Transfer of Salmonella, Escherichia coli O157:H7 and Listeria monocytogenes from contaminated soilless substrate and seeds to microgreens

Microgreens can be contaminated by various preharvest sources including soilless substrate, plant nutrition solution, water and seeds. The aim of this study was to determine the transfer level of Salmonella, Shiga toxin-producing Escherichia coli O157:H7, and Listeria monocytogenes to the edible part of various type of microgreens from plant nutrient solution-soaked perlite as soilless substrate or seeds. Ampicillin resistant 3-strain cocktails of Salmonella and E. coli O157:H7 and non-resistant L. monocytogenes were independently inoculated into plant nutrient solution-soaked perlite and seeds in low (102-103 CFU/g) and high (105-106 CFU/g) populations. Twenty types of microgreens were grown in inoculated perlite. The seed inoculation was performed on five types of microgreens. Correlations between pathogen transfer levels with seed characteristics and harvest time were assessed. Pathogen populations (1.6 ± 0.2 to 7.7 ± 0.1 log CFU/g) transferred to microgreens were dependent on type of pathogen and microgreen but not affected by contamination source and inoculation level. The level of pathogen transferred to microgreens had a moderate to high negative correlations (R2) with seed surface area (-0.551 to -0.781), seed weight (-0.735 to -0.818), and harvest time (-0.332 to -0.919) when grown in Salmonella and E. coli O157:H7 inoculated perlite. This study suggests a high risk of pathogen population transferring to microgreens in case of seed or soilless substrate contamination when pathogen growth or survival is supported in plant nutrient solution.

A comprehensive examination of microbial hazards and risks during indoor soilless leafy green production

Produce grown under controlled environment agriculture (CEA) is often assumed to have a reduced risk of pathogen contamination due to the low chance of exposure to outdoor contaminant factors. However, the 2021 outbreak and numerous recalls of CEA-grown lettuce and microgreens demonstrate the possibility of pathogen introduction during indoor production when there is a failure in the implementation of food safety management systems. Indoor production of commercial leafy greens, such as lettuce and microgreens, is performed across a range of protective structures from primitive household setups to advanced and partially automatized growing systems. Indoor production systems include hydroponic, aquaponic, and aeroponic configurations. Hydroponic systems such as deep water culture and nutrient film technique comprised of various engineering designs represent the main system types used by growers. Depending on the type of leafy green, the soilless substrate, and system selection, risk of microbial contamination will vary during indoor production. In this literature review, science-based pathogen contamination risks and mitigation strategies for indoor production of microgreens and more mature leafy greens are discussed during both pre-harvest and post-harvest stages of production.

Growing Safer Greens: Exploring Food Safety Practices and Challenges in Indoor, Soilless Production Through Thematic Analysis of Leafy Greens Grower Interviews

Indoor, soilless production-often referred to more broadly as controlled environment agriculture (CEA)-is increasingly used for the cultivation of leafy greens. Minimal information is currently available regarding food safety practices during production and distribution of leafy greens grown within indoor, soilless environments in the United States (U.S.). This study aimed to describe production challenges and implementation of good agricultural practices among CEA growers. Data collection methods included semi-structured interviews (N = 25) and a supplemental online survey completed by growers (N = 12) in the U.S. Out of 18 total responses (i.e., multiple responses allowed per completed survey), survey data indicated that lettuce (n = 5; 27.8%) was the most commonly grown leafy green, followed by culinary herbs (n = 3; 16.7%) and arugula (n = 3; 16.7%). Most growers (n = 7; 58.3%) grew other agricultural products, specifically other crops in addition to leafy greens. Revenue from sales ranged from US$500 000 per year. Meanwhile, nearly half (n = 5; 45.5%) of respondents (N = 11) were uncertain whether their produce was subject to the FSMA Produce Safety Rule. Most survey respondents used vertical farming techniques (5 out of 11; 45.5%) or some variety of greenhouse (4 out of 11; 36.4%). Based on 35 total responses, leafy greens were most commonly sold to "Commercial Restaurants" (n = 7; 20.0%), "Grocery Stores" (n = 7; 20.0%), "Institutional Foodservice Establishments (hospitals, schools, childcare, long-term care)" (n = 6; 17.1%), and "Wholesaler/Distributers" (n = 6; 17.1%). The 11 interview questions elucidated three major themes: contextual, barriers to risk management and regulatory compliance, and research needs. Thirteen subthemes were identified, and an example of a subtheme within each major theme, respectively, includes worker hygiene and training, regulatory and certification environment, and risk assessments of individual issues.

