From Alzheimer’s to Zebrafish: Eclectic Science and Regulatory Stories 90
Probiotic foods have recently become popular in the US, although such products have been
marketed for decades in Europe and Asia.1 Probiotics are defined as living organisms that,
when administered in sufficient numbers, are beneficial to the host. One example is Activia.
It is the brand name for a line of yogurt with Lactobacillus, Streptococcus thermophilus, and
Bifidobacterium animalis bacteria, and it is advertised to aid regularity. While new to the US,
it has been sold in Europe since 1987.2 Most probiotic products can be found in the dairy
case of supermarkets or as dietary supplements. There are probiotic frozen yogurts and
dairy-based drinks such as DanActive, a probiotic yogurt drink that contains Lactobacillus
casei immunitas cultures. Its manufacturer (Dannon) indicates that the product is clinically
proven to “help strengthen your body’s defenses.”3 Products sold in the pharmacy, among
others, include Culturelle (Lactobacillus GG), Lactinex (Lactobacillus acidophilus, Lactobacillus
bulgaricus) and Florastor (Saccharomyces boulardii), which are indicated to reduce the chance
of developing diarrhea due to antibiotics.4 The US Food and Drug Administration (FDA)
takes a neutral position on probiotics, policing food packages to ensure that companies do
not try to equate probiotic products with disease-curing drugs.
The growth of probiotics comes as many scientists are now focused on the role of
beneficial bacteria to aid digestion, boost natural defenses and fight off harmful bacteria
that could cause health problems. Intestinal bacteria can benefit health by breaking down
toxins, synthesizing vitamins and defending against infection. They may also play a role
in such diseases as peptic ulcers, colorectal cancer and inflammatory bowel disease.5 This
article describes the genesis and evolution of our indigenous microbial community, the
size and makeup of its inhabitants, their effects and benefits and new research.
Genesis and Evolution
Most of us are aware that bacteria are a part of a healthy human ecosystem (i.e., an assem-
bly of species and the organic and inorganic constituents characterizing a particular site).
According to one author, the armies of bacteria that sneak into our bodies the moment we
are born are the “primal illegal immigrants.”6 Most are industrious and friendly, minding
their own business in tight-knit, long-lived communities, doing the grunt biochemical work
we all rely on to stay alive.7 The ecosystem forms at birth, but the human-microbe alliance
begins months before. Midway through pregnancy, a hormonal shift directs the cells lining
the vagina to begin stockpiling sugary glycogen, the favorite food of sausage-shaped bacte-
ria called lactobacilli. By fermenting the sugar into lactic acid, these bacteria lower the pH
of the vagina to levels that discourage the growth of potentially dangerous invaders.8
The infant mouth’s first inoculation of bacteria includes a generous sampling of the
lactobacilli present in the mother’s birth canal. With the first gulp of breast milk, these
lactobacilli are joined by millions of bifidobacteria, a related group of acid-producing
microbes.9 The source of these bacteria is the mother’s nipples, where the bacteria appear
during the eighth month of pregnancy. Bifidobacteria secrete acids and antibiotic chemicals
that repel potentially dangerous organisms including Staphylococcus aureus. Bifidobacteria
and lactobacilli are soon joined with acid-tolerant Streptococcus salivarius that appear on a
baby’s tongue during the first day of life. Bifidobacteria are anaerobic, pleomorphic rods
that break down dietary carbohydrate and synthesize and excrete water-soluble vitamins.10
Their name is derived from the observation that they often exist in a Y-shaped or bifid
form.11 These organisms predominate in the colons of breast-fed babies and account for up
to 95% of all culturable bacteria and protect against infection.12 Strangely, they do not occur
in such high numbers in adults.13 Several other streptococci, along with one or more kinds
of Neisseria bacteria, settle in during the first week. The vast majority emanate from the
mother’s mouth, which is always within reach of a nursing baby’s fingers.14
As the baby begins nursing or drinking formula, the bacterial population inside the
mouth increases. These bacteria consume oxygen, creating a zone where anaerobic bacteria
can thrive. By the time the baby is two months old, a microscopic close-up of the gums will
Probiotic foods have recently become popular in the US, although such products have been
marketed for decades in Europe and Asia.1 Probiotics are defined as living organisms that,
when administered in sufficient numbers, are beneficial to the host. One example is Activia.
