Tuberculosis. Light micrograph of a section through a lymph node in tuberculosis (TB). White blood cells (dark nuclei) are seen around a tubercle containing bacteria. TB is a disease caused by infection with Mycobacterium tuberculosis bacteria. The bacteria are usually inhaled in water droplets, and can progress from the lungs to the lymphatic system. It can cause coughing, chest pain and fever, and may be fatal. It can be treated with antibiotic drugs, and the BCG vaccination can confer lifelong immunity to the disease. Magnification unknown.