Efficacy of Peracetic Acid and Chlorine on the Reduction of Shiga Toxin-producing Escherichia coli and a Nonpathogenic E. coli Strain in Preharvest Agricultural Water.

Produce-borne outbreaks of Shiga toxin-producing Escherichia coli (STEC) linked to preharvest water emphasize the need for efficacious water treatment options. This study quantified reductions of STEC and generic E. coli in preharvest agricultural water using commercially available sanitizers. Water was collected from two sources in Virginia (pond, river) and inoculated with either a seven-strain STEC panel or environmental generic E. coli strain TVS 353 (∼9 log10 CFU/100 mL). Triplicate inoculated water samples were equilibrated to 12 or 32°C and treated with peracetic acid (PAA) or chlorine (Cl) [low (PAA:6ppm, Cl:2-4 ppm) or high (PAA:10 ppm, Cl:10-12 ppm) residual concentrations] for an allotted contact time (1, 5, or 10 min). Strains were enumerated, and a log-linear model was used to characterize how treatment combinations influenced reductions. All Cl treatment combinations achieved a ≥3 log10 CFU/100 mL reduction, regardless of strain (3.43 ± 0.25 to 7.05 ± 0.00 log10 CFU/100 mL). Approximately 80% (19/24) and 67% (16/24) of PAA treatment combinations achieved a ≥3 log10 CFU/100 mL for STEC and E. coli TVS 353, respectively. The log-linear model showed contact time (10 > 5 > 1 min) and sanitizer type (Cl > PAA) had the greatest impact on STEC and E. coli TVS 353 reductions (p < 0.001). E. coli TVS 353 in water samples was more resistant to sanitizer treatment (p < 0.001) indicating applicability as a good surrogate. Results demonstrated Cl and PAA can be effective agricultural water treatment strategies when sanitizer chemistry is managed. These data will assist with the development of in-field validation studies and may identify suitable candidates for the registration of antimicrobial pesticide products for use against foodborne pathogens in preharvest agricultural water treatment.

Ranking Food Safety Priorities of the Fresh Produce Industry in the United States.

A broad understanding of community member food safety priorities in the fresh produce supply chain does not currently exist. This information is essential to improve food safety knowledge and practices effectively and efficiently throughout the fresh produce industry; therefore, the goal of this study was to identify and rank community produce safety priorities in the United States. Survey questions were designed and approved by food safety experts for participants to rank 24 fresh produce safety priorities. The anonymous survey was distributed online via Qualtrics™ to fresh produce community members from November 2020 to May 2021. A score was calculated for each priority by summing weighted ranking scores across responses. Descriptive statistics and logistic regression were used to determine frequencies and distribution of response and identify factors (e.g., role in produce safety, size/location of organization/operation) that influenced rankings. A total of 281 respondents represented fourteen different roles in the fresh produce industry, with most identified as growers (39.5%). Produce operations were distributed across the U.S. and annual produce sales ranged from below $25,000 to over $5,000,000. Health and hygiene, training, postharvest sanitation, traceability, and harvest sanitation were ranked as the top five food safety priorities. These findings provide insight into community member priorities in fresh produce safety and can be used to inform intervention efforts, ranging from specialized training for produce growers and packers, industry-driven research projects, and gaps in risk communication strategies.

Sanitizer Type and Contact Time Influence Salmonella Reductions in Preharvest Agricultural Water Used on Virginia Farms.

No Environmental Protection Agency (EPA) chemical treatments for preharvest agricultural water are currently labeled to reduce human health pathogens. The goal of this study was to examine the efficacy of peracetic acid- (PAA) and chlorine (Cl)-based sanitizers against Salmonella in Virginia irrigation water. Water samples (100 mL) were collected at three time points during the growing season (May, July, September) and inoculated with either the 7-strain EPA/FDA-prescribed cocktail or a 5-strain Salmonella produce-borne outbreak cocktail. Experiments were conducted in triplicate for 288 unique combinations of time point, residual sanitizer concentration (low: PAA, 6 ppm; Cl, 2-4 ppm or high: PAA, 10 ppm; Cl, 10-12 ppm), water type (pond, river), water temperature (12°C, 32°C), and contact time (1, 5, 10 min). Salmonella were enumerated after each treatment combination and reductions were calculated. A log-linear model was used to characterize how treatment combinations influenced Salmonella reductions. Salmonella reductions by PAA and Cl ranged from 0.0 ± 0.1 to 5.6 ± 1.3 log10 CFU/100 mL and 2.1 ± 0.2 to 7.1 ± 0.2 log10 CFU/100 mL, respectively. Physicochemical parameters significantly varied by untreated water type; however, Salmonella reductions did not (p = 0.14), likely due to adjusting the sanitizer amounts needed to achieve the target residual concentrations regardless of source water quality. Significant differences (p < 0.05) in Salmonella reductions were observed for treatment combinations, with sanitizer (Cl > PAA) and contact time (10 > 5 > 1 min) having the greatest effects. The log-linear model also revealed that outbreak strains were more treatment-resistant. Results demonstrate that certain treatment combinations with PAA- and Cl-based sanitizers were effective at reducing Salmonella populations in preharvest agricultural water. Awareness and monitoring of water quality parameters are essential for ensuring adequate dosing for the effective treatment of preharvest agricultural water.

Efficacy of cleaning and sanitation methods against Listeria innocua on apple packing equipment surfaces.

