ABSTRACT

This study was to determine the effect of biocides on microbial growth rate. A total of Six (6) different household biocides (Dettol, Septol, TCP, Izal, Savlon and Ethenol) were screened for their efficacy to control microbial growth. Environmentally isolated Escherichia coli and Staphylococcus aureus as well as ATCC strains of both organisms (S. aureus, ATCC25923 and ATCC25922) were used in this study as test organisms. To determine the effect of the various biocides on the test organisms at times 6hrs, 12hrs and 16hrs, agar well diffusion technique was employed to evaluate/determine the potency of these biocides on the test organisms. Results from this study revealed that Savlon recorded the highest zones of inhibition against Staphylococcus aureus (26 mm) at 3 hours followed by Dettol (24mm), Septol (23mm), Izal (21mm) and Ethanol (15mm) at 6 hours time interval and the two pathogens (Staphylococcus aureus and Escherichia coli) were sensitive to Savlon and Dettol at different concentrations. Results of this experiment also indicated that different pathogens acquired resistance to disinfectants (TCP and at less extent ethanol), and also suggested that the antibacterial effects of these biocides are not only dependent on the types of disinfectant but also on their concentrations. Resistance against antibiotics by pathogenic bacteria is a major concern in the antimicrobial therapy for both humans and animals. The effectives of biocides are very important to enhance the antimicrobial activity of these disinfectants towards controlling microbial population which includes prevention of diseases transmission and infection.

TABLE OF CONTENTS

Title Page     i

Certification iii

Dedication iv

Acknowledgement v

Table of Contents vi

List of Tables vii

Abstract ix

CHAPTER ONE

Introduction 1

1.1 Aim and Objectives 3

CHAPTER TWO

Literature Review 4

2.1 Microbial Resistance to Biocides 4

2.2 Reduced Microbial Susceptibility to Biocides 5

2.3 Mechanisms by Which Biocide Exert Their Antimicrobial Action 6

2.4 Mechanisms Which Reduce Microbial Susceptibility to Biocides 8

2.4.1 Intrinsic Properties of Bacteria Conferring Reduced Susceptibility to Biocides 8

2.4.2 Reduced Susceptibility to Biocides Resulting from Phenotypic Changes 11

2.4.3 Plasmid-Mediated Mechanisms 12

2.4.4 Mutational Resistance to Biocides 13

2.5 Possible Links between Antibiotic Resistance and Reduced 

Susceptibility to Biocides 14

2.5.1 Examples of Studies Showing Reduced Susceptibility to Biocides in 

Antibiotic-Resistant Bacteria 14

2.5.2 Examples of Studies Showing No Change in Susceptibility to Biocides in 

Antibiotic-Resistant Bacteria 15

2.6 Active Substances 16

2.7 Production, Use and Fate of Biocides 17

2.8 Application of Biocides 18

2.8.1 Biocides (Disinfectants) on Medical Devices and Surfaces 18

2.8.2 Biocides (Disinfectants and Antiseptics) Used on Skin and Mucosa 20

2.9 Biocides in Consumer Products 20

2.9.1 General Aspects 20

2.9.2 Cosmetics and Personal Care Products 21

2.9.3 Household Products 21

CHAPTER THREE

Materials and Methods 23

3.1 Sample Collection 23

3.2 Sterilization of Materials 23

3.3 Materials and Media Used 23

3.4 Media Preparation 23

3.4.1 Inoculation of Test Organisms 24

3.5 Biochemical Test 24

3.5.1 Catalase Test 24

3.5.2 Indole Test 24

3.5.3 Citrate Utilization Test 24

3.5.4 Hydrogen Sulphide (H2S) Production Test 24

3.5.5 Starch Hydrolysis 25

3.5.6 Motility Test 25

3.5.7 Voges-Proskauer Test 25

3.5.8 Urease Test 26

3.5.9 Methyl Red Test 26

3.5.10 Carbohydrate Fermentation 26

3.5.11 Coagulase Test 27

3.5.12 Oxidase Test 27

3.6 Biocides Testing 27

3.6.1 Determination of Biocidal Activity 27

3.6.2 Determination of Minimum Inhibitory Concentration and Minimum 

Bacteria Concentration 28

CHAPTER FOUR

Results 30

4.1 Diameter Zones of Inhibition Produced After Three Hour 30

4.2 Diameter Zones of Inhibition Produced After Six Hours of Growth 30

4.3 Diameter Zones of Inhibition after Sixteen Hours of Growth 31

4.4 Minimum Inhibitory Concentration and Minimum Bactericidal Concentration 

Value of Selected Biocides against the Test Bacteria 31

CHAPTER FIVE

Discussion, Conclusion and Recommendation 35

5.1 Discussion 35

5.2 Conclusion 37

5.3 Recommendation 37

References