Staphylococcus, << `staf` uh luh KOK uhs, >> is a common organism that belongs to a group of round bacteria. These bacteria are called cocci << KOK sy >> . Under a microscope, staphylococci are seen in bunches, growing like clusters of grapes.
There are many kinds of staphylococci. They usually can be distinguished by their surface structure or by where they grow. Staphylococci live everywhere in the environment—in the air, in water, on land, and even on the bodies of human beings and animals. Many types are harmless, but some can cause disease. For example, pimples, boils, and a skin infection called impetigo are caused by staphylococci that enter the body through a break in the skin. Other staphylococci that penetrate deeper into the body can cause pneumonia or septicemia (blood poisoning).
By the 1960’s, scientists observed that some strains of staphylococci had become resistant to most common antibiotics used to treat the infection. Powerful antibiotics, at one time including methicillin, are usually used to treat resistant staphylococci. But some strains of staphylococci have developed resistance to these antibiotics. A strain called methicillin-resistant Staphylococcus aureus (MRSA) usually causes skin infections that show up as pimples or boils. However, MRSA can also cause more serious skin infections or infect the bloodstream, causing serious illness or death. Most MRSA infections occur in hospitals and among people with weakened immune systems, but health experts worry that MRSA infections are becoming more widespread among the general population. MRSA cannot be effectively treated with most antibiotics, but physicians can usually treat the infection with an antibiotic called vancomycin. 
See also Antibiotic resistance; Bacteria; Boil; Carbuncle; Impetigo; Toxic shock syndrome.
