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Abstracts
Workgroup: Public Health and Processing
Elimination of Vibrio vulnificus in Triploid Eastern Oysters
Principal Investigator(s):
Jerome F. La Peyre, Department of Veterinary Science, Louisiana State University, jlapeyre@agctr.lsu.edu
Co-Investigator(s):
Richard K. Cooper, Dept. of Veterinary Science, Louisiana State University
Terrence R. Tiersch, School of Forestry, Wildlife and Fisheries, Louisiana State University
Terrence R. Tiersch, School of Forestry, Wildlife and Fisheries, Louisiana State University
Funding Period: 10/1/99-9/30/01
Advantages of triploidy in oysters include greater growth rate and better meat quality. It has also been postulated that triploid oysters have better host defenses; energy allocated to reproduction in diploid oysters may be allocated to host defenses in triploid oysters which have impaired gonad development. The extended spawning season of Gulf coast eastern oysters and the occurrence of the human pathogen V. vulnificus and the oyster pathogen P. marinus make triploidy attractive for this region. Our objectives were to 1) compare tissue abundance of V. vulnificus, total bacteria and P. marinus between triploid and diploid oysters during two consecutive spawning seasons and 2) evaluate the elimination of V. vulnificus in triploid and diploid oysters in conditions mimicking relaying in offshore waters devoid of V. vulnificus. Offshore relaying has been shown to significantly reduce V. vulnificus density in oysters.
A batch of oysters containing about 50 % triploid oysters was obtained from Dr. Supan and grown off-bottom at the Grand Isle Oyster Hatchery, La. The oysters were sampled monthly from July through September 2000 and 2001, and divided into three groups. The first group of 50 oysters was placed on ice, transported to Louisiana State University (LSU) and processed within 24 h of collection. The second group of 50 oysters was transported to LSU and placed in a recirculating water system equipped with high capacity ultraviolet sterilizers for one week at 25o C. Group 1 and 2 oysters were homogenized individually and the number of colony forming units of total bacteria and V. vulnificus, and P. marinus infection intensity were determined using standard procedures. A third group of 10 oysters was processed for histological evaluation of gonad development. The hearts of all oysters were collected and used to determine ploidy by flow-cytometry. Data was analyzed using the two-factor ANOVA (p<0.05) followed by the least square multiple comparison of means when significant differences were found. Pearson correlation were calculated between V. vulnificus density, total bacteria density, P. marinus intensity and oyster condition index.
No significant differences in V. vulnificus density, total bacteria density, P. marinus infection intensity, and condition index were found between diploid and triploid oysters in either group 1 or 2. Only V. vulnificus density was significantly lower in experimentally relayed triploid oysters (group 2) than in triploid oysters processed within 24 h of collection (group 1). Although the stages of gonadal development in triploid oysters were significantly lower than diploid oysters during the two spawning seasons (group 3), triploidy was not associated with lowered V. vulnificus density, total bacteria density, P. marinus infection intensity or condition index. The lack of significant difference in condition index between diploid and triploid oysters was unexpected and may indicate that the oysters were particularly stressed in the summer of 2000 and 2001; Both 2000 and 2001 summers were characterized by exceptionally high water temperature and salinity, and extreme oyster mortality. No antibacterial activities of hemocytes and tissue homogenates against V. vulnificus were found between diploid and triploid oysters.
IMPACTS AND/OR BENEFITS
Triploidy was not associated with lowered V. vulnificus density, total bacteria density, P. marinus infection intensity or condition index. Our results were obtained at a time of unusually high water temperature and salinity and may not reflect results obtained under environmental conditions more typical of the Louisiana Gulf Coast.
PROJECT PUBLICATIONS:
La Peyre, J.F., Cooper, R.K., Supan, J.E. and Volety, A.K. 1999. Total bacteria and Vibrio vulnificus load in diploid and triploid eastern oysters in Louisiana. Journal of Shellfish Research 18:324.
La Peyre, J.F. and Volety A.K.. 2000. Effect of Perkinsus marinus infection on Vibrio vulnificus numbers in eastern oysters and hemocyte killing of Vibrio spp. 3rd International Conference on Molluscan Shellfish Safety. Southhampton, NY, June 19-23. Book of abstracts p. 45.
La Peyre, J.F., Nguyen, K.-L.T. and Cooper, R.K. 2000. Potential use of synthetic antimicrobial peptides against Vibrio vulnificus in eastern oysters. 3rd International Conference on Molluscan Shellfish Safety. Southhampton, NY, June 19-23. Book of abstracts p. 44.
Nguyen, K.-L.T., La Peyre, J.F., Supan, J.E., Tiersch, T.R. and Cooper, R.K. 2002. Total Bacteria and Vibrio vulnificus densities and Perkinsus marinus infection intensity in diploid and triploid eastern oysters (Crassostrea virginica) in Louisiana. 4th International Conference on Molluscan Shellfish Safety. Santiago de Compostela, Galicia, Spain, June 4-8.
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