Fate and Growth Kinetics of Salmonella and Listeria monocytogenes on Mangoes During Storage

Imported mangoes have been linked to outbreaks of salmonellosis in the USA. The purpose of this research was to evaluate the persistence and growth kinetics of Salmonella and Listeria monocytogenes on the intact surface of whole 'Ataulfo', 'Kent', and 'Tommy Atkins' mangoes stored at three different temperatures. L. monocytogenes was also evaluated on fresh-cut 'Tommy Atkins' mangoes stored at 4, 12, 20 ± 2°C. Whole mangoes were spot inoculated with rifampicin-resistant pathogen cocktails (6 log CFU/mango) onto the midsection of whole fruit (n = 6). Fruit was stored at 12, 20, or 30 ± 2°C and sampled for up to 28 days. The specific growth rates derived from DMFit models as a function of time were used to develop secondary models. On 'Kent' mangoes, Salmonella had a population increase from 0.3 to 1.1 log CFU/mango with a linear growth rate of ∼0.004, 0.01, and 0.06 log CFU/mango/h at 12, 20, and 30°C, respectively. At 20 and 30°C, Salmonella growth rates were significantly higher than 12°C (P < 0.05). No clear Salmonella growth trend was observed; populations decreased up to 1.6 log CFU/mango on 'Tommy Atkins' and 'Ataulfo' at 12°C. Populations of L. monocytogenes on whole and fresh-cut mangoes declined regardless of temperature and storage period. Food safety during storage should be the top priority for fresh-cut tropical fruit processors.

Correlation value determined to increase Salmonella prediction success of deep neural network for agricultural waters

The use of computer-based tools has been becoming popular in the field of produce safety. Various algorithms have been applied to predict the population and presence of indicator microorganisms and pathogens in agricultural water sources. The purpose of this study is to improve the Salmonella prediction success of deep feed-forward neural network (DFNN) in agricultural surface waters with a determined correlation value based on selected features. Datasets were collected from six agricultural ponds in Central Florida. The most successful physicochemical and environmental features were selected by the gain ratio for the prediction of generic Escherichia coli population with machine learning algorithms (decision tree, random forest, support vector machine). Salmonella prediction success of DFNN was evaluated with dataset including selected environmental and physicochemical features combined with predicted E. coli populations with and without correlation value. The performance of correlation value was evaluated with all possible mathematical dataset combinations (nCr) of six ponds. The higher accuracy performances (%) were achieved through DFNN analyses with correlation value between 88.89 and 98.41 compared to values with no correlation value from 83.68 to 96.99 for all dataset combinations. The findings emphasize the success of determined correlation value for the prediction of Salmonella presence in agricultural surface waters.

