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CHAPTER 1
INTRODUCTION
The word ―probiotics‖ was earlier used as an antonym of the word ―antibiotics‖. It is derived
from Greek and termed as ―for life‖ (Hamilton-Miller et al., 2003; Vasiljevic & Shah, 2008).
The concept of probiotics was first proposed by Elie Metchnikoff, a Noble Laureate of the year
1908. He was astonished by the exceptionally long life-span of Bulgarian peasants and
subsequently studied their lifestyle as well as diet. Bulgarian peasants used to consume large
amounts of fermented milk. Metchnikoff postulated that pathogens inside the human gut produce
toxic compounds that steadily weaken the body. Lactic acid bacteria present in the sour milk
successfully defended the body against enteropathogens (Vasiljevic & Shah, 2008). Many
eminent researchers‘ defined probiotics by the manner they observed them. Mostly cited
definition was that of Fuller‘s (1992), who defined them as ―a live microbial feed supplement,
which beneficially affects the host animal by improving its intestinal microbial balance‖.
However, this definition was more applicable to animals than to humans. Another widely used
definition was ―probiotics are mono or mixed cultures of live microorganisms that might
beneficially affect the host by improving the characteristics of indigenous microflora‖ (Holzapfel
et al., 1998). FAO/WHO defined it more precisely as ―live microorganisms which when
administered in adequate amounts confer a health benefit on the host‖ (FAO/WHO, 2002).
Certain strains of bacteria have been discovered over the years to have probiotic properties,
mainly consisting of lactic acid producing bacteria (Lactobacilli, Streptococci, Enterococci,
Lactococci, Bifidobacteria), Bacillus and yeast Saccharomyces and fungi such as Aspergillus.
They chiefly harbor gut of animals, air, water, food, soil etc. These probiotic groups find wide
application nowadays due to valuable products synthesized by them and special antimicrobial,
antioxidant properties. Probiotic cultures are exploited commercially as a tool for the
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development of novel functional products. It has been estimated that there were approximately
70 probiotic containing products marketed in the world (Shah, 2004). Probiotic organisms are
available commercially in milk, sour milk, fruit juices, ice-cream, oat-based products, Luneber,
Olifus, Bogarde, Progurt etc. The consumption of probiotic based functional dairy products
across West Europe, United States and Japan increased by 12% since 2005 (Zenith International,
2007). Probiotic products are becoming popular in Japan, as more than 53 types of probiotic
containing products have hit the market recently (Vasiljevic & Shah, 2008).
Lactic acid bacteria (LAB) produce a number of antimicrobial substances including organic
acids, hydrogen peroxide, bacteriocins, and bacteriocin-like substances. Bacteriocins or
bacteriocin-like substances are peptides or proteins, which exhibit inhibitory activity against
sensitive strains of bacteria. Bacteriocins confer important defence systems against other
microorganisms. Bacteriocins differ from usual antibiotics in that they are ribosomally
synthesized while antibiotics are generally secondary metabolites (Rodriguez et al., 2002). Also,
antibiotics inhibit microorganisms by diverse mechanism of inhibition such as peptidoglycan
synthesis inhibition, protein synthesis inhibition, and blocking promoters‘ etc., but bacteriocin
generally act over the cell membrane to make pores thus leaking the metal ions K+ , Na+ and
other cellular contents. Although bacteriocins may be produced by Gram-positive and Gramnegative bacteria, those from LAB are of particular interest due to their potential use in the food
industry as natural safe food preservatives (O ‗Sullivan et al., 2002).
In the present study we explored for certain potential probiotic strains which could be employed
to preclude fish and shrimp pathogens. Shrimp and fish culture is grown as a million dollar
industry and rearing of shrimps and fish in culture system becomes popularized throughout the
world especially in Southeast Asia. Worldwide, major economic losses in cultured shrimp and
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fish result from a relatively small number of opportunistic pathogenic bacteria (Toranzo et al.,
2005). Vibrio is one of the most important pathogen recognized in larval cultures, provoking a
high mortality (Austin & Zhang, 2006; Paillard et al., 2004). Many pathogenic bacteria become
resistant to antibiotics and hence farmers resort to dump more antibiotics. The residues of
antibiotics are found in most of the seafoods (Aoki, 1975). At the same time, use of prophylactic
antibiotics is detrimental to aquatic and terrestrial environments, animal and human health
(Cabello, 2006; Zhou et al., 2009). That‘s why authorities such as the European Authority have
chosen to limit antibiotic use as a curative situation. In this context, scientific communities have
proposed friendly alternatives such as vaccines (Kurath, 2008), antibiotic substitutes (Dorrington
& Gomez-Chiarri, 2008) or use of probiotics (Kesarcodi et al., 2008). Bacteriocinogenic
bacterial strains appear to be an excellent candidate for an affable alternative since bacteriocin
would be used as an antibiotic substitute (Joerger, 2003), whereas bacteria would be a potential
probiotic (Gillor et al., 2008). Most of the candidate probiont used commercially in aquaculture
are heterolactic i.e., strains isolated from source other than host animal. In our lab, attempt was
made to use homolactic strains i.e., lactic acid bacteria (LAB) isolated from the host gut (fish
and shrimp) and applied for control of diseases during its culturing. We studied the probiotic
properties of LAB strains Streptococcus phocae PI80 and Enterococcus faecium MC13 isolated
from the gut of Penaeus indicus and Mugil cephalus respectively and also characterized its
antimicrobial protein. In vivo studies to evaluate their potential against shrimp and fish pathogens
were carried out by other researchers in the laboratory (Swain et al., 2009; Pattukumar et al.,
2010; Gopalakannan & Arul, 2011).
Furthermore, we isolated some LAB strains from the south Indian fermented foods. Fermented
foods were consumed in many countries since it has disease prevention capacity and improves
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health. We exploited certain South Indian traditional fermented foods such as Koozh, Kallappam,
and Mor Kuzhambu to isolate LAB strains. Our aim was to employ the isolated LAB against
human diseases and pathogens. From the literature survey it was evident that microbiota
influence important host activities, including the local immune response and several intestinal
metabolic traits (Servin, 2004; Round & Mazmanian, 2009). Probiotics are also known to exert
other health advantages such as improving lactose intolerance, increasing humoral immune
responses, biotransformation of isoflavone phytoestrogen to improve post-menopausal
symptoms, bioconversion of bioactive peptides for antihypertension, and reducing serum
cholesterol level (Liong, 2007). But for therapeutic purposes, probiotics should have certain
features: to be of human origin, safe for the host, and genetically stable (Holzapfelm et al.,
1998). Furthermore, it is important that probiotics, in order to be active, survive passage through
the gastrointestinal (GI) tract irrespective of gastric acids, pancreatic enzymes, and bile acids so
that they can reach the ileum and colon and colonize the intestinal mucosa (Reid et al., 2003).
We pined to investigate all such properties of the potential probiotic strain Lactobacillus
plantarum AS1 before applying it towards colorectal cancer treatment in rodent model.
Colorectal cancer was chosen for this study since it represents a major public health problem
accounting for over 1 million cases and about half a million death worldwide (Chau &
Cunningham, 2006). Diet interventions and natural bioactive supplements have now been
extensively studied to reduce the risks of colon cancer, as a cause of prevention instead of cure.
Postulated mechanisms include reduction in the activity of several cancer causing agents,
desmutagenic and anti-carcinogenic properties (Collins & Gibson, 1999).We also intended to
study the efficacy of L. plantarum AS1 against human pathogen V. parahaemolyticus using HT29 cell lines as simulating intestinal epithelial cells.
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