Culture-AFB is the gold standard test for detecting the presence of tuberculosis causing microorganisms. Tuberculosis is caused by Mycobacterium tuberculosis, which is an acid fast bacillus. Your doctor may suggest this test if you show symptoms related to lung infection or pulmonary tuberculosis. Common symptoms include chronic cough which produces sputum with bloody streaks, loss of appetite, fever, night sweats, chills, chest pain and unexplained weight loss. The symptoms of tuberculosis or other mycobacterial infections vary depending on the part of the body that is affected, such as the spine or the bone marrow.