Influence of Salmonella enterica Serovar Typhimurium ssrB on Colonization of Eastern Oysters (Crassostrea virginica) as Revealed by a Promoter Probe Screen

AlthoughSalmonella 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 bySalmonella . This study tested the hypothesis that specific regulatory changes enable a portion of the invadingSalmonella population to colonize oysters. Anin 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, inssrB , resulted in a significantly reduced ability to colonize oysters compared to that of wild-typeSalmonella . BecausessrB regulatesSalmonella pathogenicity island 2 (SPI-2)-dependent infections in vertebrate macrophages, the possibility thatssrB 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 betweenSalmonella 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 observedin vivo . ThesdiA reporter responded to salinity, suggesting that SdiA may also have a role in environmental sensing. Overall, this study suggests the initial colonization of live oysters bySalmonella is controlled by a limited number of regulators, includingssrB .