Multicentre testing of the EUCAST broth microdilution reference method for MIC determination on Mycobacterium tuberculosis

ObjectivesThe first objective of the European Committee on Antimicrobial Susceptibility Testing (EUCAST) subcommittee for antimycobacterial susceptibility testing (AMST), launched in 2016, was to set a reference method determining MICs antituberculous agents, since many protocols are used worldwide and consensus one is needed determination microbiological breakpoints.MethodsDuring 2017 2018, MIC were evaluated prospectively multicentre study within four AMST laboratories. results obtained isoniazid, levofloxacin amikacin strain Mycobacterium tuberculosis H37Rv ATCC 27294. Broth microdilution (BMD) Middlebrook 7H9 solid medium dilution (SMD) 7H10 performed using two inoculum concentrations. interpreted with regard visual 99% inhibition after 7, 14 or 21 days incubation BMD SMD.ResultsFollowing EUCAST protocol, intra- inter-assay agreements ±1 >95% observations three drugs both methods. values, presented as mode (range) SMD respectively, were: 0.03 (0.015–0.06) mg/L 0.12 (0.06–0.25) 0.25 (0.25–0.5) 0.5 (0.12–0.5) levofloxacin, (0.5–1.0) amikacin.ConclusionsBoth reproducible eligible complex (MTBC). finally selected method. From now it will be epidemiological cut-off values clinical breakpoints new old agents.