ABSTRACT
Tuberculosis (or TB) is a bacterial disease caused by several species of the genus Mycobacterium. Under the microscope, these bacteria appear as slender rods (Figure 4.1). They are not capable of movement, aerobic (i.e., requiring oxygen to survive), and Gram positive. Their cell membranes have a high concentration of lipids, and this waxy shell provides protection to the pathogen. The bacteria grow slowly, dividing about once a day versus other bacteria that divide about once an hour. They can survive outside of a host for weeks, even in a dry state. Most TB patients are infected with M. tuberculosis, and the source of their infection was another person. Humans serve as a reservoir host for these bacteria, but humans can transmit M. tuberculosis to other species. Other species of Mycobacterium can cause TB in humans. M. bovis is a disease of cattle, deer, and elk, but humans can become an accidental host. Most people contract M. bovis by drinking raw milk, and pasteurization of milk has greatly reduced this disease. M. africanum and M. canetti cause approximately half of the cases of human pulmonary TB in West Africa, but they are not a concern elsewhere. M. microti is primarily a risk to people with weakened immune systems (de Jong et al. 2010).
