False-colour transmission electron micrograph (TEM) showing a single bacterium, Actinomyces israelii, the causative agent of actinomycosis, a granulomatous infection characterized by formation of abscesses. A. israelii exists around teeth, gums and throat of healthy humans, becoming pathogenic in circumstances that are not clearly understood. Actinomycosis may be triggered by trauma, such as a tooth extraction or a fracture of the jaw; abdominal actinomycosis may follow inflammation or perforation of the appendix. Infection may be localized or spread via tissues. Treatment is with high-dose antibiotics. Magnification: X 7500 at 35mm size.