Monitoring dehydration of Salmonella Montevideo
Abstract
Survival of pathogens in dry environments is detrimental to the food industry because it increases the risk of contamination throughout the harvest, distribution and consumption cycle of the food chain. The goal of this research was to understand physical changes that occur when Salmonella Montevideo undergoes a two-step dehydration process. Specifically, cells were spotted onto glass surfaces and a coupled optical inverted and atomic force microscope was used to monitor dehydration during: (i) removal of liquid water and (ii) storage at low (<25%RH) and/or high humidity (>90%RH). A minimal salt medium was used to lessen the effects of dried medium components that can complicate the imaging and analysis of cells. Although an evenly distributed pattern of attached single cells was desirable for this study, various orientations of groups of cells were found and categorized as single, low count clusters (<4 >cells), or clumped. To ascertain if cells could survive the drying/storage process, an agar overlay method was developed to stimulate growth of living cells. Growth was monitored by covering attached cells with an agar overlay, incubating at room temperature for 5.5 h, and imaging with the optical microscope. Evidence of cell division or elongation demonstrated that a single attached cell or at least one cell within a cluster or clump was in a living culturable state. When no change in size was observed, single attached cells were presumed to be either dead or in a non-culturable state (22 hours of incubation). Generally, growth was observed when cells were stored at high humidity (>90% RH), and not observed when stored at low humidity (>25% RH). Although AFM imaging of hydrated single or low cell count clusters at high humidity was difficult due to numerous tip contamination events, results demonstrated that cells collapsed after drying at >25% RH to morphologies similar to those generally observed in the literature.
Degree
M.S.
Advisors
Nivens, Purdue University.
Subject Area
Food Science
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