Mycobacteria

Mycobacterium is thin rods with branching filamentous forms that resemble fungal mycelium. They create a mould-like pellicle in liquid cultures. As a result, the name ‘Mycobacteria,’ which means fungus-like bacteria, was coined in 1896. They do not stain easily, but once stained, they are resistant to decolourisation by dilute mineral acids. So they are also known as ‘acid-fast bacilli.’ They are nonmotile, aerobic, non-capsulated, and non-sporing.

Mycobacteria were among the first bacteria discovered to cause illness (tuberculosis and leprosy). The name does not indicate that Mycobacterium is a fungus; rather, it characterises how the tubercle bacillus develops as mould-like pellicles on the surface of liquid medium (Gangadharam & Jenkins, 1998). Based on clinical patient isolates, it became clear in the 1940s and 1950s that there were many additional species of Mycobacteria (apart from those that cause TB and leprosy) that may contribute to illness.

Mycobacteria

Mycobacteria are common organisms that live in food sources. Tuberculosis and leprosy microbes are obligate parasites and are not found in the genus as free-living individuals. Mycobacteria are acid-fast aerobic and nonmotile bacteria (with the exception of Mycobacterium marinum, which has been found to be motile within macrophages). Mycobacteria have a protective outer membrane. They lack capsules and, for the most part, do not develop endospores. 

The cell wall of all Mycobacterium species is thicker than that of many other bacteria, and it is hydrophobic, waxy, and rich in mycolic acids/mycolates. The cell wall is made up of two layers: a hydrophobic mycolate layer and a peptidoglycan layer linked together by arabinogalactan, a polysaccharide. The cell wall contributes significantly to the hardiness of this species. The biosynthesis routes of cell wall components might be used to develop novel TB medicines.

Taxonomy

• Mycobacteria are classified as belonging to the Order Actinomycetales, the Family Mycobacteriaceae, and the Genus Mycobacterium.
• Adansonian taxonomy was one of the first systems used to categorise Mycobacteria (Grange, 1996b). This technique was based on the utilisation of cultural and biochemical features to categorise related strains.
• In the mid-1950s, Dr Ernest Runyon completed the initial investigation and classifications on the taxonomy of mycobacterium. Mycobacteria, excluding those in the M. tuberculosis complex and non-cultivable taxa (e.g., M. leprae), were grouped into four categories based on growth rates and pigmentational features in Runyon’s classification.
• In 1980,  Mycobacteria species were added to the Approved Lists of Bacterial Names (Grange, 1996b). There are currently 71 known or proposed Mycobacteria species (Shinnick and Good, 1994). Over 20 of these species have been linked to human sickness.
• Mycobacteria that have not been recognised as TB or leprosy complex have been given a number of names, including atypical Mycobacteria, Mycobacteria other than tubercle bacilli (MOTT), environmental mycobacteria, or nontuberculous Mycobacteria (NTM) (Wolinsky, 1979). The NTM terminology is used in this work.
• Because of their thick, waxy exterior covering, which allows them to live in watery conditions, they have been dubbed the “ducks of the microbial world.”
• They have very low permeability cell walls, which contributes to their resistance to therapeutic treatments. The mycobacterial cell wall is extraordinarily complex, with lipids accounting for around 60% of the structure (Brennan and Nikaido, 1995). The cell wall properties enable mycobacterial species to live in a variety of settings (for example, biofilms in aquatic habitats or particulate matter in soils and water) and to withstand disinfection processes.

Runyon classification of nontuberculous Mycobacteria

Runyon classification is a method of distinguishing Mycobacteria based on pigmentation and growing circumstances. The Runyon classification of nontuberculous Mycobacteria is based on the growth rate, yellow pigment synthesis, and whether this pigment was formed in the dark or only after exposure to light. Ernest Runyon first used it in 1959. 

Nontuberculous mycobacteria are classified into four classes based on these criteria:

• Photochromogens (Group I) form non-pigmented colonies in the dark and pigmented colonies only after light exposure and re-incubation.
• Scotochromogens (Group II) develop bright yellow to orange colonies when cultivated in either light or darkness.
• Non-chromogens (Groups III and IV) are either nonpigmented in the light and dim or have a gentle yellow, buff, or tan colour that doesn’t strengthen after light openness.

