mycobacteria

• Mycobacteria


  • Aerobic, slow-growing and non-spore forming bacilli
  • Non-motile, (+) catalase, non-encapsulated and produce granules
  • Cell wall contains N-glycolylmuramic acid and mycolic acid
  • 0.2 to 0.6 um x 1 to 10 um in size
  • Obligate aerobes, growth enhanced with increased CO2
  • AFB: slender, slightly curved or straight rods that have tendency to clump
  • pH requirements: 6.5 - 6.8
  • Generation time: >12 hours, some are slow growers (>2 weeks) and some are rapid growers (3 days)
• Two groups of mycobacteria

  • Mycobacterium tuberculosis complex
  • Non-tuberculous mycobacteria (NTM)
• Mycobacterium tuberculosis complex


  • M. tuberculosis (Koch's bacillus)
  • M. bovis
  • M. africanum
  • M. canetii
  • M. microti
  • M. pinnipedii & M. caprae
• Non-tuberculous mycobacteria (NTM)


  • Slow-growing mycobacteria: M. avium complex, M. gordonae, M. kansasii, M. marinum, M. terrae complex, M. ulcerans, M. xenopi
  • Rapid-growing mycobacteria: M. fortuitum, M. chelonae, M. abscessus subsp. abscessus, M. smegmatis
• Mycobacterium tuberculosis


  Called "national bacteria our country", also known as "Koch's bacillus"
• Virulence factors of Mycobacterium tuberculosis

  • Sulfides (mycosides that resemble cord factor with sulfates attached to the disaccharide trehalose)
  • Mycoside (mycolic acid bound to a carbohydrate)
  • Cord Factor (mycoside formed by the union of two mycolic acid with a disaccharide trehalose, most common virulence factor)
  • Wax D (complicated mycoside that acts as an adjuvant and activates the protective cellular immune system)
• Biochemical tests for Mycobacterium tuberculosis

  • Positive: Niacin, Nitrate reduction, pyrazinamidase, urease
  • Negative: Thiophene-2 carboxylic acid (T2H) inhibition test, Catalase test
• Growth patterns of Mycobacterium tuberculosis on egg based media

  • Colonies are buff color, non photochromogen
  • Colonies are raised and dry, cauliflower-like appearance
  • Rough colonies exhibit "cording" (curved strands of bacilli)
• Mycobacterium bovis


  • Its attenuated or the BCG strain is used for vaccination of newborns
  • Acquired by humans through ingestion of contaminated milk from infected cows or exposure to different animals
• Biochemical tests for Mycobacterium bovis

  • Positive: Thiophene-2 carboxylic acid (T2H) inhibition test, Urease test
  • Negative: Niacin, Nitrate reduction, pyrazinamidase, catalase test
• Mycobacterium africanum


  Associated with human cases of tuberculosis in tropical Africa, detection requires the use of spacer oligotyping
• Biochemical tests for Mycobacterium africanum

  • Positive: Urease test
  • Negative: Niacin, Nitrate reduction, pyrazinamidase, catalase test
• Mycobacterium canetii


  Isolated from children with AIDS and mesenteric tuberculosis, grows more rapidly than M. tuberculosis (can grow in 6 days in a solid media)
• Biochemical tests for Mycobacterium canetii

  • Positive: Niacin, Nitrate reduction
• Mycobacterium microti


  Has been isolated from tuberculosis patients in both immunocompetent and immunocompromised individuals, found in rodents and is considered an agent of tuberculosis in animals
• Mycobacterium pinnipedii & caprae

  First isolated from animals, then further studies explained that they can also be transmitted to humans
• Tuberculosis


  • Mode of transmission: inhalation of 1um - 5um airborne droplet nuclei
  • Signs & symptoms: >2 weeks / 14 days - low grade fever, night sweats, fatigue, weight loss, cough with blood tinged sputum
  • Clinical diagnosis: (+) tuberculin test
  • Predisposing factors: malnourished patients, alcoholic patients, patients with immunosuppression (HIV/AIDS)
• First-line antituberculosis drugs


  • Isoniazid (INH)
  • Rifampicin (R)
  • Pyrazinamide (Z)
  • Streptomycin
  • Ethambutol (E)
• Second-line antituberculosis drugs


