Mycobacterium tuberculosis

Scientific Content

Tuberculosis (TB) is caused by Mycobacterium tuberculosis (MTB) that target the lungs. The main route of transmission involves sneezing, coughing and spitting where the bacteria are then spread through the air particles. An uninfected person only needs to inhale a few of the TB germs to become infected (World Health Organization). Those who are infected with the bacteria have a 10 percent chance of falling ill with TB. The disease is, however preventable, and curable.

The identification of TB is done through performing laboratory tests that are combined with clinical findings. There are two types of tests uses in the process of identifying the bacterium. The first is the TB skin test that is also referred to as the Mantoux tuberculin skin test (TST) (Centers for Disease Control and Prevention). It is performed by injecting tuberculin into the skin as a fluid on the lower part of the arm and leaving the patient to stay for 48-72 hours after which the physician looks for the reaction on the arm. The identification of MTB is through the demonstration of a raised hard swelling (Centers for Disease Control and Prevention). The other diagnostic test for TB is the TB blood test, sometimes referred to as the interferon-gamma release assays or IGRAs. In the US, two blood tests are approved including the QuantiFERON®–TB Gold In-Tube test (QFT-GIT) and the T-SPOT®.TB test (T-Spot) (Centers for Disease Control and Prevention). After the healthcare professional has drawn blood from the patient, it is sent to the laboratory for diagnosis whereby an affirmative identification of determined by a positive blood test and it will prompt additional tests for determining the latency (Centers for Disease Control and Prevention). This diagnostic method is preferred for those who have being given the TB vaccine bacille Calmette–Guérin (BCG) and patients who are having difficulty returning for a second appointment to look for a reaction to the TST.

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The treatment of TB is initiated when the bacteria becomes active, and the body’s immune system is unable to eliminate the growth of the bacteria. The treatment process usually takes 6-9 months, and currently, ten drugs have been approved by the U.S. Food and Drug Administration (Centers for Disease Control and Prevention). Among them, the first line anti-TB agents include rifampin (RIF), isoniazid (INH), pyrazinamide (PZA), and ethambutol (EMB). For those who are introduced in the treatment regimen, it is advisable to finish the dose and take the medication exactly as instructed by the physician. In case the dose is stopped before the due date, it is likely that the patient will become sick again and in case the proper protocol is not followed, there are chances that they will become resistant to the drugs that they have been prescribed. Resistance to TB is a huge problem that makes harder and more expensive to treat the disease. In the case of Drug-resistant TB, usually caused by resistance to one or two of the first-line anti-TB drug and at least isoniazid and rifampin, there should be close consultation with an expert for the progress of treatment (Centers for Disease Control and Prevention).

The signs and symptoms of those infected by the disease usually depend on the part of the body where the bacterium has resided. The most preferred site is the lungs, where the microbe is known to cause pain in the chest, a bad cough that may last for at least three weeks or may take longer, and cough up blood, called phlegm, from the inside of the lungs (Centers for Disease Control and Prevention). Other possible manifestations of the disease include weight loss, weakness, fever, chills and night sweats. However, the symptoms of the disease in other body parts are dependent on the part of the body that is affected. For those with latent TB infections, there usually are no symptoms, and they cannot infect others.

Pathogenicity of Mycobacterium Tuberculosis

The infection by TB begins when a person inhales the droplet nuclei from the air particles containing the tubercle bacilli that reach the alveoli in the lungs. The bacilli are then ingested by alveolar macrophages where a majority are destroyed, and some are inhibited. A small number may, however, penetrate and undergo intracellular multiplication and when the macrophages die, they are released (Schluger 253). This process takes place within 2-8 weeks where the macrophages ingested the cell and form granuloma. The granuloma then keeps the bacillus under control for the time.

A series of reactions then follow the granuloma formation that results either in the elimination of the bacterium or the containment of the bacilli on the macrophages. Until there is a shift in the immune system the granuloma breaks down, and the latent infection is reactivated. Research shows that the granuloma formation is a crucial step in the maintenance of the pathogenicity of the disease following the finding that cytokine tumor necrosis factor- (TNF-) is responsible for maintaining granuloma function (Schluger 253).

The bacilli are then taken to the lymphocytic channels or sometimes to the bloodstream to the far organs and tissues. The included areas of the body involve the lungs, kidney, bone, and brain, the regional lymph nodes, the apex of the lung and related areas. The dissemination processes then prime the immune system to undergo systemic response. (Schluger 253).


Currently, the World Health Organization estimate that about one-third of the world’s population is latent for TB which represents a population that has been infected but are not yet ill from the disease. Those who are latent have a 10 percent lifetime chance of getting infected with TB (World Health Organization). The risk increases substantially for those who have been infected by HIV, those with diabetes, and the tobacco users. Tobacco users specifically have more than 20 percent chance of being infected by the disease.

In 2015 an estimated 10.4 million were infected with TB while another 1.8 million died from the disease. Among those who died, 0.4 million included those who had previously been infected with HIV with an estimated 95 percent death being reported among the middle- and the low-class countries (World Health Organization). Adults are the most likely group to be infected by the disease from the fact that there is a 20-30 times chance of developing active TB. Meanwhile, one million children who are aged 0-14 were infected by TB in 2015 as another 170,000 children died from the disease.

Globally, six countries alone accounted for over 60 percent of the TB cases. India, China Indonesia, Pakistan, Nigeria, and South Africa have been cited to be among the most affected countries with the burden of TB. The rate of global disparities is, however, dependent on the TB prevention and care provided in the given countries.


Works Cited

Centers for Disease Control and Prevention. “Tuberculosis (TB).” CDC (2017): n. pag. Web.

Schluger, Neil W. “The Pathogenesis of Tuberculosis: The First One Hundred (and Twenty-Three) Years.” American Journal of Respiratory Cell and Molecular Biology 32.4 (2005): 251–256. Web.

World Health Organization. “Tuberculosis.” WHO (2017): n. pag. Web.