2 International guidelines for AST

2.1 Why the guidelines are important

Most clinical and veterinary microbiology laboratories adhere to international quality standards set by an organisation such as the International Standards Organisation (ISO) to standardise and inform laboratory best practice. In addition, to ensure uniformity, consistency, repeatability and reliability between different laboratories, standard operating procedures (SOPs) for AST should integrate international guidelines developed by either the US-based Clinical and Laboratory Standards Institute (CLSI) (CLSI, n.d.), or the European Committee on Antimicrobial Susceptibility Testing (EUCAST) (EUCAST, 2025). CLSI and EUCAST separately produce guidelines, standards and associated criteria that are used to perform and interpret AST results. You will look at some of the laboratory methods that underpin these standards later in this course.