Comparison of Three Air Sampling Methods for the Quantification of Salmonella, Shiga-toxigenic Escherichia coli (STEC), Coliforms, and Generic E. coli from Bioaerosols of Cattle and Poultry Farms

Recent fresh produce outbreaks potentially associated with bioaerosol contamination from animal operations in adjacent land highlighted the need for further study to better understand the associated risk. The purpose of this research was to evaluate three sampling methods for quantifying target bacterial bioaerosols from animal operations. A dairy cattle and poultry farm located in Georgia, U.S. were visited six times each. Air was collected for 10 min using: 2-stage Andersen impactor with and without mineral oil overlay and impingement samplers. Sampling devices were run concurrently at 0.1, 1, and 2 m heights (n = 36). Andersen samplers were loaded with CHROMagar™ Salmonella, CHROMagar™ STEC, or Brilliance™ coliforms/E. coli. The impingement sampler contained buffered peptone water (20 mL) which was vacuum filtered through a 0.45 µm filter and placed onto the respective media. Plates were incubated at 37 ℃ for 48 h. PCR confirmation followed targeting ttr for Salmonella and stx1, stx2, and eae genes for STEC. No significant differences were found among methods to quantify coliforms and E. coli. Salmonella and STEC bioaerosols were not detected by any of the methods (Limit of detection: 0.55 log CFU/m3). E. coli bioaerosols were significantly greater in the poultry (2.76-5.00 log CFU/m3) than in the cattle farm (0.55-2.82 log CFU/m3) (p < 0.05), and similarly distributed at both stages in the Andersen sampler (stage 1:>7 μm; stage 2: 0.65-7 μm particle size). Sampling day did not have a significant effect on the recovery of coliforms/E. coli bioaerosols in the poultry farm when samples were taken at the broiler house exhaust fan (p > 0.05). A greater and constant emission of coliforms and E. coli bioaerosols from the poultry farm warrants further investigation. These data will help inform bioaerosol sampling techniques which can be used for the quantification of bacterial foodborne pathogens and indicator organisms for future research.

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.

Impact of chlorine or peracetic acid on inactivation of Salmonella, Escherichia coli, and Listeria monocytogenes in agricultural water

Preharvest agricultural water has been recognized as one of the routes of contamination for foodborne pathogens during fruit and vegetable production. Several strategies have been proposed to reduce the risk of pathogens, including preharvest water chemigation, but literature is lacking with regards to microbiological inactivation of common bacterial foodborne pathogens associated with fresh produce contamination, Salmonella enterica, Shiga-toxigenic Escherichia coli (STEC), and Listeria monocytogenes, in surface irrigation water after exposure to chlorine and peracetic acid (PAA). Surface water supplied by a local irrigation district was collected over the summer of 2019. Water was autoclaved, divided into 100 mL samples, and inoculated with a cocktail of five Salmonella, STEC, or Listeria monocytogenes strains or a single strain non-pathogenic E. coli. Samples were then treated with 3, 5, or 7 ppm of free chlorine or PAA, and surviving populations were evaluated using a time-kill assay. A first-order kinetic model was used to fit the inactivation data and obtain the D-values. A secondary model was used to explain the changes due to the type of water, treatment, and microorganism. At a concentration of 3 ppm, the observed and predicted D-values of free chlorine treatments were higher than that of PAA treatments for ground and surface water. Results indicated that PAA was more effective inactivating bacteria than sodium hypochlorite at concentrations of 3 and 5 ppm for both water sources (surface and ground). However, at 7 ppm, the effectiveness of PAA and sodium hypochlorite showed no statistically significant difference for both surface and groundwater. Findings will provide information regarding efficacy of chemical sanitizers like chlorine and PAA for inactivation of Salmonella, Listeria, and STEC in surface water from which treatments can be derived. Ultimately benefitting growers in the selection of an appropriate method for in-field treatment of irrigation water if deemed necessary.

Microbial and physicochemical assessment of irrigation water treatment methods

AIMS

The presence of foodborne pathogens in preharvest agricultural water has been identified as a potential contamination source in outbreak investigations, driving markets and auditing bodies to begin requiring water treatment for high-risk produce. Therefore, it is essential that we identify water treatment methods which are effective as well as practical in their application on farm.

