- Mycobacterium tuberculosis
- Mycobacterium avium complex
- Mycobacterium leprae - Leprosy - (Hansen’s Disease) ~intracellular and slow growth - They may exhibit long period of metabolic inactivity.
A particular problem with both these organisms is that they can survive inside macrophages after phagocytosis, after phagocytosis, the organisms are contained in phagolysosomes where the pH is low.
The main mycobacterial infections in humans are tuberculosis and leprosy.
Tuberculosis and other mycobacterial diseases are difficult to treat for several reasons. Mycobacteria replicate more slowly than “typical” bacteria such as Escherichia coli or Staphylococcus aureus. This may seem to make the disease easier to control, but it makes pharmacotherapy more difficult because rapidly dividing cells are most metabolically active and therefore more susceptible to antibiotic chemotherapy.
Mycobacteria can also exist in a dormant state, making them resistant to nearly all antibiotics. In the host, they live inside human cells (Most of tubercle bacilli are intracellular with slow growth)Z, therefore antimicrobials that have poor intracellular penetration are less effective.
Mycobacteria also have cell walls that are structurally different from typical gram-positive and gram-negative bacteria. The outermost layer of mycobacteria consists of phospholipids and mycolic acids that make a waxy layer that resists penetration from antibiotics. Arabinogalactan and peptidoglycan are polysaccharide components of the cell wall, but the peptidoglycan is not accessible to beta-lactam antibiotics, and they are poorly active.