Untitled Document Pathogeneisis of Mycobacteria Tuberculosis M. tuberculosis is an obligate pathogen that can start an infection with as few as ten bacteria. This is compared to the one hundred thousand bacteria required to establish a Salmonella infection. Due mostly to their protective layer, they are very successfull at evading the human bodies natural defenses. They are protected from the high acidity of the stomach and are not sensitive to antibiotics produced by normal flora. The most common site of infection is within the lungs.
Infections can occur, however, within the lymphatic, skeletal, and nervous systems as well.
Once the bacteria reaches it's preferred site of infection, they tend to allow themselves to be engulfed by phagocytic macrophages. Within these cells, they are able to resist destruction and multiply. While it is very easy to become infected with the disease, victims do not always become sick right away. After the bacteria evade destruction within macrophages, the next immune defense mechanism is to form barriers known as granulomas around the infected cells. Layers of two different types of T-cells seal off the infected macrophage, not allowing it to escape.