1887

Abstract

The recently described type III secretion system (TTSS) of subsp. has been linked to virulence in salmonids. In this study, three TTSS effector genes, , or , were inactivated by deletion, as was , the gene encoding the outer-membrane pore of the secretion apparatus. Effects on virulence were assayed by live challenge of Atlantic salmon (). The Δ mutant strain was avirulent by both intraperitoneal (i.p.) injection and immersion, did not appear to establish a clinically inapparent infection and did not confer protection from subsequent rechallenge with the parental strain. H NMR spectroscopy-based metabolite profiling of plasma from all fish showed significant differences in the metabolite profiles between the animals exposed to the parental strain or Δ. The experimental infection by immersion with Δ was indistinguishable from that of the parental strain, that of Δ was delayed, whilst the virulence of Δ was reduced significantly but not abolished. By i.p. injection, Δ, Δ and Δ caused an experimental disease indistinguishable from that of the parental strain. These data demonstrate that while the TTSS is absolutely essential for virulence of subsp. in Atlantic salmon, removal of individual effectors has little influence on virulence but has a significant effect on colonization. The Δ i.p. injection data also suggest that in addition to host invasion there is a second step in pathogenesis that requires an active TTSS.

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2006-06-01
2020-07-03
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