Staphylococcus bacteria. Colour transmission electron micrograph of sectioned Staphylococcus aureus bacteria. They are Gram-positive coccal (spherical) bacteria. At centre a bacterium in cross section is seen with its thick cell wall (green). Above and below this bacterium are obliquely sectioned bacteria showing the irregular surface of the bacterial cell walls. Staphylococcus aureus commonly occurs on healthy human skin and mucous membranes, such as the lining of the mouth. It may, however, become pathogenic. It can be responsible for skin boils, infected hair follicles and internal abscesses. Magnification: x58,333 at 6x7cm size. Magnification: x200,000 at 10x8 inch size.