An immunohistochemical study of Flexibacter psychrophilus infection in experimentally and naturally infected rainbow trout (Oncorhynchus mykiss) fry

Abstract

ABSTRACT. An immunohistochemical method is described for the detection of Flexibacter psychrophilusin formalin-fixed, paraffin-wax-embedded fry of rainbow trout. Rabbit antiserum as well as rainbow trout hyperimmune serum were used in the study. The distribution and tissue localization of the bacterium was compared in naturally and experimentally (intraperitoneal injections) infected fry by use of immunohistochernistry. This study showed that F. psychrophilus could be detected in paraffinwax-embedded tissue of rainbow trout fry by immunohistochemistry. The principal immunohistochemical findings in naturally and experimentally infected fry showed that there was a localization of bacteria in the monocyte-macrophage system, in s h n lesions, and in the retina and the choroid gland of the eye. The dermal changes included superficial or deep ulcers extending to the subcutaneous tissue or the musculature accompanied by inflammatory cell infiltrates in which polymorphonuclear inflammatory cells were shown to contain the bactenum in the cytoplasm by imrnunostaining. The eye changes were likewise a common finding in chronic cases with severe inflammatory changes in the retina and with numerous bacteria in inflamn~atory (mainly polymorphonuclear) cells. F. psychrophilus infection in rainbow trout fry involves the n~onocyte-macrophage system extensively, and the concurrent localization of bacteria in the skin ulcers and retina1 inflammation points to the probable involvement of the bacterium in the development of the lesions which are typically found during the chronic stage of the disease.

Characterization of isolates of Flavobacterium psychrophilum associated with coldwater disease or rainbow trout fry syndrome:phenotypic and genomic studies

“…In histological studies different Gram stains always resulted in faint staining, whereas the bacteria were distinctly stained using the Warthin-Starry stain (Lorenzen et al 1991) or immunohistochemical staining (Evensen & Lorenzen 1996). With regard to shape and size of the cells, the present observations based on wet mount preparations were in accordance with the findings of Pacha (1968), Pacha & Porter (1968, Holt (1987), and Bernardet & Kerouault (1989).…”

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

“…Baudin-Laurencin (1989) described similar changes in rainbow trout naturally infected with Flavobacterium psychrophilum. The presence of the bacterium in almost all internal organs, shown by immunohistochemical staining, confirms the septicaemic nature of acute RTFS (Evensen & Lorenzen 1996).…”

“…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.…”

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

“…Not all strains of F. psychrophilum are capable of causing the same degree of disease (Holt 1987, Madetoja et al 2002, LaFrentz et al 2003 and they can be antigenically diverse (Evensen & Lorenzen 1996, Crump et al 2001, Madetoja et al 2002. Immunization with killed cells of one strain does not necessarily convey protective immunity from infection by other strains (Holt et al 1989, Obach & Laurencin 1991.…”