It is the brand name for a line of yogurt with Lactobacillus, Streptococcus thermophilus, and
Bifidobacterium animalis bacteria, and it is advertised to aid regularity. While new to the US,
it has been sold in Europe since 1987.2 Most probiotic products can be found in the dairy
case of supermarkets or as dietary supplements. There are probiotic frozen yogurts and
dairy-based drinks such as DanActive, a probiotic yogurt drink that contains Lactobacillus
casei immunitas cultures. Its manufacturer (Dannon) indicates that the product is clinically
proven to “help strengthen your body’s defenses.”3 Products sold in the pharmacy, among
others, include Culturelle (Lactobacillus GG), Lactinex (Lactobacillus acidophilus, Lactobacillus
bulgaricus) and Florastor (Saccharomyces boulardii), which are indicated to reduce the chance
of developing diarrhea due to antibiotics.4 The US Food and Drug Administration (FDA)
takes a neutral position on probiotics, policing food packages to ensure that companies do
not try to equate probiotic products with disease-curing drugs.
The growth of probiotics comes as many scientists are now focused on the role of
beneficial bacteria to aid digestion, boost natural defenses and fight off harmful bacteria
that could cause health problems. Intestinal bacteria can benefit health by breaking down
toxins, synthesizing vitamins and defending against infection. They may also play a role
in such diseases as peptic ulcers, colorectal cancer and inflammatory bowel disease.5 This
article describes the genesis and evolution of our indigenous microbial community, the
size and makeup of its inhabitants, their effects and benefits and new research.
Genesis and Evolution
Most of us are aware that bacteria are a part of a healthy human ecosystem (i.e., an assem-
bly of species and the organic and inorganic constituents characterizing a particular site).
According to one author, the armies of bacteria that sneak into our bodies the moment we
are born are the “primal illegal immigrants.”6 Most are industrious and friendly, minding
their own business in tight-knit, long-lived communities, doing the grunt biochemical work
we all rely on to stay alive.7 The ecosystem forms at birth, but the human-microbe alliance
begins months before. Midway through pregnancy, a hormonal shift directs the cells lining
the vagina to begin stockpiling sugary glycogen, the favorite food of sausage-shaped bacte-
ria called lactobacilli. By fermenting the sugar into lactic acid, these bacteria lower the pH
of the vagina to levels that discourage the growth of potentially dangerous invaders.8
The infant mouth’s first inoculation of bacteria includes a generous sampling of the
lactobacilli present in the mother’s birth canal. With the first gulp of breast milk, these
lactobacilli are joined by millions of bifidobacteria, a related group of acid-producing
microbes.9 The source of these bacteria is the mother’s nipples, where the bacteria appear
during the eighth month of pregnancy. Bifidobacteria secrete acids and antibiotic chemicals
that repel potentially dangerous organisms including Staphylococcus aureus. Bifidobacteria
and lactobacilli are soon joined with acid-tolerant Streptococcus salivarius that appear on a
baby’s tongue during the first day of life. Bifidobacteria are anaerobic, pleomorphic rods
that break down dietary carbohydrate and synthesize and excrete water-soluble vitamins.10
Their name is derived from the observation that they often exist in a Y-shaped or bifid
form.11 These organisms predominate in the colons of breast-fed babies and account for up
to 95% of all culturable bacteria and protect against infection.12 Strangely, they do not occur
in such high numbers in adults.13 Several other streptococci, along with one or more kinds
of Neisseria bacteria, settle in during the first week. The vast majority emanate from the
mother’s mouth, which is always within reach of a nursing baby’s fingers.14
As the baby begins nursing or drinking formula, the bacterial population inside the
mouth increases. These bacteria consume oxygen, creating a zone where anaerobic bacteria
can thrive. By the time the baby is two months old, a microscopic close-up of the gums will