Rapid Salmonella concentration, recovery and detection from food samples

Seockmo Ku, Purdue University

Abstract

This work utilizes the various food samples (i.e., chicken leg, chicken carcass, egg whites, and spinach) artificially spiked with Salmonella (<1 CFU>/g) which are then mixed with enzyme cocktails to hydrolyze colloidal particles. Inhibitory effects on Salmonella growth during the enzyme incubation step were evaluated under the different buffering conditions. The enzyme was found to have no significant effect on cell viability. Enzyme hydrolyzed food homogenates (chicken meat, and egg whites) and spinach rinse were concentrated by 350 to 500 fold using microfiltration followed by centrifugation. The number of recovered Salmonella cells exceeded the number initially present in the food when the enzyme treatment is coupled to a short enrichment time step (1 to 5 hours). In some cases, more than 100% of Salmonella cells appeared to have been recovered but this was an artifact due to the cell growth. An overall sequence to detect low concentrations of Salmonella consisted of sample preparation, pretreatment, concentration, cell recovery, and PCR assay (BAX® PCR System or conventional PCR), was demonstrated to be achieved in an overall elapsed time of 7 to 9 hours. This time included a 3 to 5 hour enzyme treatment step during which some enrichment also occurred. Overall, the purpose of this research was to define conditions and explain fundamental phenomena that impact enzyme-assisted, physical concentration of living microorganisms for the purpose of detecting viable food pathogens if present. This dissertation addressed research for the rapid detection of Salmonella using operating conditions that integrate principles of membrane microfiltration, proteins at interfaces, and growth of microbial cells to recover pathogens at detectable levels using PCR.

Degree

Ph.D.

Advisors

Ladisch, Purdue University.

Subject Area

Food Science|Agricultural engineering|Biomedical engineering

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