Mycobacterium tuberculosis (tuberculosis)

Tuberculosis (TB) is caused by the infectious pathogen Mycobacterium tuberculosis. Dr Robert Koch discovered this rod-shaped bacteria, known as Koch’s bacillus, in 1882. MTB is a tiny, slow-growing bacteria that can only exist in humans. It is not found in other animals, insects, dirt, or nonliving objects. An aerobic MTB is an aerobic bacteria, which means that it needs oxygen to thrive. As a result, during active tuberculosis, MTB complexes are invariably detected in the higher air sacs of the lungs. The bacterium is a facultative intracellular parasite, mainly of macrophages, with a sluggish generation period of 15-20 hours, a physiological feature that may contribute to its pathogenicity. The bacteria mainly affect the lungs, but MTB bacteria can attack any region of the body, including the kidney, spine, and brain. If not treated appropriately, the condition can be deadly. It spreads from person to person by droplets from the throat and lungs of persons suffering from active respiratory illness. 

Active Tuberculosis Signs and Symptoms

The signs and symptoms of active tuberculosis vary depending on which site(s) is/are afflicted. Although tuberculosis is most commonly associated with respiratory sickness, it can manifest itself in practically any part of the body. TB illness can potentially affect many places at the same time (disseminated TB disease)

Non-respiratory TB illness can also be seen in the following locations: Peripheral lymph nodes (TB lymphadenitis) ,Central nervous system (e.g., TB meningitis, tuberculoma), Abdominal cavity and/or digestive system Genitourinary system, bone(s) and/or joint(s).

Fever, night sweats, weight loss/loss of appetite, and fatigue are common indications and symptoms of active tuberculosis illness.

Typical signs and symptoms of TB illness involving the lungs (pulmonary TB) include: Cough lasting at least 2 to 3 weeks Chest discomfort Abnormalities on chest x-ray (e.g,upper lobe infiltrates cavitation),Hemoptysis (blood in sputum),Young children, the elderly, and those with extensive immune suppression may not exhibit normal signs or symptoms of active tuberculosis illness.

Causes

Tuberculosis is caused by bacteria that spreads from person to person by minute droplets in the air. When someone with untreated, active TB coughs, talks, sneezes, spits, laughs, or sings, this might happen.

Although TB is infectious, it is difficult to contract. You are significantly more likely to contract TB from someone with whom you live or work than from a stranger. Most persons with active tuberculosis who have had adequate medication therapy for at least two weeks are no longer infectious.

Prevention

If you test positive for latent tuberculosis infection, your doctor may urge you to take drugs to lower your chances of getting active tuberculosis. Only active tuberculosis is communicable.

Safeguard your family and friends.

If you have active tuberculosis, it usually takes a few weeks of therapy with TB drugs before you are no longer infectious. To help protect your friends and family from getting sick, follow these guidelines:

Stay at home. During the first several weeks of therapy, avoid going to work, school, or sleeping in a room with other people.

Ventilate the space. Tuberculosis germs spread more quickly in compact, tight environments with no movement of air.

Dormant tuberculosis infection (LTBI)

Latent tuberculosis infection (LTBI) is characterised by a prolonged immunological response to Mycobacterium tuberculosis antigen stimulation in the absence of clinically evident active tuberculosis. The lifetime probability of reactivation for someone with proven LTBI is estimated to be 5-10%, with the majority acquiring TB illness during the first five years of infection.

Tuberculosis that is active (TB disease)

MTB bacteria in certain persons overcome immune system defences and begin to grow, resulting in the development from latent tuberculosis infection to TB illness. Some people acquire tuberculosis (TB) shortly after an infection, whereas others develop it later when their immune system weakens.

Tuberculosis extrapulmonary

Extrapulmonary TB is defined as the infection of any organ in the body other than the lungs by Mycobacterium tuberculosis. It is usually the result of a lung infection caused by the same bacteria. The lymph nodes, pleura, belly, bone and joint, spinal cord, and brain are the most common locations of extrapulmonary TB and its covering.

Conclusion

The majority of research has shown that mycobacteria live as non-sporing acid-fast rods that multiply by binary fission (Grange, 1996b). However, other researchers believe that a more complicated life cycle exists (perhaps incorporating cell-wall-free forms or microspores). Several writers have provided evidence for atypical mycobacteria morphologies and life cycles.

Mycobacterial dormancy and persistence may be explained by unusual life cycles (Grange, 1996b). Wayne (1994) examined the mechanism of dormancy in Mycobacterium TB. There is substantial evidence that these organisms may adapt to long periods of dormancy in tissues and that this dormancy is responsible for disease latency. According to Wayne (1994), the pathway leading from active replication to dormancy may entail two or more steps. One of these phrases includes switching from fast to slow replication, whereas the second requires total replication shutdown but does not result in cell death.