus less sensitive with 12mm inhibition zone. The results therefore suggest that these extracts can be used to treat intestinal pathogens confirming the traditional claim that the Allium plants possess antibacterial properties.          




Title Page i

Certification ii

Dedication iii

Acknowledgement iv

Abstract v

Table of Contents vi

List of Tables viii

List of Figures viii


1.1 Introduction 1

1.2 Aims and Objectives 2


2.1 Literature Review 4

2.2 Onion (Allium Cepa) 4

2.2.1 Historical origin/distribution   4

2.2.2 Taxonomic classification 5

2.2.3 Plant description 6

2.2.4 Nutritional Value 6

2.2.5 Culinary Uses of Allium Cepa 6

2.2.6 Medicinal Uses of Alium Cepa 7

2.3 Phytochemicals in Allium cepa/ antibacterial properties 8

2.3.1 Organosulfur Compounds 8

2.3.2 Flavonoids 9

2.4 Allium sativum (Garlic) 10

2.4.1 Historical origin/distribution 10

2.4.2 Taxonomic classification 10

2.4.3 Plant Description 11

2.4.4 Nutritional Value 11

2.4.5 Culinary Uses of Garlic (Allium sativum) 12

2.4.6 Medicinal values of Allium sativum 12

2.5 Phytochemicals in Garlic/Antibacterial Properties   15

2.6 Intestinal pathogens      16                                                                                                                                          


3.1 Sample Collection 17

3.2 Confirmation of Isolates 17

3.3 Characterization and Identification 17

3.4 Media Preparation 17

3.5 Sterilization 17

3.6 Extraction Procedure 24

3.7    Susceptibility Testing 25


4.1   Result 27


5.1 Discussion 35

5.3    Conclusion 36.

5.2   Recommendation 37



TABLE                                              TITLE                                                                 PAGE


1: Effect of aqueous onion extract on the test organisms 29

2: Effect of ethanolic onion extract on the test organisms 30

3: Effects of aqueous garlic extract on the test organisms 31

4: Effects of ethanolic garlic extract on the test organisms   32

5: Synergistic effect of aqueous onion and garlic extracts on test organisms 33

6: Characterization of Bacterial Isolates 34




FIGURE                                      TITLE                                                                     PAGE

2.1                                        Structure of Allin 8

2.2:                                       Structure of Allicin              9

2.3                                         Basic Structure of a flavonoid   10  



1.1 Introduction

Morbidity and mortality due to diarrhea caused by intestinal pathogens continue to be a major problem in many developing countries especially among children. Escherichia coli, vibrio cholerae, Shigella species, Salmonella species, Klebsiella species among other intestinal pathogens are frequently implicated (Frazier and Westhoff, 2008).

Antibiotics have been used successfully to treat infections caused by these organisms of intestinal origin before now though most often this is not without adverse effects like hypersensitivity, depletion of beneficial gut and mucosal microorganisms, immunosuppression and allergic reactions (Lopez et al., 2001). However, the emergence of resistant strains to the antibiotics and the increased rate of multiple drug resistance exhibited by these organisms have created a serious threat to the treatment of infections caused by them.

The problems of antibiotic resistance in addition to resulting in significant increase in cost and toxicity of newer drugs is eroding our therapeutic armamentarium as resistant strains of intestinal origin are continuing to increase both in number and in variety; the wide spread use of antibiotics both for human consumption and animal production has been shown to be a major cause (Dessen et al., 2001).

The fact that microorganisms developed resistance to many drugs has created a situation where some of the common and less expensive antimicrobials are losing effectiveness (Koduru et al.,2006). Therefore alternative methods of treatment are sought after and one approach is to screen local medicinal plants for possible antimicrobial properties (Purseglove, 2005).

Traditional healers have long used plants to prevent or cure infectious conditions (Purseglove, 2005). Plant based antimicrobials have enormous therapeutic potentials as they can serve the purpose with lesser side effects that are often associated with synthetic antimicrobials (Aboaba et al., 2011).

Medicinal plants have been used in virtually all cultures as a source of medicine since times immemorial. They are rich in a wide variety of secondary metabolites such as tannins, terpeniod, alkaloids and flavonoids which have been found in vitro to have antimicrobial properties (Cowan, 2001). They have served as models for many clinically proven drugs and are now being re-assessed as antimicrobial agents (Cowan, 1999).

Literally, thousands of plants species have been tested against hundreds of bacterial strains in vitro and are active against a wide range of Gram positive and Gram negative bacteria, (Cowan, 1999).

Onion and garlic have been reported to have antibacterial, antiviral, anti-parasitic, anti fungal and anti-inflammatory effect (Onyeagba and Isu, 2002), hence the need for this study. This is in pursuance of the efforts to seek for therapy from plants with the increase in failure rate of antibiotics, a consequence of multi drug resistance by some organisms.

1.2 Aims and Objectives

· To determine the antibacterial effects of Allium sativum and Allium cepa on selected enteric bacteria.

· To determine the effectiveness of different extracts of both Allium sativum and Allium cepa.

· To determine the synergistic effect of Allium sativum and Allium cepa on selected enteric bacteria.

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