English: This electron micrograph depicted large numbers of Staphylococcus aureus bacteria, which were fond on the luminal surface of an indwelling catheter. Of importance is the sticky-looking substance woven between the round cocci bacteria, which was composed of polysaccharides, and is known as “biofilm”. This biofilm has been found to protect the bacteria that secrete the substance from attacks by antimicrobial agents such as antibiotics; Magnified 2363x.

• S. aureus, often referred to simply as "staph," are bacteria commonly carried on the skin, or in the nose of healthy people. Approximately 25% to 30% of the population is colonized, i.e., when bacteria are present, but not causing an infection, in the nose with staph bacteria.

• Sometimes, staph can cause an infection. Staph bacteria are one of the most common causes of skin infections in the United States. Most of these skin infections are minor such as pimples and boils, and can be treated without antibiotics, which are also known as antimicrobials or antibacterials. However, staph bacteria also can cause serious infections such as surgical wound infections, bloodstream infections, and pneumonia.

• Some staph bacteria are resistant to antibiotics. Methicillin-Resistant Staphylococcus aureus, or MRSA, is a type of staph that is resistant to antibiotics called beta-lactams. Beta-lactam antibiotics include methicillin and other more common antibiotics such as oxacillin, penicillin and amoxicillin. While 25% to 30% of the population is colonized with staph, approximately 1% is colonized with MRSA.