What are the typical autoclave parameters used to sterilize media in the teaching microbiology lab?

• A. 100°C at 1 atm for 60 minutes
• B. 150°C at 30 psi for 5 minutes
• C. 121°C at 15 psi for 15–20 minutes
• D. 95°C for 5 minutes

Answer: (C)

Moist heat under pressure is the reliable way to sterilize media because steam under high pressure reaches temperatures well above normal boiling and penetrates deeply into all parts of the load. The heat denatures proteins and disrupts cellular structures, and the pressure keeps the steam at that high temperature long enough to ensure even the most resistant spores are killed. In teaching microbiology labs, the standard autoclave cycle is designed to provide this combination of heat, moisture, and time so that media and equipment come out sterile.

Boiling at atmospheric pressure doesn’t reach enough heat to guarantee spore destruction, even with long exposure. A cycle that uses a much higher temperature for only a short time can risk uneven heating or damage to media components and isn’t the typical method for sterilizing media in teaching settings. A low-temperature, short-time option would not reliably sterilize.

So, the best choice is the high-temperature, pressurized steam cycle held for a sufficient duration to ensure complete sterilization of media.