Mycobacterium Tuberculosis

Introduction

One of the deadliest bacteria today is Mycobacterium tuberculosis that is the causative agent of tuberculosis for both animals and humans. Mycobacterium tuberculosis is a bacterium species of the family Mycobacteriaceae and is the causative agent of Tuberculosis. Mycobacterium tuberculosis was first discovered in 1882 by Robert Koch, and due to the availability of the mycolic acid has a waxy coat on the surface of its cell. This makes the cell to be impenetrable to Gram staining. Tuberculosis has been one of the diseases that cause the highest death rate in the world today. The bacterium is transferred through the air, and once inside a host, the macrophages ingest the bacteria. The ingestion may lead to two things: elimination of the bacteria or the infection of the host with tuberculosis. After infection, the host should get treatment, the failure of which can lead to their deaths. Understanding Mycobacterium tuberculosis and how it affects the body of the host is critical in ensuring that newer vaccines are developed to combat the bacteria. 

Tuberculosis

Tuberculosis disease that affects the lungs of a human or animal is caused by Mycobacterium tuberculosis. The symptoms of the disease include a continuous cough with blood in sputum, sweating at night, general weight loss, and fever. The disease is spread through the air when infected people a cough, spit or sneeze.

Causative Organism

The causative organism of Tuberculosis is the bacterium Mycobacterium tuberculosis. The organism is characterized by numerous granulomas that contain large Langhans cells. These cells have a nucleus that has a ‘horseshoe’ appearance. The cells of the Mycobacterium tuberculosis usually appear as wrapping together due to the presence of fatty acids in the cell wall, an appearance known as cording. Again, the surface of the cell has a waxy coat.

Virulence Factors

The virulence of Mycobacterium tuberculosis is a complicated and possesses different faces. The organism has different physiological and structural traits that enable the bacteria to cause Tuberculosis to the host. These factors can be put into four categories. The first type is the secreted factors that are the products that are taken outside the bacteria. The second category is the cell surface components that consists of the physiological elements of the cell. The third classification includes all the enzymes involved in metabolism and lastly is the transcriptional regulators.

• Unique mechanisms for cell entry: The tubercle bacillus can attach itself directly to mannose receptors on macrophages or indirectly using complement receptors.
• Intracellular growth: Mycobacterium tuberculosis can grow within its cell, and this is an effective way for the bacteria to avoid the immune system of the host.
• Detoxifying Oxygen radicals: the bacteria interfere with the toxic effects of the phagocytosis process namely the reactive oxygen intermediates (Henderson and Pockley 244).
• The antigen 85 complex: This complex is composed of fibronectin which is a group of proteins that help to protect the cell walls of the immune system. Additionally, the proteins lead to the formation of tubercle.
• Slow generation time: The Mycobacterium tuberculosis takes the slow time to generate; hence, the immune system does not recognize it or is unable to eliminate the bacteria due to inadequate triggering.
• High concentration of lipids on the cell wall: High concentration of lipids forming a capsid ensures that the cell wall of the bacterium is impermeable and is resistant to antimicrobial agents.

Pathogenesis

The bacterium enters the host’s body by inhalation of infected air through the tracheal system. After inhalation, the bacteria travel to the alveoli of the lungs where it is recognized as a foreign material and attacked by the macrophages. The macrophages attempt to ingest the bacteria and disassemble them. No matter the strength of the host’s immune, system, some bacterial cells manage to feed on the macrophages while multiplying in population. If the macrophages become infected, it either kills the bacterium inside or the bacterium continues to grow till they burst the macrophage leading to more infection (Niemi n.p.). The areas infected slowly gets transformed into granuloma which is a boundary that meant to keep the disease from spreading. This leads to the growth of the bacteria until the cells are overwhelmed. The center of the granulomas necrotizes and this is where the blood and sputum mix. Depending on the infected person, this is where the progress of the infection grows.  The defense mechanism of the attempts to fight off the growing infected areas by destroying the tissue around the area to stop the spread and deployment of T-cells. The killing of the tissue leads to inflammation among other symptoms known to be as a result of tuberculosis.

Transmission and Epidemiology

As the disease progresses in its primary stages, the dead cells used by the immune system to combat the disease are used in the growth areas, leading to a rapid increase of the infected areas known as tubercles. When these tubercles break off and travel through the bloodstream to other parts of the body, the host gets extra-pulmonary tuberculosis. If the tubercles get into a liquid state, environments that are rich in bacteria are created, and the sputum of the host thickens. The lungs are filled with the bacteria, and if the host sneezes, coughs, or spits the sputum, then the bacterium is spread to other users who might inhale the air containing traces of the sputum. The disease is transmitted through the airborne particles known as droplet nuclei. These droplets can remain in the air for up to several hours and infect any susceptible to the disease. After a person inhales the droplet nuclei that contains Mycobacterium tuberculosis, it travels via the naval cavity into the respiratory tract. It is here that they move through the tracheal system into the alveoli.

About a third of the world’s population is infected with tuberculosis. New infections of the disease are growing for 1% of the population annually. The disease is most common in developing countries, especially in the urban areas. Depending on the location, the rates of tuberculosis varies in the population. In Africa for example, the disease is most common in adolescents and young adults while in countries where the prevalence has significantly subsided, it is common to the old and those whose immune system is depressed.

Treatment

In order to begin the treatment of a person with tuberculosis, the patients must first be isolated from the rest of the patients into a room with negative pressure. The staff treating the patient must wear protective masks that would filter the bacterium from infecting them. The patient should continue to be in isolation for 2-4 weeks till sputum smears are negative. The initial treatment plan starts with a 4-drug basis: pyrazinamide, isoniazid, rifampin, and either streptomycin or ethambutol. Once the patient becomes fully susceptible, the fourth drug (streptomycin or ethambutol) can be stopped (CDC). The patients undergoing pyrazinamide should have serum acid assessments after a couple of days while those undergoing long-term ethambutol therapy should be having red-green color perception testing and visual acuity after some time. For a patient fully susceptible and is in isolation, after two months of medication, the pyrazinamide can be discontinued. The rest of the two drugs, that is, isoniazid and rifampin should be continued every day for four more months. If the patient develops some form of resistance against isoniazid, the drug should be discontinued, and treatments continue with pyrazinamide, ethambutol, and rifampin for an additional six months. If after two months of treatment are over, and the patient remains culture-positive and has the cavitary disease, therapy for the patient must be extended. It is recommended that all patients undergo directly observed therapy. Those patients whose diagnosis shows an active TB should for every week go through sputum analysis till sputum conversion is noted.