METHODS AND RESULTS

In this work, we evaluated two sanitizers which are most prominent in preharvest agricultural water treatment (calcium hypochlorite (free chlorine: 3-5 ppm) and peracetic acid (PAA: 5 ppm)), an EPA registered antimicrobial device (ultraviolet light (UV)), in addition to a combination approach (chlorine + UV, PAA + UV). Treatments were evaluated for their ability to inactivate total coliforms and generic Escherichia coli and consistency in treatment efficacy over 1 h of operation. Physicochemical variables were measured along with microbial populations at 0, 5, 15, 30, 45 and 60 min of operation. Escherichia coli and coliform counts showed a significant (P < 0·05) reduction after treatment, with combination and singular treatments equally effective at inactivating E. coli and coliforms. A significant increase (P < 0·05) in oxidation-reduction potential was seen during water treatment (Chlorine; UV + Chlorine), and a significant reduction (P < 0·05) in pH was seen after PAA and PAA + UV treatments (60 min).

CONCLUSION

Overall, the results indicate that all treatments evaluated are equally efficacious for inactivating E. coli and coliforms present in surface agricultural water.

SIGNIFICANCE AND IMPACT OF THE STUDY

This information when paired with challenge studies targeting foodborne pathogens of interest can be used to support grower decisions when selecting and validating a preharvest agricultural water treatment programme.

Utility of rapid tests to assess the prevalence of indicator organisms (Aerobic plate count, Enterobacteriaceae, coliforms, Escherichia coli, and Listeria spp.) in apple packinghouses

The 2014 listeriosis outbreak caused by caramel-coated apples was linked to apples cross-contaminated within an apple packing facility. This outbreak has increased the focus on effective cleaning and sanitation methods that must be validated and monitored during apple packing. Thus, rapid and reliable testing methods are necessary for assessing cleanliness in the apple packing industry. The objectives of this study were to assess the prevalence of common indicator organisms [Aerobic plate count (APC), Enterobacteriaceae, coliforms, Escherichia coli, and Listeria spp.] on food contact surfaces (zone 1) in apple packinghouses and to evaluate the utility and accuracy of currently used rapid tests (ATP and glucose/lactose residue swabs). Food contact surfaces were sampled over a 100 cm² area in five commercial apple packinghouses to evaluate populations of indicator organisms APC, Enterobacteriaceae, coliforms, E. coli (n = 741), and rapid test readings (n = 659). Petrifilm plates were used for the quantification of APC, Enterobacteriaceae, and coliform/E. coli. Rapid tests [ATP swabs (UltraSnap) and glucose/lactose residue swabs (SpotCheck Plus)] were processed on-site. A larger area (0.93 m²) was sampled for the detection of Listeria spp. (n = 747), following a modified protocol of the FDA's Bacteriological Analytical Manual method, and confirmed with PCR and gel electrophoresis via the iap gene. No significant association was found between either rapid test and populations of APC, Enterobacteriaceae, coliforms, E. coli, and Listeria spp. detection. However, recovery of APC (log CFU/100 cm²) was higher with a failed glucose/lactose residue swab surface hygiene result (3.1) than a passed result (2.9) (p = 0.03). Populations of APC, Enterobacteriaceae, and coliforms were significantly different at each unit operation during the packing process (p ≤ 0.05). This study concluded that ATP and glucose/lactose residue rapid tests were poorly suited for determining microbial load since they were not related to populations of any common indicator organisms or the detection of Listeria spp. These findings emphasize the need to utilize a rapid test, which can be a good indicator of residual matter on a surface, along with traditional microbiological methods to assess cleaning and sanitation practices in apple packinghouses.

Optimization of a Method for the Concentration of Genetic Material in Bacterial and Fungal Communities on Fresh Apple Peel Surfaces

Apples are the most consumed fruit in the United States and have recently been shown to exhibit some vulnerability to contamination across the supply chain. It is unclear what role a fruit microbiome analysis may serve in future food safety programs interested in understanding changes in the product and the processing environment. Ultimately, sample integrity is key if any of these approaches are to be employed; low microbial loads on apple surfaces, the inability to sample the entire surface, and inefficiency of removal may act as barriers to achieving high-quality DNA. As such, the objective of this study was to identify a reproducible method to concentrate and quantify bacterial and fungal DNA from fresh apple surfaces. Five methods were evaluated: two variations of wash solutions for bath sonication, wash filtration, epidermis excision, and surface swabbing. Epidermis excision returned the highest mean DNA quantities, followed by the sonicated washes and wash filtration. Surface swabbing was consistently below the limit of detection. Based on the quantity of host DNA contamination in surface excision, the sonicated wash solution containing a surfactant presents the greatest opportunity for consistent, high-yielding DNA recovery from the entire apple surface.

