Poultry litter is applied to crop production land in the southern United States as a waste management strategy as it is a nitrogen-rich fertilizer and plentiful throughout the region. While litter is ...a known reservoir for human enteric pathogens including Salmonella enterica, little is known regarding pathogen prevalence, concentration, and common serotypes within the material. Litter from thirteen farms across four southern states was examined for Salmonella. Samples (n = 490) from six of the thirteen (46.2%) farms tested positive. Thirty-three samples out of 490 (6.7%) were Salmonella positive. Salmonella was ca. 95% less likely to be collected from stacked litter piles than from the poultry house floor or pasture, and every day increase in litter age reduced the likelihood of recovering Salmonella by 5.1%. When present, concentrations of Salmonella in contaminated poultry litter were variable, ranging from <0.45 to >280,000 MPN/g. The most prevalent serotypes found were Kentucky (45.5%), Kiambu (18.2%), and Michigan (12.1%). Salmonella Kentucky also had the greatest distribution and was found on 4 of the 6 (66.7%) positive farms. Results from this survey demonstrated that Salmonella prevalence and concentration in poultry litter is highly variable, and good agricultural practices are critical to safely use poultry litter as a soil amendment on fresh produce fields.
Fresh produce can be contaminated by enteric pathogens throughout crop production, including through contact with contaminated agricultural water. The most common outbreaks and recalls in fresh ...produce are due to contamination by Salmonella enterica and Shiga toxin-producing E. coli (STEC). Thus, the objectives of this study were to investigate the prevalence of markers for STEC ( wzy, hly , fliC , eaeA , rfbE , stx -I, stx -II) and Salmonella ( invA ) in surface water sources ( n = 8) from produce farms in Southwest Georgia and to determine correlations among the prevalence of virulence markers for STEC, water nutrient profile, and environmental factors. Water samples (500 mL) from eight irrigation ponds were collected from February to December 2021 ( n = 88). Polymerase chain reaction (PCR) was used to screen for Salmonella and STEC genes, and Salmonella samples were confirmed by culture-based methods. Positive samples for Salmonella were further serotyped. Particularly, Salmonella was detected in 6/88 (6.81%) water samples from all ponds, and the following 4 serotypes were detected: Saintpaul 3/6 (50%), Montevideo 1/6 (16.66%), Mississippi 1/6 (16.66%), and Bareilly 1/6 (16.66%). Salmonella isolates were only found in the summer months (May-Aug.). The most prevalent STEC genes were hly 77/88 (87.50%) and stx -I 75/88 (85.22%), followed by fliC 54/88 (61.63%), stx -II 41/88 (46.59%), rfbE 31/88 (35.22%), and eaeA 28/88 (31.81%). The wzy gene was not detected in any of the samples. Based on a logistic regression analysis, the odds of codetection for STEC virulence markers ( stx -I, stx -II, and eaeA ) were negatively correlated with calcium and relative humidity ( p < 0.05). A conditional forest analysis was performed to assess predictive performance (AUC = 0.921), and the top predictors included humidity, nitrate, calcium, and solar radiation. Overall, information from this research adds to a growing body of knowledge regarding the risk that surface water sources pose to produce grown in subtropical environmental conditions and emphasizes the importance of understanding the use of abiotic factors as a holistic approach to understanding the microbial quality of water.
Listeria monocytogenes is an increasing food safety concern throughout the produce supply chain as it has been linked to produce associated outbreaks and recalls. To our knowledge, this is the first ...systematic literature review to investigate Listeria species and L. monocytogenes prevalence, persistence, and diversity at each stage along the supply chain. This review identified 64 articles of 4863 candidate articles obtained from four Boolean search queries in six databases. Included studies examined naturally detected/isolated Listeria species and L. monocytogenes in fresh produce-related environments, and/or from past fresh produce associated outbreaks or from produce directly. Listeria species and L. monocytogenes were detected in each stage of the fresh produce supply chain. The greatest prevalence of Listeria species was observed in natural environments and outdoor production, with prevalence generally decreasing with each progression of the supply chain (e.g., packinghouse to distribution to retail). L. monocytogenes prevalence ranged from 61.1% to not detected (0.00%) across the entire supply chain for included studies. Listeria persistence and diversity were also investigated more in natural, production, and processing environments, compared to other supply chain environments (e.g., retail). Data gaps were identified for future produce safety research, for example, in the transportation and distribution center environment.
