Oral Presentation The 2nd Prato Conference on the Pathogenesis of Bacterial Diseases of Animals 2012

Identification of virulence factors of fish pathogen Vibrio anguillarum using a gnotobiotic model system (#24)

Ingeborg Frans 1 2 3 4 , Chris W. Michiels 3 , Peter Bossier 4 , Kris A. Willems 1 2 , Bart Lievens 1 2 , Hans Rediers 1 2
  1. Laboratory for Process Microbial Ecology and Bioinspirational Management (PME&BIM), Consortium for Industrial Microbiology and Biotechnology (CIMB), KU Leuven Association, Lessius Mechelen, Campus De Nayer, Sint-Katelijne-Waver, Belgium
  2. Scientia Terrae Research Institute, Sint-Katelijne-Waver, Belgium
  3. Centre for Food and Microbial Technology, KU Leuven, Leuven, Belgium
  4. Laboratory of Aquaculture & Artemia Reference Center, Ghent University, Ghent, Belgium

Vibrio (Listonella) anguillarum is the causative agent of vibriosis, a highly fatal haemorrhagic septicaemic disease affecting many economically important fish, bivalves and crustaceans. In both aquaculture and larviculture, this disease is responsible for severe economic losses worldwide. Because of its high morbidity and mortality rates, substantial research activity has been carried out in order to unravel the virulence mechanisms of this pathogen and to develop rapid detection and identification techniques. Nevertheless, the virulence mechanisms of this pathogen and the critical virulence factors for pathogenesis are still insufficiently known.
In this study, the virulence of 16 wild-type V. anguillarum strains, isolated from different hosts or ecological niches was studied using a standardized gnotobiotic model system with axenic European sea bass (Dicentrarchus labrax) larvae as hosts. Larvae were challenged with 105 colony forming units of bacteria per ml of water, and larval survival was monitored by microscopical analysis at regular intervals. Significant differences in virulence were observed among the 16 tested V. anguillarum isolates. Eleven strains caused a significantly higher mortality compared to five other isolates and the axenic control.
Based on these results, three highly virulent V. anguillarum strains, VIB15, HI610 and 87-9-117 were selected to generate knock-out mutations in potential virulence factors, such as empA, encoding a zinc metalloprotease, pilA, encoding the type IV pilin, and qseC, enocoding a sensor kinase involved in quorum sensing. In addition to the selected strains, NB10, a well-studied V. anguillarum strain, was also included in the study.
Both the wild-type strains and knock-out mutants have been tested with the gnotobiotic system to screen for differences in virulence. This challenge test showed that the gnotobiotic model system can be used to study host-microbe interactions and more particularly to identify virulence genes that play an essential role in the pathogenesis of V. anguillarum.