Culture vessel should be closed with non-absorbent cotton pluge, for the first time

Options

A. Immediately after autoclaving the medium
B. Soon after inoculation
C. Before autoclaving the culture vessels
D. During incubation

Answer

### Step-by-Step Solution:

1. **Understand the Question**: The question asks when culture vessels should be closed with a non-absorbent cotton plug for the first time during the process of culturing.

2. **Identify the Processes Involved**: There are several key processes mentioned:
- Autoclaving the medium
- Inoculation
- Incubation

3. **Evaluate Each Option**:
- **After Autoclaving**: After the autoclaving process (which sterilizes the medium), there is no need for a non-absorbent cotton plug since the medium is already sterile. This option is incorrect.
- **Soon After Inoculation**: Once inoculation is done, the culture vessels do not require a cotton plug because the inoculation process is complete, and the culture is ready for further steps. This option is also incorrect.
- **During Incubation**: During incubation, the culture should be kept in a sterilized environment to prevent contamination. Therefore, a non-absorbent cotton plug is not necessary at this stage. This option is incorrect.
- **Before Autoclaving**: Before the autoclaving process, it is essential to close the culture vessels with a non-absorbent cotton plug. This prevents any contamination from the external environment before sterilization. This option is correct.

4. **Conclusion**: The correct answer is that culture vessels should be closed with a non-absorbent cotton plug **before autoclaving**.