Provisional Use of CLSI-Approved Quality Control Strains for Antimicrobial Susceptibility Testing of () .

Antimicrobial susceptibility testing (AST) should be conducted in a standardized manner prior to the start of an antimicrobial treatment. For fastidious bacteria, such as porcine () spp., specifically , neither guidelines or standards for the performance of AST, nor quality control strains for the validation of AST results are approved by organizations like the Clinical and Laboratory Standards Institute (CLSI) or the European Committee on Antimicrobial Susceptibility Testing (EUCAST). The CLSI- and EUCAST-approved quality control strains ATCC 29212 and ATCC 29213 were chosen to validate AST by broth microdilution using modified Friis broth, developed as growth medium for porcine () spp. The antimicrobial agents doxycycline, enrofloxacin, erythromycin, florfenicol, gentamicin, marbofloxacin, tetracycline, tiamulin, tilmicosin, tulathromycin, and tylosin were examined using customized Sensititre microtiter plates. Minimal inhibitory concentrations, determined after 24, 48, and 72 h, were mostly within the CLSI-approved quality control ranges for defined antimicrobial agents. We propose the use of the combination of ATCC 29212 and ATCC 29213 as surrogate quality control strains for the validation of future AST results obtained for by broth microdilution using modified Friis broth.