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Virulence of Flavobacterium psychrophilum isolates in rainbow trout Oncorhynchus mykiss (Walbaum)
Author(s) -
Jarau Maureen,
Di Natale Adrian,
Huber Paul E.,
MacInnes Janet I.,
Lumsden John S.
Publication year - 2018
Publication title -
journal of fish diseases
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.819
H-Index - 85
eISSN - 1365-2761
pISSN - 0140-7775
DOI - 10.1111/jfd.12861
Subject(s) - rainbow trout , biology , virulence , microbiology and biotechnology , spleen , flavobacterium , pathogen , fish <actinopterygii> , trout , bacteria , gene , fishery , immunology , pseudomonas , biochemistry , genetics
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 8 cfu/fish. A highly virulent strain, FPG 101, was selected for further study. When fish were injected intraperitoneally with a 10 6 , 10 7 or 10 8 cfu/fish of F. psychrophilum FPG 101, the 10 8 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 2 = 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 10 gene/copies and >3.0 log 10 gene copies/reaction, respectively, following infection with 10 8 cfu/fish.