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42 Chapter II Review of Literature The ability of numerous LAB to produce one or more bacteriocin displays an important skill sustained over many generations. Bacteriocin production is advantageous, since these peptides inhibit the growth of bacteria competing for the same ecological niche and the same resources. This is supported by the fact that their inhibition spectrum is mostly narrow and most likely to be effective against related bacteria competing for the same nutrients (Drider et al., 2006). It appears that, by producing several bacteriocins belonging to different classes with different inhibitory spectra, LAB compensates their narrow spectrum. Lactobacillus plantarum C11 for example, produces two types of bacteriocins which have different target cell specificities (Anderssen, Diep, Nes, Eijsink and Nissen-Meyer, 1998). Moll et al. (1999) demonstrated that plantaricin EF shows high conductivity for monovalent cations, while plantaricin JK is more selective for anions. Consequently, having opposite ion selectivity, plantaricin EF forms pores with cation selectivity and plantaricin JK with anion selectivity. This may also help to overcome the development of resistance mechanisms in target organisms (Eijsink, Axelsson, Diep Dzung, Håvarstein, Holo and Nes, 2002). Table 2.6 Presents some examples of antimicrobial-producing organisms. (Fuller, 1992) Probiotic Compound Lactobacillus GG Wide spectrum antibiotic L. acidophilus Acidolin, Acidophilin, Lactocidin L. delbrueckii ssp. bulgaricus Bulgarican L. plantarum Lactolin L. brevis Lactobacillin, Lactobrevin L. reuteri Reuterin
2.4.1 Mode of action 43 Chapter II Review of Literature Although the mode of activity of bacteriocins can differ, the cell envelope is commonly their target. The majority is active by inducing membrane permeabilization. This is reflected by the fact that Class II bacteriocins have an amphiphilic helical structure, which allows them to insert into the membrane of the target cell, leading to depolarization and death (Fig. 2.3), (Cotter et al., 2005). To form the core of the pores, this structure is believed to face with the polar side towards the centre of the channel, while the non-polar side faces the hydrophobic phase of the phospholipid bilayer (Diep et al., 2002). This creation of pores in the membrane of their target cells results in dissipation of the proton motive force, intracellular ATP depletion and leakage of nutrients and metabolites (Deegan et al., 2006). Moreover, to form a pore, interactions with the cytoplasmic membrane Source: of the Oscariz target and Pisabarro, cell are 2001necessary. Initial electrostatic interactions between the positively charged peptide and anionic lipids, which are in large quantities present in the membranes of Gram-positive bacteria, play a role to some extent in this mode of action. Thus, the sensitivity to bacteriocins depends partly on the physiological state of the cell (Eijsink et al., 2002). Up to this stage, it is not entirely clear whether bacteriocins act through receptors in the target cell membrane or if there is specificity in possible receptors. Fig: 2.2 Killing mechanism propose for bacteriocin
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Characterization of Lactobacilli is
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their encouragement, insightful com
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5. Mukesh Kumar and Abhijit Ganguli
Page 9 and 10: 2.3.2.9 Cholesterol lowering 2.3.2.
Page 11 and 12: 3.12.4 Measurement of intracellular
Page 13 and 14: List of Abbreviations ABTS 2,2-azin
Page 15 and 16: LIST OF TABLES Tables Page No. Tabl
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Page 69 and 70: 50 Chapter III Material and methods
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Page 101 and 102: 4.6 Molecular characterization of t
Page 103 and 104: 4.6.1 Sequence alignment of Lactoba
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91 Chapter IV: Results Table 4.12 A
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4.7.2 Survival of Lactobacillus str
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4.7.4 Antagonistic activity against
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97 Chapter IV: Results Table 4.17 H
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Table 4.19 Adhesion of potential pr
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Table 4.20 Coaggregation a of poten
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103 Chapter IV: Results Fig. 4.6 Ad
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105 Chapter IV: Results Table 4.21
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Table 4.23 Effect of pH and Tempara
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109 Chapter IV: Results Fig. 4.9 CL
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111 Chapter IV: Results 4.11.1 Effe
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113 Chapter IV: Results monocytogen
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115 Chapter IV: Results A B C D Fig
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4.13.3 Membrane permeability 117 Ch
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Chapter V DISCUSSION
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120 Chapter V Discussion al., 2003)
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122 Chapter V Discussion Lactobacil
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124 Chapter V Discussion or natural
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126 Chapter V Discussion trait may
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128 Chapter V Discussion and the el
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130 Chapter V Discussion hexadecane
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132 Chapter V Discussion hypothesiz
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134 Chapter V Discussion would prev
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136 Chapter V Discussion gave maxim
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138 Chapter V Discussion for 90 min
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140 Chapter V Discussion To test th
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CONCLUSIONS The main objective of t
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145 Chapter V: References Aasen, I.
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147 Chapter V: References Bjorksten
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149 Chapter V: References negative,
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151 Chapter V: References Delves-Br
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153 Chapter V: References Franz, C.
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155 Chapter V: References Gordon, D
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157 Chapter V: References Isolauri,
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159 Chapter V: References Kolenbran
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161 Chapter V: References Marekova,
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163 Chapter V: References Nagy, A.,
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165 Chapter V: References Bifidobac
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167 Chapter V: References Schilling
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169 Chapter V: References Teuber, M
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171 Chapter V: References Yoon, Y.C
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Rogosa agar Ingredients Quantity (g
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Denaturing solution. guanidinium is
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Appendix II Fig. 3.1. Standard curv
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