Food safety knowledge, hygiene practices, and eating attitudes of academics and university students during the coronavirus (COVID-19) pandemic in Turkey

The purpose of this study is to assess the effect of the coronavirus (COVID‐19) pandemic on food safety knowledge, hygiene practices, and eating attitudes of academics and university students in Turkey. A cross‐sectional survey invitation was emailed to the participants from various academic ranks and departments at chosen universities from different region of country. Academics were requested to forward the invitation email to enrolled students to their classes. Responds were accepted in the period of 45 days in April and May 2020 during this pandemic. The relationships between socio‐demographic factors (gender, marital status, parental status, faculty/student status, academic rank, and age) and food safety knowledge, hygiene practices, and eating attitudes of respondents were determined. Academics (n = 240) and university students (n = 479) responded to food safety knowledge statements with similar percentages during the coronavirus pandemic. Improved hygiene practices were observed for both groups to avoid disease during the coronavirus pandemic. Both groups had eating attitudes toward consumption at home due to the coronavirus pandemic. Gender was the most prominent factor associated with 9 out of 10 hygiene practices before and during the coronavirus pandemic (p < .05). No, single, and multiple socio‐demographic factors were in association with food safety knowledge or eating attitudes of respondents. This study indicates that reactions of both academics and university students are similar during the coronavirus pandemic for food safety‐associated knowledge, practices, and attitudes.

Survival of Shiga Toxin-Producing Escherichia coli in Various Wild Animal Feces That May Contaminate Produce

ABSTRACT

Domestic and wild animal intrusions are identified as a food safety risk during fresh produce production. The purpose of this study was to evaluate the survival of Shiga toxin-producing Escherichia coli (STEC) in cattle, feral pig, waterfowl, deer, and raccoon feces from sources in California, Delaware, Florida, and Ohio. Fecal samples were inoculated with a cocktail of rifampin-resistant STEC serotypes (O103, O104, O111, O145, and O157) (104 to 106 CFU/g of feces). Inoculated feces were held at ambient temperature. Populations of surviving cells were monitored throughout 1 year (364 days), with viable populations being enumerated by spread plating and enrichment when the bacteria were no longer detected by plating. Representative colonies were collected at various time intervals based on availability from different locations to determine the persistence of surviving STEC serotypes. Over the 364-day storage period, similar survival trends were observed for each type of animal feces from all states except for cattle and deer feces from Ohio. STEC populations remained the highest in cattle and deer feces from all states between days 28 and 364, except for those from Ohio. Feral pig, waterfowl, and raccoon feces had populations of STEC of <1.0 log CFU/g starting from day 112 in feces from all states. E. coli O103 and O104 were the predominant serotypes throughout the entire storage period in feces from all animals and from all states. The survival of both O157 and non-O157 STEC strains in domesticated and wild animal feces indicates a potential risk of contamination from animal intrusion.

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Survival of Salmonella in Various Wild Animal Feces That May Contaminate Produce

ABSTRACT

Heightened concerns about wildlife on produce farms and possible introduction of pathogens to the food supply have resulted in required actions following intrusion events. The purpose of this study was to evaluate the survival of Salmonella in feces from cattle and various wild animals (feral pigs, waterfowl, deer, and raccoons) in California, Delaware, Florida, and Ohio. Feces were inoculated with rifampin-resistant Salmonella enterica cocktails that included six serotypes: Typhimurium, Montevideo, Anatum, Javiana, Braenderup, and Newport (104 to 106 CFU/g). Fecal samples were stored at ambient temperature. Populations were enumerated for up to 1 year (364 days) by spread plating onto tryptic soy agar supplemented with rifampin. When no colonies were detected, samples were enriched. Colonies were banked on various sampling days based on availability of serotyping in each state. During the 364-day storage period, Salmonella populations decreased to ≤2.0 log CFU/g by day 84 in pig, waterfowl, and raccoon feces from all states. Salmonella populations in cattle and deer feces were 3.3 to 6.1 log CFU/g on day 336 or 364; however, in Ohio Salmonella was not detected after 120 days. Salmonella serotypes Anatum, Braenderup, and Javiana were the predominant serotypes throughout the storage period in all animal feces and states. Determination of appropriate risk mitigation strategies following animal intrusions can improve our understanding of pathogen survival in animal feces.

