Raw is risky: I only eat cooked oysters (and didn’t get any for our 7 fishes feast tonight)

Although Salmonella has been isolated from 7.4 to 8.6% of domestic raw oysters, representing a significant risk for food-borne illness, little is known about the factors that influence their initial colonization by Salmonella.

oysters.grillThis study tested the hypothesis that specific regulatory changes enable a portion of the invadingSalmonella population to colonize oysters.

An in vivo promoter probe library screen identified 19 unique regions as regulated during colonization. The mutants in the nearest corresponding downstream genes were tested for colonization defects in oysters. Only one mutation, in ssrB, resulted in a significantly reduced ability to colonize oysters compared to that of wild-type Salmonella. Because ssrBregulates Salmonella pathogenicity island 2 (SPI-2)-dependent infections in vertebrate macrophages, the possibility that ssrB mediated colonization of oyster hemocytes in a similar manner was examined. However, no difference in hemocyte colonization was observed.

The complementary hypothesis that signal exchange between Salmonella and the oyster’s native microbial community aids colonization was also tested. Signals that triggered responses in quorum sensing (QS) reporters were shown to be produced by oyster-associated bacteria and present in oyster tissue. However, no evidence for signal exchange was observed in vivo.

The sdiAreporter responded to salinity, suggesting that SdiA may also have a role in environmental sensing. Overall, this study suggests the initial colonization of live oysters by Salmonella is controlled by a limited number of regulators, includingssrB.

 Influence of Salmonella enterica Serovar Typhimurium ssrB on colonization of eastern oysters (Crassostrea virginica) as revealed by a promoter probe screen

Appl. Environ. Microbiol. January 2016 82:328-339; Accepted manuscript
posted online 23 October 2015, doi:10.1128/AEM.02870-15

Clayton E. Cox, Anita C. Wright, Michael McClelland, and Max Teplitski