Thesis bio-engineer in Environmental Technology, by Yves Muyssen, Faculty of Agronomic and Applied Biological Sciences, University of Gent, Belgium, 103 pp.
Abstract:
The pathogenecity of the bacterial strain STD3-1188, formerly identified as a V. harveyi (oral communication), was checked by performing 2 types of challenge-tests.
Zoea-mysis larvae of P. vannamei were orally infected through Artemia nauplii which were inoculated at a bacterial concentration of 5.10^6 CFU/5000 nauplii. The Artemia nauplii were fed to the larvae at a density of 5000 Artemia nauplii/80 larvae. The mortality of the infected larvae varied from 25 to 40% after 5 days and was significantly different from the mortality in the controls. The STD3-1188 strain could be re-isolated from diseased animals only. The re-isolation of the infection-strain STD3-1188 was confirmed by an immunological test (Dot-blot) and a DNA-analysis (Randomly Amplified Polymorphic DNA). Plating of Artemia after washing them showed that most of the bacteria were attached to the ectoderm of the Artemia.
Also juveniles of P. vannamei were infected with the same strain by means of injection with a bacterial concentration of 2.10^3 CFU/juvenile. No mortalities were observed, neither could the STD3-1188 strain be re-isolated.
In order to confirm the identification of the STD3-1188 strain as a V. harveyi three identification techniques were applied: a biochemical identification according to a modified protocol by West & Colwell (1984), a carbon-source analysis (Biolog) and a fatty acid analysis (Fame). These results were compared with the results from a DNA-analysis (AFLP) performed by the Laboratory of Microbiology (University of Gent). AFLP identified the STD3-1188 strain as V. campbellii. The modified West & Colwell-test identified the strain as a V. vulnificus and Biolog identified it as V. sp. Zoea which is closely related to V. parahaemolyticus. The identification of the strain could not be specified by the Fame-analysis. The confusion about the identification of the STD3-1188 strain was due to the similarity of V. harveyi, V. vulnificus, V. campbellii and V. parahaemolyticus strains. The results of a DNA-analysis give the most reliable results so the strain could be considered as a V. campbellii.
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