Why was the agar plate not sealed completely after placing the discs?

The reason for not sealing the agar plate completely after placing the discs is primarily to avoid the growth of anaerobic microbes. Anaerobic microbes thrive in environments lacking oxygen, and by leaving the agar plate partially unsealed, it allows for necessary airflow and access to oxygen. This helps in creating the optimal conditions for the aerobic organisms being tested, as well as preventing the proliferation of anaerobes that could skew the experimental results.

In many microbiological tests, including those that assess the effectiveness of antimicrobial agents, it is crucial to maintain the right environment for the microbes of interest, which often requires a balance of oxygen and other factors. This practice demonstrates an understanding of microbial needs and helps ensure that the growth conditions are appropriate for the target organisms rather than allowing for unintended microbial growth.