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Fate of Salmonella in Central Florida Surface Waters and Evaluation of EPA Worst Case Water as a Standard Medium

HIGHLIGHTS

Survival of Salmonella was studied in surface waters. Salmonella stayed alive in nonsterile microcosms for 168 days. Limited decline was seen in sterile surface, deionized, and EPA Worst Case water. EPA Worst Case water offers potential as a standardized medium.

Evaluating the U.S. Food Safety Modernization Act Produce Safety Rule Standard for Microbial Quality of Agricultural Water for Growing Produce

The U.S. Food and Drug Administration (FDA) has defined standards for the microbial quality of agricultural surface water used for irrigation. According to the FDA produce safety rule (PSR), a microbial water quality profile requires analysis of a minimum of 20 samples for Escherichia coli over 2 to 4 years. The geometric mean (GM) level of E. coli should not exceed 126 CFU/100 mL, and the statistical threshold value (STV) should not exceed 410 CFU/100 mL. The water quality profile should be updated by analysis of a minimum of five samples per year. We used an extensive set of data on levels of E. coli and other fecal indicator organisms, the presence or absence of Salmonella, and physicochemical parameters in six agricultural irrigation ponds in West Central Florida to evaluate the empirical and theoretical basis of this PSR. We found highly variable log-transformed E. coli levels, with standard deviations exceeding those assumed in the PSR by up to threefold. Lognormal distributions provided an acceptable fit to the data in most cases but may underestimate extreme levels. Replacing censored data with the detection limit of the microbial tests underestimated the true variability, leading to biased estimates of GM and STV. Maximum likelihood estimation using truncated lognormal distributions is recommended. Twenty samples are not sufficient to characterize the bacteriological quality of irrigation ponds, and a rolling data set of five samples per year used to update GM and STV values results in highly uncertain results and delays in detecting a shift in water quality. In these ponds, E. coli was an adequate predictor of the presence of Salmonella in 150-mL samples, and turbidity was a second significant variable. The variability in levels of E. coli in agricultural water was higher than that anticipated when the PSR was finalized, and more detailed information based on mechanistic modeling is necessary to develop targeted risk management strategies.

Microbial quality of agricultural water in Central Florida

The microbial quality of water that comes into the edible portion of produce is believed to directly relate to the safety of produce, and metrics describing indicator organisms are commonly used to ensure safety. The US FDA Produce Safety Rule (PSR) sets very specific microbiological water quality metrics for agricultural water that contacts the harvestable portion of produce. Validation of these metrics for agricultural water is essential for produce safety. Water samples (500 mL) from six agricultural ponds were collected during the 2012/2013 and 2013/2014 growing seasons (46 and 44 samples respectively, 540 from all ponds). Microbial indicator populations (total coliforms, generic Escherichia coli, and enterococci) were enumerated, environmental variables (temperature, pH, conductivity, redox potential, and turbidity) measured, and pathogen presence evaluated by PCR. Salmonella isolates were serotyped and analyzed by pulsed-field gel electrophoresis. Following rain events, coliforms increased up to 4.2 log MPN/100 mL. Populations of coliforms and enterococci ranged from 2 to 8 and 1 to 5 log MPN/100 mL, respectively. Microbial indicators did not correlate with environmental variables, except pH (P<0.0001). The invA gene (Salmonella) was detected in 26/540 (4.8%) samples, in all ponds and growing seasons, and 14 serotypes detected. Six STEC genes were detected in samples: hly (83.3%), fliC (51.8%), eaeA (17.4%), rfbE (17.4%), stx-I (32.6%), stx-II (9.4%). While all ponds met the PSR requirements, at least one virulence gene from Salmonella (invA-4.8%) or STEC (stx-I-32.6%, stx-II-9.4%) was detected in each pond. Water quality for tested agricultural ponds, below recommended standards, did not guarantee the absence of pathogens. Investigating the relationships among physicochemical attributes, environmental factors, indicator microorganisms, and pathogen presence allows researchers to have a greater understanding of contamination risks from agricultural surface waters in the field.