1887

Abstract

subsp. is the causative agent of furunculosis, a severe systemic disease affecting salmonid fish. This bacterium contains a type III protein secretion system that is responsible for the secretion and translocation of the ADP-ribosylating toxin, AexT, into the cytosol of fish cells. This study showed that inactivation of the type III secretion system by marker-replacement mutagenesis of the gene , which encodes an inner-membrane component of the type III secretion system, attenuated virulence in a rainbow trout model. The isogenic deletion mutant was phagocytosed by peripheral blood leukocytes but the wild-type (wt) subsp. isolate was not. Histological examination of fish experimentally infected with the wt bacterium revealed extensive tissue necrosis and bacterial aggregates in all organs examined, including the heart, kidney and liver, indicating that the isolate established a systemic infection. Cumulative mortality of fish experimentally infected with the wt bacterium reached 88 %. In contrast, no mortality was observed among fish infected with the same dose of the mutant, and histological examination of fish infected with this strain revealed healthy organs. The results indicate that the type III secretion system of subsp. is required to establish systemic infection.

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2005-06-01
2019-11-17
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