ABSTRACT
This study aims to compare the antimicrobial activity of lactic acid bacteria (LAB) species isolated from ogiri against three common human pathogens. The LAB isolates and pathogens was identified following a four step analysis namely; cultural, microscopic, biochemical examination and sugar utilization. The antagonistic properties of these isolates against Escherichia coli, Staphylococcus aureus and Salmonella species were examined using agar well diffusion method. Three LAB isolates namely LAB 1, LAB 2, and LAB3 identified as Lactobacillus brevis, Lactobacillus plantarum and Lactobacillus fermentum respectively were effective against all selected pathogen strains. Amongst the three isolates, LAB2 exhibited the highest antibacterial activity, against all the indicator pathogens tested followed by LAB 1 and the least LAB3. LAB2 showed antibacterial activity was maximum against E.coli with a zone of inhibition ranging from (12.6mm) and least for Salmonella spp (6.9mm). LAB1 also showed antimicrobial property against all tested pathogens showing highest activity against E.coli (12.5mm) and least against Staphylococcus aureus (6.1mm). The least antimicrobial activity showed in isolate LAB3 against E.coli (11.2mm) and against S.aureus (9.4mm). The degree of antimicrobial property among the isolates was in the order of LAB2>LAB1>LAB3. Generally, the LAB isolates showed remarkable inhibitory effect against both Gram positive and Gram negative pathogenic strains. However, the spectrum of inhibition was different for the isolates tested. These results suggest that these LAB isolates could be used as a natural bio-preservatives in different food products or even as therapeutic agent (probiotics) .
TABLE OF CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgements iv
Table of Contents v
List of Tables viii
List of Figures ix
Abstract
x
CHAPTER ONE
1.0 Introduction 1
1.1 Lactic acid bacteria (LAB) 1
1.2 Aim
and objectives 3
CHAPTER TWO
2.0 Literature review 4
2.1 Lactic acid bacteria 4
2.2 Microorganisms
under LAB 4
2.3 Benefits
of LAB 6
2.4 Lactic
acid bacteria as starter cultures 7
2.5 Antimicrobial
mechanism of LAB 8
2.6 Lactic acid bacteria as beneficial
microorganisms 8
2.7 Ogiri 9`
CHAPTER THREE
3.0 Materials and methods 11
3.1 Media and reagent 11
3.2 Isolation of bacteria 11
3.3.0 Identification of isolates 11
3.3.1 Gram staining techniques 11
3.3.2 Motility test 12
3.3.3 Catalase test 12
3.3.4 Coagulase test 12
3.3.5 Methyl red test 12
3.3.6 Voges-proskaeur test 12
3.3.7 Indole test 13
3.3.8 Citrate test 13
3.3.9 Oxidase test 13
3.3.10 Sugar fermentation 13
3.4.0 Determination of anti-microbial activity of LAB1,
LAB2, LAB3. 14
3.4.1 Preparation of sample filtrate 14
3.4.2 Media for growth of pathogens 14
3.4.3 Anti- microbial activity test by agar well
diffusion method 14
CHAPTER FOUR
4.0 Results 15
CHAPTER FIVE
5.0 Discussion 18
5.1 Conclusion 19
5.2 Recommendation 20
REFERENCES
LIST OF TABLES
Tables
Title
Page
I Characterization
and identification of LAB isolates and 16
the test organisms
used
II Antimicrobial
activity of LAB against human selected pathogens 17
LIST
OF FIGURES
Figure Title
Page
I Flow
chart for the production of ogiri 10
CHAPTER ONE
1.0 INTRODUCTION
1.1 LACTICACID BACTERIA(LAB)
Lactic
Acid Bacteria are ubiquitous microorganisms that produce Lactic acid as a
by-product of digesting their food source (usually carbohydrates). The lactic
acid accumulated to ferment or pickle the food, are capable of surviving in
acidic (low-pH) environment (David etal.,
2013). Lactic Acid Bacteria are characterized as been wide spread in nature and
are beneficial probiotics in the digestive systems. They are among the most
important groups of microorganisms used in food fermentation contributing to
taste and texture of fermented products and inhibiting food spoilage caused by
other microorganisms. Lactic Acid Bacteria are responsible for the production
of yoghurt, cheese, cultured butter, sour cream, sausage, kimchee, olives and
sauerkraut (Nordqvist, 2004).
Pathogenic
microorganisms are found virtually everywhere, and they cause severe damage and
spoilage to foods in the food industry. Therefore bio-preservation systems in
food are becoming increasingly interesting for the industry and consumers.
(Fatima and Mebrouk, 2012). Bacteriocinogenic lactic acid bacteria and or their
bacteriocins are considered safe addictives (General Regarded as safe- GRAS), useful to control
the frequent development of pathogens
and spoiling microorganisms in
food and feed. (Paradaetal.,2007).
Alternative methods for controlling
the pathogenic bacteria, including the production of
antimicrobial
peptides bacteriocins, are now highlyconsidered.
Lineetal.,(2008)
reported
thatbacteriocins are compounds
produced by the bacteria that have a biologically active protein
moiety and bactericidal action.
Baceriocins from a Gram-positive microorganisms such as
Lactic Acid bacteria has attracted
much extensive incorporation as bio-preservative
ingredients
into model food, mostly in dairy industry (Diopet al., 2007) and also in human therapeutics (Martin Visscheret al., 2008).
With their long history of use in
food preservation by many world cultures (Nordquist, 2004),
LAB are generally recognized as safe
for human consumption. By producing lactic acid as a
fermentation metabolites, these
microorganisms prolong storage, preserve nutritive value and
enhance flavors of otherwise
perishable foods. Lactic acid bacteria are easy to collect and
economical to culture, store and use
(David et al., 2013).
The deliberate fermentation of foods
by man or generally done using plant ingredients
in
combination with fungi or bacteria which are either sourced from the
environment, or carefully kept in cultures maintained by humans. (Chamberlain et al., 1997). All lactic acid
fermentation centers on the ability of LAB to produce acid, which then inhibits
the growth of other non-desirable organisms. The Lactobacillus mesenteroides. (Chung et al., 2010) initiates growth in vegetables over a range of
temperatures and salt concentrations than any other LAB. It produces carbon
dioxide and acids which rapidly lower the pH and inhibit the development of
undesirable microorganisms.
1.2AIM
AND OBJECTIVES
To isolate, characterize
and identify, lactic acid bacteria from aOgiri.
To compare the
antimicrobial effects of the LAB isolates from ogirion different pathogenic
organisms.
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