Microbiology Of Tb

Question 1

Characteristics of tb

Answer 1

Gram positive. Obligate aerobe
Facultative intracellular
Gen time is 15-20hrs
Mycolic acid- acid fastness

Question 2

Zn staining method
Stain
Counter stain
Decolouriser

Answer 2

10000 bacilli/ml
Carbol fuschin
Loeffler methylene blue
20%h2so4. Alcohol 95% 3%hcl

Question 3

Zn steps

Answer 3

Air dry , heat fix
Colour- steam 5 min- cool 5 min
Wash with distilled water 
Decolourize 15 sec
Tilt , add alcohol until colour stops dripping- rinse
Counter stain - 15 sec
Rinse and dry 
Use oil immersion

Question 4

How does the AFB seen under microscope

Answer 4

Bright red rods in blue background

Question 5

What is the procedure for k i n y o u n staining

Answer 5

Same as zn staining except for the heating

Question 6

Procedure of auromaine rhodamine staining

Answer 6

Coluriser- flouroscent dye
Decolourizer- mild
Counter stain- k permonganate

Question 7

Advantages odf auromanine rhodamine

Answer 7

Faster
Detects when few
10% more sens
No heat for staining
Disadvantages:
All negative have to be confirmed with zn staining
Negative doesnt mean negative

Question 8

Causes of false positive

Answer 8

Food particles
Precipitated stains 
Afb environmental 
Ntb/nocardia
Bacillus subtilis
Yeasts
Fibers 
Pollens

Question 9

False negative

Answer 9

Improper collection 
Staining
Poor selection 
Exam
Administration error
Reading error