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Chapter II Review of Literature choice of new microbial strains to be used as probiotics should be their safety and origin. GRAS (generally recognised as safe) microorganisms include Lactobacillus spp. and Bifidobacterium spp., which are bacteria with a long history of safe use, as they have been consumed by humans for centuries. Selection of other microorganisms must include expensive and time consuming short- and long-term toxicological studies (Morelli, 2000; Chesson et al., 2002). Havenaar et al. (1992) considered that the origin of the strain regarding host species and location specificity play an important role if colonization is essential for achieving the desired effect of the probiotic. In this study, strains from human origin and from traditional fermented food were compared in their in vitro probiotic potential. The bacterial isolates screened to be selected as potential probiotics in this study were isolated from Indian traditionally fermented food products and human meconium. 2.4 Antimicrobial properties As indicated previously, the intestinal microflora is a complex ecosystem. Introducing new organisms into this highly competitive environment is difficult. Thus organisms which can produce such products which inhibit the growth or kill existing organisms in the intestinal milieu have a distinct advantage. The growth media filtrates and sonicates from the bacterial cells of prospective probiotics should be tested for bactericidal and bacteriostatic activity in well-plates against a wide variety of pathogens. The ability of probiotics to establish in the gastrointestinal tract will be enhanced by their ability to eliminate competitors. Antimicrobial activity is one of the most important selection criteria for probiotics. Antimicrobial activity targets the enteric undesirables and pathogens (Klaenhammer Kullen 1999). Antimicrobial effects of lactic acid bacteria are formed by producing some substances such as organic acids (lactic, acetic, propionic acids), carbon dioxide, hydrogen peroxide, 38
Chapter II Review of Literature diacetyl, low molecular weight antimicrobial substances and bacteriocins (Quwehand and Vesterlund 2004, Çakır 2003). They are active against other bacteria, either in the same species (narrow spectrum) or across genera (broad spectrum) (Klaenhammer, 1988). Producer organisms are immune to their own bacteriocin(s), a property that is mediated by specific immunity proteins (Cotter et al., 2005). Both Gram-negative and Gram-positive bacteria produce small heat-stable bacteriocins, but so far they are found less frequently in Gram- negative bacteria (Diep and Nes, 2002), while within the Gram-positive bacteria group LAB seem to produce a large variety of these compounds (Drider, Fimland, Hechard, McMullen and Prévost, 2006; Nes and Johnsborg, 2004). Most of the bacteriocin-producing LAB are isolated from endogenous fermented food. It appears that the preservative effect of many LAB is partly due to their bacteriocin production, which is considered to give the producers an advantage in competing with other bacteria sharing the same ecological niches (Diep et al., 2002). Bacteriocins produced by LAB can be categorized into three different classes according to their biochemical and genetic properties (Table 2.1). The present review focuses on class II bacteriocins, since all bacteriocins produced by LAB isolated from wine are classified as class II. Class II bacteriocins can be divided into three subclasses. Class IIa is the largest group. It has a conserved N-terminal amino acid sequence (YGNGVXC) and displays a high specific activity against the food pathogen Listeria monocytogenes (Hechard and Sahl, 2002). A large variety of LAB belonging to the genera Lactobacillus, Enterococcus, Pediococcus, Carnobacterium, and Leuconostoc is producing subclass IIa bacteriocins. Subclass IIb includes bacteriocins with two peptides which require the combined activity of both peptides and show very low, if any, bacteriocin activity when tested individually. Moreover, no sequence similarities appear between these complementary peptides. Subclass 39
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Characterization of Lactobacilli is
Page 5 and 6: their encouragement, insightful com
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Page 9 and 10: 2.3.2.9 Cholesterol lowering 2.3.2.
Page 11 and 12: 3.12.4 Measurement of intracellular
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87 Chapter IV: Results Table 4.8 Al
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89 Chapter IV: Results Table 4.10 A
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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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