As a medical doctor specializing in medical microbiology, my scientific interest is
the patient-related importance of the gastrointestinal microflora. This concerns the
defense function of the microflora, the conditions that lead to distortion of this
"win-win" arrangement, the medical consequences of such distortions, and a simplified
classification of microorganisms that can cause infectious disease.
The past decade has seen a somewhat amazingly increased interest in the use of
intestinal species of lactic acid-producing bacteria in the production of milk products.
Lactobacillus acidophilus and Bifidobacterium species are now common components
of yogurts that are retailed throughout the world.
Although the history of fermented milks goes back many hundreds of years to
prebiblical times, the real study of the health benefits derived from consumption of
soured milks begins with the work of Metchnikoff.
Probiotics are defined as "a live microbial feed supplement which beneficially affects
the host animal by improving its intestinal microbial balance." Examples of
desired effects include competitive exclusion of pathogenic microorganisms and
altered metabolism of the intestinal flora
The intestinal microflora of an adult person is a complex ecosystem, estimated to
harbor about 400 different bacterial species. Anaerobic bacteria outnumber aerobic
and facultative bacteria by a factor of 100 to 1000.
All free-living macroorganisms, including humans, are normally born without any
microorganisms. Shortly after birth, microbial colonization begins. At first, with
plenty of space and nutrients, microbes with a high multiplication rate may predominate.
The identification of the now classical enteric pathogens was accomplished during
the first few decades of this century. It was the first spectacular success of medical
Helicobacter pylori has markedly changed our views of host-microbial interactions
in general and the pathogenesis of peptic ulcer disease in particular. The discovery
by Marshall and Warren (1) illustrates the seemingly endless ability of prokaryotic
life forms to adapt to their environment.
It is well known that human milk has not only nutritive value but also many other
physiological functions, including the supply of prebiotics. With regard to its biological
functions, it has recently been shown that the carbohydrate moiety of glycoconjugates
may play an important role (1).
The human intestinal tract is colonized by a huge number of microbes (around 1014).
These grow predominately in the region of the large bowel (1). These microbes
consist of more than 400 different species and subspecies and are either nonpathogenic
or pathogenic to the host.
Diarrheal diseases remain important causes of morbidity and mortality in many areas
of the world. They can cause health problems in every age group; however, their
major effects are most evident in infants and young children (1).
With a potential annual market of over $100 billion, it is unsurprising that the concept
of "functional foods" is currently attracting much interest.
It has been known for a long time that the fecal flora of breast-fed infants is quite
different from that of infants fed adapted cow's milk or infant formula (1,2).
The primary role of the diet is to provide enough of the various nutrients to fulfill
the recommendations for a balanced diet, while giving the consumer a feeling of
satisfaction and well-being.
The complicated task of the gut mucosa in accepting nutrients at the same time as
protecting against infectious agents is reflected in the size of its immune system.
There are more lymphoid cells in the gut than in the spleen, peripheral lymph glands,
and blood together.
The mucosal surface of the gastrointestinal tract forms an important organ of host
defense. In addition to its principal physiological function—digestion and absorption
of nutrients—the intestinal mucosa provides a protective interface between the internal
environment and the constant challenge from antigens in food and microorganisms
from the external environment.
Food manufacturers have used different strategies for increasing the level of beneficial
bacteria in the human gastrointestinal tract following consumption of dairy
Probiotics are commonly defined as viable microorganisms (yeasts or bacteria) that
have a beneficial effect on the health of the host when they are ingested. They are
used in drug formulations, but also in foods, especially in fermented dairy products.
The deliberate addition of microorganisms to the diet of humans dates back to ancient
times. Initially, these were probably ingested in the form of fermented milk products,
where the bacteria were used to preserve dairy foods.
Extensive clinical and epidemiological studies have shown that breastfeeding is
effective at reducing the risks of infantile diarrhea and other infectious diseases
(1-3). Acute infectious diarrhea continues to be one of the most common causes
of infant morbidity and mortality in developing countries (4).
I have been given the very last word, which I promise will be brief.
We have over these 3 days been talking about two very large, very complex