Aseptic Technique and Serial Dilutions

Aseptic technique is a set of procedures used to prevent contamination of cultures by unwanted microorganisms from the environment. Serial dilutions are used to produce manageable concentrations for counting bacteria or testing antimicrobial agents. Both are required practical skills for the Edexcel A-Level Biology (9BI0) specification.

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Why is Aseptic Technique Important?

In microbiology, contamination can:

• Invalidate results by introducing unintended organisms that confound the experiment.
• Create a health hazard if environmental organisms include pathogens.
• Compromise culture purity — mixed cultures are difficult to analyse.

Aseptic technique aims to:

1. Prevent contamination of the culture by environmental microorganisms.
2. Prevent the release of cultured microorganisms into the environment.
3. Protect the experimenter from infection.

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Principles of Aseptic Technique

General Rules