3 Performing phenotypic AST: the disk diffusion test

The majority of microbiology laboratories use disk diffusion testing for AST. This section focuses on performing these laboratory tests. It is assumed that you are reasonably familiar with good laboratory practice and good microbiological practice; however, if you are unfamiliar with basic microbiology techniques, you may find it helpful to look at the Quality assurance and AMR surveillance module from this course.

The most commonly used disk diffusion method is the Kirby-Bauer method, which uses disks impregnated with antibiotics to test their effectiveness on a specific bacterial isolate.

You may also be familiar with the older Stokes method, where the isolate and a control organism are compared on the same plate. The Kirby-Bauer method is recommended here because it produces more accurate and reproducible data, which is essential for surveillance and comparison.