Mycobacteria - Prac. Microbiology
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Transcript of Mycobacteria - Prac. Microbiology
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MYCOBACTERIA
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Characters
• Acid-alcohol fastness
• Slow rate of growth
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Members of the Genus Mycobacterium
1. Mycobacterium tuberculosis Complex: M. tuberculosis, M. bovis, M. africanum & M. microti.
2. Non-tuberculous mycobacteria (NTM): e.g. M. avium complex & M. fortuitum.
3. Mycobacterium leprae: causes leprosy.
4.The Bacillus of Calmette-Guerin (BCG)
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Mycobacterium Tuberculosis
Morphology:- Acid-alcohol-fast bacillus- Slender - Straight or curved - Arranged singly or in small groups
- Ziehl-Neelsen (Z-N) --- pink in a blue background.
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Ziehl-Neelsen (Z-N) Stain
• Carbol-fuchsin dye
• Heat
• Acid-alcohol (decolourization)
• Methylene blue
• Acid-fast = Mycobacteria
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Cultural Characters
Media include:
- Lowenstein-Jensen (L-J) medium
- Middlebrook's medium
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Cultural Characters
• Strict aerobe (5 - 10% CO2 stimulates its
growth).
• Colonies appear after 2-4 weeks of incubation at 37°C and may be delayed to 8 weeks.
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Human TuberculosisMode of Infection
Inhalation of droplet nuclei from a patient with open pulmonary tuberculosis.
Ingestion of milk contaminated with M. bovis.
TB may affect other systems (e.g. TB meningitis, lymphadenitis, renal, genital & intestinal TB).
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Oral mainfestations of tuberculosis
1. Primary complex
2. Oral ulceration secondary to pulmonary tuberculosis
3. Lupus vulgaris
4. Tuberculous periapical infection and osteomyelitis.
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Laboratory Diagnosis of Open Pulmonary TB
Specimens: include sputum, BAL
Early morning sputum specimens collected on 3 consecutive days, from a
deep productive cough, give the best results
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Direct Detection:
1. Smears:
Ziehl-Neelsen (Z-N).
Under the ordinary light microscope, AFB appear pink in a blue background.
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2. Molecular tests:
• For rapid detection
• Expensive
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Cultivation:
Conventional culture media: (incubated in 5 – 10% CO2 at 37oC):
L-J tube
- Results may be relatively delayed (2-8 weeks).
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Fluid Medium Systems(4-14 days identification)
Middle brook broth and Bactec AFB media
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Laboratory Diagnosis of Extra-Pulmonary TB
Same as mentioned for pulmonary TB, but by collecting the appropriate specimens.
However, specimens collected from normally sterile sites, e.g. CSF, do not require decontamination.
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Tuberculin Skin Test (TST)
Principle:
detects a delayed type hypersensitivity (DTH)
response to previous exposure of the host to
tubercle bacilli.
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Interpretation of the Tuberculin Skin Test
An induration of 10 millimeters or more is considered positive
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Prevention is Always Better than Treatment
1. General Measures e.g., Pasteurization of milk.
2. Treatment of latent tuberculosis.
3. BCG Vaccine.
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MCQ Questions
1.M. tuberculosis are characterized by being:
a.Strict anaerobes
b.Acid fast bacilli
c.Capsulated
d.Motile
e.Able to grow on ordinary media
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2.One of the following media is used for growing M. tuberculosis:
a.MacConkey’s agar
b.Blood agar
c.Nutrient agar
d.Lowenstein Jensen medium
e.Loeffler’s serum
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3.The following methods are used in the diagnosis of pulmonary tuberculosis except:
a.Examination of ZN stained direct sputum smear
b.PCR of sputum
c.Culture on selective medium
d.BACTEC AFB system
e.Detection of specific antibodies
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Thank You