EUCAST breakpoints can be used to interpret direct susceptibility testing of Enterobacteriaceae from urine samples

Increasing resistance calls for rapid antibiotic susceptibility testing (AST). This study validated the use of EUCAST breakpoints for AST using disk diffusion directly from urine samples. Two hundred and thirty-three urine samples with growth of varying amounts of Enterobacteriaceae were included and susceptibility testing (disk diffusion) was performed on Mueller-Hinton agar with overnight incubation directly from urine samples in parallel with disk diffusion according to EUCAST methodology. Confluent growth was obtained in 188 of 233 urine samples and used as criteria for zone measurements. Only 15 discrepancies (3 very major errors, 5 major errors and 7 minor errors) were observed in a total of 855 tests showing the safety of this approach. Direct susceptibility testing from urine samples can be interpreted using EUCAST clinical breakpoints and can thus safely be used to achieve more rapid AST result.