Antibiotic Susceptibility Testing

SA Pathology uses guidelines from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) to perform and interpret our antibiotic susceptibility testing.

EUCAST develops breakpoints for “susceptible” and “resistant” results, assuming clinicians are prescribing certain antibiotic doses. These predetermined antibiotic dosages are becoming increasingly important due to EUCAST’s redefinition of the “I” category from “intermediate” to “susceptible, increased exposure”. This category is for organisms where there is a high likelihood of therapeutic success because exposure to the antibiotic is increased by increasing the dose, increasing the frequency of administration (or using an infusion), or the antibiotic concentrates at the site of infection (eg B-lactam antibiotics in the urinary tract).

SA Pathology will transition to the new “I” definition when the necessary computing changes are made. In addition to a standard dose, the EUCAST dosage tables include a “high dose” and an “uncomplicated UTI” dose for use when an “I” result is obtained. Some of these dosages reflect European practices but the tables are largely consistent with the Australian Therapeutic Guidelines.

SA Pathology encourages clinicians to use these tables in conjunction with our antibiotic susceptibility reports. For further information, please contact one of our consultant microbiologists on 08 8222 3000.

See EUCAST clinical breakpoint tables