Coloured scanning electron micrograph (SEM) of Staphylococcus aureus (round, yellow) and white blood cells (blue). Staphylococcus aureus, also known as golden staph and Oro staphira, is a facultative anaerobic Gram-positive coccal (round) bacterium. Staph bacteria are one of the most common causes of skin infections. Most of these skin infections are minor such as pimples and boils, and can be treated without antibiotics. However, staph bacteria also can cause serious infections such as surgical wound infections, bloodstream infections and pneumonia.