Survival, transfer, and inactivation of Salmonella on plastic materials used in tomato harvest.

In an effort to improve sanitation, growers are increasingly using plastic materials to handle and pack fresh produce, replacing traditional wood crates and paperboard cartons. Further, many workers have begun wearing gloves in an effort to reduce pathogen contamination of hand harvested produce. However, there is a lack of practical, translatable research data that identifies what materials and cleaning/sanitization practices will most effectively manage food safety risks. Since bacterial transfer is a biophysical process that occurs between a surface and produce, we will evaluate the physical characteristics of glove and plastic bin materials, and their influence on bacterial transfer and cleaning/sanitation. We will then assess survival of Salmonella on plastic materials and the potential for cross contamination from bin and glove materials to tomatoes. Finally, we will quantitatively assess cleaning and sanitation efficiency of plastic materials at various stages in their lifecycle (new, repeatedly sanitized, abraded by cleaning brushes). Research results will be translated into recommendations of best practices for cleaning and sanitation to prevent contamination of produce. We will work closely with the Center for Produce Safety and our local, regional, and national industry partners to develop practical, science-based food safety training materials to support sanitary on-farm practices.

In an effort to improve sanitation, growers are increasingly using plastic materials to handle and pack fresh produce, replacing traditional wood crates and paperboard cartons. Further, many workers have begun wearing vinyl or nitrile gloves in an effort to reduce pathogen contamination of hand harvested produce. However, there is a lack of practical, translatable research data that identifies what materials and cleaning/sanitization practices will most effectively manage food safety risks. Herein, we propose three specific research objectives to bridge this knowledge gap. Since bacterial transfer is a biophysical process that occurs between a surface and produce, we will evaluate the fundamental physical characteristics of glove and plastic bin materials, and their influence on bacterial transfer and cleaning/sanitation. We will then determine if Salmonella can survive on plastic materials and will evaluate the potential for cross contamination from bin and glove materials to tomatoes. Finally, we will quantitatively assess cleaning and sanitation efficiency of plastic materials at various stages in their lifecycle (new, repeatedly sanitized, abraded by cleaning brushes). We will work closely with the Center for Produce Safety and our local, regional, and national industry partners to develop practical, science‐based food safety training materials to support sanitary on‐farm practices. Results from the proposed research will be translated into practical recommendations of best practices for cleaning and sanitation of plastic harvest bins and gloves in order to ultimately minimize the instances of produce‐related outbreaks of food borne illness.

1: Identify and evaluate surface characteristics of materials used for glove and produce tote/bins. Surface characteristics such as hydrophilicity, wetting behavior, surface energy, surface charge, chemistry, and topography determine the molecular mechanisms behind adhesion of soil and bacteria to plastic materials (glove and tote/bin). Factors such as age, roughness and wear from repeated cleaning, and chemical deterioration from repeated sanitization, can affect surface characteristics. These characteristics therefore greatly impact cleanability and can aid in identifying which materials (composition, texture, and age) are less likely to harbor microbial hazards. 

2: Evaluate bacterial survival on and transfer from glove and tote/bin materials used in produce harvest. We will test survival of Salmonella sp. on plastic tote/bin materials under different levels of soil and relative humidity and then evaluate the transfer of Salmonella 3 sp. from inoculated glove and tote materials to tomatoes, as a model system. Tomatoes were selected because of their association to recent outbreaks of food borne illness, and because their uniform size, shape, and surface area facilitate the design of repeatable microbial transfer methodology, as described below. The proposed scientific experimental design enables the results to be transferable to other bacteria and produce systems. 

3: Evaluate the cleanability and sanitation efficiency of Salmonella sp. on glove and tote plastics. The proposed study will evaluate cleaning and sanitation methods against a cocktail of Salmonella sp. inoculated on glove and tote materials. The efficiency of these methods will be evaluated by microbial testing and ATP testing. The microbiological tests will give hard scientific data on bacterial reduction after cleaning and sanitation and the ATP tests with help to determine if the use of a rapid test method has the potential to be used in the field to validate HACCP documentation of cleaning and sanitizing

- The surface hydrophobicity, chemical spectra and surface topography were determined for new and worn bucket materials and glove materials. An abrasion method was developed to simulate abraded bucket materials in the laboratory. Abraded materials showed showed changes in contact angle hysteresis. 

- Bin materials inoculated with a cocktail of Salmonella sp. were observed to have a 1.5‐3 log reduction after two days of incubation with lower numbers recovered as the storage progressed over the 28 day study. The level of persistently surviving organisms varied based upon the inoculation method, with the presence of soil having the greater influence of bacterial recovery, with a 3‐4 log higher recovery of “persister” cells. 

- Bacterial transfer from gloves to tomatoes varied according to glove material type (vinyl, latex, nitrile and low density polyethylene) or tomato type (ripe grape tomatoes or green breaker Lynne McLandsborough, University of Massachusetts Survival, transfer, and inactivation of Salmonella on plastic materials used in tomato harvest tomatoes). In general, vinyl and nitrile showed statistically less transfer to tomatoes than latex or LDPE materials, indicating stronger adhesion to Salmonella sp to these materials. 

- Sanitation efficiency was observed in the presence of soil or serum, however no statistical difference in sanitation sensitivity as observed when materials were abraded to simulate worn conditions.