Bagthasingh, C.; Thiyagarajan, S., and Alavandi, S.V., 2019. Pulsotypes and virulence of Vibrio harveyi from shrimp hatcheries in south-east coast of India. In: Jithendran, K.P.; Saraswathy, R.; Balasubramanian, C.P.; Kumaraguru Vasagam, K.P.; Jayasankar, V.; Raghavan, R.; Alavandi, S.V., and Vijayan, K.K. (eds.), BRAQCON 2019: World Brackishwater Aquaculture Conference. Journal of Coastal Research, Special Issue No. 86, pp. 112-118. Coconut Creek (Florida), ISSN 0749-0208.

Luminescent Vibrio harveyi has been reported to be one of the major causes of mass mortality of larval stages in penaeid shrimp hatcheries throughout the world. Therefore, understanding the virulence mechanism of V. harveyi and identifying traits has been our quest to detect pathogenic strains in shrimp aquaculture ecosystem. In this study pulsed field gel electrophoresis (PFGE)was used for differentiating V. harveyi isolates recovered from shrimp larvae affected by luminescent bacterial disease in hatcheries and water samples from various sources within the hatcheries. Forty two of the 400 V. harveyi isolates recovered from shrimp hatcheries over a period of two years were used in this study. Cluster analysis of PFGE profiles of 32 V. harveyi isolates in conjunction with virulence factors revealed that the isolates from disease episode were grouped in Cluster II. Further, the isolates in the cluster were all sucrose fermentative and had LD50 value in the order of 103cfu ml-1 and ranged from 1.17 × 103 cfu ml-1 to 3.16 × 103 cfu ml-1. However, the clustering pattern could not be associated with LD50 values based on in vivo pathogenicity experiment. An interesting observation was that majority of the isolates capable of producing siderophores were clustered in IA (11 of 13) although 10 of the 16 isolates in cluster IB also produced siderophores. Six of 13 isolates in cluster IA and 7 of 16 isolates in cluster IB produced extracellular proteins (ECP) and this property was not found to be associated with any of the clustering pattern. This study could not show definite relationship between pulsotypes and virulence of V. harveyi. However, PFGE typing cluster analysis could help in differentiating isolates from disease episodes and normal shrimp seed production cycle. Further, the study has also revealed that sucrose fermenting trait seems to be an important phenotypic trait indicative of virulence of V. harveyi in shrimp hatchery ecosystems.

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