•Produce-associated foodborne pathogens were not detected in an aquaponics farm.•A. hydrophila was isolated from 59.53% of aquaponic samples.•A. hydrophila in water and sponge samples increased after ...6 months of production.•Physicochemical water quality was influenced by collection location and system’s age.
Aquaponic production of fresh produce is a sustainable agricultural method becoming widely adopted, though few studies have investigated potential food safety hazards within commercial systems. A longitudinal study was conducted to isolate and quantify several foodborne pathogens from a commercial, aquaponic farm, and to elucidate their distribution throughout. The survey was conducted over 2 years on a controlled-environment farm containing Nile tilapia (Oreochromis niloticus) and lettuce (Lactuca sativa). Samples (N = 1,047) were collected bimonthly from three identical, independent systems, and included lettuce leaves, roots, fingerlings (7–126 d old), feces from mature fish (>126 d old), water, and sponge swabs collected from the tank interior surface. Most probable number of generic Escherichia coli were determined using IDEXX Colilert Quanti-Tray. Enumeration and enrichment were used to detect Shiga toxin-producing E. coli (STEC), Salmonella enterica, Listeria monocytogenes, Aeromonas spp., Aeromonas hydrophilia, and Pseudomonas aeruginosa. Generic E. coli, STEC, L. monocytogenes, and S. enterica were not detected in collected samples. P. aeruginosa was isolated from water (7/351; 1.99%), swabs (3/351; 0.85%), feces (2/108; 1.85%), and lettuce leaves (2/99; 2.02%). A. hydrophila was isolated from all sample types (623/1047; 59.50%). The incidence of A. hydrophila in water (X2 = 23.234, p < 0.001) and sponge samples (X2 = 21.352, p < 0.001) increased over time.
Wild birds pose a difficult food safety risk to manage because they can avoid traditional wildlife mitigation strategies, such as fences. Birds often use agricultural fields and structures as ...foraging and nesting areas, which can lead to defecation on crops and subsequent transfer of foodborne pathogens. To assess the food safety risk associated with these events, wild bird feces were collected from produce fields across the southeastern United States during the 2021 and 2022 growing seasons. In total 773 fecal samples were collected from 45 farms across Florida, Georgia, South Carolina, and Tennessee, and 2.1% (
n
= 16) of samples were
Salmonella-
positive. Importantly, 75% of
Salmonella
were isolated from moist feces, showing reduced
Salmonella
viability when feces dry out. 16S microbiome analysis showed that presence of culturable
Salmonella
in moist feces correlated to a higher proportion of the Enterobacteriaceae family. From the
Salmonella
-positive samples, 62.5% (10/16) contained multi-serovar
Salmonella
populations. Overall, 13 serovars were detected, including six most commonly attributed to human illness (Enteriditis, Newport, Typhimurium, Infantis, Saintpaul, and Muenchen). PCR screening identified an additional 59
Salmonella
-positive fecal samples, which were distributed across moist (
n
= 44) and dried feces (
n
= 15). On-farm point counts and molecular identification from fecal samples identified 57 bird species, including for 10
Salmonella
-positive fecal samples. Overall, there was a low prevalence of
Salmonella
in fecal samples, especially in dried feces, and we found no evidence of
Salmonella
transmission to proximal foliage or produce. Fecal samples collected in farms close together shared highly related isolates by whole genome sequencing and also had highly similar
Salmonella
populations with comparable relative frequencies of the same serovars, suggesting the birds acquired
Salmonella
from a common source.
