prEN ISO 20776-3

Clinical laboratory testing and in vitro diagnostic test systems -- Susceptibility testing of infectious agents and evaluation of performance of antimicrobial susceptibility test devices -- Part 3: Discdiffusion agar reference method for testing the in vitro activity of antimicrobial agents against rapidly growing aerobic bacteria involved in infectious diseases prEN ISO 20776-3

Scope

This part of ISO 20776 describes one reference method, disc diffusion agar, for determination of general antimicrobial susceptibility or resistance. The disc diffusion interpretive result may be a guide for the clinician, and reflects the activity of the drug under the described test conditions, by taking into account other factors, such as drug pharmacology, pharmacokinetics, or bacterial resistance mechanisms. This allows categorisation of bacteria as “susceptible” (S), “intermediate” (I), or “resistant” (R). In addition, disc diffusion testing distributions can be used to define wild type or non-wild type bacterial populations. Although clinical interpretation of the disc diffusion zone of inhibition diameter value is beyond the scope of this part of ISO 20776, modifications of the basic method are required for certain antimicrobial agent - bacteria combinations to facilitate clinical interpretation. These modifications are included in a separate Annex of this document. It is necessary to compare other susceptibility testing methods (e.g. broth micro-dilution or diagnostic test devices) with this reference method for validation, in order to ensure comparable and reliable results.