Date of Award

Fall 2017

Project Type

Dissertation

Program or Major

Microbiology

Degree Name

Doctor of Philosophy

First Advisor

Stephen H Jones

Second Advisor

Cheryl A Whistler

Third Advisor

Vaughn S Cooper

Abstract

The CDC estimates that 45,000 people are sickened each year by foodborne Vibrio parahaemolyticus in the United States. Filter-feeding bivalve shellfish, such as oysters, are routinely inhabited by human pathogenic V. parahaemolyticus and there currently is not a contaminant management process that effectively reduces concentrations of V. parahaemolyticus in oysters. The transplanting of V. parahaemolyticus -laden oysters to an area with low concentrations or no V. parahaemolyticus, called oyster relay, is one reduction strategy that holds promise for treating live oysters. A key consideration for effective strategies to reduce Vibrio spp. in shellfish is the influence of microbiota in natural seawater. Our aim for this study was to identify taxa shifts in the microbial composition of oyster and water samples during relay that correlated with the reduction of V. parahaemolyticus. We hypothesize that changes in bacterial taxa within the oyster microbiome occur during relay and influence the reduction of V. parahaemolyticus in relayed oysters. Oysters with varying concentrations of V. parahaemolyticus were evident from relay experiments carried out in a local body of water with elevated salinity and low concentrations of V. parahaemolyticus over 4 consecutive years. Overall, V. parahaemolyticus levels were reduced during 14-day relay in 9 of the 14 monthly trials to target reduction levels (<100 V. parahaemolyticus/g). Sequence analysis of the 16S rRNA gene from relayed oyster tissue and the associated water samples unveiled that the composition of oyster microbial communities shifts during relay. We determined that oyster and water taxa profiles are dissimilar while harvest and relay waters were similar in overall taxa composition, even though there was also evidence of some taxa differences that may have been influential in reducing V. parahaemolyticus concentrations during the 14-day relay. Oyster samples from relay experiments in years that successfully reduced V. parahaemolyticus concentrations had consistent, similar taxa patterns compared to different and inconsistent patterns for 2013 when relay was not successful. Interspecies competition experiments informed by these analyses suggested one potential mechanistic explanation (competition) for why relaying to higher salinity water reduces V. parahaemolyticus concentrations. Oyster microbiome competition may aid in developing a consistent approach for reducing V. parahaemolyticus in oysters to reduce the risk of illness for oyster consumers.

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