Disc diffusion susceptibility test

Kirby-Bauer test is widely used to determine the sensitivity or resistance of bacteria to various antimicrobial compounds, and it uses the Mueller Hinton agar.

Mueller-Hinton agar is a non-selective, non-differential medium capable of growing a wide range of non-fastidious organisms. It is considered a ‘loose’ agar, which helps to mediate the rate of diffusion of the antimicrobial more effectively than any other types of media.

The Kirby-Bauer procedure

Mueller Hinton agar is aseptically inoculated with bacteria via the spread method.

Things to note 


Whilst this method is primarily used for antibiotic susceptibility, it can be used to test other antimicrobials, such as the effectiveness of detergents and hand sanitisers.

Testing using the Kirby-Bauer method can for example determine whether a microorganism, such as MRSA, is resistant to a specific antimicrobial. This could be useful to support research in finding a suitable detergent for laboratories to help make informed decisions on the applicability of a cleaning agent.

In recent years, there has been a lot of interest in antimicrobials, such as research into the antimicrobial activity of silver nanoparticles with and without the combination of antibiotics.