Monocytogenes Prevalence Research Articles

Prevalence of Listeria monocytogenes in Milk and Dairy Product Supply Chains: A Global Systematic Review and Meta-analysis.

Listeria monocytogenes, one of the main foodborne pathogens, is commonly found in milk and dairy products. This study aimed to estimate the presence of L. monocytogenes in milk and dairy product supply chains using a meta-analysis based on PubMed, Embase, Web of Science, and Scopus databases. A total of 173 studies were included in this meta-analysis. The pooled prevalence in the supply chain environment was 8.69% (95% confidence interval [CI]: 5.30%-12.78%), which was higher than that in dairy products (4.60%, 95% CI: 1.72%-8.60%) and milk products (2.93%, 95% CI: 2.14%-3.82%). Subgroup analysis showed that L. monocytogenes prevalence in raw milk (3.44%, 95% CI: 2.61%-4.28%) was significantly higher than in pasteurized milk (0.60%, 95% CI: 0.00%-2.06%). The highest prevalence of L. monocytogenes in milk and dairy products was observed in North America (5.27%, 95% CI: 2.19%-8.35%) and South America (13.54%, 95% CI: 3.71%-23.37%). In addition, studies using culture and molecular methods (5.17%, 95% CI: 2.29%-8.06%) had higher prevalence than other detection methods. Serogroup 1/2a and 3a (45.34%, 95% CI: 28.74%-62.37%), serogroup 1/2b and 3b (14.23%, 95% CI: 6.05%-24.24%), and serogroup 4b/4e (13.71%, 95% CI: 6.18%-22.83%) were dominant in these studies. The results of this study provide a better understanding of the prevalence of L. monocytogenes in milk and dairy product supply chains and suggest a potential foodborne pathogen burden.

A comprehensive systematic review and meta-analysis of Listeria monocytogenes prevalence in food products in South Korea

Listeria monocytogenes is a foodborne pathogen that can cause deadly severe listeriosis. While systematic review and meta-analysis are powerful tools for comprehensive analysis by pooling every related study, these approaches to L.monocytogenes contamination food have yet to be studied in South Korea. We aimed to identify high-risk L.monocytogenes foods in South Korea through a prevalence survey of retail food products for the first time. A total of 13,684 samples of 59 articles were used for meta-analysis through the systematic review, and the results were synthesized using a random-effects model considering the heterogeneity. The overall pooled prevalence was 2.26 % (95 % CI: 1.44–3.52 %). Among nine food categories, meat exhibited the highest prevalence at 8.32 % (95 % CI: 4.42–12.14 %) after sample size restriction. Specifically, a post-hoc sensitivity analysis was conducted to identify the prevalence difference among subgroups and the source of heterogeneity. Intriguingly, the analysis revealed chicken as the primary contributor to the elevated prevalence of L.monocytogenes, a key factor deriving the observed heterogeneity. This study carries significant implications for public health and food safety in Korea. Furthermore, knowledge of differences in prevalence levels in various foods will be able to be used as a predictive guideline for foodborne outbreaks.

Potential public health hazards related to consumption of poultry contaminated with antibiotic resistant Listeria monocytogenes in Egypt

Listeria monocytogenes is an important foodborne pathogen that incorporated into many serious infections in human especially immunocompromised individuals, pregnant women, the elderly, and newborns. The consumption of food contaminated with such bacteria is considered a source of potential risk for consumers. Therefore, a total of 250 poultry purchased in highly popular poultry stores besides 50 swabs from workers hands in the same stores, in Mansoura City had been tested for the L. monocytogenes prevalence, virulence genes, and antibiotic resistance profile illustrating the health hazards from such poultry. The L. monocytogenes were recovered from 9.6% of poultry samples while not detected from workers hand swabs. The antimicrobial susceptibility of 24 L. monocytogenes strains against 24 antibiotics of seven different classes revealed high susceptibility rates to erythromycin (79.17%), streptomycin (66.67%), gentamycin (66.67%), vancomycin (58.33%), chloramphenicol (58.33%) and cefotaxime (41.67%). The majority (79.2%) of L. monocytogenes were classified as multidrug resistant strains with high resistance to tetracyclines and β-lactams antibiotics while 16.7% of the strains were categorized as extensively resistant ones. The iap virulence-specific determination gene had been detected in all recovered L. monocytogenes isolates while 83.33 and 70.83% of the isolates harbored hylA and actA genes. In addition, the study confirmed the capability of most L. monocytogenes isolates for biofilm formation by moderate to strong production and the quantitative risk assessment illustrated the risk of developing listeriosis as the risk value exceeded 100. The current results illustrate that poultry meat can be a source of pathogenic antibiotic resistant strains that may cause infection with limited or no treatment in immunosuppressed consumers via the food chain.

