Broth Microdilution

Whilst disc testing is relatively cheap and simple to do, occasionally a more accurate minimum inhibitory concentration (MIC) value is needed. The EUCAST gold standard method of MIC determination is the broth micro dilution method.

Principles of the procedure: The aim of this procedure is to determine the minimum inhibitory concentration (MIC) of a bacterial strain to a particular antimicrobial. This is done by making several dilutions of an antimicrobial in a 96-well plate format. The MIC is the dilution at which there is no visible growth of bacteria. In this practical we will be following the EUCAST (http://www.eucast.org -European Committee on Antimicrobial Susceptibility Testing) guidelines used in previous steps. Make sure you are using the most updated version.

The choice of dilutions to test will depend on your reason for testing. If for clinical reasons, you will want to test a therapeutic range of dilutions. If for research reasons, you may want to test a wider range. It is normal to test 8-10 dilutions, each one double the dilution of the last.

Notes on the video

A flame curtain is not normally used in the UK

Safety cabinets are not routinely used for non-respiratory CL2 pathogens so long as aerosols are not being generated

It is not normally advisable to talk while inoculating media, and was only done in this video for the purposes of demonstrating