Mycobacterium 1-2

• What does the term Mycobacterium mean?

  Fungus-like bacterium
• What are the general characteristics of Mycobacterium?

  They are strict aerobic, non-motile, non-capsulated, and non-sporing.
• How do Mycobacterium appear under a microscope?

  Weakly gram-positive, straight or slightly curved rod-shaped bacteria.
• What is the generation time for Mycobacterium?

  15 to 20 hours.
• What is the significance of the high lipid content in Mycobacterium walls?

  It makes them relatively impermeable to stains and difficult to decolorize.
• What are Mycobacterium classified as?

  Obligate parasites, opportunistic pathogens, and saprophytes.
• How many species are in the genus Mycobacterium?

  More than 70 species.
• What disease is caused by Mycobacterium tuberculosis complex?

  Tuberculosis.
• What is the causative agent of leprosy?

  Mycobacterium leprae.
• What are non-tuberculous mycobacteria (NTM)?

  Diverse group of mycobacteria that are saprophytic in nature and cause tuberculosis-like conditions.
• What is the primary mode of transmission for tuberculosis?

  Inhalation of aerosols from infected patients.
• What percentage of people infected with M. tuberculosis develop the disease?

  About 5%.
• What are some risk factors for TB transmission?

  Sputum positive patients, overcrowding, low cell-mediated immunity, age, genetic factors, and malnutrition.
• What are the important virulence factors of Mycobacterium?

  The waxy surface and the ability to stimulate a strong cell-mediated immune response.
• What is the incubation period for tuberculosis?

  2 to 12 weeks.
• What are common symptoms of tuberculosis?

  Fatigue, low-grade fever, unexplained weight loss, loss of appetite, persistent coughing, and difficulty breathing.
• What are the types of clinical tuberculosis?

  • Primary tuberculosis
  • Secondary tuberculosis
  • Disseminated tuberculosis (miliary TB)
• What is the minimum infectious dose of M. tuberculosis?

  Around 10 bacterial cells.
• What happens during primary tuberculosis?

  1. tuberculosis enters the respiratory airways, is phagocytized by macrophages, and continues to multiply inside them.
• What are tubercles?

  Granulomas that consist of a central core containing TB bacteria and an outer wall made of fibroblasts, lymphocytes, and macrophages.
• What occurs after the formation of tubercles in primary tuberculosis?

  The immune system mounts a response, and the bacteria can remain dormant or be reactivated later.
• What characterizes secondary/reactivated tuberculosis?

  1. tuberculosis breaks the stalemate, ruptures the tubercle, and re-establishes an active infection.
• What are the symptoms of secondary tuberculosis?

  Violent coughing, greenish or bloody sputum, low-grade fever, anorexia, weight loss, extreme fatigue, night sweats, and chest pain.
• What is the mortality rate of untreated secondary tuberculosis?

  Nearly 60%.
• What is disseminated tuberculosis?

  When TB spreads to other sites or proceeds to a generalized infection.
• How does TB spread in disseminated tuberculosis?

  Macrophages carry the pathogen via blood and lymph nodes to other sites.
• What are common sites affected by disseminated tuberculosis?

  Regional lymph nodes, bone marrow, spleen, intestines, kidneys, spinal cord, and brain.
• What is the most usual specimen for diagnosing pulmonary tuberculosis?

  Sputum.
• How should sputum specimens be collected for TB diagnosis?

  Three or more consecutive samples should be examined, collected first thing in the morning if possible.
• What is the purpose of decontaminating sputum specimens?

  To kill many other bacteria and fungi before processing.
• What staining technique is used for sputum smears?

  Ziehl–Neelsen technique or fluoro-chrome stain.
• What is the gold standard method for diagnosing TB?

  Culturing the bacteria.
• What is the incubation temperature for LJ media used in TB culture?

  35–37°C.
• How long does it typically take for M. tuberculosis to grow on LJ media?

  2–8 weeks.
• What is the colony morphology of M. tuberculosis?

  Rough, tough, and yellowish colonies.
• How does M. bovis colony morphology differ from M. tuberculosis?

  1. bovis produces smooth, moist, and white-colored colonies.
• What does Ziehl-Neelsen staining reveal about Mycobacterium tuberculosis?

  It appears as red bacillus.
• What is the first step in identifying M. tuberculosis from colonies grown on LJ media?

  Subjecting the colonies to acid-fast stain.
• What is the significance of the niacin test in M. tuberculosis identification?

  It differentiates between human M. tuberculosis and M. bovis strains.
• What does the nitrate reduction test indicate about M. tuberculosis?


  It produces the enzyme nitroreductase and reduces nitrate to nitrite.