Color enhanced scanning electron micrograph (SEM) of propionibacterium acnes. This bacteria inhabits sebaceous follicles and is usually a harmless commensal bacterium inhabiting human skin but is known to cause the formation of acne vulgaris (pimples). The bacterium is anaerobic, gram-positive and does not form spores. It produces propionic acid, indole, nitrate, and catalase but it is not toxigenic. Morphologically, it resembles corynebacteria. Image width: 9.85 micrometers. Magnification: 10,150x if printed 10 cm wide.