Wildlife feces can contaminate vegetables when enteric bacteria are released by rain and splashed onto crops. Regulations require growers to identify and not harvest produce that is likely ...contaminated, but U.S. federal standards do not define dimensions for no-harvest zones. Moreover, mulching, used to retain soil moisture and maximize crop yield may impact rain-mediated bacterial dispersal from feces.
To assess
dissemination from a fecal point source to lettuce grown on various mulches, lettuce cv. 'Magenta' was transplanted into raised beds with plastic, biodegradable plastic, straw, or left uncovered at field sites in Maryland and Georgia. Eleven days post-transplant, 10 g of rabbit manure spiked with ~8 log CFU g
were deposited in each bed. One day following natural or simulated rain events, lettuce was sampled along 1.5 m transects on either side of fecal deposits. Lettuce-associated
was semi-quantified with an MPN assay and dependence on fecal age (stale or fresh), lettuce age (baby leaf or mature head), distance from point source, mulch and post-rain days were statistically evaluated.
Distance (
<0.001), fecal age (
<0.001) and mulch (
<0.01) were factors for
transfer from point source to lettuce. The highest and lowest
estimates were measured from lettuce grown on biodegradable plastic and straw, respectively, with a 2-log MPN difference (
<0.001). Mulch and distance were also significant factors in
recovery 3 days post-rain (both
<0.001), where plastic mulches differed from bare ground and straw (
<0.01). For all treatments, fewer
were retrieved from lettuce at 0.3 m, 3 days post-rain compared to 1 day (
0.001). Fitting the data to a Weibull Model predicated that a 7-log reduction in
from fecal levels would be achieved at 1.2-1.4 m from the point source on plastic mulches, 0.75 m on bare soil (
<0.05) and 0.43 m on straw (
0.01).
Straw and bare ground limited rain-mediated
dispersal from feces to lettuce compared to plastic mulches. Fecal age was negatively associated with
dispersal. These findings can inform harvesting recommendations for measures related to animal intrusion in vegetable production areas.
Listeria species prevalence has been investigated at nearly all stages of the fresh produce supply chain; however, it has not been examined in transportation and distribution center (DC) related ...environments. Between December 2019 and March 2021, 18 DCs handling fresh produce were environmentally sampled for Listeria. Swab samples were collected from a variety of surfaces (e.g., floors, pallets, forklifts) in several areas of each DC (e.g., cold storage, shipping and receiving docks). Impaction air samples, relative humidity, and temperature data were also collected. While no Listeria spp. were isolated from air samples (n = 170), they were isolated from 49 of 982 (ca. 5%) environmental samples. The proportion of Listeria spp. positive samples varied significantly across individual DCs (P < 0.01). Several facility characteristics were significantly associated with a Listeria spp. positive sample, such as zone, sampling site dryness, and cleaning regimen. A random forest model (sensitivity: 0.786, specificity: 0.874) identified geographical location and general sampling location (e.g., cold storage rooms, shipping docks) as the two most important variables associated with Listeria spp. detection. This study identified likely harborage sites (e.g., floors, cleaning equipment) of Listeria spp. in DCs across the US and emphasized the importance of sanitation operations in Listeria-prone areas.
•Listeria spp. were isolated from ca. 5% of environmental sponge swabs.•Listeria spp. were found more frequently at shipping and receiving docks.•Nine variables were significantly associated with Listeria detection.•Random forest model identified geography as a predictor for Listeria detection.
