Probiotics are defined as “live micro-organisms that when administered in adequate amounts confer a health benefit on the host” (World Health Organization, 2001). Probiotics are traditionally used to restore the balance of the intestinal microflora which can become unbalanced due to illness, stress, age, travelling, or the use of medication such as antibiotics. It is important to note that the effects are strain specific and cannot be regarded as general for the various probiotics.

Most probiotic organisms belong to the lactobacillus and bifidobacteria genera. However, there are many genera, species, and strains of bacteria that inhabit the intestinal flora of the human gastrointestinal tract at any one time. It is estimated the human gut contains more than 100 trillion bacterial cells from over 500 different species. It should be noted that “probiotic” bacteria are considered only those that have documented effects.

Clinical studies have demonstrated that probiotics can offer many health benefits. Some of the scientifically established health effects are:

• Reduction in the occurrence and duration of rotavirus diarrhea.
• Reduction in duration of antibiotic-associated diarrhea.
• Alleviation of symptoms of lactose intolerance.
• Alleviation of symptoms of food and skin allergies in children.
• Reduction of recurrent ear and bladder infections.
• Reducing incidence and/or duration of bacterial vaginosis.
• Improvement of halitosis.

Some of the common probiotics that have shown to have beneficial health effects belong to the following species. (Please note that not all within one species can be regarded as probiotics).

• Lactobacillus acidophilus.
• Lactobacillus fermentum.
• Lactobacillus casei/paracasei.
• Lactobacillus plantarum.
• Lactobacillus reuteri.
• Lactobacillus delbrueckii subsp. bulgaricus.
• Lactobacillus rhamnosus.
• Bifidobacterium longum ssp. longum.
• Bifidobacterium longum ssp. infantis.
• Bifidobacterium bifidum.
• Bifidobacterium animalis ssp. lactis.
• Pediococcus acidilactici.
• Saccharomyces boulardii (yeast).
• Bacillus Coagulans.

Lactobacillus is one of the most common and well-known genus of probiotic bacteria. It contains about 80 recognized species, with the most well-known being Lactobacillus acidophilus. The name “Lactobacillus” is broken down into “lacto,” derived from “lactic” acid, and “bacillus,” meaning rod-shaped. Thus, lactobacillus species are rod-shaped bacteria that produce lactic acid from fermentable sugars such as glucose, fructose, lactose and/or galactose. The major by-products of lactobacilli fermentation are lactic and acetic acids.

Bifidobacterium is the most abundant genus of good bacteria in the human gastro-intestinal tract. The “bifido” part of the term “bifidobacteria” comes from “bifidus,” meaning “split in two, separated by a cleft.” Thus, bifidobacteria can often be identified by their Y-shaped, or bifid, structure. However, bifidobacteria also exist in V-, or X-shaped forms, and can be found in more rounded shapes as well. The major by-products of bifidobacteria fermentation are lactic, acetic, and butyric acids; additionally succinic acid can also be produced by some strains of bifidobacteria.

Probiotic bacteria are very strain dependent, not species dependent. A strain is a type of a bacterial species, similar as to the example below:

Bacterial group = German car = lactic acid bacteria
Bacterial genus = Volkswagen = Lactobacillus
Bacterial species = VW Golf = Lactobacillus acidophilus
Bacterial strain = VW Golf 1.4 D = Lb. acidophilus LC1

Everybody knows that a Volkswagen Golf 1.4 D has other characteristics than a Volkswagen Golf 2.0i turbo, but you can't see the difference on the outside.

The same is true for bacteria; they all look the same, but the biological characteristics (‘the engine') are different. Hence, claims on health effects of a certain probiotic are only valid for that specific strain, not species.

The field of probiotic study is relatively new, getting started only around 1908, when a Russian immunologist named Dr. Eli Metchnikoff studied Russian and Bulgarian peasants who had long life spans. Dr. Metchnikoff linked their longevity to their diet, which included large amounts of fermented milks (yoghurts). He proposed a link between better health and longer life by consuming lactic acid bacteria (probiotics) that were delivered to the intestine by the consumption of yogurt.

For the next several decades, scientific research into probiotics moved slowly, with renewed interest in the 1960’s. In 1935, the Yakult Company of Japan introduced a fermented milk product containing a probiotic culture. Today in Japan, one will find dozens of probiotic-containing products on supermarket shelves, ranging from fortified drinks to candy containing strains from the Lactobacillus and Bifidobacterium genera.

In Europe, the dairy sector is the most developed segment of the market. Probiotic yogurts and fermented milks that are sold in a convenient "daily dose" format are the most widely used. Consumer acceptance of probiotic-containing products varies greatly across Europe. Northern European and Scandinavian countries, which have a long traditional consumption of fermented dairy products, demonstrate the highest acceptance in the European probiotic market. Within Europe, the use of probiotic dietary supplements has been slow to gain acceptance, but it is fast becoming a booming category.

In the U.S., the situation is reversed, with dietary supplements by far being the most accepted product format (vs. probiotic-containing foods such as yogurt and fermented milk). It is generally established that US consumers are far more willing than their European counterparts to take supplements, which may explain the large difference. Conversely, the functional dairy food market in the US for probiotic-containing products is still quite underdeveloped. However, this situation is changing rapidly, as major probiotic manufacturers are teaming up with large U.S. dairy and food companies to produce more probiotic containing functional foods such as smoothies, yogurts, bars, cereal, candy, and other fortified food and beverage items.

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