Mycobacterium leprae

Hello, everyone. My name is Dr. Sarah Fouch. Within this short recording, we will be discussing Mycobacterium leprae, the clinical condition that this organism is associated with, and the virulence factors that it can produce to cause the symptoms of the condition that it's associated with.

Mycobacterium leprae is an obligate intracellular organism. This means it can only survive inside host cells, and it requires the host cell for replication. They are microaerophilic organisms, which means that they can survive in oxygen, but at lower concentrations compared to the normal atmosphere. If I drew some test tubes, and I had four test tubes, and we had liquid in the test tubes. If we inoculated an aerobic organism in one test tube, it would grow at the top because it would need oxygen. If I inoculated an anaerobic organism in the next test tube, it would grow at the bottom because anaerobic organisms cannot survive in the presence of oxygen. If I inoculated a facultatively anaerobic organism in the third test tube, it could grow anywhere because facultatively anaerobic organisms can survive in the presence or absence of oxygen. But if I inoculated a microaerophilic organism in the fourth test tube, it would grow slightly down the test tube. It can't survive in the absence of oxygen. It requires oxygen, but not at the normal amount in the atmosphere. Now, as with many other species of Mycobacterium, they grow very slowly, and they have a generation time of around 12-14 days. This is one of the longest generation times for organisms. When we compare the bacterial cell wall of Mycobacterium to that of gram-positive or gram-negative organisms, they have what we call an acid-fast cell wall. Within this cell wall, we will have the presence of peptidoglycan, and obviously, that will be present of all bacterial cell walls. However, it's thinner in comparison to both gram-positive and gram-negative organisms. What makes this acid-fast cell wall different? Well, there's the presence of arabinogalactan. The outer membrane also contains mycolic acids, glycolipids, and polypeptides. Now, the acid-fast cell wall is almost waxy in comparison to other cell structures found within bacteria. Now, interestingly, we cannot use the Gram stain to visualize acid-fast organisms. We will need to consider other types of strains, such as Ziehl-Neelsen or an auramine stain. Now, Mycobacterium leprae will infect cooler areas of the body, such as the skin, the nasal mucosa, and the ears. That's due to the fact that they preferentially grow in a temperature range between 27 and 30 degrees Centigrade. Now, remember, our body temperature is 37 degrees. That's why it would be on the external parts. Now, Mycobacterium leprae has tissue tropism or a preference for Schwann cells, which are glial cells in the peripheral nervous system. They will also replicate within macrophages. Now, when we think about the macrophages, replicating within a macrophage is an excellent way to evade the immune response, as replicating within these cells will reduce detection from antigen-presenting cells and also phagocytes. The result of this will be a chronic infection with very little immune response. The reason why patients tend to have a chronic infection, lasting for a long period of time, is due to the slow replication of the organism. Now, interestingly, Mycobacterium leprae has been shown to survive outside of the body, as well, for about 46 days. It can survive in the environment, and survival is normally associated with moist soil. Longer survival time has also been documented, and Mycobacterium leprae has been shown to survive for up to eight months in amoebic cysts.