Influence of Salmonella enterica Serovar Typhimurium ssrB on Colonization of Eastern Oysters (Crassostrea virginica) as Revealed by a Promoter Probe Screen.
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. This study tested the hypothesis that specific regulatory changes enable a portion of the invading Salmonella 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 ssrB regulates 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 sdiA 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 by Salmonella is controlled by a limited number of regulators, including ssrB.
Interdisciplinary Ecology Program, Department of Soil and Water Science, University of Florida-Institute of Food and Agricultural Sciences, Gainesville, Florida, USA.
Clayton E
CE
Cox
Department of Food Science and Human Nutrition, University of Florida-Institute of Food and Agricultural Sciences, Gainesville, Florida, USA.
Anita C
AC
Wright
Department of Microbiology and Molecular Biology and Department of Pathology, University of California, Irvine, California, USA.
Michael
M
McClelland
Interdisciplinary Ecology Program, Department of Soil and Water Science, University of Florida-Institute of Food and Agricultural Sciences, Gainesville, Florida, USA maxtep@ufl.edu.
Max
M
Teplitski
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D049896:Crassostrea / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D044404:Genomic Islands / Q000235:genetics; D006434:Hemocytes / Q000382:microbiology; D006801:Humans; D059013:Microbial Consortia / Q000502:physiology; D011401:Promoter Regions, Genetic; D053038:Quorum Sensing / Q000235:genetics; D012486:Salmonella typhimurium / Q000235:genetics / Q000254:growth & development*; D065288:Serogroup; D012758:Shellfish; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D037521:Virulence Factors / Q000235:genetics
D001426:Bacterial Proteins; C097686:SdiA protein, bacteria; C119761:SsrB protein, Salmonella typhimurium; D015534:Trans-Activators; D014157:Transcription Factors; D037521:Virulence Factors