Listeria monocytogenes in ready-to-eat (RTE) delicatessen foods: Prevalence, genomic characterization of isolates and growth potential

This study investigated Listeria monocytogenes prevalence and count in 132 ready-to-eat (RTE) delicatessen samples belonging to different categories (starters with/without mayonnaise pasta/rice-based courses, meat/fish-based main courses) produced by an Italian industry. Whole Genome Sequencing characterized the isolates to map the pathogen circulation. Moreover, the growth potential of L. monocytogenes in the most contaminated product was investigated by a challenge test.L. monocytogenes was detected in 23 samples, giving an estimated prevalence of 17.4 %. Starters with mayonnaise showed a very high prevalence (56.7 %), showing the role of the sauce in the diffusion of the pathogen within the plant. A total of 49 isolates were obtained; they belonged to two different serogroups, IIb and IIa, and were related to two clonal complexes (CCs) and sequence types (STs) (CC288-ST330 and CC121-ST717), suggesting the possible persistence and circulation of the pathogen within the plant.The results of the challenge test showed a limited ability to grow in the selected product thanks to the presence of lactic microflora.

Factors associated with foodborne pathogens and indicator organisms in agricultural soils

Soil can be a route for contamination of fresh fruits and vegetables. While growers routinely manage soil nutrient levels, little research exists on the synergistic or antagonistic effects of soil nutrients on foodborne pathogens. Data on foodborne pathogen prevalence in unamended soils is also relatively limited in literature. This study evaluated foodborne pathogen prevalence (Salmonella, Listeria monocytogenes) and concentration of indicator bacteria (total coliforms, generic Escherichia coli) in agricultural soils, and characterized associations between soil properties (e.g., macro- and micro-nutrient levels) and each microbial target. Three Virginia produce farms, representing different regions and soil types, were sampled four times over 1 year (October 2021–November 2022). For each individual farm visit, composite soil samples were collected from 20 sample sites (25 m2) per farm per visit for microbial and nutrient analysis (n = 240). Samples (25 g) were processed for Listeria spp. and Salmonella using a modified FDA BAM method; samples (5 g) were enumerated for generic E. coli and total coliforms (TC) using Petrifilm. Presumptive Listeria spp. and Salmonella isolates were confirmed by PCR using the sigB and invA genes, respectively. Soil nutrients from each sample were tested and evaluated for their association with each microbial target by Bayesian Mixed Models. Salmonella prevalence was 4.2% (10/240), with 90% (9/10) recovered on Farm C. Listeria spp. and L. monocytogenes prevalence were 10% (24/240) and 2.5% (6/240), respectively. When samples were positive for generic E. coli (107/240), the average concentration was 1.53 ± 0.77 log10 CFU/g. Soil pH was positively associated with L. monocytogenes [Odds Ratio (OR) = 5.5] and generic E. coli (OR = 4.9) prevalence. There was no association between Salmonella prevalence and any evaluated factor; however, Salmonella was 11.6 times more likely to be detected on Farm C, compared to other farms. Results show pathogen prevalence was relatively low in unamended soils, and that factors influencing prevalence and concentration varied by microbial target and farm.

Risk factors associated with the prevalence of Listeria monocytogenes in manured soils on certified organic farms in four regions of the United States