Potential of Cinnamon Oil Emulsions as Alternative Washing Solutions of Carrots

The objective of this study was to evaluate the potential of cinnamon oil emulsions as alternative washing solutions to improve the microbial safety of carrots. Whey protein concentrate (WPC), gum arabic (GA), lecithin, and their combinations were used to prepare cinnamon oil emulsions. The emulsions were characterized for their hydrodynamic diameter (D_h) during 7 days of storage and their antimicrobial activity against cocktails of Salmonella enterica , Escherichia coli O157:H7, and Listeria monocytogenes . The D_h of the emulsion prepared with the GA+WPC blend did not change significantly (195.0 to 184.1 nm), whereas all other emulsions showed varying degrees of increases in D_h. Compared with free cinnamon oil dissolved in 5% ethanol, all emulsions showed similar or lower MICs and MBCs. Emulsions prepared with GA and equal masses of GA and WPC were chosen and diluted to 0.2 and 0.5% cinnamon oil to wash carrots that were surface inoculated with bacterial cocktails because of their lower MICs and MBCs than free oil. Emulsions resulted in significantly higher reductions of pathogens on carrots than free cinnamon oil, 3.0 to 3.7 versus 2.1 to 2.3 log CFU/g at 0.5% cinnamon oil and 2.0 to 3.0 versus 1.0 to 1.7 log CFU/g at 0.2% cinnamon oil. No transfer of bacteria from inoculated carrots to wash solutions and no effects of organic load on log reductions were only observed for wash treatments with 0.5% emulsified cinnamon oil. Thus, the cinnamon oil emulsions are potential alternative postharvest washing solutions for fresh produce production.

Self-emulsification of alkaline-dissolved clove bud oil by whey protein, gum arabic, lecithin, and their combinations

Low-cost emulsification technologies using food ingredients are critical to various applications. In the present study, a novel self-emulsification technique was studied to prepare clove bud oil (CBO) emulsions, without specialized equipment or organic solvents. CBO was first dissolved in hot alkaline solutions, added at 1% v/v into neutral solutions with 1% w/v emulsifier composed of whey protein concentrate (WPC), gum arabic, lecithin, or their equal mass mixtures, and adjusted to pH 7.0. The self-emulsification process did not affect UV-vis absorption spectrum, reversed-phase HPLC chromatogram, or antimicrobial activity of CBO against Escherichia coli O157:H7, Listeria monocytogenes Scott A, and Salmonella Enteritidis. The entrapment efficiency after extraction by petroleum ether was determined to be about 80%. Most emulsions were stable during 7 days of storage. Emulsions prepared with WPC had smaller particles, whereas emulsions prepared with emulsifier mixtures had more stable particle dimensions. The studied self-emulsification technique may find numerous applications in the preparation of low-cost food emulsions.

Survival of Salmonella enterica in poultry feed is strain dependent

Feed components have low water activity, making bacterial survival difficult. The mechanisms of Salmonella survival in feed and subsequent colonization of poultry are unknown. The purpose of this research was to compare the ability of Salmonella serovars and strains to survive in broiler feed and to evaluate molecular mechanisms associated with survival and colonization by measuring the expression of genes associated with colonization (hilA, invA) and survival via fatty acid synthesis (cfa, fabA, fabB, fabD). Feed was inoculated with 1 of 15 strains of Salmonella enterica consisting of 11 serovars (Typhimurium, Enteriditis, Kentucky, Seftenburg, Heidelberg, Mbandanka, Newport, Bairely, Javiana, Montevideo, and Infantis). To inoculate feed, cultures were suspended in PBS and survival was evaluated by plating samples onto XLT4 agar plates at specific time points (0 h, 4 h, 8 h, 24 h, 4 d, and 7 d). To evaluate gene expression, RNA was extracted from the samples at the specific time points (0, 4, 8, and 24 h) and gene expression measured with real-time PCR. The largest reduction in Salmonella occurred at the first and third sampling time points (4 h and 4 d) with the average reductions being 1.9 and 1.6 log cfu per g, respectively. For the remaining time points (8 h, 24 h, and 7 d), the average reduction was less than 1 log cfu per g (0.6, 0.4, and 0.6, respectively). Most strains upregulated cfa (cyclopropane fatty acid synthesis) within 8 h, which would modify the fluidity of the cell wall to aid in survival. There was a weak negative correlation between survival and virulence gene expression indicating downregulation to focus energy on other gene expression efforts such as survival-related genes. These data indicate the ability of strains to survive over time in poultry feed was strain dependent and that upregulation of cyclopropane fatty acid synthesis and downregulation of virulence genes were associated with a response to desiccation stress.