Hello everyone and welcome back! This past week I had done some reading on TB, otherwise known as tuberculosis, a disease most people would have heard of at some point in their life.
Mycobacterium tuberculosis is just one of nearly 200 species of microorganisms that belong to this genus/group. Mycobacteria need oxygen, are not motile, reproduce very slowly, do not mutate too often, but have some how successfully managed to be around for thousands of years, sometimes causing serious problems in terms of human health and disease. Mycobacterium leprae, is another species from the same genus, for example, and is the organism responsible for causing leprosy in humans. If you are a student, can you quickly research two other Mycobacterium species that may be important with respect to human health and disease?
In talking about slow growth of Mycobacteria…and I mean slow…growth, our good old friend E. coli can go through one division cycle in roughly 20 minutes, whereas M. tuberculosis divides once in roughly 20 hours. M. leprae will take about 20 days! That’s an amazing comparison!
TB itself is just one strain of Mycobacteria, but is actually part of a multipart group, or complex, of different Mycobacterium species. This rod-shaped cell called M. tuberculosis has a cell wall very rich in lipids, and the characteristic acid-fast staining technique is used to observe them under the microscope (as opposed to being described as gram-positive or gram-negative).
What is their strategy do you ask? Well, they infect the lungs, where they are swallowed by special cells called macrophages. Typically, cells that undergo this ‘swallowing’ process are broken down/ killed inside of the macrophages. For TB, this does not happen, and the TB cells multiply. This can happen over several months, or years, and is protected in an inflamed tissue called a granuloma. It is estimated that maybe 1 in 3 people host TB in their lungs, undetected, and the success of the organism is really in how long they can survive this stage in their hosts. When this granuloma breaks down, transmission of TB to other people can occur through infected air droplets.
Although some Mycobacterium species are detrimental to human health, many others are found in the environment (such as in soil), and are much less so.
With so many Mycobacterium species found around the world, together with the prevalence of tuberculosis, it really is a good question as to who may or may not have TB.
Take care until next time! 🙂
For more reading seeing the following links on Mycobacterium, and Mycobacterium tuberculosis and granuloma. Credit is given for use of lungs image and TB giant microbe.
jtbtrinbagomicrobiologist 