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Diseases of Aquatic Organisms

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DAO 101:207-215 (2012)  -  DOI:

Quality control ranges for testing broth microdilution susceptibility of Flavobacterium columnare and F. psychrophilum to nine antimicrobials

Charles M. Gieseker1,*, Tamara D. Mayer1, Tina C. Crosby1, Jeremy Carson2, Inger Dalsgaard3, Ahmed M. Darwish4, Patricia S. Gaunt5, Dana X. Gao5, Hui-Min Hsu6, Tsang L. Lin9, J. Lindsay Oaks7, Melissa Pyecroft2, Charlene Teitzel7, Temdoung Somsiri8, Ching C. Wu9

1Food and Drug Administration, Center for Veterinary Medicine, Office of Research, Laurel, Maryland 20708, USA
2Fish Health Unit, Department of Primary Industries, Parks, Water & Environment, Launceston, Tasmania 7249, Australia
3National Veterinary Institute, Technical University of Denmark, 1870 Frederiksberg C, Denmark
4United States Department of Agriculture, Agriculture Research Service, Harry K. Dupree Stuttgart National Aquaculture Research Center, Stuttgart, Arkansas 72160, USA
5Thad Cochran National Warmwater Aquaculture Center, College of Veterinary Medicine, Mississippi State University, Stoneville, Mississippi 38766, USA
6Wisconsin Veterinary Diagnostic Laboratory, University of Wisconsin, Madison, Wisconsin 53706, USA
7Washington Animal Disease Diagnostic Laboratory, University of Washington, Pullman, Washington 99164, USA
8Inland Aquatic Animal Health Research Institute, Kasetsart University, Jatuchak, Bangkok 10900, Thailand
9Animal Disease Diagnostic Laboratory, Purdue University, West Lafayette, Indiana 47907, USA

ABSTRACT: A multi-laboratory broth microdilution method trial was performed to standardize the specialized test conditions required for the fish pathogens Flavobacterium columnare and F. psychrophilum. Nine laboratories tested the quality control (QC) strains Escherichia coli ATCC 25922 and Aeromonas salmonicida subsp. salmonicida ATCC 33658 against 10 antimicrobials (ampicillin, enrofloxacin, erythromycin, florfenicol, flumequine, gentamicin, ormetoprim/sulfadimethoxine, oxolinic acid, oxytetracycline, and trimethoprim/sulfamethoxazole) in diluted (4 g l−1) cation-adjusted Mueller-Hinton broth incubated at 28 and 18°C for 44–48 and 92–96 h, respectively. QC ranges were set for 9 of the 10 antimicrobials. Most of the minimal inhibitory concentration (MIC) distributions (16 of 18, 9 drugs at both temperatures) for A. salmonicida ATCC 33658 were centered on a single median MIC ± 1 two-fold drug dilution resulting in a QC range that spanned 3 dilutions. More of the E. coli ATCC 25922 MIC distributions (7 of 16) were centered between 2 MIC dilutions requiring a QC range that spanned 4 dilutions. A QC range could not be determined for E. coli ATCC 25922 against 2 antimicrobials at the low temperature. These data and their associated QC ranges have been approved by the Clinical and Laboratory Standards Institute (CLSI), and will be included in the next edition of the CLSI M49-A Guideline. This method represents the first standardized reference method for testing fish pathogenic Flavobacterium spp.

KEY WORDS: Standard methods · Antimicrobial susceptibility testing · Fish · Flavobacteria

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Cite this article as: Gieseker CM, Mayer TD, Crosby TC, Carson J and others (2012) Quality control ranges for testing broth microdilution susceptibility of Flavobacterium columnare and F. psychrophilum to nine antimicrobials. Dis Aquat Org 101:207-215.

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