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Causes
By Mayo Clinic staffMRSA is a strain of staph that's resistant to the broad-spectrum antibiotics commonly used to treat it.
Staph infections
Staph bacteria are normally found on the skin or in the nose of about one-third of the population. If you have staph on your skin or in your nose but aren't sick, you are said to be "colonized" but not infected. Healthy people can be colonized and have no ill effects. However, they can pass the germ to others.
Staph bacteria are generally harmless unless they enter the body through a cut or other wound, and even then they often cause only minor skin problems in healthy people. However, staph infections can cause serious illness. This most often happens in older adults and people who have weakened immune systems, usually in hospitals and long term care facilities. But in the past several years, serious infections have been occurring in otherwise healthy people in the community, for example athletes who share equipment or personal items.
Antibiotic resistance
Although the survival tactics of bacteria contribute to antibiotic resistance, humans bear most of the responsibility for the problem. Leading causes of antibiotic resistance include:
- Unnecessary antibiotic use. Like other superbugs, MRSA is the result of decades of excessive and unnecessary antibiotic use. For years, antibiotics have been prescribed for colds, flu and other viral infections that don't respond to these drugs, as well as for simple bacterial infections that normally clear on their own.
- Antibiotics in food and water. Prescription drugs aren't the only source of antibiotics. In the United States, antibiotics can be found in livestock. These antibiotics find their way into municipal water systems when the runoff from feedlots contaminates streams and groundwater.
- Germ mutation. Even when antibiotics are used appropriately, they contribute to the rise of drug-resistant bacteria because they don't destroy every germ they target. Bacteria live on an evolutionary fast track, so germs that survive treatment with one antibiotic soon learn to resist others. And because bacteria mutate much more quickly than new drugs can be produced, some germs end up resistant to just about everything. That's why only a handful of drugs are now effective against most forms of staph.
