Mycobacterium tuberculosis

MYCOBACTERIUM TUBERCULOSIS

IS a weak gram + bacteria, aerobic, facultative intracelular, no movility, no capsule and no spore former. Is alchol acid resistant bacilli and has a very width cellular wall. The wall consist in N-acetyl glucosamine, arabinose polymers, mycolic acids, glicolipids and lipoarabinomanam.




Virulence

Cordon factor which is a mycolic acid is very immunogenic and interrupts fagolisosome fusion and electron transporter chain. Lipoarabinomanam is an immune-modulator that elicits inflammatory response due TOLL like receptors. Bacterian urease adjust cytoplasmic ambient becoming alkaline allowing his survival.

The infection occurs when a patient elicits bacilli in aerosol shaped secretions, the bacilli arrives to the alveoli and is phagocitated by dust macrophages, this cell is not able to destroy it so travel to the hiliar nodes in the lymphatic system creating ghon complex, which is a calcificated and fibrous node. This action constitute the first stage, the second is spread via bloodstream to other organs. The thirs stage is very slow, and is very usual with pleurisy. The latest stage constitutes the resolution in which the patient stops the bacilli colonization.

The macrophage with the bacilli is surrounded by other inflammatory cells and dies becoming caseose forming granulome, with lymphocytes CD4 and Cd8, fibroblasts and giant cells. This stoping situation is the normal, but when is immune depletion the bacilli can become wild again and multiply. HIV can elicit bacilli reinfection, so is very normal this co-infection.

Clinical manifestations

There is a wide spectrum of disease’s ways.

1º pulmonary TB: is more frecuent in children and affects the middle and lower lobes of the lungs, is usually accompanied by pleural effusion . It occurs when the infection with bacilli is new. There are lymphatic nodes in the hilious region.

Pulmonary Tb pos-first: Is usual in adults and affects more frequent the apex because of the major oxygen ability, it can cause cavitations with abces and necrosys regions. There are lymphatic nodes that can compress the bronchium and elicit collapse of a lung segment. Is very usual due to reactivation of the bacilli. Clasical symptoms include: fever, malaise, night sweat, weight loss, comsumption and anorexy. Hemoptisys and anforic bruit are very frequent. Tha X-ray shows bilateral infiltrate and nodes in the hilio.

This Image shows a bilateral and nodular infiltrates on the superior left lung. There is an air-level in the low right lung. (Cortesy of NEJM)

Extrapulmonar TB: Can affect the nervous system, digestive system, cutaneous lesions, millliar disease, bone and articulation lesions (pott’s disease) and only lymphatic nodes affection (Scrafula).

Vaccination

Is a replicative vaccine and consists of BCG attenuated that bring immune contact and allow the immune system his recognition and resolution of the infection.

Dx

The diagnosis is with the culture of sputum and PPD test, X-ray, clinical manifestations.

Treatment

Isoniazide
Rifampicine
Piperazinamide
Etambuthol