Antimicrobial susceptibility testing in Sweden. IV. Quality assurance

The performance of susceptibility testing depends on high-quality material (disks and media), good laboratory practice (robust methodology and correct handling of material) and antimicrobial breakpoints being set in such a way that they allow for some intralaboratory variation. Thus, breakpoints must not divide homogeneous bacterial populations. Routine susceptibility testing should be checked with both internal and external quality control programs. The internal quality control should be designed to demonstrate the importance of minimizing random errors and to rapidly disclose systematic errors. This can be achieved either through the repeated testing of defined control strains or by systematic comparison of histograms of routine zone diameters with reference histograms supplied by the Swedish Reference Group for Antibiotics (SRGA and SRGA-M). The SRGA-M offers an external quality control program which by its design also functions as an epidemiological surveillance program. The quality control programs are supported by an educational program for laboratory personnel.