Intestinal Bacteria and Probiotics ◾ 195
of infants from the environment. From these, the normal flora of the GI tract are established. In
both breast-fed and formula-fed babies during the first couple of days, Escherichia coli and Enterococcus
appear in large numbers in the feces. Then, in the breast-fed babies, large numbers of Bifidobacterium
species and a lower level of both Esc. coli and Enterococcus species appear. In formula-fed babies, in
contrast, Esc. coli and Enterococcus, together with Clostridium and Bacteroides, predominate, with
Bifidobacterium being almost absent; this situation may lead to diarrhea. As breast-fed babies are
introduced to other foods, the levels of Esc. coli, Enterococcus, Bacteroides, Clostridium, and others increase, but Bifidobacterium still remains high. When breast-feeding is completely stopped,
Bacteroides, Bifidobacterium, and Lactobacillus species predominate, along with some Esc. coli,
Enterococcus, Clostridium, and others. By the second year of life, the different microflora establish
themselves at their specific ecological niche in the GI tract, and the population resembles that of
adult GI tracts.
The intestinal microflora are divided into indigenous (autochthonous) and transient (allochthonous) types. Many indigenous species can adhere to intestinal cells, which helps maintain them in
their specific niche. Whereas the indigenous types are permanent inhabitants, the transient types
are either passing through or temporarily colonizing a site from where the specific indigenous type
has been removed because of some inherent or environmental factors (such as antibiotic intake).
Among the indigenous microbial flora, several species of Lactobacillus in the jejunum and
ilium, and Bifidobacterium in the large intestine are thought to have beneficial effects on the health
of the GI tracts of the hosts. From the intestines and intestinal content of humans, Lactobacillus
acidophilus, Lactobacillus fermentum, Lactobacillus rhamonosus, Lactobacillus reuteri, Lactobacillus
casei, Lactobacillus lactis, Lactobacillus leichmannii, Lactobacillus plantarum, Bifidobacterium bifidus, Bif. longum, Bif. adolescentis, Bif. infantis, and others have been isolated. However, age, food
habits, and health conditions greatly influence the species and their levels. There is some belief
that a portion of the intestinal Lactobacillus species is transient. Initially, it was considered that
Lactobacillus acidophilus, Lactobacillus reuteri, and some Bifidobacterium are the main indigenous
species. At present, several other Lactobacillus species, such as Lactobacillus casei and Lactobacillus
rhamnosus, have been tested to be beneficial. The presence of high numbers of the indigenous
Lactobacillus species in the feces (and content of the large intestine) probably results from their
constant removal from the small intestine.
Gut Microbiota, Health, and Chronic Diseases
In recent years, enormous interest has been generated in understanding the role of the intestinal
microbial community in brain development, psychological well being, infectious diseases, inflammatory bowel diseases, and chronic metabolic disorders, such as obesity and diabetes. 2 The human
microbiome project conducted by the National Institute of Health 3 revealed that microbial communities from different parts of the body (skin, gut, and vagina) differ greatly among healthy
individuals. Furthermore, the variation may also be attributed to diet, host genetics, race and
ethnicity, and environment. Metagenomic data, however, pointed to the stability in microbial
metabolic pathways despite variation in microbial community structure. 3 A diverse colonization of
the microbial community in the gut early in life promotes a balanced immune response and prevents allergic diseases, obesity, and diabetes. 4 In obese hosts, the microbial community consists of
a high ratio of Firmicutes to Bacteriodetes, 5 and this dominant phylum is responsible for enhanced
hydrolysis of complex carbohydrates to produce energy and increased nutrient adsorption. Gut
microbiota are also responsible for insulin resistance, increased adsorption of triglycerides, and
of infants from the environment. From these, the normal flora of the GI tract are established. In
both breast-fed and formula-fed babies during the first couple of days, Escherichia coli and Enterococcus
appear in large numbers in the feces. Then, in the breast-fed babies, large numbers of Bifidobacterium
species and a lower level of both Esc. coli and Enterococcus species appear. In formula-fed babies, in
contrast, Esc. coli and Enterococcus, together with Clostridium and Bacteroides, predominate, with
Bifidobacterium being almost absent; this situation may lead to diarrhea. As breast-fed babies are
introduced to other foods, the levels of Esc. coli, Enterococcus, Bacteroides, Clostridium, and others increase, but Bifidobacterium still remains high. When breast-feeding is completely stopped,
Bacteroides, Bifidobacterium, and Lactobacillus species predominate, along with some Esc. coli,
Enterococcus, Clostridium, and others. By the second year of life, the different microflora establish
themselves at their specific ecological niche in the GI tract, and the population resembles that of
adult GI tracts.
The intestinal microflora are divided into indigenous (autochthonous) and transient (allochthonous) types. Many indigenous species can adhere to intestinal cells, which helps maintain them in
their specific niche. Whereas the indigenous types are permanent inhabitants, the transient types
are either passing through or temporarily colonizing a site from where the specific indigenous type
has been removed because of some inherent or environmental factors (such as antibiotic intake).
Among the indigenous microbial flora, several species of Lactobacillus in the jejunum and
ilium, and Bifidobacterium in the large intestine are thought to have beneficial effects on the health
of the GI tracts of the hosts. From the intestines and intestinal content of humans, Lactobacillus
acidophilus, Lactobacillus fermentum, Lactobacillus rhamonosus, Lactobacillus reuteri, Lactobacillus
casei, Lactobacillus lactis, Lactobacillus leichmannii, Lactobacillus plantarum, Bifidobacterium bifidus, Bif. longum, Bif. adolescentis, Bif. infantis, and others have been isolated. However, age, food
habits, and health conditions greatly influence the species and their levels. There is some belief
that a portion of the intestinal Lactobacillus species is transient. Initially, it was considered that
Lactobacillus acidophilus, Lactobacillus reuteri, and some Bifidobacterium are the main indigenous
species. At present, several other Lactobacillus species, such as Lactobacillus casei and Lactobacillus
rhamnosus, have been tested to be beneficial. The presence of high numbers of the indigenous
Lactobacillus species in the feces (and content of the large intestine) probably results from their
constant removal from the small intestine.
Gut Microbiota, Health, and Chronic Diseases
In recent years, enormous interest has been generated in understanding the role of the intestinal
microbial community in brain development, psychological well being, infectious diseases, inflammatory bowel diseases, and chronic metabolic disorders, such as obesity and diabetes. 2 The human
microbiome project conducted by the National Institute of Health 3 revealed that microbial communities from different parts of the body (skin, gut, and vagina) differ greatly among healthy
individuals. Furthermore, the variation may also be attributed to diet, host genetics, race and
ethnicity, and environment. Metagenomic data, however, pointed to the stability in microbial
metabolic pathways despite variation in microbial community structure. 3 A diverse colonization of
the microbial community in the gut early in life promotes a balanced immune response and prevents allergic diseases, obesity, and diabetes. 4 In obese hosts, the microbial community consists of
a high ratio of Firmicutes to Bacteriodetes, 5 and this dominant phylum is responsible for enhanced
hydrolysis of complex carbohydrates to produce energy and increased nutrient adsorption. Gut
microbiota are also responsible for insulin resistance, increased adsorption of triglycerides, and