Question

1. What is the concentration of bleach that is used to disinfect your work area? Why is it      used to disinfect rather than to sterilize? When do you disinfect your work area? (3             points)
2. Can a pure culture be prepared directly from a mixed-broth or a mixed-slant culture?             Explain. (3 points)
3. As demonstrated in the video, why do you pass the mouth of the tube through the flame? What is the correct angle? (3 points)

5. How do you know that you have used aseptic technique correctly and have achieved a pure culture? (3 points)
6. What are some advantages and disadvantages of the serial dilution agar plate        technique? (3 points)

7. Describe the different cultural characteristics identified when you use agar plates,         agar slants, and nutrient broth. (3 points)

8. Distinguish between the following: (2 points)

1. Disinfectant (1 point)
2. Antiseptic (1 point)

9. What are some advantages of an agar plate over a slant tube? (3 points)
10. Describe how discrete colonies can appear from a mixed culture using the streak-           plate subculture process. (4 points)

Answer 1

Ans 1) The active form of the beach is used in a concentration of around 5 to 8% which helps in cleaning and disinfecting the work area. This bleach is further diluted in a ratio of 1:10 and hence can be used for cleaning and disinfecting the work area. However, the rate of dilution depends on what needs to be cleaned as it might vary from 1:10 to 1:100.

The bleach is used for disinfecting and not sterilization because the beach cannot eliminate or kill the micro-organisms, but it can reduce the number of micro-organisms. It does not require a complex standard protocol and hence it helps in decontamination by reducing the number of microbes. The guideline for using the disinfectant like bleach does not have to very stringent. Generally,these bleach are oxidative agents and as soon as they come in contact with a micro-organism, it leads to causing oxidation and hence helps in disinfection.

The work area is disinfected when it is cleaned and tidied up. With the disinfection of work area, it helps in reducing the microbes and hence helps with keeping the area clean. It can be used to avoid being sick and encountering germs and microbes. It is good to regularly disinfect the area to be more productive.

Ans 2) The pure culture can be prepared from a mixed slant culture because it is easy to pick up the colonies from a agar slant rather than a liquid agar broth. In this a single colony can be picked from the agar plate and it can be streaked on an agar plate which helps in developing individual colonies from mixed culture which is a pure culture.