mycobacteria - prac. microbiology
TRANSCRIPT
MYCOBACTERIA
Characters
• Acid-alcohol fastness
• Slow rate of growth
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)
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.
Ziehl-Neelsen (Z-N) Stain
• Carbol-fuchsin dye
• Heat
• Acid-alcohol (decolourization)
• Methylene blue
• Acid-fast = Mycobacteria
Cultural Characters
Media include:
- Lowenstein-Jensen (L-J) medium
- Middlebrook's medium
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.
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).
Oral mainfestations of tuberculosis
1. Primary complex
2. Oral ulceration secondary to pulmonary tuberculosis
3. Lupus vulgaris
4. Tuberculous periapical infection and osteomyelitis.
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
Direct Detection:
1. Smears:
Ziehl-Neelsen (Z-N).
Under the ordinary light microscope, AFB appear pink in a blue background.
2. Molecular tests:
• For rapid detection
• Expensive
Cultivation:
Conventional culture media: (incubated in 5 – 10% CO2 at 37oC):
L-J tube
- Results may be relatively delayed (2-8 weeks).
Fluid Medium Systems(4-14 days identification)
Middle brook broth and Bactec AFB media
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.
Tuberculin Skin Test (TST)
Principle:
detects a delayed type hypersensitivity (DTH)
response to previous exposure of the host to
tubercle bacilli.
Interpretation of the Tuberculin Skin Test
An induration of 10 millimeters or more is considered positive
Prevention is Always Better than Treatment
1. General Measures e.g., Pasteurization of milk.
2. Treatment of latent tuberculosis.
3. BCG Vaccine.
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
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
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
Thank You