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The influence of the viable but non-culturable (VBNC) state on specific phenotypic traits of Escherichia coli O157:H7 as well as its transport behaviour in porous media was examined in this study. E.coli O157:H7 is a human pathogen capable of entering a VBNC state following exposure to sublethal stress. In the VBNC state, E.coli O157:H7 is not detectable by culture assays; yet, is able to retain its ability to cause human illness. This study examined specific transport-related properties of culturable and VBNC E.coli O157:H7 cells. As well, transport behaviors of the two cellular states were compared using sand-packed columns under steady-state flow. When E.coli O157:H7 cells entered a VBNC state, significant decreases in the hydrophobicity and lengths/widths of the cells, and a significant increase in extracellular polymeric substances on the cell surfaces were measured. Transport experiments indicated significantly (p<0.05) greater mass transport of VBNC cells through unwashed sand compared to culturable cells. This research contributes to the current knowledge describing VBNC E.coli O157:H7 cells, raises questions concerning the accuracy of culture-based E.coli O157:H7 identification protocols, and suggests that bacteria transport in the subsurface is a truly dynamic process. / Soil Science

Escherichia coli O157:H7 can contaminate dropped apples used for juicing via contact with manure or fecally tainted irrigation water and attach to the flesh of the apple through bruises and wounds where surface sanitizers are not effective. The goal of this project was to determine the efficacy of gamma irradiation at the maximum allowed dose of 1000 Gy to inactivate Escherichia coli O157: H7 in whole apples used for juicing. Whole apples were punctured to simulate wounds which were then inoculated with an outbreak strain of E.coli O157:H7 and subjected to gamma irradiation at doses upto 1000 Gy. The D-value of the E.coli O157:H7 strain was 334 Gy indicating that irradiation at 1000 Gy would result in a 3-log reduction of this pathogen. Contaminated apples were also stored for 3 weeks at refrigerated temperature during which time E.coli O157:H7 survived but did not grow. The inoculated apples were juiced, and the juice was stored up to 72 h. There was no change in counts of E.coli O157:H7 in the juice from the control apples, but irradiation at >600 Gy reduced counts by >3 logs, and survivors were not detected after 72 h storage. Sensory testing of juice treated at 652 Gy indicated consumers could tell the difference from control juice, due mostly to greater sweetness of the juice from irradiated apples. These results show that E.coli O157:H7 can easily survive in bruised apples and the juice made from them. Irradiation at 1000 Gy can provide significant lethality of E.coli O157:H7 in apples and juice conferring a greater level of safety without negative effects on sensory quality.

A survey was developed and sent out to each sector of the beef industry (slaughter, non-intact processing and grinding) by using the FSIS Meat, Poultry and Egg Product Inspection Directory. Survey questions were specific to processes and interventions being applied, and the use and familiarity with Industry Best Practices documents for beef processing. Returned completed surveys. A total of 469 beef processing operations responded and of survey respondents, 119 establishments were called and asked additional questions. Critical Control Points (CCPs) and testing for E. coli O157:H7 were common discussion point during phone calls. Plant visits were made to confirm the answers that were provided in the written survey. Plants that further processed beef were found to need to reassess their HACCP plan based on their response to the question, "Is E. coli O157:H7 a reasonably likely to occur food safety hazard?" E. coli O157:H7 is considered an adulterant in the products that they produced if they answered yes to this question. Based on survey responses, slaughter establishments were using available technologies to reduce or eliminate possible microbiological contamination. Further process operations, especially those plants that produced intact steaks and roasts, marinated/enhanced steaks and roasts, and plants that produced needle/blade tenderized steaks and roasts, used documentation such as supplier purchasing specifications instead of using processes to control, reduce, or eliminated microbiological food safety hazards. Industry Best Practices were being utilized most frequently by slaughter and ground beef operations. Plants that further process beef still need to implement the use of the Industry Best Practices specific to them. Plants used testing for E. coli O157:H7 throughout the beef industry regardless of plant size or type.

