ABSTRACT

Essential oil is an aromatic volatile substance that has antibacterial, antifungal, antiviral, insecticidal, preservative and aromatic properties. They are widely used in pharmaceutical, food, cosmetic and agricultural industries. The antibacterial activity of essential oils of Eucalyptus globulus, Rosmarinus officanalis and Citrus limon was tested against Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis and Stapylococcus aureus using the agar well diffusion method, a range of 7-32mm zone of inhibition was obtained. Gram positive organisms were more sensitive to the action of the oil than Gram negative organisms in which Stapylococcus aureus was the most sensitive of the bacteria having 32mm zone of inhibition while Pseudomonas aeruginosa was the least sensitive bacteria having 7mm zone of inhibition. The minimum inhibitory concentration and minimum bactericidal concentrations was evaluated using the micro dilution broth method and the result showed that essential oil of Eucalyptus (1.11µl/ml) and Rosemary (0.11µl/ml) had greater antibacterial activity than lemon (visible growth). Also a time-kill analysis was done to access the antibacterial effect of the essential oil over time at 1, 5, 10 and 20 minutes. The antibacterial effect of essential oils against some of the most important pathogens provide an exciting potential for the future especially as there is an increased interest towards the use of natural products as alternatives for synthetic antibacterial agents.

TABLE OF CONTENTS

Title page i

Certification ii

Dedication iii

Acknowledgements iv

Table of contents v

List of Tables vii

List of figures viii

Abstract ix

CHAPTER ONE

1.1 Introduction 1

1.2 Statement of problem 3

1.3 Aim and objectives 4 

CHAPTER TWO

2.0 Literature review 5

2.1 Extraction of Essential oils 6

2.2 Composition of essential oils 8

2.3 Interactions between components of essential oils 10

2.4 Mechanism of action 11

2.5 Bacterial cell targets 12

2.6 Susceptibility of Gram positive and Gram negative bacteria 15

2.7 Application of essential oils 15

CHAPTER THREE

3.0 Materials and methods 17

3.1 Screening for antibacterial activity 17

3.2 Determination of minimum inhibitory concentrations and minimum bactericidal

      Concentrations 18

3.3 Time-kill analysis 19

CHAPTER FOUR

4.0 Results 20

CHAPTER FIVE

5.0 Discussion 29

5.1 Conclusion 30

5.2 Recommendation 31

References 32

Appendices 39

LIST OF TABLES

Table                                                           Title                                                                        Page

1.1 Major raw materials used for the extraction of essential oil 7

4.1 Antimicrobial properties of plant essential oil 21

4.2 Minimal Inhibition Concentration values of the essential oils .22

4.3 Minimal Bactericidal Concentration values of the essential oils on the organisms 23

LIST OF FIGURES

Figure                                                           Title                                                                       Page

2:1 Components of essential oil 9

4:1 Survivor curves for Enterococcus faecalis 24

4:2 Survivor curves for Salmonella typhi 25

4:3 Survivor curves for Escherichia coli 26

4:4 Survivor curves for Staphylococcus aureus 27

4:5 Survivor curves for Pseudomonas aeruginosa 28