title: Provisional epidemiological cutoff values for standard broth microdilution susceptibility testing of Flavobacterium columnare.
abstract: The gliding aquatic bacterium Flavobacterium columnare causes columnaris disease, a common problem for wild and farmed freshwater fish worldwide. Recently, a broth microdilution method was standardized to test the susceptibility of F. columnare against antimicrobials commonly used in aquaculture. We used this new method to measure the minimal inhibitory concentrations (MICs) of ten antimicrobials against 120 F. columnare isolates. The resulting MIC frequency distributions for each antimicrobial (1 MIC/isolate) were used to estimate epidemiological cut-off values (ECVs) which separate isolates with typical wild-type (WT) susceptibility from isolates with decreased non-wild-type (NWT) susceptibility. We identified 22 NWT isolates with elevated MICs relative to the ECV that covered 99.9% of the MIC distribution against one or more of the antimicrobials: ampicillin, enrofloxacin, erythromycin, florfenicol, flumequine, oxolinic acid or oxytetracycline. Ten of the NWT isolates had decreased susceptibility to a single antimicrobial class, six isolates to two antimicrobial classes and six isolates to three or more antimicrobial classes. The MIC frequency distributions and provisional cut-off values provide data needed to set epidemiological cut-off values to monitor for the development of antimicrobial resistance among F. columnare.
authors.affiliation: Food and Drug Administration, Office of Research, Center for Veterinary Medicine, Laurel, MD, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Gieseker
authors.affiliation: Food and Drug Administration, Office of Research, Center for Veterinary Medicine, Laurel, MD, USA.
authors.forename: T C
authors.initials: TC
authors.lastname: Crosby
authors.affiliation: Department of Animal and Avian Sciences, University of Maryland, College Park, MD, USA.
authors.forename: L C
authors.initials: LC
authors.lastname: Woods
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017756:Aquaculture; D024881:Drug Resistance, Bacterial; D005393:Fish Diseases / Q000382:microbiology; D045826:Flavobacteriaceae Infections / Q000382:microbiology / Q000662:veterinary*; D005417:Flavobacterium / Q000187:drug effects*; D008826:Microbial Sensitivity Tests / Q000662:veterinary*
chemical_list: D000900:Anti-Bacterial Agents
keywords: 
  Flavobacterium columnare
  ; antimicrobial; standard testing; susceptibility