Show simple item record

dc.contributor.authorAviles, Bryanen_US
dc.date.accessioned2017-04-04T19:50:53Z
dc.date.available2017-04-04T19:50:53Z
dc.date.issued2012-04-09en_US
dc.identifier.otheretd-05092012-205205en_US
dc.identifier.urihttp://hdl.handle.net/10919/77002
dc.description.abstractSalmonella enterica serotypes have been linked to outbreaks associated with low water activity foods. The ability of biofilm forming pathogens, such as Salmonella, to survive thermal and chemical processes is improved; it is unclear if biofilms will also improve survival to desiccation and gastric stresses. The purpose of this study was to quantify the effect of physiological state (planktonic versus biofilm) and prior exposure to desiccation on Salmonella survival and gene expression after passage through an in-vitro digestion model. Cells of Salmonella enterica serotype Tennessee were deposited onto membranes for planktonic cells or on glass beads to create biofilms. The cells were subsequently dried at room temperature and stored in dried milk powder (aw = 0.3) for up to 30 days. Salmonella survival was quantified by serial dilution onto brilliant green agar before desiccation, after desiccation, after 1-day storage and after 30-day storage. At each sampling both physiological states were tested for survival through a simulated gastrointestinal system. RNA was extracted at the identical time points and relative gene expression determined for genes associated with stress response (rpoS, otsB), virulence (hilA, hilD, invA, sipC) and a housekeeping gene 16S rRNA using quantitative real-time PCR. The physiological state and length of storage effected the survival and gene expression of Salmonella within the desiccated milk powder environment and after passage through an in-vitro digestion system (p<0.05). Larger numbers of S. Tennessee were recovered by plate counts for biofilm cells, compared to planktonic cells. However, the numbers of 16S rRNA gene copies were not significantly different suggesting entry of S. Tennessee into a viable but non-culturable state. Prolonged storage in dry milk powder was not associated with increased cross-protection to gastric stress. Increased expression of stress response genes rpoS and otsB correlated with survival, indicating cross protection of low water activity and acid stress. Increased expression of virulence-associated genes was seen in cells exposed to short periods of dry storage, suggesting an increased virulence potential.
dc.language.isoen_USen_US
dc.publisherVirginia Techen_US
dc.rightsI hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Virginia Tech or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.en_US
dc.subjectin vitro digestionen_US
dc.subjectstress responseen_US
dc.subjectvirulenceen_US
dc.subject16S rDNAen_US
dc.subjectbiofilmsen_US
dc.subjectlow moistureen_US
dc.subjectdesiccation stressen_US
dc.subjectSalmonella entericaen_US
dc.subjectViable but non-culturableen_US
dc.titleInfluence of Physiological State, Prolonged Dry Storage, and Passage through Simulated Digestion on the Survival and Gene Expression of Salmonella enterica sv. Tennesseeen_US
dc.typeThesisen_US
dc.contributor.departmentFood Science and Technologyen_US
dc.description.degreeMaster of Science in Life Sciencesen_US
thesis.degree.nameMaster of Science in Life Sciencesen_US
thesis.degree.levelmastersen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineFood Science and Technologyen_US
dc.contributor.committeechairPonder, Monica Anneen_US
dc.contributor.committeememberEifert, Joseph D.en_US
dc.contributor.committeememberWilliams, Robert C.en_US
dc.type.dcmitypeTexten_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-05092012-205205/en_US
dc.date.sdate2012-05-09en_US
dc.date.rdate2016-09-23
dc.date.adate2012-06-04en_US


Files in this item

Thumbnail

This item appears in the following Collection(s)

Show simple item record