Previous foodborne listeriosis outbreaks and recalls of fresh produce have been linked to cross-contamination with food contact surfaces (FCS) of packing equipment. Thus, effective cleaning and sanitation practices should be implemented in the short-term to contribute to the overall food safety objective for FCS which have a suboptimal hygienic design. This research aimed to evaluate the efficacy of seven cleaning and sanitation treatment combinations against Listeria innocua populations on FCS common to produce packinghouses that have been found to have a higher prevalence of Listeria spp. harborage. Polishing brushes made of two different materials (100% nylon and nylon/horsehair mix), 100% polyethylene wash brushes, stainless steel rollers and polytetrafluorethylene (Teflon®) wrapped rollers, and interlocking conveyor belts were evaluated (n = 6 per treatment). These FCS were inoculated with L. innocua (9 log CFU/mL) and fouled with food-grade wax, with the exception of brush rollers that are encountered before waxing. Treatments included the use chlorine (200 ppm), peroxyacetic acid (PAA) (500 ppm) for 15 min, alone or in combination with an alkaline detergent (1.6%) or a degreaser, and the use of steam at 95 °C for 15 s. L. innocua was enumerated and the log reduction was calculated and compared to untreated controls. Horsehair mix polishing brushes were the surface with the lowest log reduction regardless of treatment applied (p < 0.05). Compared to 100% nylon polishing brushes, where a >3 log reduction was reached, horsehair mix brushes only reached this level of reduction when degreaser + PAA was applied. For both types of rollers and interlocking conveyor belt, an effective wax removal using a degreaser or detergent followed by sanitizer application caused the greatest L. innocua reduction (>5 log reduction). The application of steam did not show a significant log reduction on any surface (p > 0.05). This study highlights that cleaning and sanitation strategies must focus on effective wax removal if applied postharvest. In addition, 100% nylon polishing brushes could potentially offer a better hygienic design in produce packinghouses compared to the horsehair mix.

Prevalence of Salmonella enterica in Flies on a Diversified Cattle and Fresh Produce Farm across Two Growing Seasons.

ABSTRACT: Flies are a vector for spreading foodborne pathogens pertinent to fresh produce, such as Shiga toxigenic Escherichia coli and Salmonella; however, most studies focus on concentrated animal feeding operations, which do not reflect low-density animal farming practices that often adjoin fruit and vegetable acreage. In this study, we determined the prevalence of Salmonella in flies collected biweekly on an integrated animal and produce operation over two growing seasons. Eleven of 889 pooled samples tested positive for Salmonella. Flies from the Calliphoridae, Muscidae, Sarcophagidae, and Tachinidae families were associated with Salmonella carriage, but fly family was not a significant factor for isolation of Salmonella (P = 0.303). Fly species were a significant factor (P = 0.026), with five Pentacricia aldrichii pools testing positive for Salmonella. With the exception of single specimen isolation, prevalence ranged from 2.2 to 15.2%. With the exception of the Tachinidae family, these results reflect a strong association of flies that are commonly associated with feces or are pests of animals. Trap location was not significantly associated with isolation of Salmonella-positive flies (P = 0.236). Overall, the population of flies was not as abundant as studies conducted with produce grown close to concentrated animal feeding operations, indicating a reduced risk of transmission; however, similar to these studies, fly families that are commonly isolated from fecal and decaying matter were most frequently associated with Salmonella isolation. Further work is warranted to elucidate the foodborne pathogen transmission rates to produce and subsequent survival over time.

Prevalence, Persistence, and Diversity of Listeria monocytogenes and Listeria Species in Produce Packinghouses in Three U.S. States.

ABSTRACT: Listeria monocytogenes has emerged as a food safety concern for several produce commodities. Although L. monocytogenes contamination can occur throughout the supply chain, contamination from the packinghouse environment represents a particular challenge and has been linked to outbreaks and recalls. This study aimed to investigate the prevalence, persistence, and diversity of L. monocytogenes and other species of Listeria in produce packinghouses. A longitudinal study was performed in 11 packinghouses (whose commodities included microgreen, peach, apple, tomato, broccoli, cauliflower, and cucumber) in three U.S. states. In each packinghouse, 34 to 47 sites representing zones 2 to 4 were selected and swabbed. Packinghouses were visited four times over the packing season, and samples were tested for Listeria by following the U.S. Food and Drug Administration's Bacteriological Analytical Manual methods. Presumptive Listeria-positive isolates were confirmed by PCR. Species and allelic type (AT) were identified by sigB sequencing for up to eight isolates per sample. Among 1,588 samples tested, 50 (3.2%), 42 (2.7%), and 10 (0.6%) samples were positive for L. monocytogenes only, Listeria spp. (excluding L. monocytogenes) only, and both L. monocytogenes and Listeria spp., respectively. Five species of Listeria (L. monocytogenes, L. innocua, L. seeligeri, L. welshimeri, and L. marthii) were identified, and L. monocytogenes was the most prevalent species. The 102 Listeria-positive samples yielded 128 representative isolates (i.e., defined as isolates from a given sample with a different AT). Approximately 21% (21 of 102) of the Listeria-positive samples contained two or more ATs. A high AT diversity (0.95 Simpson's diversity index) was observed among Listeria isolates. There were three cases of L. monocytogenes or Listeria spp. repeated isolation (site testing positive at least twice) based on AT data. Data from this study also support the importance of drain and moisture management, because Listeria were most prevalent in samples collected from drain, cold storage, and wet nonfood contact surface sites.