Sample inoculum preparation: a UK ring trial of the Inoclic device

Disk diffusion has been a much used method for antimicrobial susceptibility testing (AST) in most clinical microbiological laboratories since Bauer et al. first described this technique in the 1960s.¹ In the UK this method has been further supported by the British Society for Antimicrobial Chemotherapy (BSAC) guidelines, which were first published in 2001.

            However, in 2016, BSAC announced that it would cease active support, maintenance and development of the BSAC method, and instead would focus on helping laboratories in the UK to move over to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) method. There are several differences between each method, including confluent growth as opposed to the semi-confluent growth, different media and antibiotic concentrations.

The EUCAST disk method was developed in 2009. It is a robust and standardised method, providing evidence-based guidance on performing susceptibility tests for organism/antibiotic combinations via extensive studies. These studies are performed in accordance with the international standard method for testing antimicrobial susceptibility (ISO20776-1:2006). The EUCAST disk-diffusion method is now the most commonly used standardised method in most European countries and increasingly those outside Europe.