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9 Cards in this Set
- Front
- Back
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Mycobacteria
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Causative agents of tuberculosis and leprosy
• Waxy coat NO Gram stain Resistant to disinfectants • Acid-fast bacilli Resist decolorisation • Use Ziehl-Neelsen staining technique |
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Ziehl-Neelson staining technique
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1. Ziehl-Neelsen carbol fuchsin to the slide for five minutes while applying heat.
2. Follow with a gentle wash with water to cool the slide. 3. Acid alcohol is now added to decolorize the slide. 4. Wash the slide in water again and counterstain with methylene blue for 1-2 minutes. |
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Mycobacterium tuberculosis
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Chronic slow-progressing pulmonary
infection; transmission by aerosol droplets • Obligate aerobe, facultative intracellular parasite • 4-6 WEEKS to see colonies on a plate • Lowenstein-Jensen medium • Use microscopy of sputum smears as first line of diagnosis • Leading cause of death world-wide form a single infection (Bacteriology, Kenneth Todar, 2005) • Affects 1.7billion/year • Declining in US • Infection develops in stages |
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Primary Tuberculosis
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Aerosol inhalation
Bacteria multiplication in alveoli Macrophage ingestion of bacilli and formation of 1º complex Foci of infection in lungs (may be spread to kidneys, bones, meninges) at six weeks: (next two are positive tbtests) CMI is fully active, infection is stopped (majority of cases) Some bacilli survive, reactivation several years later |
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Mycobacterium tuberculosis post-primary
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Post-primary tuberculosis
• Late reactivation of lesions in lungs, kidneys, bones etc • 5% of cases; higher in patients with AIDS • Chronic infection |
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Immunity in Tuberculosis
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Cell mediated immunity is most important (T-cells)
• Mantoux test • Tuberculin solution is injected INTRADERMALLY, wait 48-72 hrs, check for redness • Record diameter of redness • >10mm POSITIVE • 5-9 mm Doubtful, maybe cross reaction with other Mycobacteria • <4mm NEGATIVE • **A positive test does not necessarily mean there is currently an active infection** |
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Atypical Mycobacteria
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Occasionally isolated from patients with chronic
• pulmonary disease indistinguishable from TB • M. kansassi, M. avium, M. intracellulare • Higher resistance to anti-TB drugs • Give “doubtful” Mantoux test (5-9 mm) • M. marinum: skin infections • M. fortuitum: soft tissue abscesses • All these infections are most typically seen in the immunecompromised |
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Mycobacterium leprae
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Causes leprosy
• 2 kinds • Tuberculoid leprosy: visible nerve enlargement, few erythmatous plaques, few bacilli in infected tissues, but many lymphocytes and granulomas; low infectivity • Lepromatous leprosy: no visible nerve enlargement, many erythromatous nodules, many bacilli in infected tissue; high infectivity • Rarely found in developed countries |
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Mycobacterium leprae
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Causes leprosy
• 2 kinds • Tuberculoid leprosy: visible nerve enlargement, few erythmatous plaques, few bacilli in infected tissues, but many lymphocytes and granulomas; low infectivity • Lepromatous leprosy: no visible nerve enlargement, many erythromatous nodules, many bacilli in infected tissue; high infectivity • Rarely found in developed countries |
