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Defining the Role of Salmonella Newport in Contaminated Oysters


The long range goal of the proposed research is to minimize the occurrence of gastroenteritis associated with the consumption of raw oysters farmed in U.S. Coastal waters. Potential human pathogens are concentrated when oysters feed. Preliminary studies indicate an overall prevalence of 7.4% of Salmonella in oysters with up to 78.9% prevalence in some bays. The majority of the isolates were of one genotype of S. Newport. S. Newport is currently ranked third by CDC in causing human intestinal infections, with an increasing number of S. Newport isolates being multi-drug resistant to nine or more antimicrobial agents. Submission of this PFGE pattern to CDC/PulseNet matched the S. Newport pattern JJPX01.0014, already representing 3.1% of all S. Newport isolates in the National Database from 39 states and Canada. This PFGE pattern was the first MDR AmpC pattern identified by PulseNet and has been persistent since 1999. Previous FoodNet and NARMS studies indicate the pattern being associated with dairy cattle with numerous outbreaks from ground beef or unpasturized cheese. We hypothesize that the presence of this genotype in oysters suggests a role for dairy sheds as a source of S. Newport contamination of coastal surface waters.

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NON-TECHNICAL SUMMARY: Episodes of human illness are associated with the consumption of raw oysters as potential human pathogens are concentrated when oysters feed. Preliminary studies indicate an overall prevalence of 7.4% of Salmonella in oysters with up to 78.9% prevalence in some bays. The purpose of this research is to test the ability of Salmonella to survive in oysters and to track the source of Salmonella in surface waters in order to develop viable surveillance strategies to prevent episodes of illness associated with the consumption of farmed oysters. <P>

APPROACH: We will test this hypothesis by using fecal source-tracking methods in the Yaquina basin and by correlating the degree of river or tributary contamination with S. Newport with the overall land use patterns in various watersheds. We also hypothesize that S. Newport JJPX01.0014 has unique survival characteristics that result in its high prevalence in market oysters. We will perform survival assays testing both bovine and human genotypes in oysters and seawater, and in vitro epithelial and macrophage assays and microscopy studies to examine invasive and survival properties. This project will enhance our understanding of the ecology of S. Newport in surface waters, clarify the potential association of S. Newport from oysters with human bouts of gastroenteritis, and allow development of viable surveillance strategies for classifying the acceptability of surface waters for molluscan shellfish harvesting. The information generated will aid efforts to prevent and minimize the episodes of illness associated with the consumption of farmed oysters.

PROGRESS: 2006/09 TO 2007/08 <BR>
OUTPUTS: Despite highly regulated coliform testing of both shellfish and their growing waters, a previous study in our lab found Salmonella in 7% of oysters tested across the country with no correlation between positive fecal coliform tests and the presence of Salmonella. A great majority of the isolates found during that study were the S. Newport serovar with the same PFGE pattern. In this study, we have further studied this S. Newport isolate's ability to survive in oysters and have compared the results to the ATCC 25922 strain of E. coli, which serves as a representative fecal coliform. Immunohistochemical analysis of oyster tissues have also been conducted to analyze where Salmonella resides in the oyster. Furthermore, to determine the nature of the interactions between Salmonella Newport and the aquatic environment, three parameters were examined: 1) vertical transmission between generations of the Pacific Oyster Crassostrea gigas, 2) survival of Salmonella Newport and E. coli in seawater containing plankton, and 3) depuration studies in oysters infected with Salmonella Newport or E. coli. <BR> PARTICIPANTS: Lynn Joens, PI, to supervise all aspects of project; Bibiana Law, Assistant Research Professor, to design protocols, train students, and communicate with collaborators; Chris Morrison, Graduate student, to conduct experiments; Alex Armstrong, Graduate student, to conduct experiments; Rita Mild, Research Technician, to conduct experiments; Robert Medler and Julio Valdiviezo, undergraduate students, to help in making media, changing water for artificial aquaria, wash dishes, etc. <BR> TARGET AUDIENCES: Project provided laboratory training for students and technician. Project provided experiental learning for Bibiana Law at Hatfield Marine Science Center to understand oyster rearing to submit more proposals. Project provided experiential learning for Chris Morrison and Alex Armstrong at Hatfield Marine Science Center.
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IMPACT: 2006/09 TO 2007/08 <BR>
Our studies demonstrate that this Salmonella isolate, with pattern JJPX01.0014, is capable of surviving in oysters after exposure to a variety of contamination levels and can do so at significantly higher levels and for longer periods of time than E. coli. Immunohistochemical analysis of oyster exposed tissues show that Salmonella can breach the oyster's epithelial barriers and can reside within the deeper connective tissues of the oyster. These data imply that Salmonella Newport may not be just a transient resident of the oyster's gut, along with other wastewater indicators, and that merely testing growing waters, or even the oysters themselves, for coliforms is likely inadequate for preventing oyster-borne Salmonellosis. In regards to determining the nature of the interactions between Salmonella Newport and the aquatic environment, results indicate that vertical transmission is not responsible for infection of multiple oyster generations. Salmonella Newport was found to survive at significantly higher numbers in oysters than E. coli following a 72-h depuration period. Finally, Salmonella Newport survived longer in seawater containing plankton than an environmental E. coli strain, supporting previous studies that suggest fecal coliform testing may not be sufficient to guarantee the safety of consuming oysters on the half-shell.

Joens, Lynn
University of Arizona
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