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Applied and Environmental Microbiology, February 2001, p. 750-759, Vol. 67, No. 2
Department of Biochemistry and Microbiology,
University of Victoria, Victoria, British Columbia V8W
3P6,1 National Research Council,
Institute of Biological Sciences, Ottawa K1A
0R6,2 and Microtek International
Ltd., Saanichton, British Columbia V8M 1Z8,3
Canada
Received 21 July 2000/Accepted 7 December 2000
Flavobacteria are a poorly understood and speciated group of
commensal bacteria and opportunistic pathogens. The psychrotroph Flavobacterium psychrophilum is the etiological agent of
rainbow trout fry syndrome and bacterial cold water disease, septicemic diseases that heavily impact salmonids. Consequently, two verified but
geographically diverse isolates were characterized phenotypically and
biochemically. A facile typing system was devised which readily discriminated between closely related species and was verified against
a pool of recent prospective isolates. F. psychrophilum was
found to be enveloped in a loosely attached, strongly antigenic outer
layer comprised of a predominant, highly immunogenic,
low-molecular-mass carbohydrate antigen as well as several protein
antigens. Surface-exposed antigens were visualized by a combination of
immunoflourescence microscopy, immunogold transmission, and
thin-section electron microscopy and were discriminated by Western
blotting using rabbit antisera, by selective extraction with
EDTA-polymyxin B agarose beads, and by extrinsic labeling of amines
with sulfo-N-hydoxysuccinimide-biotin and glycosyl groups
with biotin hydrazide. The predominant ~16 kDa antigen was identified
as low-molecular-mass lipopolysaccharide (LPS), whereas
high-molecular-mass LPS containing O antigen was not as prevalent on
whole cells but was abundant in culture supernatants. Rainbow trout
convalescent antisera recognized both molecular mass classes of LPS as
well as a predominant ~20-kDa protein. This study represents the
first description at the molecular level of the surface characteristics
and potential vaccine targets of confirmed F. psychrophilum strains.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.2.750-759.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Antigenic Characterization of the Fish Pathogen
Flavobacterium psychrophilum
*
Corresponding author. Mailing address: Department of
Biochemistry and Microbiology, Petch Building, University of Victoria, P.O. Box 3055, Victoria, British Columbia V8W 3P6, Canada. Phone: (250)
721-7078. Fax: (250) 721-8882. E-mail: wkay{at}uvic.ca.
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