This image is a Gram stain of film from an infected wound. The slide shows gram-positive cocci both intracellular and extracellular to polymorphonuclear leukocytes or pus cells. The organisms display the characteristic "clumping" of staphylococci.
Staphylococcus aureus is a Gram-positive, nonmotile, nonsporeforming facultative anaerobe which forms characteristic grape-like clusters of cocci seen in purple on this slide(http://www.bact.wisc.edu/Bact330/lecturestaph). This image depicts a Gram stain of exudate (fluid and cellular material) from an infected wound. The smaller S. aureus clusters are stained purple against the reddish background of human leukocytes.
S. aureus has several distinguishing characteristics that ease laboratory diagnosis. S. aureus is a Gram-positive bacterium, as previously mentioned, appearing a dark purple when stained. The bacterium is also able to ferment glucose anaerobically producing lactic acid (http://medic.med.uth.tmc.edu/path/00001456.htm). Additionally, S. aureus produces catalase, nitrate, and coagulase, and has Lysostaphin sensitivity and Bacitracin resistance (http://www.u.arizona.edu/ic/srl/micro/nazillastaph.html).
As part of the harmless normal flora of humans, found in nasal passages and on skin and mucous membranes, S. aureus can cause an assortment of suppurative (pus-forming) infections should it breech the host’s natural barriers, commonly through a break in the skin. Such infections include folliculitis (inflammation of one or more hair follicles), boils, scalded skin syndrome, impetigo (large fluid-containing blisters), toxic shock syndrome, and cellulitis (inflammation of the dermis and subcutaneous tissues). S. aureus is also a major cause of nosocomial infection of surgical wounds and infections associated with needles and sutures as it colonizes readily around punctures (http://kidshealth.org/parent/infections/bacterial_viral/staphylococcus.html). While staphylococcal infections are relatively frequent in humans, normal host defenses are usually successful at localizing the infection to the portal of entry.
The host typically responds to infection via inflammation, creating elevated temperature at the localized site, swelling, accumulation of pus, and necrosis or death of the surrounding cells and tissues.
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Colorado State University
Fort Collins, Colorado