from indigenous fermented foods and human gut ... - Thapar University

5
Chapter I: Introduction
Moreover, the antimicrobial effects and safety of LAB in food preservation is widely
accepted (EFSA, 2005). Their preservative effect is mainly due to the production of lactic
acid and other organic acids which results in lowering of pH (Daeschel, 1989). Preservation
is enhanced by the production of other antimicrobial compounds, including hydrogen
peroxide, CO2, diacetyl, acetaldehyde, and bacteriocins (Klaenhammer, 1988; 1993). In
addition to the antimicrobial effects, specific LAB also possesses health promoting
properties. Evidence from in vitro systems, animal models and human clinical studies
suggests that LAB function as immune-modulators and can enhance both specific and
nonspecific immune responses (Ouwehand et al. 2002; O’Flaherty and Klaenhammer, 2009),
justifying their use as health promoting supplements or probiotics both for humans and
animals.
Antimicrobial peptides produced by Lactobacillus spp.
Lactic acid bacteria are capable of producing a wide range of ribosomally
synthesized proteins and peptides which have antimicrobial activity to compete with other
bacteria of the same species (narrow spectrum) or to counteract bacteria of other genera
(broad spectrum) (Cotter et al., 2005). The first description of bacteriocin-mediated growth
inhibition was reported 85 years ago, when antagonism between strains of Escherichia coli
was first discovered (Gartia, 1925). The inhibitory substances were called ‘colicins’, to
reflect the producer organism, whereas gene-encoded antibacterial peptides produced by
bacteria are now referred to as ‘bacteriocins’. In 2005, an estimated 1.8 million people died
from diarrhoeal diseases, largely attributable to contaminated food and drinking water
(Newell et al., 2010). About 76 million cases of food-borne diseases, resulting in 325,000
hospitalizations and 5000 deaths, are estimated to occur each year in the United States of
America (USA) alone (Newell et al., 2010). In Finland, a total of 39,500 persons contracted