Staphylococcus bacteria. Transmission electron micrograph (TEM) of sectioned Staphylococcus aureus bacteria. Staphylococcus aureus are Gram- positive coccal (spherical) bacteria. Surrounding the bacterium at centre is the cell wall (dark). The wall extending down the centre indicates that the bacterium is dividing to form two daughter cells. Staphylococcus aureus commonly occurs on healthy human skin and mucous membranes, such as the lining of the mouth. It may, however, become pathogenic. It is commonly responsible for boils on the skin, infected hair follicles and internal abscesses. Magnification: x200,000 at 10x8 inch size.