| Abstract |
Since 1997, a new pathology seasonally occurs in new caledonian shrimp farms during the warm season. Diseased Litopenaeus stylirostris shrimp suffer from a systemic vibriosis which was attributed to highly pathogenic Vibrio nigripulchritudo. At the present time, only two farms among 17 are affected by the so called "summer syndrome". In such a context it appears urgent to develop reliable diagnostic tools to detect V. nigripulchritudo strains and to differentiate highly virulent strains from non virulent ones in order to understand the mechanisms of infection and overcome disease spreading. Multilocus Sequencing Typing (MLST) analysis on 24 bacterial strains isolated in geographically distinct shrimp farms highlighted the existence of a cluster A containing only strains displaying moderate to high virulence. Since experimental infection procedure for virulence status determination is material intensive and time consuming, and MLST method not accurate enough to inform on the virulence status of strains, it appeared of great interest to develop other diagnostic tools. Two phylogenetically closed strains, one highly virulent SFn1 and the other non-virulent SFn118 were selected in order to characterize genes specific of the virulent strain by Substractive Suppression Hybridization (SSH). Firstly, a total of 622 DNA fragments specific of SFn1 were sequenced, characterized and further used as probes in a DNA macroarray. Testing 24 strains, hybridization profiles were found to be strongly correlated with both MLST genotypes and bacterial virulence status. A total of 96 representative probes were secondly selected to validate macroarray results on 34 more additionnal strains, allowing identification of genetic markers of virulence. Most of DNA fragments specific of highly virulent strains associated to summer syndrome were found to be bore by a plasmid successfully isolated in the laboratory. In next future, these results would permit the development of relevant diagnostic tools useful for accurate epidemiological survey of the summer syndrome. |
