Tuberculosis

Corynebacteria: Gram-positive bacteria, part of the CMN group.
Mycobacteria: Includes Mycobacterium tuberculosis, M. bovis, and non-tuberculous mycobacteria.
Nocardia: Another group in the CMN classification.
Peptidoglycan: A polymer that forms the cell wall of bacteria.
Mycolic Acids: Fatty acids found in the cell walls of mycobacteria contributing to their pathogenicity.
Acid-fast: Characteristic of certain bacteria that retain stains despite decolorization; identified using Ziehl-Neelsen staining which yields red dyes.
Tuberculosis (TB): Infectious disease usually caused by Mycobacterium tuberculosis.
Ghon complex: Associated with TB, it comprises a parenchymal lesion and an involved lymph node.
Granuloma: A mass formed of immune cells in response to infection, used for walling off pathogens.
Caseous necrosis: A form of tissue necrosis associated with TB, characterized by a cheese-like appearance.
Miliary tuberculosis: Widespread infection characterized by multiple small lesions in various organs.
Isoniazid, Rifampin, Ethambutol: First-line medications for TB treatment.
Macrophage: Immune cells that engulf and digest cellular debris and pathogens.
HIV, immunosuppression: Conditions increasing susceptibility to TB.
PPD test (Tuberculin skin test): A diagnostic skin test for TB infection.
Quantiferon: A blood test for detecting TB infection.

Historical context: TB has existed for millennia, referred to as consumption or the White Plague, being a leading cause of death.
Adaptation and resilience: TB has evolved into a well-adapted human pathogen that is difficult to eradicate; latent infections can re-activate under certain conditions.
Global and local significance: Important public health issue, especially in areas with high HIV prevalence or in certain parts of the US, highlighting the need for awareness in global medical outreach.

General characteristics: Rod-like and filamentous bacteria that are acid-fast due to mycolic acids. They are catalase-positive and exhibit a very slow growth rate.
Classification: Part of the CMN group (corynebacteria, mycobacteria, nocardia). Differentiation based on growth rate, niacin production, nitrate reduction, etc.
Mycobacterium tuberculosis complex: Includes M. tuberculosis (causative agent of TB), M. bovis (causes TB via unpasteurized dairy), M. africanum, M. canettii, M. caprae, and others.
Non-tuberculous mycobacteria: Refers to other mycobacterial species that do not cause tuberculosis.

Primary Infection: - Formation of the Ghon complex, which consists of a lesion in lung parenchyma and related lymph node. - Typically asymptomatic, it can be self-limiting, but about 5% may have clinical symptoms.
Secondary Infection (Reactivation): - Reactivation of dormant lesions often located in the apices of the lungs, leading to cavitary caseous necrosis. - Miliary TB occurs if a tubercle erodes into a blood vessel, spreading the infection. - Patients with immunosuppression may not form granulomas, leading to dissemination without the classic presentation.
Diagnostics: - PPD test, acid-fast stain of sputum, and mycobacterial cultures are employed for diagnosis.
Treatment: - First-line treatment includes isoniazid, rifampin, and ethambutol, keeping in mind the potential for drug resistance. - Prevention through BCG vaccine can result in a positive PPD test.

Granuloma Formation: - Activation of T cells and macrophages leads to the formation of granulomas that encapsulate the TB organism, which may remain viable for long periods, resulting in a latent TB state.
Cell-mediated Immunity: - Antibodies are less effective against intracellular pathogens like TB; macrophages are activated to effectively kill the bacteria.
Latent vs Active TB:
- Latent TB is marked by the presence of granulomas without clinical symptoms, whereas active TB results in symptomatic disease.

Testing Approaches: - A positive PPD test indicates exposure to TB but does not distinguish between latent and active TB. - Newer tests like Quantiferon assess cell-mediated response to TB antigens.
Caveats in Testing: - Patients with disseminated TB may lose the ability to react to skin tests (anergy), complicating diagnosis.

Reactivation: - Complications arise due to weakened immunity, often presenting with cough, hemoptysis, and risk of contagion due to active lesions.
Miliary TB: - Can result in large dissemination of bacteria leading to multiple organ involvement.
TB Meningitis: - Rare but serious complication, often presenting as basilar meningitis characterized by lymphocytic pleocytosis.

Initial Diagnostic Tests for Suspected TB:
- Acid-fast staining of sputum is deemed the most reliable first test in patients with chronic cough and weight loss.
Management of Latent TB:
- Isoniazid monotherapy is recommended for latent TB infections to prevent progression to active disease.
Common Pathogens in Immunocompromised Patients:
- Mycobacterium avium complex is frequently isolated in advanced HIV patients presenting with systemic symptoms.
Multidrug Therapy Purpose:
- To counteract resistance arising due to spontaneous mutations in the TB pathogen, necessitating combination therapy in active cases.