ANGUILLARUM; IDENTIFICATION, SEROLOGY, HISTOPATHOLOGY AND SELECTED ASPECTS OF VIRULENCE.
PhD thesis submitted by Luc Grisez at the Catholic University of Leuven, Belgium (March 1997).
Summary: Vibrio anguillarum is a marine fish pathogenic bacterium. This bacterial species is responsible for a disease, called vibriosis, which causes severe economic losses in the marine aquaculture industry, independently of the fish species cultured or the geographical region. Although this bacterium has been known for a considerable period, many questions remain concerning the identification, the serological variability as well as the virulence mechanisms it contains.
In this thesis, the bacterial species Vibrio anguillarum is studied from four different approaches.
In part 1, we focus on the identification of V. anguillarum. A large collection of bacterial strains, including type and reference strains from most Vibrio species, together with species representing the genera Aeromonas, Photobacterium and Pleisiomonas, and mainly originating from the marine environment or from fish, was subjected to 101 morphological and biochemical identification tests. The results allowed us to establish a comprehensive diagnostic table for all genera and species included.
Furthermore, several new Vibrio species are indicated and the phenotypic variability within the species V. anguillarum is discussed.
In part 2, the serological variability present in the species V. anguillarum is discussed. Besides a comparison and alignment of all serotyping systems previously described, we describe and characterise 7 additional serotypes.
In part 3, the infection route of V. anguillarum after oral challenge of fish larvae through the live feed is elucidated immunohistochemically. Our results show that the fish intestine is one of the portals of entry for this bacterium, and that the infection starts by the trans-epithelial transport of bacterial cells.
In the blood, the bacteria start to multiply, giving rise to a septicaemia. In a number of cases, typical perinuclear arranged inclusions were observed, both in natural infected fish as in artificial infected fish. Our results showed that these inclusions were composed of dead V. anguillarum cells, which were positioned in between both nuclear membranes of the host cell.
In part 4 the serum resistance of V. anguillarum is studied. We demonstrate that the capability of selected strains to survive the lytic effect of normal trout serum is correlated with their serotype. Furthermore, our results indicate that magnesium plays an important but highly underestimated role in the survival and growth of V. anguillarum in serum and for the virulence of this species in general.
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