MTB is slow growing and colonies take 4-6 weeks to grow
Colony appearance is dry, rough, raised with wrinkled surface and creamy white in color
Conatmination and liquifaction of egg based medium is a disadvantage
Culture on solid media
Agar based media
Middlebrook 7H10 agar
and Middlebrook 7H11 agar
Less affected by contamination
Growth in two weeks
BACTEC MGIT 960
The MGIT tube contains a fluorochrome that is suppressed by oxygen in tube. During bacterial growth within the tube, the free oxygen is utilized by bacteria. With depletion of free oxygen, the fluorochrome is no longer inhibited, resulting in fluorescence within the MGIT tube .
This flourescence is measured by the machine . The intensity of fluorescence is directly proportional to the bacterial growth.
PCR is highly sensitive(1-10 bacilli/ml of sample)
Diagnosis of latent tuberculosis
Montoux skin test
is the standard method of determining whether a person is exposed to Mycobacterium tuberculosis
The TST is performed by injecting 0.1 ml of tuberculin purified protein derivative (PPD) into the inner surface of the forearm. The TST is an intradermal injection. When placed correctly, the injection should produce a pale elevation of the skin (a wheal)
Monteux test (cond.)
The skin test reaction should be read between 48 and 72 hours after administration.
The reaction should be measured in millimeters of the induration (palpable, raised, hardened area or swelling). The reader should not measure erythema (redness).