Out of the hundreds of strains of bacteria resident in the human gastrointestinal tract, Lactobacillus acidophilus is but one – but an extremely important one.
Around 500 species of bacteria
, as well as many species of yeast
and other organisms, inhabit the human gastrointestinal
tract and make up the "gut flora". In an average adult the bacteria weigh about 1kg and the number of individual organisms easily outnumbers the total number of cells in the human body.
Luckily for us a large number of these organisms don't cause disease – instead, they help protect us from disease. The gut flora perform many functions that contribute to the health of the human host; "friendly bacteria" mostly have names beginning with 'Lactobacillus' or 'Bifidobacteria'. You may have noticed food products like yogurt that contain these bacteria. It is becoming more common for them to be added, just as vitamins and minerals are added to some food products.
The friendly bacteria aren't the only type of microorganism present in the human gastrointestinal
tract however. There are also a number of organisms that don't provide the human host with any benefits; these include coliform bacteria, yeasts and bacteroides. Usually these other organisms are kept in balance with the friendly bacteria.
Function; Why it is RecommendedLactobacillus
type strains are capable of fermenting food stuffs to lactic acid. L. acidophilus
and similar strains are used in cultured dairy products such as yogurt. Other major useful functions of friendly bacteria
- Producing short chain fatty acids which supply a valuable proportion of human energy requirements
- Producing a number of valuable nutrients notably B vitamins and vitamin K
- Participating in the metabolism of drugs, hormones and carcinogens
- Protecting the host from infection by pathogenic bacteria (through competing for space and production of anti-bacterial substances amongst other methods.)
- Maintaining a healthy intestinal pH
- Enhancing immune function.
For many years, the addition of these "good" bacteria
to our intestinal tract has been used to promote health. As a class, they have been referred to as probiotics
, since they stimulate organismal growth is the intestines. Uses of probiotics have been especially helpful when antibiotic use kills many of the good bacteria, allowing other less beneficial bacteria to take up residence in the gut.
Lactobacilli have active anti-microbial characteristics and are able to kill various pathogens such as Streptococcus
, E. coli
and the yeast Candida
. The benefits of lactobacillus
and other probiotics are only now coming to full light, so expect much more research to be forthcoming in the next few years.
Illness can occur when the amount of friendly bacteria is reduced and the other organisms are able to increase their numbers and become the majority. There are a number of factors that can disrupt the balance of organisms in the intestines and lead to overgrowth of the less desirable species.
The most important factors are:
- Antibiotic use
- Use of the birth control pill
- Use of other hormones, especially immunosupressants like steroids
Probably the most important factor is the use of broad spectrum antibiotics. These medications don't discriminate between friendly and unfriendly bacteria. This means that every time you take one of these drugs for an infection your are wiping out large numbers of the friendly bacteria in your intestines that give protection from other, potentially harmful, intestinal residents. This fact has long been known by researchers and is taught to microbiology students.