Photograph of a petri dish culture of the bacteria Staphylococcus aureus (pyogenes) (2 strains) after 24 hours growth on blood agar. This bacteria is found on healthy human skin and mucous membranes, but is responsible for pus containing infections such as boils, abscesses & wounds generally. The infection occurs when the bacteria enter the body through a hair follicle or a break in the skin, releasing toxins and causing the breakdown of tissue (necrosis). The individual organism is spherical, nonmotile and occurs in grapelike clusters.