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Tuberculosis bacteria. Coloured scanning electron micrograph (SEM) of a group of Mycobacterium tuberculosis bacteria, cause of human tuberculosis (consumption). These Gram-positive rod-shaped bacteria appear red. If M. tuberculosis reaches the lungs from a cough or sneeze it will multiply to form a primary tubercle (localized bacterial colony). The bacteria then either spread through the lymphatic system to other parts of the body, which can be fatal, or lie dormant, only becoming active again many years later. Treatment is with antibiotics. Magnification: x10,000 at 6x6cm size. (KEYSTONE/SCIENCE PHOTO LIBRARY/EYE OF SCIENCE)