1. Dilution of the mixed culture is a common step in all the three methods: the streak-plate, the spread-plate and the pour-plate technique.
a) True
b) False
Explanation: The streak-plate technique does not require dilution as a portion of the mixed culture is placed on the surface of an agar medium and streaked across the surface.
2. Which of the following are not performed in lyophilization?
a) agar slant is covered with mineral oil
b) cell suspension is frozen at -60 degree to -78 degree C
c) vials are connected to high-vacuum line
d) bacterial sample is dehydrated
Explanation: In lyophilization or freeze-drying, a dense cell suspension is placed in small vials and frozen at -60 degree to -78 degree C. The vials are then connected to a high-vacuum line. The ice present in the frozen suspension sublimes under the vacuum and results in dehydration of the bacteria.
3. Which of the following is a function of cryoprotective agents?
a) for long-term preservation of cultures
b) prevents cell damage due to ice crystal formation
c) prevents formation of ice
d) to trap the liquid nitrogen
Explanation: For preservation at low temperatures the cells are prepared as a dense suspension in a medium containing cryoprotective agents such as glycerol or dimethyl sulphoxide which prevents cell damage due to ice crystal formation.
4. What is the temperature of liquid nitrogen?
a) -120 degree C
b) 0 degree C
c) -150 degree C
d) -196 degree C
Explanation: Liquid nitrogen has a temperature of -196 degree C and is used for the storage of culture medium.
5. Nichrome loop wire is used in which of the following techniques?
a) Pour-plate
b) Streak-plate
c) Spread-plate
d) Roll-tube technique
Explanation: In the streak plate technique, with the help of a nichrome loop wire, a portion of mixed culture is placed on the surface of an agar medium and streaked across the surface.
6. Which device is used to pick a single bacterial cell from a mixed culture?
a) microscope
b) micropipette
c) microprobe
d) micromanipulator
Explanation: A device called the micromanipulator can be used in conjunction with a microscope to pick a single bacterial cell from a mixed culture. The micro manipulator permits the operator to control the movements of a micropipette or a microprobe so that a single cell can be isolated.
7. The National Collection of Type Cultures is situated in ____________
a) France
b) England
c) Germany
d) Japan
Explanation: In England, the National Collection of Type Culture is in London which is a large central collection whose main purpose would be the acquisition, preservation, and distribution of authentic cultures of living organisms.
8. The American Type Culture Collection, located in Rockville, Maryland in the year 1980 has a collection of bacterial strain in what numbers?
a) 10,000
b) 11,000
c) 500
d) 11,500
Explanation: In the US the major collection is the American Type Culture Collection, located in Rockville, Maryland. In 1980 the collection included the following number of strains: bacteria-11,500; bacteriophages-300; algae-130; protozoa-720; fungi and fungal viruses-13700 etc.
9. Which of the following has a larger diameter?
a) well-separated colonies
b) crowded colonies
c) young colonies
d) old colonies
Explanation: Well-separated colonies have a larger diameter than those which are crowded together because widely separated colonies are subject to less competition for nutrients and less inhibition by toxic products of metabolism.
10. Surface texture of strains are related to virulence.
a) True
b) False
Explanation: For several species of pathogenic species, the surface texture of colonies may bear a relation to virulence. For example, Smooth colonies of S.pneumoniae or of Salmonella species are usually virulent, whereas Rough colonies are not.