Monday, May 12, 2008

Commensal bacteria

In an age when antibiotics are available in soap, sprays, and cleaning supplies, bacteria have gotten a bad reputation. Though it is true that many diseases, some extremely horrible, are caused by these microbes, there are also many beneficial, and sometimes necessary, bacterial species for human life. A normal healthy person is actually colonized by bacteria both on their skin and in their body. When depleted, there are supplements available to aid in their recolonization.

Roles of bacteria

Bacterial species living inside a human being are found in the gastrointestinal (GI), or digestive, tract. There are actually more bacteria in the large intestine alone, than there are cells in the human body. From the mouth to the anus, these tiny life forms aid in breaking down and digesting food, converting nutrients and dietary fiber for absorption, synthesizing vitamins, and degrading toxins. They also aid the immune system to develop vigorous responses. More than half of the body’s immune tissue is located in the lining of the small intestines, called Peyer’s patches. All of the bacteria in the GI tract are expelled and renewed daily.

Both within and without, friendly bacteria compete with infectious agents for space. We inhale and ingest virulent bacteria on a daily basis. Without the normal oral and intestinal flora, disease would be much more common and severe. In fact, when taking antibiotics, a person is much more susceptible to infection because the beneficial bacteria are depleted and leave space for other cultures to grow. This also occurs when antibiotic lotions or creams are used in excess upon the skin.

Useful bacteria - Acidophilus

The most well-known bacterial inhabitant of the digestive tract is Lactobacillus acidophilus, which aids in the digestion of lactose. The byproducts of this breakdown discourage colonization by other bacteria. This bacterium is sometimes found in yogurts to aid in dairy consumption. There are also now other bacteria being added to foods such as yogurt, which is itself a probiotic (live bacteria) culture. These are expected to aid in immune responses and digestion, as well as alleviate lactose intolerance.

Acidophilus also aids in niacin, folic acid, and vitamin K formation, and it assists in the recycling of amino acids from bile. This bacterium is also found in the vagina, as the lactic acid it produces discourages fungal growth. This is one reason why women are susceptible to yeast infections when on antibiotics. There are acidophilus powder or pill supplements available in most health stores.

Other types of commensal bacteria

Staphylococcus epidermidis and Proprionibacterium acnes are two bacterial species that are naturally present on the skin and are less virulent alternatives to flesh-eating bacteria (Staphylococcus aureus for example) that could take their places if given the opportunity. P. acnes is often the cause of skin acne, but is usually commensal, meaning that it exists on the skin without doing harm. The bacterium lives off of fatty acids and sebaceous fluid secreted by the pores of the skin. The microbe is sensitive to ultraviolet light. S. epidermidis is actually resistant to the antibiotics penicillin and methicillin, but is generally non-virulent, except in the case of patients with suppressed immune systems or catheters.

Streptococcus mutans is present in the mouth and converts sucrose, sugar, to lactic acid. If not kept in check, this species can cause dental plaque and tooth decay. Like acidophilus, this bacterium creates an acidic environment, which competes out much more virulent microbes, including fungal infections and virulent Strep and Staph.


For an interactive graphic see CAN-BIND


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