Light micrograph (LM) of a sputum smear showing Staphylococcus bacteria in a patient with Staphylococcal pneumonia. Staphylococcus aureus is a Gram-positive diplococcal organism, usually affecting the debilitated, elderly or the immunocompromised individual, and is often responsible for nosocomial infections acquired during lengthy hospital stays. Gram staining technique; magnification unknown.