Mycobacteria and Tuberculosis Laboratory Diagnosis

• Mycobacteria have a unique cell wall composed of mycolic acid, making them acid-fast bacilli (AFB) and resistant to Gram staining.
• Staining methods for mycobacteria include acid-fast stain, Kinyoun stain, and the Ziehl-Neelsen stain.
• Mycobacteria are aerobic and can be enhanced by exposure to 5-10% CO2.
• Mycobacterium tuberculosis is the most common mycobacterium worldwide, causing tuberculosis (TB).
• TB can affect various organs and can disseminate in individuals with weakened immune systems.
• TB can be diagnosed through culture and sensitivity testing, with treatment typically involving 9 months of isoniazid and rifampin.
• Mycobacterium bovis is another significant human pathogen, transmitted from animals to humans.
• Non-tuberculosis mycobacteria include slow-growing and rapid-growing types, with various species causing infections in humans.
• Laboratory diagnosis of mycobacteria involves collecting specimens like sputum, bronchial washings, urine, and tissue samples for acid-fast bacilli staining and culture.
• Culture media such as Lowenstein-Jensen, Petragnani, and American Thoracic Society media are commonly used for mycobacterial culture.- 7H11 agar contains 0.1% casein hydrosolid to improve recovery of isoniazid resistant strain of Mycobacterium tuberculosis, making it preferred for drug susceptibility testing.
• Liquid media like MGIT is used to propagate bacteria for stock culture, while H9 broth is used for subculturing stock strains.
• Primary identification of Mycobacteria includes rough, raised colonies and cord growth pattern, indicating tuberculosis.
• Biochemical tests for Mycobacteria include niacin accumulation test (positive in M. tuberculosis), nitrate reduction test (positive in M. tuberculosis), and catalase test (positive in all Mycobacteria).
• Hydrolysis of Tween 80 by Mycobacteria releases oleic acid and polyoxyethylated sorbitol, turning neutral red indicator amber in color.
• Iron uptake test challenges Mycobacteria to convert ferric ammonium citrate to iron oxide, seen as rusty brown colonies.
• Arylsulfatase test detects enzyme activity within 3 or 14 days, causing a pH change indicated by pink color.
• Urease test distinguishes Mycobacterium species based on pink (positive) or white (negative) color change in the medium.

Learn about the unique characteristics of mycobacteria, including their acid-fast nature, staining methods, common species like M. tuberculosis and M. bovis, as well as laboratory diagnostic techniques such as culture, sensitivity testing, and biochemical tests. Explore the various culture media and identification methods used for mycobacteria.