1. Which of the following is a negative stain?

(a) Fontana
(b) ZN stain
(c) Nigrosin
(d) Albert stain

ANSWER c

Negative staining is a technique in which the background is stained, leaving the actual specimen untouched, and thus visible. In contrast, with ‘positive staining’, the actual specimen is stained.

• Examples of negative stains include nigrosin and India Ink.
• India ink is used to make a diagnosis of cryotococcal infection by making
  its capsule prominent.

2. Stain used for melanin is:

(a) Oil red
(b) Gomori methamine silver stain
(c) Masson fontana stain
(d) PAS stain

ANSWER c

3. Which of the following statements about Telomerase is true?

(a) Has RNA polymerase activity
(b) Causes carcinogenesis
(c) Present in somatic cells
(d) Absent in germ cells

ANSWER b

Telomerase is a specialized RNA-protein complex that uses its own RNA as a template for adding nucleotides to the ends of chromosomes.

• Regulatory protein sense the telomere length and they restrict the activity of telomerase to prevent unnecessary elongation.
• Telomerase activity is highest in germ cells and present at lower levels in stem cells, but it is usually undetectable in most somatic tissues.

Decreased activity of telomerase is associated with ageing whereas its excessive activity is associated with cancers.

4. An AIDS patient Khalil develops symptoms of pneumonia, and Pneumocystis carinii is suspected as the causative organism. Bronchial lavage is performed.

Which of the following stains would be most helpful in demonstrating the organism’s cysts on slides made from the lavage fluid?

(a) Alcian blue
(b) Hematoxylin and eosin
(c) Methenamine silver
(d) Trichrome stain

ANSWER c

The appropriate stain is methenamine silver. The routine hematoxylin and eosin does not adequately demonstrate the organisms. The cysts, when stained with methenamine silver, have a characteristic cup or boat shape; the trophozoites are difficult to demonstrate without electron microscopy.

• Alcian blue (choice A) is good for demonstrating mucopolysaccharides.
• Hematoxylin and eosin (choice B) is the routine tissue stainQ used in pathology laboratories.
• Trichrome stain (choice D) is good for distinguishing fibrous tissue from nerve and muscle.

5. Which process makes the bacteria ‘tasty’ to the macrophages:

(a) Margination
(b) Diapedesis
(c) Opsonisation
(d) Chemotaxis

ANSWER c

Opsonization is an immune process which uses opsonins to tag foreign pathogens for elimination by phagocytes. Without an opsonin, such as an antibody, the negatively-charged cell walls of the pathogen and phagocyte repel each other