Mycobacterium Tuberculosis

Tuberculosis is the leading disease killer in the world; while microbial drug use and surveillance in more industrialized countries like the United States has reduced its impact in their populations, epidemiologists warn that being less than vigilant may allow a resurgence of the disease (Bauman, 2018). According to the World Health Organization (2018), "10 million people fell ill with TB in 2017, including 0.9 million among people living with HIV". Last year, Tuberculosis infection was listed as one of the top 10 causes of death in the world. Globally, an estimated 558,000 people contracted a strain of Tuberculosis that is resistant first-line drug therapies, and a staggering 82% of those cases had multidrug-resistant Tuberculosis (WHO, 2018). The World Health Organization warns that the United States holds a "$3.5 billion funding shortfall for Tuberculosis implementation in 2018, and over $2.0 billion per year for Tuberculosis research" (WHO, 2018). Given that the Center for Disease Control (2018) cites that over 9,000 cases were reported in 2017 in the U.S., this lack of funding for research and education should be of grave concern to health providers. Given this information, it is vitally important as future nurses to understand the nature of this disease state and the bacterium causes it so that we may effectively prevent it.

Tuberculosis is caused by the bacterium Mycobacterium Tuberculosis: A small bacillus (rod-shaped) bacteria that is non-spore-forming (Knetchel, 2009). This gram-positive rod has thick cell walls that contain a high amount of mycolic acid – a waxy lipid formed from carbon atom chains. They possess a high G and C content. Due to the thickness of the cell wall and the mycolic acid content, M. Tuberculosis bacteria are resistant to gram staining; staining only weakly, if at all. Acid-fast staining was designed in order to stain them and allow for a better method of identification of the microbe (Bauman, 2018).

The main virulence factor of Mycobacterium Tuberculosis is this high concentration of mycolic acid in its cell wall. This mycolic acid creates a lipid barrier cell wall that allows this bacterium to resist gram staining, weak detergents, and drying out. Once phagocytized, these bacteria are also protected from lysis by their thick, waxy cell wall, making them practically impossible for our immune cells to destroy; the best the body can do is to separate the invader from healthy cells. Highly virulent strains of M. Tuberculosis also have a component in their cell walls called cord factor. Cord factor allows for daughter cells of M. Tuberculosis to remain attached together in parallel chains. These chains block off neutrophils from being able to migrate to the infection site, and are toxic to host cells in humans (Bauman, 2018). A further important virulence factor to note is that many strains of M. Tuberculosis are antimicrobial drug resistant, posing potential barriers to treatment in patients who contract this infection. To be classified as a multi-drug-resistant (MDR) strain, the M. Tuberculosis in question must be resistant to isoniazid and rifampin, the two most common drugs utilized in treatment of this bacterium. Other treatments include levofloxacin in combination with other antibacterial drugs to treat MDR-TB (Bauman, 2018). In addition to MDR strains of M. Tuberculosis, there is also an extensively drug-resistant variation of the pathogen which is resistant in vitro to isoniazid, rifampin, and several other anti-tubercular drug treatments (Bauman, 2018).

Mycobacterium Tuberculosis invades mammalian cells and is capable of intracellular growth. The bacterium is highly aerobic and requires lots of oxygen (hence our respiratory system is a good locale for it to colonize). Ideal growth conditions happen at human body temperature, which is one of the reasons we make such a good host organism for the bacteria. M. Tuberculosis growth is relatively slow, however, because the amount of mycolic acid molecules present in the bacterium take a lot of time to synthesize (Bauman, 2018). The pathogen is passed from person to person in airborne droplet form; an infected patient should be required to wear an N95 respirator mask to prevent spread of the bacterium to others. Only human beings are a reservoir for this microbe (Bauman, 2018).