IntroductionBiological soil amendments, including raw or untreated manure, are currently used to improve soil fertility, especially in organic operations that prohibit use of synthetic fertilizers. However, addition of untreated manure may pose a risk of contamination of fresh produce by pathogens of public health significance, including Listeria monocytogenes. Organic growers follow United States Department of Agriculture (USDA) National Organic Program regulations for raw manure use, which stipulate that harvest should commence no earlier than 90- or 120-days post-application, depending on direct contact between the edible portion of the produce and the soil. To inform the protection that such time-intervals provide, this study explored the farm-level risk factors associated with L. monocytogenes prevalence in USDA-certified organic farm soils amended with untreated manures.MethodsA longitudinal, multi-regional study was conducted on 19 farms in four states (California, Minnesota, Maine, and Maryland) over two growing seasons (2017 and 2018). Untreated manure, soil, irrigation water, and produce samples were collected and cultured for L. monocytogenes. Mixed effect logistic regression was used to investigate risk factors associated with L. monocytogenes prevalence in soil.Results and DiscussionResults showed that multiple factors influenced the odds of a soil-positive sample, including temporal [year (OR = 0.19), sampling day (OR = 0.09–0.48)] and weather-related [temperature range (OR = 0.48)] variables, manure characteristics [season of application (OR = 0.04, summer), presence of L. monocytogenes (OR = 2.89) and other pathogens in manure (OR = 5.24)], farm management factors [water source (OR = 2.73, mixed), number of year-round staff (OR = 0.02)], and soil characteristics [concentration of generic Escherichia coli (OR = 1.45), moisture (OR = 0.46), organic matter (OR = 7.30), nitrate (OR = 3.07), potassium (OR = 0.09) and calcium (OR = 2.48)]. This study highlights the complexity of L. monocytogenes prevalence in soil and contributes science-based metrics that may be used when determining risk-mitigation strategies for pathogen contamination.

Salmonella Prevalence Is Strongly Associated with Spatial Factors while Listeria monocytogenes Prevalence Is Strongly Associated with Temporal Factors on Virginia Produce Farms.

The heterogeneity of produce production environments complicates the development of universal strategies for managing preharvest produce safety risks. Understanding pathogen ecology in different produce-growing regions is important for developing targeted mitigation strategies. This study aimed to identify environmental and spatiotemporal factors associated with isolating Salmonella and Listeria from environmental samples collected from 10 Virginia produce farms. Soil (n = 400), drag swab (n = 400), and irrigation water (n = 120) samples were tested for Salmonella and Listeria, and results were confirmed by PCR. Salmonella serovar and Listeria species were identified by the Kauffmann-White-Le Minor scheme and partial sigB sequencing, respectively. Conditional forest analysis and Bayesian mixed models were used to characterize associations between environmental factors and the likelihood of isolating Salmonella, Listeria monocytogenes (LM), and other targets (e.g., Listeria spp. and Salmonella enterica serovar Newport). Surrogate trees were used to visualize hierarchical associations identified by the forest analyses. Salmonella and LM prevalence was 5.3% (49/920) and 2.3% (21/920), respectively. The likelihood of isolating Salmonella was highest in water samples collected from the Eastern Shore of Virginia with a dew point of >9.4°C. The likelihood of isolating LM was highest in water samples collected in winter from sites where <36% of the land use within 122 m was forest wetland cover. Conditional forest results were consistent with the mixed models, which also found that the likelihood of detecting Salmonella and LM differed between sample type, region, and season. These findings identified factors that increased the likelihood of isolating Salmonella- and LM-positive samples in produce production environments and support preharvest mitigation strategies on a regional scale. IMPORTANCE This study sought to examine different growing regions across the state of Virginia and to determine how factors associated with pathogen prevalence may differ between regions. Spatial and temporal data were modeled to identify factors associated with an increased pathogen likelihood in various on-farm sources. The findings of the study show that prevalence of Salmonella and L. monocytogenes is low overall in the produce preharvest environment but does vary by space (e.g., region in Virginia) and time (e.g., season), and the likelihood of pathogen-positive samples is influenced by different spatial and temporal factors. Therefore, the results support regional or scale-dependent food safety standards and guidance documents for controlling hazards to minimize risk. This study also suggests that water source assessments are important tools for developing monitoring programs and mitigation measures, as spatiotemporal factors differ on a regional scale.

Transmission Scenarios of Listeria monocytogenes on Small Ruminant On-Farm Dairies.

Listeria monocytogenes can cause severe foodborne infections in humans and invasive diseases in different animal species, especially in small ruminants. Infection of sheep and goats can occur via contaminated feed or through the teat canal. Both infection pathways result in direct (e.g., raw milk from an infected udder or fresh cheese produced from such milk) or indirect exposure of consumers. The majority of dairy farmers produces a high-risk product, namely fresh cheese made from raw ewe's and goat's milk. This, and the fact that L. monocytogenes has an extraordinary viability, poses a significant challenge to on-farm dairies. Yet, surprisingly, almost no scientific studies have been conducted dealing with the hygiene and food safety aspects of directly marketed dairy products. L. monocytogenes prevalence studies on small ruminant on-farm dairies are especially limited. Therefore, it was our aim to focus on three main transmission scenarios of this important major foodborne pathogen: (i) the impact of caprine and ovine listerial mastitis; (ii) the significance of clinical listeriosis and outbreak scenarios; and (iii) the impact of farm management and feeding practices.

