DAO 67:67-72 (2005)  -  doi:10.3354/dao067067

Association of Flavobacterium psychrophilum strains with intestinal explants of rainbow trout Oncorhynchus mykiss

Amin Nematollahi1,3,*, Frank Pasmans1, Wim Van den Broeck2, Richard Ducatelle1,Freddy Haesebrouck1, Annemie Decostere1

1Department of Pathology, Bacteriology and Avian Diseases, and 2Department of Morphology, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
3Department of Food Hygiene and Quality Control, Faculty of Veterinary Medicine, Shahrekord University, Saman Road, PO Box 115, Shahrekord, Iran

ABSTRACT: Flavobacterium psychrophilum is an important pathogen in rainbow trout Onco-rhynchus mykiss. The portal of entry for F. psychrophilum is not well known. In this study, the role of the intestine as a colonization site for F. psychrophilum was determined. For this purpose, the ability of a high (Dubois) and a low (99/10A) virulence strain of F. psychrophilum to adhere to intestinal explants of rainbow trout was evaluated. After incubation, samples of the gut were examined bacteriologically, histologically and by electron microscopy. The number of gut-associated F. psychrophilum bacteria was significantly higher for the Dubois than for the 99/10A strain. Histological samples clearly showed numerous bacteria of the high virulence strain associated with the intestinal tissue as opposed to only a few bacteria of the low virulence strain. Additionally, extensive exfoliation of intestinal epithelium was noted after incubation with the high virulence strain, but less with the low virulence strain. These findings were confirmed using scanning electron microscopy and suggest that the intestinal epithelium might represent an important site for colonization of the F. psychrophilum strain and may act as a portal of entry for high virulence F. psychrophilum.

KEY WORDS: Flavobacterium psychrophilum · Rainbow trout · Intestinal explant · Colonization

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