Contaminating bacteria are ubiquitous and are found on fingertips, bench tops, and in the air. It is important to avoid contaminating the experiment by keep surfaces clean and exposure of culture media to air minimal.

• 1. Clean surfaces such as bench top with ethanol (70%). Pipet aid should also be cleaned with ethanol (70%).
• 2. Wear gloves and/or clean hands with ethanol (70%).
• 3. Sterilize all media, agar plate, toothpicks, ddH₂O, and pipet tips by autoclave.
• 4. Avoid contacts of inoculation loops, pipet tips, and agar plates to surfaces.
• 5. Avoid prolonged exposure of media, plates to air without cover.
• 6. Although some researchers work under a sterile hood with controlled air flow when working with bacteria to keep airborne contaminants minimum, many prefer their bench tops. A small flame (e.g., Bunsen burner) usually is used to sterilize inoculation loop. Necks of medium bottles and culture tubes are sterilized by flaming briefly before opening and closing. Never bring bacteria into a laminar flow hood reserved for tissue culture!
• 7. Open media and plates should be kept close to a small flame (e.g., Bunsen burner), so the upward movement of hot air can keep bacteria from falling to the media or plates.