Microbiological Analysis Of Fresh Fruits And Vegetables And Effect Of Antimicrobial Agents On Microbial Load

Abstract

Fresh fruits and vegetables promote good health but harbour a wide range of microbial contaminants. To assess the microbial quality of fruits and vegetables, twenty-eight (28) samples of different fruits and vegetables were purchased from various vendors. Samples were analyzed to study the density of microorganisms. The spread plate method was used for the isolation of bacteria on nutrient media. Mean bacterial load ranged from 4.4x106cfu/g to 1.07x107cfu/g with garden eggs recording the lowest count and cabbage samples harbouring more bacteria than the rest of the samples. Sliced watermelon samples recorded a mean viable count of 9.2x106cfu/g. Mean coliform count was highest in cabbage (7.4x104cfu/g) and lowest in pineapple (1.1x104cfu/g).  Six bacteria belonging to eight genera were identified. Staphylococcus aureus (82.1%) was the most frequently isolated followed by Salmonella species 13(46.4%), Bacillus species 12(42.9%), Enterobacter aerogenes 9(32.1%). Micrococcus species 6(21.4%) and Escherichia coli (25%) were the least frequently isolated. Resistance to a wide range of antibiotics was observed. Resistance to augmentin, cefuroxime, ceftazidime and ceftriaxone was observed as 100%, 100%, 100% and 69.2% respectively for the Salmonella isolates. Drug susceptibility assay revealed that 84.6%, 69.2%, 61.5% and 30.8% of the Salmonella isolates investigated were susceptible to ciprofloxacin, Ofloxacin, gentamicin and ceftriaxone respectively. Eighty-seven percent of the S. aureus isolates were resistant against erythromycin whereas 82.6% and 73.9% of the isolates were resistant to augmentin and ceftriaxone respectively. Resistance to ofloxacin was seen in 14.3% while 100% were resistant to Augmentin for the E. coli isolates. The presence of potential food-borne pathogens makes the fruits to be microbiologically unsafe and they should be pre- treated thoroughly before human consumption, so as to reduce the risk of food- borne outbreaks.

TABLE OF CONTENT 

Cover page ﾿ i

Title page ﾿ ii

Certification ﾿ iii

Declaration ﾿ iv

Dedication ﾿ v

Acknowledgments ﾿ vi

Table of contents ﾿ vii

List of Tables ﾿ x

Abstracts ﾿ xi

CHAPTER ONE

1.1 ﾿ Introduction ﾿ 1

1.2 ﾿ Aims and Objectives ﾿ 6

CHAPTER TWO: LITERATURE REVIEW

2.1 ﾿ An Overview of Fruits ﾿ 7

2.2 ﾿ Bacteria in Fruits as a cause of Disease ﾿ 8

2.2.1 ﾿ Risk associated with consumption of fruits (Microbial hazards) ﾿ 9

2.3 ﾿ Microbial Contamination ﾿ 11

2.3.1 ﾿ Soft Rot ﾿ 12

2.4 ﾿ Contamination Sources of Vegetables ﾿ 12

2.4.1 ﾿ Pre-Harvest Contamination ﾿ 13

2.4.2 ﾿ Quality of Irrigation Water ﾿ 14

2.4.3 ﾿ Post-Harvest Contamination ﾿ 15

2.5 ﾿ Common Fruits and Vegetable Spoilage Organisms ﾿ 16

2.5.1 ﾿ Listeria Monocytogenes ﾿ 16

2.6 ﾿ Global Relevance of Food Safety and Foodborne Illness ﾿ 17

2.7 ﾿ Food Poisoning ﾿ 20

2.8 ﾿ Antibiotics Resistance ﾿ 21

CHAPTER THREE: MATERIAL AND METHODS

3.1 ﾿ Sample Collection ﾿ 23

3.2 ﾿ Media Preparation ﾿ 23

3.3 ﾿ Preparation of Sample Homogenate ﾿ 23

3.3.1 ﾿ For The Isolation Of Salmonella Species ﾿ 24

3.4 ﾿ Gram Staining ﾿ 25

3.5 ﾿ Biochemical Tests ﾿ 25

3.5.1 ﾿ Catalase Test ﾿ 25

3.5.2 ﾿ Methyl Red Test ﾿ 26

 3.5.3 ﾿ Voges- Proskauer Test ﾿ 26

3.5.4 ﾿ Indole Test ﾿ 26

3.5.5 ﾿ Citrate Utilization Test ﾿ 27

3.5.6 ﾿ Hydrogen Sulphide (H2s) Production Test ﾿ 27

3.6 ﾿ Antibiotics Sensitivity Test ﾿ 27

CHAPTER FOUR

Results ﾿ 29

CHAPTER FIVE

5.1 ﾿ Discussion ﾿ 35

5.2 ﾿ Conclusion ﾿ 40

REFERENCES ﾿ 41