  • Cyclosporine
  • Ethionamide
  • P-amino-salicylic acid
  • Viomycin
  • Capreomycin
• Pott's disease


  Tuberculosis spondylitis, serious form of tuberculosis caused by invasion of M. tuberculosis into the spinal vertebra, confirmed through culture of bones and tissues, common sites are hip and knee bones, common symptom is severe back pain, requires 6 months to 1 year of treatment
• Miliary tuberculosis


  Potentially fatal form of disseminated TB characterized by millet-seed-like granuloma formation in various organs, arises from a primarily pulmonary infection that spreads hematogenously, common sites are spleen, lungs, bone marrow, kidneys, adrenal glands, eyes
• Individuals develop tuberculosis based on the degree of exposure to M. tuberculosis and other members of MTB complex, the virulence nature of the strain, and the cellular immune response of an individual against the tubercle bacilli
• Ghon lesions

  Located in the lungs, site of primary tuberculosis, possible storage source of the M. tuberculosis
• Multidrug-resistant Mycobacterium tuberculosis (MDR-TB)


  Developed as a result of resistance of MTB complex to anti-TB drugs caused by spontaneous mutation and close contact with person diagnosed with MDR-TB after receiving a specific treatment for tuberculosis
• Types of MDR-TB

  • Primary MDR-TB (without previous history of tuberculosis and is showing resistance to at least two anti-TB drugs - isoniazid & rifampicin)
  • Extensively resistant TB (XDR TB) (resistance to isoniazid, rifampicin and fluoroquinolone)
• Non-tuberculous mycobacteria (NTM)


  • Organisms known as atypical mycobacteria or mycobacteria other than tubercle bacilli
  • Found in the environment: soil, dust, water
  • They colonize the skin, respiratory tract, and the gastrointestinal tract of healthy individuals
  • They can cause chronic pulmonary disease resembling tuberculosis
  • Major causes of NTM human infections: Mycobacterium avium complex (MAC), Mycobacterium kansasii
• Runyon's classification of mycobacteria

  • Group I - Photochromogens (producing yellow to orange pigmented colonies only on exposure to light, growth rate: 10-21 days)
  • Group II - Scotochromogens (producing yellow to orange pigmented colonies even without light exposure, growth rate: 10-21 days)
  • Group III - Non photochromogens (producing non-pigmented colonies in light and darkness)
  • Group IV - Rapid growers (produce visible growth within less than 7 days)
• Mycobacterium avium complex (MAC)


  Most common cause of pulmonary infection in humans, similar to tuberculosis, the disease caused by MAC resembles the clinical feature of pulmonary tuberculosis, pathogen in immunocompetent and immunocompromised individuals, the gastrointestinal tract is the most common site of colonization, microscopy: pleomorphic, short, coccobacilli without beading, PAS: (+), isolated from: sputum, blood, bone marrow, reservoir: natural water, portal of entry: respiratory tract
• Biochemical tests for Mycobacterium avium complex

  • Positive: Tellurite reduction, Pyrazinamidase, variable in heat-stable catalase
• Mycobacterium avium subsp. paratuberculosis

  Causative agent of Johne's disease, causes chronic diarrhea in cattle, sheep, and goat, slow growing bacteria: 3-4 months of incubation
• Mycobacterium gordonae


  "Tap water bacillus", contaminates tap water used by patients in rinsing their mouths prior to sputum collection, a contaminant in the preparation of bacteriologic smears, rarely cause infections in humans
• Biochemical tests for Mycobacterium gordonae

  • Positive: Tween 80 hydrolysis, catalase test
• Mycobacterium kansasii


  "Yellow bacillus"
• Sputum


  Specimen collected from respiratory tract
• Reservoir


  Natural water
• Portal of entry


  Respiratory tract
• Culture


  • Transparent or opaque
  • Smooth colonies with mostly nonpigmented
• Positive biochemical tests


  • Tellurite reduction
  • Pyrazinamidase
  • Variable in heat-stable catalase
• Major species


  M. avium and M. intracellulare
• M. avium subsp. paratuberculosis


  • Causative agent of Johne's disease
  • Causes chronic diarrhea in cattle, sheep, and goat
  • Slow growing bacteria: 3-4 months of incubation