Aspects of bacterial community ecology within the American oyster (Crassostrea virginica), and surveillance of post-harvest Vibrio vulnificus occurrence

Kenneth John La Valley, University of Rhode Island


This dissertation research addressed the fundamental question of what the general microbial flora within the oyster is and what influence depuration and relay have on bacterial communities in the oyster. Comparisons of bacterial community profiles were made using culture-dependent and culture-independent isolation techniques and a nested PCR-DGGE (Denaturing Gradient Gel Electrophoresis) approach. Differences in the composition of the bacterial community between culture-dependent and culture-independent profiles were detected. The effect of culture-based techniques is significant and results in a biased representation of community structure. This bias may be minimized for the oyster compared to the large differences typically detected between culturable and total microbial communities from a sample, since external and internal surfaces of the oyster supply a nutrient rich micro-environment not unlike an enrichment broth. These micro-environments may allow proliferation of the majority of bacterial species who specialize in these environments, thus inhibiting many of the transient non-specialist bacterial species inadvertently ingested during respiratory and feeding mechanisms. Using API 20E test strips, dominant culturable species were identified as members of the genera Vibrio. Approximately 60% of Vibrio isolates were V. parahaemolyticus. Additional Vibrio species included, V. alginolyticus, V. cholerae, and V. vulnificus. The remaining isolates identified by the API system were Aeromonas and Photobacterium species. ^ Oyster-associated bacterial community profiles generated from depurated and relay samples were compared using the same nested PCR-DGGE approach. Oyster-associated profiles between replicate samples within a harvest area and treatment only showed minor variations. Depuration significantly altered the relative species diversity and abundance of dominant ribotypes. Cluster analysis identified groups of ribotypes that persisted or disappeared following depuration. Relay was shown to significantly increase both relative ribotype diversity and relative abundance measures. ^ Post-harvest surveillance for Vibrio vulnificus by a commercial processing facility was conducted from May 2001 to September 2003. Harvest areas included Delaware Bay, Long Island Sound, and Prince Edward Island. Occurrence followed a seasonal distribution. Low densities were observed in June, increased through August, and became rare by September. Post-harvest handling was identified as a critical control point for elevated pathogen densities. ^

Subject Area

Agriculture, Food Science and Technology|Biology, Microbiology|Agriculture, Fisheries and Aquaculture

Recommended Citation

Kenneth John La Valley, "Aspects of bacterial community ecology within the American oyster (Crassostrea virginica), and surveillance of post-harvest Vibrio vulnificus occurrence" (2005). Dissertations and Master's Theses (Campus Access). Paper AAI3188062.