In recent years, a growing body of research evaluating human health has supported the importance of establishing a favorable colonic environment. Much attention has focused on how colonic microorganisms affect human health and nutrition. The human gut contains a diverse array of bacteria that can produce a variety of physiological effects. Some have pathogenic (harmful) effects such as diarrhea, infections, liver damage, carcinogenesis and intestinal putrefaction. Others have health-promoting effects, including inhibition of pathogenic bacteria growth, stimulation of immune function, improvement in digestion and nutrient absorption, and enhanced vitamin synthesis.
At birth, babies have nearly sterile gastrointestinal (GI) tracts, which are soon colonized with large numbers of Bifidobacterium and Lactobacillus, particularly in breast-fed infants. By adulthood, more than 400 different species of bacteria may be present in the gut. Resident bacteria can be found from the mouth through the length of the GI tract. The greatest population is in the colon, where bacteria account for 35 percent to 50 percent of colonic volume.
Bacterial interactions and competition among species is believed to play a major role in the composition of colonic microflora. Generally, for bacteria to colonize the colon they must have the capability to attach to the intestinal epithelium. A microbe’s ability to compete for nutrients and adhesion sites on the colonic mucosa largely determines its survival. Diet has also been found to influence bacterial population, as different types of bacteria prefer different nutrient sources. In general, undigested dietary fibers are a good source of nutrients for intestinal bacteria. Fiber resists hydrolysis by the salivary and intestinal enzymes and reaches the colon intact, becoming available for further fermentation by colonic bacteria.
The primary function of the colon is recycling water and disposing of waste by changing food into solid material. The process must happen efficiently before residual matter putrefies and becomes toxic. Also, many pathogenic microorganisms feed off putrefying waste. When beneficial bacteria are present in sufficient numbers, little putrefaction occurs. Bacterioides and Bifidobacterium species appear to possess the versatility necessary for survival in the large intestine and colonization in the colon. These species synthesize a wide variety of polysaccharide depolymerases and glycosilases. As such, they create an environment that inhibits survival of pathogenic bacteria, particularly by forming short chain fatty acids (i.e., propionate, butyrate and acetate) that lower the colon pH, which adversely affects the growth of those pathogens. The acids further neutralize toxic ammonia and lower its concentration in the blood.
Humans have developed a symbiotic relationship with beneficial bacteria. In fact, there are benefits to probiotic (meaning “for life” in Greek) therapies. In the Orient, there is a long tradition of believing health is dependent on food and the importance of beneficial intestinal bacteria. Probiotics may be defined as products containing live organisms that may beneficially affect the host upon ingestion by improving the balance of intestinal microflora.
The effectiveness of probiotics depends on their survival through both the acidic stomach environment and the alkaline conditions of the duodenum, as well as the ability to adhere to the intestinal mucosa of the colon. Probiotics exhibit antimicrobial, immunomodulatory, anticarcinogenic, antidiarrheal and antioxidant activities. Among the specific examples are:
- Lactobacillus plantarum improves the recovery of patients with enteric bacterial infections.1 This bacterium adheres to and reinforces the barrier function of the intestinal mucosa, preventing attachment of pathogenic bacteria.
- Lactobacillus casei has been demonstrated to increase levels of circulating immunoglobulin IgA in infants infected with rotavirus and correlated with shortening duration of diarrhea due to the virus.2
- Lactobacillus GG has been shown to inhibit chemically induced intestinal tumors in rats.3 It has also been found to inhibit the production of pro-inflammatory cytokines.4
- Saccharomyces boulardii has been shown to prevent antibiotic-associated diarrhea,5 and also to prevent diarrhea in critically ill tube-fed patients.6
- Bifidobacterium lactis results in significant improvement of atopic eczema in children with food allergies.7
There are many probiotic products available, containing various strains individually and in combination. Some products also include a “boost” of food (prebiotics) to enhance the probiotic survival and efficacy. For most individuals, a product delivering 5 billion to 10 billion live bacteria per day is an appropriate dose to maintain a healthy GI environment.8 In the dietary supplement market, most consumers use probiotics for general health and wellness and to address digestive dysfunction. However, some health conditions specifically warrant probiotic ingestion, particularly in cases where the intestinal environment has been appreciably changed. Some of these situations include excessive use of antacids, which change the pH of the intestines; overdoses of laxatives, which reduce normal intestinal peristalsis; and irresponsible use of broadspectrum antibiotics that destroy intestinal microflora,9 which allows pathogenic microorganisms such as staphylococcus, candida or pseudomonas to proliferate.
It is important that manufacturers of probiotic products supply consumers with live microorganisms. In most cases, probiotic bacteria are easily degraded by exposure to heat, oxygen and moisture. Suppliers must control the manufacturing process through use of such products as cryoprotective agents and buffers. Subsequent packaging in moisture impermeable or moisture-resistant containers preferably under inert gas assures product viability.
Quality issues have been researched and approached in two general ways. One calls for formulation of a suitable delivery system, such as using microencapsulation, enteric coating, embedding the bacteria in lipid water-repelling matrices, or buffering the pH. The other approach is directly selecting or modifying the bacteria in a spore form that is more resistant to degradation. Most manufacturers also prefer to use endogenous human strains that exhibit high survival rates, prefer body temperatures for optimal growth and have a strong affinity to adhere to and colonize intestinal walls.
Manufacturers looking to meet label claims should ensure the product contains the right strain in viable quantities and in a proper formulation for the intended use. For example, probiotics in yogurt expire rapidly due to the semiliquid nature of the product; within a month’s period all probiotics in yogurt are inactive, even when kept refrigerated.10 In addition, manufacturers should advise both retailers and consumers (through product labeling) of proper storage requirements. Viable bacteria levels as stated at date of manufacture may not be maintained without proper storage.
Despite the difficulties probiotics pose in formulation and quality, consumers will likely be increasingly interested in using these beneficial bacteria as knowledge of the intestinal microflora and its role in maintenance of health and disease resistance advances.