Probiotics help maintain human health and support environmental balance. Seven major probiotics species benefit human physical and mental health, and help internal ecosystems run smoothly.
The seven major probiotics genera are Lactobacillus, Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Escherichia and Bacillus. They dwell in the varied climates of the human gastrointestinal (GI) tract.
The GI tract runs from the mouth through esophagus, stomach, intestines and anus, providing various habitats along the way. Intestines and colon are less acidic than the stomach, appealing to more acid-sensitive bacteria.
Digestion begins with the salivary glands in the mouth. Saliva starts the digestive process, helps people chew and swallow food, and tries to protect the teeth.
In the stomach, gastric juice is a combination of hydrochloric acid (HCl), lipase and pepsin. The pH of stomach acid is 1.5 - 3.5, extremely acidic. Not all probiotics can live there, and it provides a buffer against pathogens.
In contrast, the average pH is 6.1 in the duodenum, which is directly connected to the stomach. The pH increases to a neutral 7.1 in the midsection of the small intestine and reaches 7.5 in the distal section.
1. Lactobacillus
Lactobacillus is among the most recognized probiotic bacteria, often seen as rod-shaped organisms. These non-motile bacteria thrive in fermented foods such as yogurt, kefir and sauerkraut.
They're rod-shaped and non-motile though some show "twitching". Facultative anaerobes, they can survive with or without oxygen but prefer anaerobic environments.
Lactobacillus can produce lactic acid to lower the pH of its environment, discouraging harmful bacteria. It's a major genus involved in lactic acid fermentation.
These friendly bacteria break down lactose or milk sugar into lactic acid, aiding digestion. They maintain the GI tract pH, preventing harmful bacterial overgrowth, and stimulate the immune system.
Lactobacillus feeds primarily on sugars like lactose and glucose, producing lactic acid as a byproduct. The fermentation process creates a tangy flavor, helps preserve food and enhance health benefits.
Species such as Lactobacillus reuteri produce substances to combat dental cavities. However, overgrowth can sometimes contribute to dental issues such as tooth erosion from lactic acid.
People with weakened immune systems should be extra careful. Lactobacillus can, rarely, lead to infections.
2. Bifidobacterium
Bifidobacterium is a Y-shaped, non-motile and obligate anaerobe. It can live only in oxygen-free environments.
These bacteria are predominantly found in digestive tracts of mammals, as well as in fermented foods, dairy products like yogurt and some dietary supplements. Bifidobacterium ferments fibers and oligosaccharides.
It then generates hydrogen gas and short-chain fatty acids (SCFAs) like acetate, beneficial for cell and colon health, and vitamins B12 and K. The activity of these bacteria may decrease the risk of colon cancer.
Bifidobacterium helps form a protective barrier or biofilm in the intestines, cultivating a sheltered habitat for other species. It also helps maintain pH and fluid levels.
Bifidobacterium spp are rarely pathogenic. They may cause complications when introduced into sterile body areas (eg, surgery).
3. Saccharomyces
This popular yeast genera is spherical or oval-shaped. The single-celled organisms are non-motile, and facultative anaerobes. They enjoy oxygen-free, acidic environments and make biofilms to cultivate their happy homes.
Saccharomyces cerevisiae is baker's or brewer's yeast, commercially available for beer, bread and microbiology. It has a long history linked to nourishment.
Naturally present in soil, water and skin of fruits like grapes, Saccharomyces spp help balance the digestive ecosystem in humans. They repulse pathogens like Clostridium difficile who like to wreak havoc on the colon.
Saccharomyces spp produce vitamins such as B12 and folate. They protect against diarrhea caused by antibiotics.
The yeasts ferment sugars such as glucose, fructose and sucrose, creating ethanol and carbon dioxide as byproducts. Saccharomyces boulardii has strong heat tolerance thus a high survival rate as a probiotic.
Saccharomyces reproduces asexually through budding, with new yeast cells forming from existing ones. Although technically immotile, it can expand into new territory by forming pseudohyphae or branches of daughter cells.
These probiotics can cause infections in immunocompromised individuals. People with weak immune systems should be careful supplementing.
4. Streptococcus
Streptococcus are spherical (cocci), typically forming chains, and non-motile. They're found in the human oral cavity, skin, and some dairy products.
The Streptococcus genus includes both beneficial and harmful species. These bacteria consume sugars and excrete lactic acid like Lactobacillus. They reproduce by binary fission, forming chains during this process.
Species like Streptococcus thermophilus are used in yogurt production and promote GI tract health. These bacteria enhance lactose digestion, helping lactose-intolerant individuals metabolize "milk sugar".
Streptococcus pyogenes is the pathogenic strain causing strep throat.
Certain species outside the definition of probiotics can contribute to dental plaque, a bacterial and fungal biofilm, or infections.
Beneficial strains promote digestive health and have practical applications in cheese production. Harmful strains can lead to serious illness if not identified and treated.
5. Enterococcus
The Enterococcus group is another set of lactic acid bacteria (LAB) commonly found in probiotic supplements. These spherical bacteria can exist in pairs or chains.
Enertococcus are non-motile, facultative anaerobes. They're found in soil, water, and the gastrointestinal tracts of humans and other animals. They aid nutrient absorption and inhibit pathogens.
They produce bacteriocins, or protein-based antimicrobials, to fight harmful bacteria. Enterococcus species obtain nutrients through lactose fermentation, generating lactic acid and other byproducts.
Enertococcus spp have remarkable antibiotic resistance, allowing survival in various environments. The strains E. faecalis and E. faecium are opportunistic pathogens known for causing hospital-acquired infections.
6. Escherichia (E. coli)
Escherichia spp are rod-shaped, motile (via flagella) or non-motile, facultative anaerobes. Some strains, such as E. coli Nissle 1917, are robust probiotics.
They commonly live in the intestines of animals and humans. Most strains are harmless and help synthesize vitamins like K2. They assist in nutrient absorption and health of the GI tract.
Escherichia feed on nutrients from digested food, primarily sugars and amino acids. They excrete metabolic byproducts like carbon dioxide gas and create SCFAs vital for health.
While harmless E. coli strains are beneficial, pathogenic ones (e.g., O157:H7) can cause foodborne illnesses. The beneficial strains of E. coli are known for crowding out harmful bacteria and enhancing digestive health.
Some pathogenic strains produce toxins that severely damage GI tract lining. They cause serious inflammation, diarrhea, urinary tract infections and other complications.
7. Bacillus
Bacillus are rod-shaped, motile (via flagella), and facultative aerobes. They can survive without oxygen, but prefer it in the environment. They're found in soil, water, and fermented foods.
Probiotic strains such as B. subtilis and B. coagulans promote GI tract health and produce digestive enzymes. They can enhance immune response and reduce inflammation.
Bacillus spp feed on organic matter, excreting enzymes, SCFAs and gases.
They reproduce asexually by binary fission and can form endospores to survive extreme environments.
Their spore-forming process enables them to reproduce when the environment is favorable. In WWII, Bacillus subtilis is used by soldiers as a "natural antibiotic" for dysentery.
Bacillus coagulans has strong probiotic properties and shows calming effects on the digestive system. However, mishandling some Bacillus strains can cause food spoilage or contamination, and food poisoning.
Overall, some species of these genera are more conducive to human health than others. The symbiotic relationship between humans and their microbes is complex and varied, an evolution of millions of years.
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