Virulence of Flavobacterium psychrophilum isolates in rainbow trout Oncorhynchus mykiss (Walbaum)

Abstract

Flavobacterium psychrophilum, the causative agent of bacterial cold-water disease (BCWD) in freshwater-reared salmonids, is also a common commensal organism of healthy fish. The virulence potential of F. psychrophilum isolates obtained from BCWD cases in Ontario between 1994 and 2009 was evaluated. In preliminary infection trials of rainbow trout juveniles, significant differences (0% to 63% mortality) in the virulence of the 22 isolates tested were noted following intraperitoneal injection with 10 cfu/fish. A highly virulent strain, FPG 101, was selected for further study. When fish were injected intraperitoneally with a 10 , 10 or 10 cfu/fish of F. psychrophilum FPG 101, the 10 cfu/fish dose produced significantly greater mortality (p < 0.05). The bacterial load in spleen samples collected from fish every 3 days after infection was determined using rpoC quantitative polymerase chain reaction amplification and by plate counting. Bacterial culture and rpoC qPCR were highly correlated (R = 0.92); however, culture was more sensitive than the qPCR assay for the detection of F. psychrophilum in spleen tissue. Ninety-seven per cent of the asymptomatic and the morbid fish had splenic bacterial loads of <2.8 log gene/copies and >3.0 log gene copies/reaction, respectively, following infection with 10 cfu/fish.

Rainbow trout Oncorhynchus mykiss (Walbaum) type IV ice‐structuring protein LS‐12 in the acute‐phase response to Flavobacterium psychrophilum infection

“…F. psychrophilum is well studied as an infection model (Barnes & Brown, ; Madsen & Dalsgaard, ; Starliper, ) and it has been used to investigate aspects of innate immunity involved in protection against BCWD (Henriksen, Kania, Buchmann, & Dalsgaard, ; Semple et al, ). Intraperitoneal infection with F. psychrophilum stimulates a peritonitis and a splenitis with additional lesions often present in the muscle and dermis (Jarau et al, ). Experimental infection with F. psychrophilum produces moderate to high mortality but allows sufficient time for a population to develop a marked inflammatory response (LaPatra, Fehringer, & Cain, ; Ryerse et al, ).…”

“…Flavobacterium psychrophilum FPG101 was a low‐passage isolate originally obtained from the spleen of clinically affected rainbow trout experiencing a mortality event. FPG101 is highly virulent to rainbow trout in experimental trials (Jarau, Di Natale, Huber, MacInnes, & Lumsden, ). Bacteria were prepared for experimental infection as described (Ryerse, Hooft, Bureau, Hayes, & Lumsden, ).…”

Erythromycin and florfenicol treatment of rainbow trout Oncorhynchus mykiss (Walbaum) experimentally infected with Flavobacterium psychrophilum

“…Six virulent F. psychrophilum isolates (FPG10, FPG100, FPG101, FPG102, FPG105 and FPG108) that produced at least 50% mortality in rainbow trout juveniles experimentally infected by intraperitoneal (i.p.) injection were used (Jarau et al, ). Two quality control strains, Escherichia coli (ATCC 25,922) and Aeromonas salmonicida subsp.…”

“…salmonicida (ATCC 33,658), were included in the MIC test to validate the antimicrobial susceptibility test results. The bacterial maintenance and preparation of F. psychrophilum isolates were as described (Jarau et al, ). Briefly, the F. psychrophilum isolates were maintained in Cytophaga broth (CB; Anacker & Ordal, ) containing 15% glycerol and stored at −80˚C until use.…”

“…Several F. psychrophilum isolates from Ontario rainbow trout were found to be virulent by experimental infection (Jarau, Di Natale, Huber, MacInnes, & Lumsden, ); however, their susceptibility to in vivo antimicrobial treatments had not been tested. Therefore, the objectives of this study were to: (a) determine the antimicrobial resistance of selected virulent F. psychrophilum isolates to FFN and ERY using the broth microdilution test and (b) determine the ability of ERY‐ and FFN‐medicated diets to control experimentally induced F. psychrophilum infection in juvenile rainbow trout once clinical signs of disease were apparent.…”