TB

Mycobacterium

General characteristics: Slender rods bacteria slightly curved rod with rounded ends. Mycobacteria do not stain by gram stain ,they are able to resist decolorization by acid or alcohol. Stained by Ziehl-Neelsen technique (unusual complex lipid (mycolic acid) in the cell wall)

Aerobic bacteria Non motile Non capsulated Can be destroyed pasteurization u.v light autoclaving methods phenol alcohol

M. tuberculosis cause T.B in human M. bovis Cause T.B in human and cattle M. africanum Cause T.B in human

(mycobacteria other than tuberculosis) (MOTT) M. avium , M. intracellulare cause disease in person with chronic lung disease, leukemia, and AIDS.

M. leprae cause leprosy

Damage to nerves Secondary infection cause tissue loss and hand deformed
First skin patches then ulceration in skin URT and eyes
Transmission by close contact with patients Nasal droplets By animal called armadilos


1-Sputum testing The specimen is treated with 3% KOH or NaOH for liquefaction. The specimen is centrifuged at high speed to concentrate the mycobacterium at the bottom of centrifuge tube. Stain by Ziehl- Neelsen technique.

* 1- Cover the smear with basic carbol fuchsin & steam over boiling water bath for 5 min, adding additional stain, if necessary to prevent the smear drying
3- Allow slid to cool & wash with water
4- Decolorizing by adding acid alcohol (95% ethyl alcohol containing 3%HCL) drop by drop to the slide until the primary stain removed from the smear

6- Counterstain with methylene blue for 30 sec.

5- Wash with water
7- Wash with water & dry

Other bacteria .

AFB

. Result Fast bacteria appear as red Red=acid fast baceteria

Blue=Non acid-fast bacteria

Mycobacterium tuberculosis. Acid-fast stain

Malachite green which inhibit all bacteria except Mycobacteria species Glycerol which inhibit the growth of M. bovis and allow the growth of M. tuberculosis

2. Lowenstein-Jensen medium: special selective media contains:

*The medium appears green, opaque . *Slow growing (2-3 weeks) at 37oC The growth rate is slower than most other bacteria. The doubling time is about 18 hours.

Colony on Lowenstein-Jensen medium appears as brown, granular colonies sometimes called (rough, tough, and buff). Rough :due to dry irregular growth Tough :due to difficulty in lifting the colony from the surface. Buff : due to the pale yellow colour

The colonies are formed after 3-6 weeks of incubation on Lowenstein-Jensen medium. The colonies are buff colored and dry breadcrumb-like.

Abnormalities on chest radiographs may be suggestive of, but are never alone diagnostic of, TB.

A tuberculin reaction of >= 5 mm of induration is classified as positive result. However ,a positive test only means to exposure once to the microorganism but does not certainly indicate active disease.

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