Date of Award

2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Nutrition and Food Sciences

First Advisor

Catherine W. Donnelly

Abstract

This dissertation examined recently issued regulatory standards using cheese and produce as model systems. FDA's 2015 Domestic and Imported Cheese and Cheese Products Compliance Program Guidelines (CPG) E. coli standards on cheese safety, and the extent to which these standards affect domestic and imported cheese commerce, was assessed. Results from FDA's Domestic and Imported Cheese Compliance Program for samples collected between January 1, 2004 and December 31, 2006 were analyzed. Of 3,007 cheese samples tested for non-toxigenic E. coli, 76% (2,300) of samples exceeded 10/g, FDA's target for regulatory activity. In cheese samples containing E. coli levels of 10/g and 100/g, there was no statistically significant association with presence of Listeria monocytogenes. However, associations between Staphylococcus aureus levels of 10,000 CFU/g and presence of Salmonella and L. monocytogenes were statistically significant, indicating that EU regulations targeting S. aureus as the pathogen of concern may be more appropriate than E. coli for cheese safety assessment.

Compost amended soils in the Northeastern U.S. were assessed for the presence and survival of E. coli and Listeria spp. against FDA Food Safety Modernization Act (FSMA) requirements. Manure and poultry litter-based biological soil amendments of animal origin (BSAAO) must achieve pathogen reduction to reduce risk of pathogen contamination on the harvested produce. Two trials of replicated field plots of loamy (L) or sandy (S) soils were tilled and un-amended (NC) or amended with dairy compost (DC), poultry litter compost (PL), or poultry pellets (PP). Colony count and most probable number (MPN) methods were used to determine persistence of E. coli in these plots over 104 days post-inoculation. Detection of indigenous Listeria spp. were also examined in all plots. Higher E. coli populations were observed in PL and PP amended soils when compared to DC and NC plots. E. coli was detected at low levels on radish crops, where PL treatments encouraged greater levels of survival and growth than DC or NC. Study results verify that a 120 day interval following BSAAO application should be sufficient to ensure food safety of edible crops subsequently planted on these soils.

The sensitivity of environmental monitoring methods and collection formats were evaluated to identify optimal procedures for detection of Listeria spp. on product contact surfaces within artisan cheese production environments. Four environmental surfaces (dairy brick, stainless steel, plastic, and wood; n=405/surface type) were inoculated with L. innocua, L.m. ATTC® 19115 and L.m. 1042, at high (106-107/cm2) and low (0.1-1/cm2) target concentrations. Inoculated surfaces were swabbed with World Bioproducts© EZ ReachTM and 3MTM environmental swabs (3MTM). Five enrichment and enumeration methods were used to compare sensitivity of recovery between environmental swabs. All swab formats performed equally on all environmental surfaces at high target concentrations. At low concentrations, PetrifilmTM and WBEZ swabs recovered Listeria spp. from 87.5% of plastic, stainless steel, and dairy brick surfaces, but only 62.7% of wooden surfaces; recovering 14.8%, 77%, and 96.3% of cells from initial inoculations of 0.01, 0.1, and 1/cm2, respectively . Our data demonstrate that results may be discrepant due to variation in the porosity of environmental surfaces and should be taken into consideration when implementing environmental sampling plans. Results from this thesis can be used to inform regulatory policy and help to achieve improved food safety.

Language

en

Number of Pages

390 p.

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