Microbiology Multiple Choice Questions on “Pure Cultures”.
1. Roll-tube technique is used to isolate ___________
A. aerobes
B. anaerobes
C. facultatives
D. stringent anaerobes
Answer: D
Clarification: Roll-tube technique which is a modification of streak-plate technique is used to isolate stringent anaerobes.
2. In pour-plate method, the medium should be maintained at what temperature?
A. 37 degree C
B. 67 degree C
C. 45 degree C
D. 0 degree C
Answer: C
Clarification: In pour plate method, the medium is maintained in a liquid state at a temperature of 45 degrees C to allow thorough distribution of inoculum.
3. Which of the following method can be used to determine the number of bacteria quantitatively?
A. Streak-plate
B. Spread-plate
C. Pour plate
D. Pour-plate and spread plate
Answer: D
Clarification: Due to a higher degree of dilution, pour-plate and spread-plate techniques may be performed in a quantitative manner to determine the number of bacteria present in a specimen.
4. 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
Answer: B
Clarification: 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.
5. 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
Answer: A
Clarification: 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.
6. 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
Answer: B
Clarification: 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.
7. What is the temperature of liquid nitrogen?
A. -120 degree C
B. 0 degree C
C. -150 degree C
D. -196 degree C
Answer: D
Clarification: Liquid nitrogen has a temperature of -196 degree C and is used for the storage of culture medium.
8. Nichrome loop wire is used in which of the following techniques?
A. Pour-plate
B. Streak-plate
C. Spread-plate
D. Roll-tube technique
Answer: B
Clarification: 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.
9. Which device is used to pick a single bacterial cell from a mixed culture?
A. microscope
B. micropipette
C. microprobe
D. micromanipulator
Answer: D
Clarification: 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.
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