Flavobacterium psychrophilum, invasion into and shedding by rainbow trout Oncorhynchus mykiss

Abstract

The infection route of Flavobacterium psychrophilum into rainbow trout Oncorhynchus mykiss was studied using bath and cohabitation challenges as well as oral challenge with live feed as a vector. Additionally, the number of bacterial cells shed by infected fish into the surrounding water was determined in the cohabitation experiment and in challenge experiments at 3 different water temperatures. The experiments showed that skin and skin mucus abrasion dramatically enhanced the invasion of F. psychrophilum into the affected fish in bath and cohabitation challenges. Disruption of the skin is discussed as an important invasion route for F. psychrophilum into the fish. The shedding rate of F. psychrophilum by infected fish was associated with water temperature and the mortality of the infected fish. High numbers of F. psychrophilum cells were released into the water by dead rainbow trout during a long time period compared to the numbers of cells shed by live fish. The results emphasise the importance of removing dead and moribund fish from rearing tanks in order to diminish the infection pressure against uninfected fish in commercial fish farms. In immunohistochemical examinations of organs and tissues of orally infected fish, F. psychrophilum cells were detected in only 1 fish out of 31 studied. Mortality of the orally challenged fish was not observed in the experiment.

Detection of Flavobacterium psychrophilum in Chum Salmon Oncorhynchus keta and Virulence of Isolated Strains to Salmonid Fishes

“…This is the first report on the detection of culturable F. psychrophilum in chum salmon in Japan. Previous studies showed that F. psychrophilum is transmitted both horizontally (Madsen and Dalsgaard, 1999;Garcia et al, 2000;Madetoja et al, 2000) and vertically (Brown et al, 1997;Kumagai et al, 2000;Cipriano, 2005). Furthermore, F. psychrophilum has been detected in ovarian fluid, skin mucous, and internal organs of salmonid fish with no disease signs (Holt et al, 1993;Madetoja et al, 2002;Madsen et al, 2005).…”

Nanoinjection as a tool to mimic vertical transmission of Flavobacterium psychrophilum in rainbow trout Oncorhynchus mykiss

“…The most reliable methods are intramuscular (Holt 1987, Garcia et al 2000 and intraperitoneal (Evensen & Lorenzen 1996, Madsen & Dalsgaard 1999, Rangdale et al 1999, Garcia et al 2000 injection. Cohabitant and bath infections have also been performed (Holt 1987, Lorenzen 1994, Madsen & Dalsgaard 1999, Garcia et al 2000, Madetoja et al 2000 with varying results. The nanoinjection technique used in this study might prove to be a new useful method in experimental infection with F. psychrophilum and possibly also for other pathogens that can be vertically transmitted.…”

Polymorphisms in 16S rRNA genes of Flavobacterium psychrophilum correlate with elastin hydrolysis and tetracycline resistance

“…Ideally, these studies will be backed by experimental infection models, although it has been difficult to develop a reliable model that mimics a natural infection (i.e. waterborne) for F. psychrophilum (Garcia et al 2000, Madetoja et al 2000.The presence of multiple and distinct 16S rRNA sequences within single genomes is reportedly common for strains of the genus Vibrio (Moreno et al 2002). This latter study also shows that the majority of polymorphisms are concentrated in the variable stemloop region of bacterial 16S rDNA.…”