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Diseases of Aquatic Organisms

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DAO 57:167-171 (2003)  -  doi:10.3354/dao057167

Association of Type III secretion genes with virulence of Aeromonas salmonicida subsp. salmonicida

Sarah E. Burr1, Thomas Wahli2, Helmut Segner2, Dmitri Pugovkin2, Joachim Frey1,*

1Institute of Veterinary Bacteriology, and 2Centre for Fish and Wildlife Health, Institute of Animal Pathology, University of Berne, Laenggassstrasse 122, 3012 Berne, Switzerland
*Corresponding author. Email:

ABSTRACT: Aeromonas salmonicida subsp. salmonicida possesses a number of potential virulence factors, including a recently identified plasmid-encoded Type III secretion system. A number of field isolates of A. salmonicida subsp. salmonicida were examined for the presence of Type III secretion genes. Using in vitro experiments, it was found that field isolates containing such genes are cytotoxic to fish cell lines, whereas those that lack these genes are not. Using a rainbow trout in vivo model, the virulence of a wild type A. salmonicida subsp. salmonicida strain (Strain JF2267), which possesses Type III secretion genes, was compared to that of a laboratory derivative of the same strain that has lost these genes. While Strain JF2267 was virulent towards rainbow trout, its derivative was not. The A. salmonicida subsp. salmonicida Type Strain ATCC 33658T, which also lacks Type III secretion genes, was also found to be avirulent by this challenge model. The findings from both the in vitro and in vivo experiments suggest that the presence of Type III secretion genes is associated with the virulence of this important fish pathogen.

KEY WORDS: In vivo · In vitro · Virulence · Furunculosis · Type III protein secretion

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