Multisite Reproducibility of the Broth Microdilution Method for 1 Susceptibility Testing of Nocardia species 2 3 Running Title : Multisite Reproducibility Study of Nocardia MIC Testing 4 5

26 Antimicrobial susceptibility testing (AST) of clinical isolates of Nocardia is recommended to 27 detect resistance to commonly used antimicrobial agents; such testing is complicated by 28 difficulties in inoculum preparation and test interpretation. In this study, six laboratories 29 performed repetitive broth microdilution testing on single strains of Nocardia brasiliensis, 30 Nocardia cyriacigeorgica, Nocardia farcinica, Nocardia nova and Nocardia wallacei. For each 31 isolate, a total of 30 microdilution panels from three different lots were tested at most sites. The 32 goal of the study was to determine the interand intra-laboratory reproducibility of susceptibility 33 testing of this group of isolates. Acceptable agreement [> 90% agreement at (±) 1 dilution of the 34 minimum inhibitory concentration (MIC) mode] was found for amikacin, ciprofloxacin, 35 clarithromycin and moxifloxacin. After eliminating MIC values from single laboratories whose 36 results showed the greatest deviation from those of the remaining laboratories, acceptable 37 agreement was also found for amoxicillin/clavulanic acid, linezolid, minocycline and 38 tobramycin. Results showed unsatisfactory reproducibility of broth microdilution testing of 39 ceftriaxone with N. cyriacigeorgica and N. wallacei, tigecycline with N. brasiliensis and N. 40 cyriacigeorgica and sulfonamides with N. farcinica and N. wallacei. N. nova ATCC BAA-2227 41 is proposed as a quality control organism for AST of Nocardia sp., and the use of a disk 42 diffusion test for sulfisoxazole is proposed as a check of the adequacy of the inoculum and to 43 confirm sulfonamide MIC results. 44 on N ovem er 3, 2017 by gest ht://jcm .sm .rg/ D ow nladed fom