Probiotics and Prebiotics
Probiotic means “for life” (Latin and
Greek) and probiotic bacteria influence general health and well-being through
their association with the gastrointestinal tract (GIT) and its normal
microbiota. The concept of probiotics was first coined by Elie
Metchnikoff. He proposed that a normal,
healthy gastrointestinal microbiota in humans and animals provided resistance against
“putrefactive” intestinal pathogens and he isolated a Lactobacillus culture
from a fermented milk which provided health benefits.
Our body are colonized by thousands of
microbial species that exist as commensals, largely on mucosal tissues of the
nose, mouth, GIT, and vagina. Some of
the most widely used probiotic species are part of the natural commensal microbiota.
They have proteins helping them for metabolic activities for sugar harvesting
and adherence to host.
1014 bacterial cells are found in
the human body, 10-fold more cells than the 1013 mammalian cells comprising
the human body itself. Most of these
bacterial cells reside in the GIT. The composition
of the GIT microbiota is complex, dynamic, and specific to each host and change
markedly with diet, age, and lifestyle. They are responsible for many important
properties that affect the metabolism of food and drugs, the renewal of gut
epithelial cells, immune system development, heart size, and general behavioral
characteristics. The impact of the microbiota on the host can depend on many
factors such as diet, age, exposure to exogenous microorganisms, the genetic makeup
of the host, and physiological conditions of the host tissues.
The digestive tract is composed of four
major categories
·
Autochthonous
microbiota: populations of microbes that have permanently colonized the host
and are present in large numbers
·
Normal
microbiota: microorganisms that are frequently present but can vary in number
and be sporadically absent
·
Pathogens:
microorganisms that are periodically acquired but can persist and cause infection
and disease
·
Allochthonous
microbiota: microbes of another origin that are present temporarily (most
probiotic cultures are allochthonous)
Only a small proportion of the GIT microflora
is culturable. Molecular biology techniques are used for their studies. Each person
has a persistent flora that can be recovered repeatedly over extended periods.
Severe disturbances to the GIT, such as antibiotic therapy, enteric infections,
or dietary stress, can temporarily disrupt the autochthonous and normal microbiota.
However, these populations quickly recover.
Lactobacillus and Bifidobacterium species are
natural residents of the GIT and are beneficial to the health of their hosts
and pose no risk to the host. Some species of Bacillus and Escherichia
are also proposed as probiotics, but the two major species around which the
probiotic concept has evolved are Lactobacillus and Bifidobacterium.
Probiotics is a substance produced by one microorganism
that stimulates the growth of another microorganism. It is a live microbial
supplement which improves the host intestinal balance and is beneficial to the
host. There are many types of probiotic cultures (mono- and mixed strain cultures,
multiple probiotic species), applications (gastrointestinal versus topical), and
mechanisms of probiotic activity (live cells, dead cells, and cellular components).
According to WHO they are “live microorganisms which when administered in
adequate amounts confer a health benefit on the host”.
Abiotics are probiotic strains that have been inactivated by lysis, heat,
or UV irradiation and have some effectiveness in downregulating inflammatory
response in intestinal epithelial cells.
The mechanisms through which probiotics
exert their beneficial effects are
1. Interaction with the immune system. Some
probiotics can alter cytokine production by exposed macrophages and dendritic
cells and can shift the production of cytokines from the inflammation-inducing
interleukin- 12 (IL-12) pathway to the anti-inflammatory IL-10 pathway
2. Strengthening the mucosal barrier. The GIT
functions as a semipermeable barrier that allows the selective passage of
certain molecules. Dysfunctional barriers are involved with diseases of the GIT
such as inflammatory bowel disease. Probiotic strains reinforce and repair this
barrier by stimulating the production of protective proteins, such as mucins,
by intestinal epithelial cells.
3. Exclusion of pathogens. Probiotic strains
can inhibit the adherence of bacterial and viral pathogens and prevent
infection by them.
Probiotics are
used for Animal Nutrition, for Human Health and as Therapeutics for treatment of diseases, including the treatment
of diarrheal conditions, inflammatory bowel disease, allergies, and infections
of the upper respiratory tract.
Prebiotics
Prebiotics are ingredients that selectively promote the
growth of the existing beneficial microbiota. Growth factors in human breast milk,
which stimulate the growth of Bifidobacterium is an example.
Prebiotic is a nondigestible food
ingredient that beneficially affects the host by selectively stimulating the growth
and/or activity of one or a limited number of bacteria in the colon and Synbiotic
is a combination of a prebiotic ingredient with a probiotic culture.
Food ingredients classified as prebiotics exhibit
the following characteristics:
·
Limited
hydrolysis and absorption in the upper GIT
·
Selective
growth stimulation of beneficial bacteria in the colon
·
Potential
to repress pathogens and limit virulence (by attenuation of virulence, immunostimulation,
and stimulation of a beneficial flora)
The best-known prebiotics are
fructo-oligosaccharides derived from food sources. The largest natural source is
inulin from the chicory root which is also found in edible plants like onions, asparagus,
bananas, wheat, etc.
Examples of other
prebiotic factors are Oligosaccharides, Fructans,
Human milk, Lactitol, Synthetic derivative of lactose, etc
References
Food Microbiology: Fundamentals and
Frontiers, 4th Edition,
Michael P. Doyle, Robert L. Buchanan, ASM Press, Washington, DC 20036
No comments:
Post a Comment