Epidemiological cut-off values for Vibrio parahaemolyticus calculated from disc diffusion inhibition zone size data generated at 35 and 28°C

This work was performed to generate the data needed to set epidemiological cut-off values for inhibition zone data of 8 antimicrobial agents against Vibrio parahaemolyticus determined using standardised disc diffusion protocols with incubation at 35 ± 2°C for 16 to 20 h and at 28 ± 2°C for 24 to 28 h. The zone diameter data aggregated from 3 to 5 laboratories were analysed by the normalised resistance interpretation algorithm. Cut-off values calculated from data obtained at 35 and 28°C were ≥23 and ≥24 mm for ceftazidime, ≥18 and ≥20 mm for enrofloxacin, ≥28 and ≥29 mm for florfenicol, ≥14 and ≥14 mm for gentamicin, ≥29 and ≥32 mm for meropenem, ≥17 and ≥18 mm for oxolinic acid, ≥22 and ≥24 mm for oxytetracycline, as well as ≥19 and ≥21 mm for trimethoprim/sulfamethoxazole. The influence of the incubation temperature on inhibition zone sizes was investigated by calculating the difference between the zones obtained at 35 and 28°C for a specific antimicrobial agent with a particular isolate by an individual laboratory. The mean of the differences calculated for 1314 paired observations was 0.38 mm with a standard deviation of 2.68 mm. The data generated in this work will be submitted to the Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing for consideration in their setting of internationally agreed-upon epidemiological cut-off values for V. parahaemolyticus that are essential for interpreting antimicrobial susceptibility testing data of this species.