StaphInfections - Microbiology March 8 2006 Staphylococcus...

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Microbiology March 8, 2006 Staphylococcus is Everywhere. Staphylococci are small spherical gram-positive bacteria which form grape- like clusters only seen under a microscope. They form clusters because the cells divide in two planes. There are approximately 20 species of Staphylococci but only two have significant interactions with humans. The two are S. aureus and S. epidermis . S. aureus is mainly found in the nose and mucosal areas and S. epidermis is found on the skin. Differentiation between the two species can be achieved by plating on a rich medium. The S. aureus colony will be large and yellow, whereas the S. epidermis colony will be small and white. Another differentiating technique is to incubate on a blood agar plate. S. aureus will grow often on the hemolytic plate and S. epidermis will not. Staphylococci are facultative aerobes, which mean they can grow by either aerobic respiration or fermentation. These are both also oxidase negative and catalase positive. S. aureus can always be considered a pathogen but S. epidermis is usually only considered pathogenic in clinical situations (1). S. aureus can cause a myriad of infections in the human body. Some of the more serious infections are pneumonia, mastitis, phlebitis, meningitis, and urinary tract infections. S. aureus is also a very common infection in hospitals where skin is broken, whether it be surgery or injury. Staphylococcus can be transmitted through the air, on surfaces, and through intrapersonal contact. Since Staph cells are gram
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positive, they are fairly tough and can survive in unforgiving environments. The site of infection usually stays localized due to the body’s immune response to the infection. The port of entry can be a hair follicle, a needle puncture, or an incision made during surgery. Another mode of infection common to hospitals is from foreign bodies behind the defense barrier of the skin. If a person has screws, pins, or other healing aids, chances are that there is Staphylococcus on them. Sutures are another common area where Staphylococci may colonize (2), (3). Some symptoms of staph infections are localized inflammation and pain, a rise in the temperature of affected area, and necrosis of the tissue. Other more visible symptoms are boils, cellulitis, folliculitis, impetigo, and paronychia. Those are all infections on the skin around hair follicles or finger/toe nails. A boil is a raised, painful, red area on the skin. The lump will fill with pus until it is drained or it bursts. Theses usually occur between the legs or underarms, any place where hair can
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StaphInfections - Microbiology March 8 2006 Staphylococcus...

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