• 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)
- Acid-alcohol-fast bacillus
- Straight or curved
- Arranged singly or in small
- Ziehl-Neelsen (Z-N) ---
pink in a blue background.
- Lowenstein-Jensen (L-J) medium
- Middlebrook's medium
• Strict aerobe (5 - 10% CO2
• Colonies appear after 2-4 weeks of incubation
at 37°C and may be delayed to 8 weeks.
Mode of Infection
Inhalation of droplet nuclei from a
patient with open pulmonary
Ingestion of milk contaminated with
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
3. Lupus vulgaris
4. Tuberculous periapical infection and osteomyelitis.
Laboratory Diagnosis of Open
Specimens: include sputum, BAL
Early morning sputum specimens
collected on 3 consecutive days, from a
deep productive cough, give the best
Under the ordinary light
appear pink in a blue
2. Molecular tests:
• For rapid detection
Conventional culture media:
(incubated in 5 – 10% CO2 at
- 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
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
detects a delayed type
response to previous
exposure of the host to
Interpretation of the Tuberculin Skin Test
An induration of 10 millimeters or more is considered
Prevention is Always Better
1. General Measures
e.g., Pasteurization of milk.
2. Treatment of latent
3. BCG Vaccine.
1.M. tuberculosis are characterized by
b.Acid fast bacilli
e.Able to grow on ordinary media
2.One of the following media is used for
growing M. tuberculosis:
d.Lowenstein Jensen medium
3.The following methods are used in the
diagnosis of pulmonary tuberculosis
a.Examination of ZN stained direct sputum
b.PCR of sputum
c.Culture on selective medium
d.BACTEC AFB system
e.Detection of specific antibodies