Enhanced training, employee-led deep cleans, and complete sanitation execution are effective Listeria monocytogenes controls in retail produce environments

Our recent study on Listeria monocytogenes prevalence and persistence in 30 retail produce environments across seven U.S. states revealed that some produce departments harbored persistent L. monocytogenes isolates. Alongside food safety and sanitation experts in the retail grocery sector our research team implemented an intervention consisting of re-training on and reinforcement of sanitation standard operating procedures (SSOPs) concurrent with an employee-led deep clean in eight departments with high prevalence of L. monocytogenes. SSOPs were unchanged, apart from adding emphasis on known harborage sites. The goal was to improve the frequency and quality of sanitation tasks to their prescribed levels. Training was reinforced with regular consultative visits including weekly audits of a subset of seven departments in order to elucidate factors driving intervention outcomes. We found that our approach was able to decrease L. monocytogenes prevalence overall, however, only three of eight stores significantly reduced their prevalence. Audits revealed that the presence of foam squeegees, damaged equipment or plumbing leaks was predictive of intervention outcome. A significant reduction in prevalence on food contact surfaces (FCS) was observed; we saw no FCS positive samples post-intervention. The monthly prevalence on non-food contact surfaces wasn't significantly reduced post-intervention until the third month of sampling. Survey data demonstrated that cross-contamination risk and timing of sanitation execution were significant behavioral variables influencing L. monocytogenes prevalence. Collectively, the data indicate that a combination of enhanced retraining on sanitation and cross-contamination, employee-led deep cleans, consultative audits, a cleaning tools program, and equipment maintenance together can reduce the prevalence of L.monocytogenes in retail produce departments.

Sanitation and customer service strategies implemented during COVID-19 correlated with lower Listeria monocytogenes prevalence in retail delicatessens

The purpose of this study was to evaluate the prevalence of L. monocytogenes and validate a predictive statistical model for assessing L. monocytogenes contamination risk at retail which coincided with the COVID-19 pandemic. Ten environmental samples per store were collected during daily operations two times over 12 months in 44 retail deli departments across seven states. Each sample was tested for L. monocytogenes and other Listeria spp.; confirmation was conducted via whole genome sequencing and PCR amplification of the sigB gene, respectively. A 117-question survey was developed based on previous work in retail deli departments and distributed to store or deli managers once during sampling. Survey questions were correlated with L. monocytogenes using linear regression and ANOVA statistical models. A Firth's bias-corrected logistic regression model was developed to predict the probability of a deli having high L. monocytogenes prevalence (>10%). L. monocytogenes prevalence decreased from 5.8% prior to March 2020 to 4.3% during the pandemic. Squeegees and standing water had the highest L. monocytogenes prevalence of all sampling sites in the study; L. monocytogenes was not found on scales or trash cans. Cleaning and sanitation protocols most highly correlated with L. monocytogenes prevalence. The logistic regression model accurately predicted high L. monocytogenes prevalence in 10/17 stores with high prevalence (α < 0.0001, β = 0.1186) during the COVID-19 pandemic. The COVID-19 pandemic heightened awareness of disease transmission and the importance of sanitation to prevent spread of SARS-CoV-2. This study indicates that there were additional benefits to enhanced sanitation and changes in service practices (i.e., reduced L. monocytogenes prevalence and therefore reduced risk of transmission to foods) beyond decreasing SARS-CoV-2 transmission. • Retailers made significant changes in stores in response to the COVID-19 pandemic. • Proper sanitation programs were highly correlated with lower L. monocytogenes . • L. monocytogenes was still highly prevalent in some retail delis during COVID-19. • The predictive model underpredicted high risk stores under COVID-19 sanitation and changes.

Nonhemolytic Listeria monocytogenes-Prevalence Rate, Reasons Underlying Atypical Phenotype, and Methods for Accurate Hemolysis Assessment.

