Without bacteria, people simply could not survive. They help with food digestion and maintain the natural flora of bacteria in the gut. Some bacteria, while beneficial, can become virulent depending on the immunity of the individual person. These bacteria are called opportunistic pathogens. They take advantage of weak immune systems or open wounds to invade tissue and create problems.
Mouth
Many types of bacteria exist in the mouth. According to Charles Ophardt at Elmhurst College, Streptococcus mutans causes cavities by converting sugars from food into lactic acid. This lactic acid proceeds to eat away at the enamel of the teeth, leading to cavities. Many types of bacteria in the mouth could cause harm, but don't in a healthy mouth. A mouth with gingivitis or gum disease could enable the bacteria to get into the blood stream and travel to other parts of the body tissues, causing infection. The types of bacteria located in the mouth vary throughout the world, depending on diet. The environment of the mouth changes drastically depending on what foods people consume. The differing environments can make the mouth hospitable to one bacteria, and unacceptable to the next. Other types of bacteria in the mouth include Streptococcus, Provotella, Neisseria, Haemophilus and Porphyromonas.
Gastrointestinal Tract
The gastrointestinal or GI tract of humans contains an extraordinary amount of bacteria that exists in a mutually beneficial relationship. The bacteria receive nutrients from the digested foods, and the bacteria provide immune function, essential vitamin production and fermentation of unused sugars. Especially important is the function of GI tract bacteria in immune function. These bacteria help to "prime" the immune system against bacterial infection. Additionally, the good bacteria often outcompete a pathogen in the GI tract for nutrients, rendering the pathogen unable to grow and make an individual sick. Normal bacteria present in the GI tract include E. coli, Bacteroides fragilis and Clostridia.
Skin
The skin is exposed daily to a vast amount of airborne bacteria and bacteria located on contact surfaces. Species of the genus Staphylococcus make up a majority of the bacteria located on the skin. The textbook "Microbiology: 6th edition" states that Staphylococcus epidermidis and Staphylococcus aureus do not cause infection in healthy people. In the event of broken skin, or a person who has reduced immunity due to an infection or disease, these bacteria can become opportunistic pathogens. Opportunistic pathogens only cause problems when an opportunity to do so presents itself. Environmental factors can change the make-up of the normal skin flora, but in general the ubiquity of these organisms in nature makes them fairly standard in any location on Earth.
References
- "Genome Research"; Global Diversity in the Human Salivary Microbiome; Ivan Nasidze, Jing Li, Dominique Quinque, et al.; February 2009
- "Microbiology: 6th Edition"; Lansing Prescott, John Harley and Donald Klein; 2005
- "Current Issues in Intestinal Microbiology"; Gut Flora in Health and Disease: Potential Role of Probiotics; M. Heselmans, G. Reid, L.M.A. Akkermans, et.al; April 2004
- "Medical Microbiology: 4th Edition"; Samuel Baron; 1996
- Elmhurst College: Sugar and Tooth Decay
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