Awake …!!! What’s in your air?

Don’t breath without anxiety…!!! A tiny foes seeking of your lungs that are in your air!!! These are Mycobacterium… the obligate aerobic, Gram-resistant,non-motile, pleomorphic rods and intracellular pathogen. It causes tuberculosis, which is most common in the 3^rd world. Tuberculosis kills 3,000,000 people in the world every year, more than AIDS, malaria, and other tropical disease combined. One third of the world's population is infected with tuberculosis. Tuberculosis is the leading infectious disease cause of death and represents more than a quarter of the world's preventable deaths.

Mycobacterium tuberculosis (reservoir human), along with M. bovis (reservoir cattle), M. africanum (reservoir human), and M. microti all cause this disease. These acid-fast bacilli showing sign of tuberculosis infection are over 9000 years old. Even in Egyptian mummies its existence is observed. During 8000-4000 BC human attacked by M. bovis through milk consumption. In 1000 BC it spreaded whole over the world. It first discovered by Robert Koch in 24 March, 1882.

The rods are 2-4 micrometers in length and 0.2-0.5 um in width. It grows slowly with a generation time of 12-18 hrs. It takes 4-6 weeks to get visual colonies on either type of media. It can be cultured on bacteriologic medium. Two media are used to grow MTB Middlebrook's  medium which is an agar based medium and Lowenstein-Jensen medium which is an egg based medium. MTB colonies are small and buff colored when grown on either medium. Though it is obligate aerobe, it mostly found in highly oxygenated tissues, e.g., upper lobe of lung & kidney. But TB can occur in whole part of the body except thyroid, pancreas, cardiac & skeletal muscle. It’s cell wall is composed of several complex lipid including mycolic acid, wax D & phosphatide.

Cord factor is correlated with virulence of the organism. It’s waxy cell wall makes it resistance to many antibiotics, acidic and alkaline compounds, osmotic lysis via complement deposition, lethal oxidations and survival inside of macrophages.

                                         Fig.Colonies of Mycobacterium tuberculosis on Lowenstein-Jensen medium

M. tuberculosis is transmitted by the aerosol route but can also occur through the gastrointestinal tract. They enjoy themselves in your macrophage without producing any endotoxin & exotoxin. They enter the periphery of the lung during respiration & are engulfed by macrophages. In response to antigen presentation, CD4+ T lymphocytes produce cytokines , IFN-γ, that drive the recruitment of monocytes & direct the formation of granulomas limiting the replication & spread of organism. Classical tuberculous granulomas display central caseous necrosis. Resistance to this organism is mediated by cellular immunity. It can live in your body with(active TB) or without(inactive TB) making you sick. In most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria to stop them from growing. People with latent TB infection are not infectious and cannot spread TB bacteria to others. However, if TB bacteria become active in the body and multiply, the person will get sick with TB disease. It causes lesion termed as “Ghon focus” & “Ghon complex”, & later consolidation, cavitation, collapse, fibrosis, calcification etc.

Pulmonary tuberculosis may cause a bad cough that lasts longer than three weeks, pain in the chest and coughing up of blood or sputum. Other symptoms of TB disease include weakness or fatigue, weight loss, lack of appetite, chills, fever and night sweats.

The most frequently used diagnostic methods for TB are the tuberculin skin test, acid-fast  stain, and chest radiographs.

During the first half of the 20th century, no effective treatment was available. But now the view has changed. Active tuberculosis disease can almost always be cured with a combination of antibiotics. The variety of treatments and drug options depend on the country you are in. The most common drugs are: Isoniazid, Rifampin (Rifadin, Rimactane) Ethambutol (Myambutol) Pyrazinamide. BCG vaccine & strptomycine are given by injection.

To ensure thorough treatment, it is often recommended that the patient takes his or her pills in the presence of someone who can supervise the therapy. This approach is called DOTS (directly observed treatment, short course).

When a strain of tuberculosis bacteria is resistant to two or more 'first-line' antibiotic drugs it is called multi-drug resistant TB or MDR-TB. When it is resistant to three or more 'second-line' antibiotics as well, it is classed as extreme drug resistant tuberculosis, or XDR-TB. Drug resistance usually arises when tuberculosis patients do not or cannot take their medicine as prescribed, and drug-resistant mutations of the bacteria are allowed to replicate. People can also catch MDR and XDR-TB from others. So proper & regular use of the antitubercular drug should be encouraged to check this bacterial mutation.