Little is known about the microbial communities found in distribution centers (DCs), especially in those storing and handling food. As many foodborne bacteria are known to establish residence in food ...facilities, it is reasonable to assume that DCs handling foods are also susceptible to pathogen colonization. To investigate the microbial communities within DCs, 16S amplicon sequencing was completed on 317 environmental surface sponge swabs collected in DCs (
= 18) across the United States. An additional 317 swabs were collected in parallel to determine if any viable
species were also present at each sampling site. There were significant differences in median diversity measures (observed, Shannon, and Chao1) across individual DCs, and top genera across all reads were
_A,
,
_E,
, and
based on taxonomic classifications using the Genome Taxonomy Database. Of the 39 16S samples containing
ASVs, four of these samples had corresponding
positive microbiological samples. Data indicated a predominance of ASVs identified as cold-tolerant bacteria in environmental samples collected in DCs. Differential abundance analysis identified
,
, and
present at a significantly greater abundance in
positive microbiological compared to those negative for
. Additionally, microbiome composition varied significantly across groupings within variables (e.g., DC, season, general sampling location).
The Produce Safety Alliance (PSA) grower training was introduced in 2016 as the standardized curriculum to meet the training requirements of the Food and Drug Administration’s (FDA) Food Safety ...Modernization Act’s (FSMA) Produce Safety Rule (PSR). The PSR states that at least one supervisor or responsible party from each farm must have successfully completed this food safety training or one equivalent to the standardized curriculum, as recognized by the FDA. This study evaluated the effectiveness of PSA trainings conducted between 2017 and 2019 in the Southern United States by the Southern Regional Center for Food Safety Training, Outreach, and Technical Assistance by analyzing pre- and posttest assessments. Effectiveness was based on a 25-question knowledge assessment administered to participants before (n = 2494) and after (n = 2460) each training. The knowledge assessment indicated the overall effectiveness of the training, with average scores increasing significantly from pretest (15.9/25, 63.4%) to posttest (20.3/25, 81.3%) (P < 0.001). The greatest knowledge gains were seen in the Postharvest Handling and Sanitation, How to Develop a Farm Food Safety Plan, and Agricultural Water modules. Notably, these modules had lower posttest scores compared to the other modules, indicating that the amount of knowledge gained did not necessarily correspond with a sufficient understanding of the material. To ensure that participants understand all aspects of the PSR and best practices to minimize food safety risks, additional or advanced trainings may be needed. Additionally, the current testing instrument (pre-/posttest) used for PSA grower training, while validated, may not be optimal, thus alternative methods to assess the training effectiveness are likely needed.
Prior to the 2013 cantaloupe season, the US Food and Drug Administration notified the industry that inspections of a subset of packinghouses would commence that year in response to the 2011 Listeria ...monocytogenes outbreak associated with cantaloupe. In May 2013, five Florida cantaloupe packinghouses participated in an environmental monitoring survey to evaluate their sanitary conditions prior to a potential FDA inspection. Two facilities participated again in 2014. Surface swabs (n = 374) were collected in each facility and included up to 60 food contact and non-food contact surfaces, including water. Samples were enumerated for total plate counts (TPC), generic Escherichia coli, and coliforms, and enriched for Listeria. Listeria were confirmed and speciated by sequencing of the partial sigB gene, and further characterized by pulsed field gel electrophoresis (AscI and Apal). In 2013, two zone 1 surfaces in same facility, were positive for L. monocytogenes (2/233). No L. monocytogenes was detected (n = 103) in the two facilities sampled the following year, including the previously L. monocytogenes-positive facility. Prevalence of L. monocytogenes in FL cantaloupe packinghouses was generally low (2/374), compared to other food environments. TPC, coliforms, E. coli and Listeria spp. were poor indicators of L. monocytogenes contamination in Florida packinghouses.
•Two zone 1 surfaces (n = 233) were L. monocytogenes positive in 2013.•In 2014, no surfaces (n = 103) were L. monocytogenes positive from 2 packinghouses.•E. coli, coliforms, TPC and Listeria spp. were poor predictors of L. monocytogenes.•L. monocytogenes prevalence (2/347) in Florida cantaloupe packinghouses was low.
PDF
