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Product Code: 00007114

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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 coliStaphylococcus aureus and Salmonella species were examined using agar well diffusion method. Three LAB isolates namely LAB 1, LAB 2, and LAB3 identified as Lactobacillus brevisLactobacillus 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) .


Title page                                                                                                                               i

Certification                                                                                                                           ii

Dedication                                                                                                                              iii

Acknowledgements                                                                                                               iv

Table of Contents                                                                                                                  v

List of Tables                                                                                                                         viii

List of Figures                                                                                                                     ix

Abstract                                                                                                                                 x


1.0       Introduction                                                                                                                1

1.1       Lactic acid bacteria (LAB)                                                                                         1

1.2       Aim and objectives                                                                                                     3


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`


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                   


4.0       Results                                                                                                                        15

CHAPTER FIVE                                                                                                                       

5.0       Discussion                                                                                                                   18

5.1       Conclusion                                                                                                                 19

5.2       Recommendation                                                                                                        20






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      






Figure                               Title                                                                                  Page

    I                   Flow chart for the production of ogiri                                                            10










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.


*      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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