The most common manifestation of disease caused by M. Tuberculosis is typically shortened to the name 'Tuberculosis', an infection of the respiratory system. (Bauman, 2018). According to the Center for Disease Control (CDC), "Tuberculosis bacteria are spread through the air from one person to another??when a person with TB disease of the lungs or throat coughs, speaks, or sings. [Then] the bacteria can settle in the lungs and begin to grow. From there, they can move through the blood to other parts of the body, such as the kidney, spine, and brain" (CDC, 2018). A secondary form of TB infection is what is referred to as latent Tuberculosis. The CDC states that for "most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria" but that those people are still carriers for the pathogen and can still end up 'activating' the pathogen later on, even though they currently display no symptoms (CDC, 2018). While Mycobacterium Tuberculosis may remain inactive for a lifetime without causing disease, this latent bacteria sealed within the tubercles can become activated (CDC, 2018). Of highest concern are individuals with an existing diagnosis of Human Immunodeficiency Virus (HIV). According to the Center for Disease Control, "People living with HIV are more likely than others to become sick with Tuberculosis. Worldwide, Tuberculosis is one of the leading causes of death among people living with HIV" (CDC, 2018). Tuberculosis and HIV coinfection is another reason to take prevention of the spread of this pathogen very seriously.

The typical body systems affected by infection of this bacterium is the respiratory system. Primary Tuberculosis occurs in lower/central areas of the lung; secondary Tuberculosis commonly appears in the upper lobes. (Bauman, 2018) However, it has been known to occur in other parts of the body as an opportunistic pathogen, typically if the individual has had a surgery or injury which exposes the host to M. Tuberculosis in an area otherwise not typically affected, such as bone tissue. It can also make its way into the blood stream and travel to other areas of the body that way (Knechel, 2009).Symptoms often include: a cough lasting 3 or more weeks; chest pain; coughing up sputum or blood; weakness or fatigue; weight loss; loss of appetite; chills; fever; and night sweats, are the most common symptoms (CDC, 2018).

Diagnosing an M. Tuberculosis infection can be multifactorial. Generally, screening is done using a Tuberculosis skin test or Mantoux skin test. This is performed by injecting a weakened version of protein derived from the bacterium in a bubble under the skin and observing after 48 to 72 hours to see if there has been an inflammatory response. If there has, this identifies the presence of M. Tuberculosis antibodies only; meaning that a person has had exposure to M. Tuberculosis, but does not necessarily have the disease. A chest x-ray is typically done for confirmation (CDC, 2018). A positive chest x-ray will show the sites of M. Tuberculosis infection as white patches on the image where tubercles have formed/calcified or scar tissue appears around site of infection (Knechel, 2009).

Treatments for M. Tuberculosis infection primarily include a course of multiple antimicrobial drugs in conjunction with each other. The most common combination of drug therapies is pyrazinamide with rifampin, isoniazid, and either ethambutol or streptomycin. This is taken over a period of two months. After that two months has passed, the patient continues taking isoniazid and rifampin, as well as either ethambutol or streptomycin for an additional four months of treatment. Some parts of the world also have access to the BCG vaccine, which offers some protection against contracting Tuberculosis. Like all attenuated vaccinations, this should never be administered in patients who are immunocompromised (i.e. infants, elderly, and patients with genetic immune disorders or acquired immune deficiencies) (Bauman, 2018).

Given the information available about the virulence of Mycobacterium Tuberculosis and the statistical prevalence of fatal cases, it is clear that as future nurses we must understand how to educate ourselves and our patients on the importance of screening and prevention when it comes to this disease. Following aseptic techniques like hand washing, complying with regular PPD screenings, and knowing what signs or symptoms to look for to judge whether a patient needs droplet precautions enacted, are all ways in which we as future nurses can help prevent the spread of this pathogenic bacteria.

References

1. Bauman, R. W. & Primm, T. P. (2018). Microbiology: With Diseases by Body System. Upper Saddle River, NJ: Pearson.
2. Knechel, N. A. (2009, April 01). Tuberculosis: Pathophysiology, Clinical Features, and Diagnosis. Retrieved December 09, 2018, from http://ccn.aacnjournals.org/content/29/2/34.full
3. TB Determined: Tuberculous Osteomyelitis Lebowitz, Dan et al.
4. The American Journal of Medicine , Volume 127 , Issue 3 , 198 - 201
5. Tuberculosis (TB). (2018, December 04). Retrieved December 08, 2018, from https://www.who.int/tb/en/
6. Tuberculosis (TB). (2018, October 22). Retrieved December 08, 2018, from https://www.cdc.gov/tb/default.htm

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