Intestinal Bacteria and Probiotics ◾ 197
indigenous or transient bacteria to grow to high levels and produce enteric disturbances, including
diarrhea, flatulence, and infection by enteric pathogens.
Beneficial effects of Probiotics
The word “probiotic” is derived from the Greek word meaning “for life.” Probiotics are defined as
live microorganisms, which, when administered in adequate amounts, confer a health benefit on
the host. In the last 40 years, studies have been conducted to determine specific health benefits
from the consumption of live cells of beneficial bacteria. Live cells have been consumed from
three principal sources: (1) as fermented milk products, such as yogurt, which contains live cells
of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus and is supplemented with
Lab. acidophilus and others, and pasteurized milk, which contains Lactobacillus acidophilus; (2) as
supplementation of foods and drinks with live cells of one, two, or more types of probiotics, such
as Lactobacillus acidophilus, Lactobacillus reuteri, Lactobacillus casei, and Bifidobacterium species;
and (3) as pharmaceutical products of live cells of a monoculture or a mixture in the form of
tablets, capsules, granules, and freeze-dried sachets. For example VSL #3 is a commercial product, and it consists of four species of Lactobacillus (casei, plantarum, acidophilus, and delbrueckii
subsp. bulgaricus), three species of Bifidobacterium (longum, breve, and infantis), and one strain of
Streptococcus salivarius subsp. thermophilus. Probiotic preparations consisting of multiple species or
strains are functionally superior because of their synergistic effects, and if one culture fails, others
can compensate, which is not possible for probiotics of a monoculture. The beneficial effects from
consuming these live cells were attributed to their ability to provide protection against enteric
pathogens, supply enzymes to help metabolize some food nutrients (such as lactase to hydrolyze lactose), detoxify some harmful food components and metabolites in the intestine, stimulate
intestinal immune systems, improve intestinal peristaltic activity, reduce tumerogenesis (colorectal cancer), and ameliorate chronic disorders, such as ulcerative colitis (UC) and inflammatory
bowel disease (IBD). Some of the benefits are briefly discussed here (Figure 16.2). In addition,
many other benefits have been claimed by entrepreneurs without any scientific basis, and they are
not discussed.
Lactose Hydrolysis
Lactose-intolerant individuals, because of a genetic disorder, are unable to produce lactase
(β-galactosidase) in the small intestine. When these people consume milk, lactose molecules are
not hydrolyzed in or absorbed from the small intestine but are passed to the colon. They are then
hydrolyzed in the colon by lactase of different bacteria to glucose and galactose and then further
metabolized to produce acids and gas, resulting in fluid accumulation, diarrhea, and flatulence.
Consumption of yogurt, acidophilus milk, and live cells of Lactobacillus, especially Lactobacillus
acidophilus in fresh milk and pharmaceutical products, reduces the symptoms in lactose-intolerant
individuals. This benefit is attributed to the ability of beneficial bacteria to supply the needed
lactase in the small intestine. However, as Lactobacillus delbrueckii ssp. bulgaricus and Str. thermophilus do not survive stomach acidity well and are not normal intestinal bacteria, the benefit of
consuming normal yogurt is considered to be a result of the reduced amounts of lactose in yogurt
as compared to milk and to the supply of lactase from the dead cells. In contrast, the intestinal
bacteria, especially some Lactobacillus species, could, under proper conditions, colonize the small
intestine and subsequently supply lactase. Different studies, however, did not unequivocally prove
indigenous or transient bacteria to grow to high levels and produce enteric disturbances, including
diarrhea, flatulence, and infection by enteric pathogens.
Beneficial effects of Probiotics
The word “probiotic” is derived from the Greek word meaning “for life.” Probiotics are defined as
live microorganisms, which, when administered in adequate amounts, confer a health benefit on
the host. In the last 40 years, studies have been conducted to determine specific health benefits
from the consumption of live cells of beneficial bacteria. Live cells have been consumed from
three principal sources: (1) as fermented milk products, such as yogurt, which contains live cells
of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus and is supplemented with
Lab. acidophilus and others, and pasteurized milk, which contains Lactobacillus acidophilus; (2) as
supplementation of foods and drinks with live cells of one, two, or more types of probiotics, such
as Lactobacillus acidophilus, Lactobacillus reuteri, Lactobacillus casei, and Bifidobacterium species;
and (3) as pharmaceutical products of live cells of a monoculture or a mixture in the form of
tablets, capsules, granules, and freeze-dried sachets. For example VSL #3 is a commercial product, and it consists of four species of Lactobacillus (casei, plantarum, acidophilus, and delbrueckii
subsp. bulgaricus), three species of Bifidobacterium (longum, breve, and infantis), and one strain of
Streptococcus salivarius subsp. thermophilus. Probiotic preparations consisting of multiple species or
strains are functionally superior because of their synergistic effects, and if one culture fails, others
can compensate, which is not possible for probiotics of a monoculture. The beneficial effects from
consuming these live cells were attributed to their ability to provide protection against enteric
pathogens, supply enzymes to help metabolize some food nutrients (such as lactase to hydrolyze lactose), detoxify some harmful food components and metabolites in the intestine, stimulate
intestinal immune systems, improve intestinal peristaltic activity, reduce tumerogenesis (colorectal cancer), and ameliorate chronic disorders, such as ulcerative colitis (UC) and inflammatory
bowel disease (IBD). Some of the benefits are briefly discussed here (Figure 16.2). In addition,
many other benefits have been claimed by entrepreneurs without any scientific basis, and they are
not discussed.
Lactose Hydrolysis
Lactose-intolerant individuals, because of a genetic disorder, are unable to produce lactase
(β-galactosidase) in the small intestine. When these people consume milk, lactose molecules are
not hydrolyzed in or absorbed from the small intestine but are passed to the colon. They are then
hydrolyzed in the colon by lactase of different bacteria to glucose and galactose and then further
metabolized to produce acids and gas, resulting in fluid accumulation, diarrhea, and flatulence.
Consumption of yogurt, acidophilus milk, and live cells of Lactobacillus, especially Lactobacillus
acidophilus in fresh milk and pharmaceutical products, reduces the symptoms in lactose-intolerant
individuals. This benefit is attributed to the ability of beneficial bacteria to supply the needed
lactase in the small intestine. However, as Lactobacillus delbrueckii ssp. bulgaricus and Str. thermophilus do not survive stomach acidity well and are not normal intestinal bacteria, the benefit of
consuming normal yogurt is considered to be a result of the reduced amounts of lactose in yogurt
as compared to milk and to the supply of lactase from the dead cells. In contrast, the intestinal
bacteria, especially some Lactobacillus species, could, under proper conditions, colonize the small
intestine and subsequently supply lactase. Different studies, however, did not unequivocally prove