title: Pheno- and genotypic analysis of antimicrobial resistance properties of Yersinia ruckeri from fish.
abstract: Enteric red-mouth disease, caused by Yersinia ruckeri, is an important disease in rainbow trout aquaculture. Antimicrobial agents are frequently used in aquaculture, thereby causing a selective pressure on bacteria from aquatic organisms under which they may develop resistance to antimicrobial agents. In this study, the distribution of minimal inhibitory concentrations (MICs) of antimicrobial agents for 83 clinical and non-clinical epidemiologically unrelated Y. ruckeri isolates from north west Germany was determined. Antimicrobial susceptibility was conducted by broth microdilution at 22 ± 2°C for 24, 28 and 48 h. Incubation for 24h at 22 ± 2°C appeared to be suitable for susceptibility testing of Y. ruckeri. In contrast to other antimicrobial agents tested, enrofloxacin and nalidixic acid showed a bimodal distribution of MICs, with one subpopulation showing lower MICs for enrofloxacin (0.008-0.015 μg/mL) and nalidixic acid (0.25-0.5 μg/mL) and another subpopulation exhibiting elevated MICs of 0.06-0.25 and 8-64 μg/mL, respectively. Isolates showing elevated MICs revealed single amino acid substitutions in the quinolone resistance-determining region (QRDR) of the GyrA protein at positions 83 (Ser83-Arg or -Ile) or 87 (Asn87-Tyr), which raised the MIC values 8- to 32-fold for enrofloxacin or 32- to 128-fold for nalidixic acid. An isolate showing elevated MICs for sulfonamides and trimethoprim harbored a ∼ 8.9 kb plasmid, which carried the genes sul2, strB and a dfrA14 gene cassette integrated into the strA gene. These observations showed that Y. ruckeri isolates were able to develop mutations that reduce their susceptibility to (fluoro)quinolones and to acquire plasmid-borne resistance genes.
authors: Fish Disease Research Unit, University of Veterinary Medicine Hannover, Foundation, Germany.
authors: Yidan
authors: Y
authors: Huang
authors: Institute of Farm Animal Genetics, Friedrich-Loeffler-Institut (FLI), Neustadt-Mariensee, Germany.
authors: Geovana Brenner
authors: GB
authors: Michael
authors: Institute of Farm Animal Genetics, Friedrich-Loeffler-Institut (FLI), Neustadt-Mariensee, Germany.
authors: Roswitha
authors: R
authors: Becker
authors: Federal Office of Consumer Protection and Food safety (BVL), Berlin, Germany.
authors: Heike
authors: H
authors: Kaspar
authors: Federal Office of Consumer Protection and Food safety (BVL), Berlin, Germany.
authors: Joachim
authors: J
authors: Mankertz
authors: Institute of Farm Animal Genetics, Friedrich-Loeffler-Institut (FLI), Neustadt-Mariensee, Germany.
authors: Stefan
authors: S
authors: Schwarz
authors: Lower Saxony State Office for Consumer Protection and Food Safety (LAVES), Food and Veterinary Institute Braunschweig/Hannover, Germany.
authors: Martin
authors: M
authors: Runge
authors: Fish Disease Research Unit, University of Veterinary Medicine Hannover, Foundation, Germany. Electronic address: dieter.steinhagen@tiho-hannover.de.
authors: Dieter
authors: D
authors: Steinhagen
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D017756:Aquaculture; D027081:DNA Gyrase / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics* / Q000502:physiology; D000077422:Enrofloxacin; D005393:Fish Diseases / Q000382:microbiology*; D024841:Fluoroquinolones / Q000494:pharmacology; D005860:Germany, West; D008826:Microbial Sensitivity Tests; D009268:Nalidixic Acid / Q000494:pharmacology; D017686:Oncorhynchus mykiss / Q000382:microbiology*; D010641:Phenotype; D015363:Quinolones / Q000494:pharmacology; D015009:Yersinia Infections / Q000662:veterinary*; D044124:Yersinia ruckeri / Q000187:drug effects / Q000235:genetics*
chemical_list: D000890:Anti-Infective Agents; D024841:Fluoroquinolones; D015363:Quinolones; D009268:Nalidixic Acid; D000077422:Enrofloxacin; D027081:DNA Gyrase
keywords: Antimicrobial susceptibility testing; Gene cassette; Minimal inhibitory concentration; Plasmid; Target site mutation