• Slim rod
• acid-alcohol fastness
• fluoresces bright orange-yellow against a dark background with flourochrome stain
• Aerobic
• growth slow 3-6 weeks to be visible in standard media
• Bactec radiometric system detects growth in 7-16 days.
• Resistant to desiccation
• heat sensitive
• Intracellular and extracellular

• By inhalation of droplets generated by infected person while coughing.

Primary infection :

• The patient inhales M. tuberculosis on droplet nuclei,  transmitted from an infected patient. 

• The organism is phagocytosed by alveolar macrophages. 

• Bacterial multiplication continues, destroying the macrophage, Lymphocytes and monocytes are attracted to the focus and monocytes are differentiated into macrophages which ingest bacilli. 

• Infected macrophages are carried to lymph nodes and may spread throughout the body. 

• Some bacilli spread through the blood stream to distant tissues

• In most within 2 weeks cell mediated immunity arrests further progression

• In minority it can progress to disease state (Pneumonia, Meningitis, Miliary tuberculosis)

• PPD becomes positive

Secondary infection:

• The patient has reactivated a focus of infection which was acquired in the past. This is not a new infection

• This occurs  when the cell mediated immunity fails due to any reason 

• Reactivation occurs at sites with high 02 tension (in the apices of lungs)  or because of deficient lymph production. 

• Most of the clinical disease is secondary reactivation

• These are intracellular organism
• Cell mediated immunity is the primary defense
• Ability to multiply in activated macrophages
• To survive low pH, high lactic acid and high CO2

Pathology

• Granulomas is the hallmark of tuberculous infection.
• Caseation necrosis

Diagnosis

• AFB stain of concentrated sputum 
• Culture of sputum or fluids or tissue
• Biopsy demonstrating granulomas with organisms
• Suggestive radiological exams

Our patient has the compatible clinical history, CXR and demonstrable organism in sputum smear. You should send the sputum for culture and sensitivity studies.

Therapeutic strategy

• Four drugs: isoniazid, rifampin, ethambutol, pyrazinamide for 3 months followed by INH and Rifampin for 6 months. 
• Directly observed therapy (DOT) with above 4 drugs for two weeks, then 2x or 3x weekly DOT for six months.

The infection is spread by droplet nuclei generated from a person who is coughing. The nuclei are inhaled. The infection is prevented by 

• Covering the mouth of an infected person during coughing. 

• Respirators (masks) used by health care providers while caring for the patient

• Gowns and gloves

• Negative pressure isolation rooms and UV lights in the rooms

• Part of prevention is suspecting infection in high risk patients and keeping them in isolation if they have a compatible clinical picture

  • Hospitalization when there is a medical need 

  • Home confinement for not needing hospital care

  • Isolation is required for a period of two weeks on antituberculous therapy

Isoniazid should be prescribed for prevention of infection to PPD positive patients

• with no demonstrable disease state 

• who are at a high risk for activation

• with less risk for developing  INH induced hepatitis

It can practically infect any organ. Common clinical infections are

• Pulmonary
• Meningitis
• Miliary tuberculosis
• Pelvic inflammatory disease
• Bone (Pott's disease of spine) and joints