Bacterial pathogens in rainbow trout, Oncorhynchus mykiss (Walbaum), reared at Danish freshwater farms

Abstract

During a 2‐year period, bacterial fish pathogens were monitored on five rainbow trout, Oncorhynchus mykiss (Walbaum), freshwater farms in Denmark. A total of 1206 fish were examined and 361 bacterial isolates were identified phenotypically. Enteric redmouth disease, furunculosis and rainbow trout fry syndrome/coldwater disease were recorded. Infections caused by Flavobacterium psychrophilum occurred most frequently, but only one outbreak of enteric redmouth disease caused by Yersinia ruckeri serotype O1 and one of furunculosis caused by Aeromonas salmonicida were recorded during the monitoring period. Flavobacterium psychrophilum was isolated on all farms, both during disease outbreaks and from fish without any signs of disease. Serological investigations of F. psychrophilum showed that serotype Th was the dominant serotype found. The serotypes Th and Fd were involved in disease outbreaks of fry and larger fish. All isolates of F. psychrophilum showed proteolytic activities; however, a few isolates, belonging to serotype FpT did not degrade elastin and were not associated with mortality. Increasing resistance problems to oxytetracycline were demonstrated. More than half of the F. psychrophilum isolates showed resistance to oxolinic acid and oxytetracycline. No antibiotic resistant isolates were found among Y. ruckeri and A. salmonicida.

Insight from Molecular, Pathological, and Immunohistochemical Studies on Cellular and Humoral Mechanisms Responsible for Vaccine-Induced Protection of Rainbow Trout against Yersinia ruckeri

“…Y. ruckeri strain 100415-1/4 (serotype O1, biotype 2) which was originally obtained from a clinical outbreak of ERM in a freshwater trout farm, was utilized for all challenge studies. The bacterium was identified (19), cultured in Luria-Bertani (LB) broth, and incubated on an orbital shaker at 22°C for 48 h until reaching peak exponential phase, at which time the culture was harvested via centrifugation (at 22°C and 4,000 ϫ g for 10 min) and serial 10-fold dilutions were prepared with sterile phosphate-buffered saline (PBS) to determine the bacterial cell concentration (i.e., CFU) by the plate count method.…”

Combining Suppression Subtractive Hybridization and Microarrays To Map the Intraspecies Phylogeny of Flavobacterium psychrophilum

“…Unique clones were sequenced and their distribution assessed among 34 strains. The analysis showed that F. psychrophilum is composed of two genetic lineages, possibly reflecting host specificity.Flavobacterium psychrophilum is the causative agent of bacterial coldwater disease and rainbow trout fry syndrome, both of which affect salmonid fish and impact commercial aquaculture and resource enhancement hatcheries worldwide (12,19,21). Coho salmon (Oncorhynchus kisutch [Walbaum]) and rainbow trout (O. mykiss) are particularly susceptible, although F. psychrophilum also infects other fish species (21).…”

Involvement of a Sialic Acid-Binding Lectin with Hemagglutination and Hydrophobicity of Flavobacterium psychrophilum

“…F. psychrophilum primarily affects juvenile salmonids and results in high mortality rates among fry and fingerlings in hatcheries. In Europe this bacterium constitutes a large problem for the aquacultural production of rainbow trout (Oncorhynchus mykiss) (5). Outbreaks of the disease are mainly seen at low temperatures, with the most serious problems occurring at temperatures below 15°C (17).…”