Increase in consumption of fresh cut produce over the past decade has resulted in a rise in incidents of food borne outbreaks due to pathogens. Conventional techniques of sanitizing washes may not be effective since the organic matter released from the fresh produce use up the free chlorine thus reducing the sanitizing potential of wash water just when it is needed most and a heat treatment step to kill pathogens cannot be applied if the purpose is to consume fresh produce. Electron beam (e-beam) irradiation was used to treat cut cantaloupe, cut roma tomatoes, baby spinach, romaine lettuce which were surface inoculated with a cocktail of Salmonella and E. coli O157:H7. Results showed that irradiation reduced Salmonella and E. coli O157:H7 significantly with increasing doses at 0.2, 0.4, 0.6, 0.8, and 1.0 kGy. The D10-value for Salmonella on irradiated cut cantaloupe, cut roma tomatoes, baby spinach, and romaine lettuce was found to be 0.71 kGy, 0.64 kGy, 0.19 kGy, and 0.23 kGy respectively. The D10-value for E. coli O157:H7 on the produce listed above was found to be 0.73 kGy, 0.54 kGy, 0.18 kGy, and 0.20 kGy respectively. Low dose e-beam irradiation was found to be an excellent tool for ensuring the reduction of spoilage organisms and extending shelf life in cut cantaloupe, cut roma tomatoes, baby spinach, romaine lettuce, strawberries, and green onion. The produce were tested for 12 days of storage for aerobic plate count, yeast and mold, lactic bacteria, color, texture, and respiration rate as a function of irradiation doses 0, 1, 3, and 5 kGy. Aerobic plate counts, yeast counts, and lactic acid bacteria were reduced appreciably at all doses tested on all commodities. Molds did not grow on any samples including control for cut cantaloupe, cut tomatoes, and green onion but for the other commodities, mold was reduced at the same rate as yeasts and vegetative bacteria. Lactic acid bacteria were reduced at all doses while the reduction was highest with 5 kGy in all commodities. When irradiated with 5 kGy, during storage, strawberries, spinach, and green onion displayed wet, soggy and mushy appearance, romaine lettuce leaves were wilted, had a translucent midrib and brown pigmentation. E-beam irradiation increased respiration rate for all samples on day 0 compared to non-irradiated control irrespective of the commodity type and the effect was dose dependent. Firmness reduced appreciably for cut roma tomatoes, baby spinach, strawberries, romaine lettuce, and green onion with increasing doses. Cut cantaloupe was low in firmness but the effect was not dose dependent. Irradiation at low doses is a promising tool to reduce pathogens and enhance keeping quality of cut cantaloupe, cut tomatoes, baby spinach, romaine lettuce, strawberries, and green onion. Irradiation is to be implemented as part of an overall HACCP plan and is not meant to replace existing control measures.

Listeria monocytogenes continues to challenge the dairy industry in causing post-process contamination of cheeses. To reduce risk of contamination, it is crucial to understand the growth and survival of pathogenic bacteria in cheese products and to develop post-process mitigation strategies. This study evaluated the fate of pathogens in reduced and regular sodium Mozzarella cheese, and the potential of Supercritical Fluid Extraction with CO2 (SFE) to reduce Listeria innocua on Mozzarella and Queso Fresco. The survival of L. monocytogenes, Salmonella, and E.coli O157:H7 (2-3 log CFU/g) in reduced sodium Mozzarella (1.62%), compared to regular sodium Mozzarella cheese (2.15%) at 4ºC and 12ºC for 90 and 30 days, respectively, was evaluated. Salmonella and E. coli O157:H7 populations decreased over incubation time at both temperatures and no difference (pListeria monocytogenes population also decreased during incubation time at 4°C regardless of the sodium concentration in Mozzarella cheese. However, there was a difference in the population of L. monocytogenes for regular and reduced sodium incubated 12°C, and its populations increased 1 log CFU/g in reduced sodium Mozzarella cheese. Additionally, this study determined the bactericidal effect of SFE on the population of L. innocua, a surrogate for L. monocytogenes, in Mozzarella and Queso Fresco cheese (6 log CFU/g) treated with SFE at two pressures and temperatures (120 bar at 40°C and 150 bar at 50°C) for 30 min. SFE treatment at 120 bar, 40°C for 30 min decreased L. innocua by approximately 3.0 and 3.5 log CFU/g in Mozzarella and Queso Fresco cheeses, respectively. SFE at 150 bar and 50°C reduced L. innocua by approximately 3.78 and 5.2 log CFU/g in Mozzarella and Queso Fresco cheeses, respectively. Since SFE had a minimal effect on the physico-chemical characteristics of the cheeses assayed, the results suggest SFE might be used to reduce L. monocytogenes in cheeses without negatively impacting product quality.