title: Antimicrobial Susceptibilities of Flavobacterium psychrophilum Isolates from the Great Lakes Basin, Michigan.
abstract: Flavobacterium psychrophilum is a serious pathogen of salmonids worldwide, a matter that is compounded by the lack of effective vaccine preparations. As a result, biosecurity measures and antimicrobial agents remain the only available methods to control diseases caused by F. psychrophilum. It is feared that antimicrobial use may have led to the development of F. psychrophilum strains with reduced susceptibility. Therefore, the primary objective of this study was to determine the antimicrobial susceptibility profiles of 50 F. psychrophilum isolates from Michigan in response to 10 antimicrobial compounds. As recommended by the Clinical and Laboratory Standard Institute and the World Organization of Animal Health, a standardized microdilution broth assay was employed to determine the minimum inhibitory concentrations (MICs) for ampicillin (AMP), gentamicin (GEN), enrofloxacin (ENRO), oxolinic acid (OXO), flumequine (FLUQ), trimethoprim-sulphamethoxazole (SXT), ormetoprim-sulphadimethoxine (PRI), erythromycin (ERY), florfenicol (FFN), and oxytetracycline (OXY). Epidemiological cutoff values were calculated using the normalized resistance interpretation (CONRI) and the ECOFFinder analysis methods (COECOFF). The MIC distributions in response to OXY exhibited bimodality, indicating the presence of isolates with reduced susceptibility in addition to the wild-type isolates. The OXY epidemiological cutoff values (COECOFF<0.06 μg/ml; CONRI<0.12 μg/ml) demonstrated that 24% of Michigan isolates exhibited reduced susceptibility to this commonly used drug. No other antimicrobial exhibited a bimodal distribution of MICs. This study represents the first antimicrobial susceptibility assessment of F. psychrophilum strains recovered from Michigan and contributes valuable data to the worldwide validation efforts to determine universal epidemiological cutoff values of this deadly fish pathogen.
authors.affiliation: 1 Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University , East Lansing, Michigan.
authors.forename: Danielle
authors.initials: D
authors.lastname: Van Vliet
authors.affiliation: 2 Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University , East Lansing, Michigan.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Loch
authors.affiliation: 3 Department of Microbiology, School of Natural Sciences, National University of Ireland , Galway, Ireland .
authors.forename: Peter
authors.initials: P
authors.lastname: Smith
authors.affiliation: 1 Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University , East Lansing, Michigan.|2 Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University , East Lansing, Michigan.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Faisal
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000187:drug effects; D005399:Fishes / Q000382:microbiology; D005417:Flavobacterium / Q000187:drug effects*; D060106:Lakes / Q000382:microbiology*; D008824:Michigan; D008826:Microbial Sensitivity Tests / Q000379:methods
chemical_list: D000890:Anti-Infective Agents
keywords: Flavobacterium psychrophilum; antibiotic susceptibility; bacterial cold water disease; broth microdilution