ABSTRACT
Five samples each of Ogi, Ogiri, Ugba and Fermented Yoghurt were collected from different sites at Ahiaeke in Abia State, from which forty-eight organisms were isolated using spread plate method and belong to four genera and six species: Lactobacillus plantarum, Lactobacillus salivarius, Lactococcus lactis, Leuconostoc mesentroides, Streptococcus thermophilus and Lactobacillus sakei. Agar well diffusion method was used to test the isolated lactic acid bacteria on Escherichia coli, Staphylococcus aureus and Salmonella typhi. The lactic acid bacterial were found to exhibit antibacterial activity against the pathogenic food organisms. The inhibition diameter obtained ranged between 6mm to 28mm. the highest inhibition was obtained from Lactobacillus sakei against Escherichia coli (28mm) and the smallest inhibition was obtained with Streptococcus thermophilus against Salmonella typhi (6mm), and no inhibition obtained with Streptococcus thermophilus against Staphylococcus aureus. The antimicrobial activity is attributed to bacteriocin, hydrogen peroxide, hypothiocyanate, lactic acid and fatty acid. Lactic acid bacterial have potential application for assuring and improving food quality and safety.
TABLE OF CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgement iv
Table of contents v
Lists of table’s viii
Abstract ix
CHAPTER ONE
1.1 Introduction 1
1.2 Aim and
Objectives
2
CHAPTER TWO
2.1 Literature
review 3
2.2 Classification
of lactic acid bacterial 4
2.3 Sources of
lactic acid bacterial
5
2.3.1 Conditions
for the growth of lactic acid bacterial
6
2.4 Mode of action
of lactic acid bacterial
8
2.5 Uses of lactic
acid bacterial
9
2.6 Lactic acid
bacterial and food fermentation 10
2.6.1 Dairy
products 11
2.6.2
Vegetables
12
2.7 Lactic acid
bacterial as spoilage organisms 13
2.7.1 Wine
spoilage
14
2.7.2 Beer
spoilage
14
2.7.3 Milk
spoilage
15
2.8 lactic acid
bacterial as probiotic
15
2.8.1 Anticancer
effects
16
2.8.2 Principal
factors contributing to antimicrobial effect of lactic acid bacterial 17
2.9
Bacteriocins 17
2.9.1
Classification of bacteriocins
17
2.9.2 Synthesis of
bacteriocins
20
2.10 Test
Organisms 21
2.10.1 Escherichia coli
21
2.10.2 Staphylococcus aureus
22
2.10.3 Salmonella typhi
22
CHAPTER THREE
3.0 Materials
and methods 24
3.1 Sample
collection
24
3.2Pathogenic
organisms and Re-idetification 24
3.2.1 Methyl Red
Test 24
3.2.2 Indoles Test 24
3.3 Media
preparation
25
3.3.1 De Man
Rogosa Sharpe (MRS) Broth 25
3.3.2 Mueller-
Hinton Agar
25
3.3.3 Nutrient
Agar 25
3.3.4
Salmonella shigella
Agar (SSA) 25
3.4
Sample analysis 26
3.5 Isolated of
lactic acid bacterial 26
3.6 Identification
and characterization of isolates 26
3.6.1
Macroscopy
26
3.6.2
Microscopy
27
3.6.2.1 Gram
stain 27
3.6.2.2 Motility
Test 27
3.6.3 Biochemical
Test 27
3.6.3.1
Catalase 27
3.6.3.2
Oxidase
28
3.6.3.3
Coagulase 28
3.6.3.4
Carbohydrate fermentation 28
3.7 Preparation of
MRS Lactic acid Bacteria Broth 28
3.7.1 Preparation
of Antimicrobial sensitivity disc with lactic acid bacteria Isolate 29
3.7.2 Preparation
of control disc using Amoxylcillin 29
3.8 Selection of
bacteriocin producing lactic acid bacterial
29
3.9 Screening for
Antimicrobial Activity 30
CHAPTER FOUR
1.0 Results 31
CHAPTER FIVE
5.1
Discussion 36
5.2
Conclusion
38
5.3
Recommendation
38
Reference
LISTS OF TABLES
Table 1: Identification and characterization of
isolated lactic acid bacterial
32
Table 2: Sources and distribution of
isolates
33
Table 3: Re-identification of pathogenic Test organisms 34
Table 4: Inhibition of pathogenic organisms by
lactic acid bacterial 35
CHAPTER ONE
1.1 INTRODUCTION
Technologies
on processing and preservation of food products, which help in maintaining its
nutritional values besides ensuring safety issues are the area of current food
research (Kabuki et al., 2007). Many
chemicals are being used for inactivation of food borne pathogens so as to
preserve food products for long duration (Baliet et al., 2011). Lactic acid bacteria produce various compounds such
as organic acids, diacetyl, hydrogen peroxide and bacteriocin or bactericidal
proteins during lactic fermentations (Oyetayo et al., 2003). The antimicrobial effect of LAB has been appreciated
by man from more than 10,000 years and has enabled him to extend the shelf life
of many foods through fermentation processes (Sarika et al., 2010). Control of both pathogenic and spoilage microbe in a
variety of foods is important to guarantee food quality and safety.
Lactic acid bacteria exert strong antagonistic
activity against many microorganisms including food spoilage organisms and
pathogens. This technique is used as an alternative to chemical additives for
increasing self-life storage and enhancing safety of food by using natural micro
flora and their antimicrobial products (Stiles, 1996). Lactic acid bacteria are
believed to be safe because, they have been long established as the normal
flora in fermented food; thus, they have great potential for use in bio
preservation. The preserving effects of LAB are due to the production of
antimicrobial agents such as organic acids, hydrogen peroxide and bacteriocin
or related substances (Cocolin et al.,
2007). Bacteriocins are proteinaceous compounds that mainly inhibit closely
related species (Klaenhammer, 1993). Although some bacteriocins have been shown
to possess the ability to inhibit the actions of unrelated genera such as Clostridia, Listeria, Enteropathogenicbacteria
and Gram-negative bacteria. Most bacteriocins are heat stable and sensitive to certain
proteolytic enzymes. The bacteriocins produced inhibited food spoilage and
pathogenic bacteria such as Staphylococcus
aureus, Escherichia coli, Bacillus cereus, Bacillus subtilis, Listeria monocytogens
and Clostridium perfringens which are
recalcitrant to traditional food preservation method (Bizani et al., 2002). Several bacteriocins from
Gram-positive bacteria are very effective, have broad inhibitory spectra and
may be used as antimicrobial agents for various practical applications (Torodov
et al., 2007). These bacteriocins are
harmless against its own producers because the secretory bacterial strains have
genetically pre-determined genes of immunity (Abada, 2008). The use of lactic
acid bacterial bacteriocins in the food industry can help to reduce the
addition of chemical preservatives as well as the intensity of heat treatments,
resulting in foods which are more naturally preserved and richer in
organoleptic and nutritional properties.
1.2
Aim
and Objectives
This project work aimed
as to isolate Lactic acid bacteria that produce antimicrobial substances
belonging to bacteriocin type able to inhibit the bacteria which causes food
poisoning and spoilage.
i.
Isolation and
identification of crude Lactic acid bacteria isolated from fermented foods
ii.
Determination of the
antimicrobial activity of crude Lactic acid bacteria.
iii.
Evaluation of antibiotic
susceptibility of Lactic acid bacteria.
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