Staphylococcus sp. Coloured scanning electron micrograph (SEM) of a colony of Staphylococcus sp. bacteria on the epithelial cells of the trachea. The trachea (windpipe) is lined with cilia (hair- like projections) which help keep it free of dust and other irritants. These Gram-positive bacteria often appear in groups that resemble clusters of grapes (as here). They are significant human pathogens, causing diseases ranging from minor skin infections (boils, abscesses) to potentially fatal systemic illnesses such as pneumonia and bacterial endocarditis. Treatment is with antibiotics. Magnification: x1050 at 6x4.5cm size.