Listeria monocytogenes is a foodborne pathogen that typically presents β-hemolytic activity. However, there are literature reports indicating that L. monocytogenes strains are sometimes nonhemolytic or their zones of hemolysis are perceivable only after removal of the colonies from the agar plate. Nonhemolytic L. monocytogenes are most commonly encountered in food products, but some have also been detected in clinical samples. Usually, atypical bacteria of this species belong to serotype 1/2a. Mutations of the prfA gene sequence are the most common reason for changed phenotype, and mutations of the hly gene are the second most common cause. There are also reports that the methodology used for detecting hemolysis may influence the results. Sheep or horse blood, although most commonly used in modern studies, may not allow for the production of clear hemolytic zones on blood agar, whereas other types of blood (guinea pig, rabbit, piglet, and human) are more suitable according to some studies. Furthermore, the standard blood agar plate technique is less sensitive than its modifications such as bilayer or top-layer (overlay) techniques. The microplate technique (employing erythrocyte suspensions) is probably the most informative when assessing listerial hemolysis and is the least susceptible to subjective interpretation.

Ruminant-associated Listeria monocytogenes isolates belong preferentially to dairy-associated hypervirulent clones: a longitudinal study in 19 farms.

Studies have shown that ruminants constitute reservoirs of Listeria monocytogenes, but little is known about the epidemiology and genetic diversity of this pathogen within farms. Here we conducted a large-scale longitudinal study to monitor Listeria spp. in 19 dairy farms during three consecutive seasons (N= 3251 samples). L. innocua was the most prevalent species, followed by L. monocytogenes. Listeria monocytogenes was detected in 52.6% of farms and more frequently in cattle (4.1%) and sheep (4.5%) than in goat farms (0.2%). Lineage I accounted for 69% of L. monocytogenes isolates. Among animal samples, the most prevalent sublineages (SL) and clonal complexes (CC) were SL1/CC1, SL219/CC4, SL26/CC26 and SL87/CC87, whereas SL666/CC666 was most prevalent in environmental samples. Sixty-one different L. monocytogenes cgMLST types were found, 28% common to different animals and/or surfaces within the same farm and 21% previously reported elsewhere in the context of food and human surveillance. Listeria monocytogenes prevalence was not affected by farm hygiene but by season: higher prevalence was observed during winter in cattle, and during winter and spring in sheep farms. Cows in their second lactation had a higher probability of L. monocytogenes faecal shedding. This study highlights dairy farms as a reservoir for hypervirulent L. monocytogenes.

Prevalence of Listeria Species and Listeria monocytogenes on Raw Produce Arriving at Frozen Food Manufacturing Facilities

The ubiquity of Listeria monocytogenes in the environment affects the food industry and presents concerns for frozen food facilities. This study determined the prevalence and numbers of Listeria species and L. monocytogenes on raw produce arriving at frozen food facilities. Raw produce was collected using multilevel blinding protocols to ensure anonymity of participants and avoid traceback. Five raw vegetables were selected: corn, carrots, green beans, peas, and spinach. Raw products were collected after arrival at the facilities but before cleaning or other preprocessing steps that are typically performed inside the facility. The U.S. Food and Drug Administration's Bacteriological Analytical Manual method for detection of Listeria spp. and L. monocytogenes was followed, with PCR screening followed by selective plating methods. Listeria numbers were estimated from positive samples using the most-probable-number (MPN) methodology. A total of 290 samples were collected, with 96 and 17 samples positive for Listeria spp. (33.1%) and L. monocytogenes (5.9%), respectively. Enumeration data for the 96 Listeria spp. samples indicated 82 samples had greater than 100 MPN of Listeria spp. per g and 14 samples had less than 100 MPN Listeria spp. per g. The prevalence of Listeria spp. varied by commodity: spinach (66.7%), peas (50%), corn (32.2%), green beans (22.2%), and carrots (13%). L. monocytogenes prevalence was determined in corn (13.6%), peas (6.3%), and green beans (4.2%) arriving at processing facilities. Such data were previously unavailable to frozen vegetable processors and are valuable in implementing process control standards. The prevalence and pathogen concentration data from raw commodities found in this study can provide the industry with information to conduct more accurate quantitative risk assessments and a baseline to model and target appropriate pathogen reduction steps during processing.

A global perspective of antibiotic-resistant Listeria monocytogenes prevalence in assorted ready to eat foods: A systematic review.

Background and Aim:Listeria monocytogenes in ready-to-eat (RTE) foods remains consistently under-reported globally. Nevertheless, several independent studies conducted to investigate have elucidated the prevalence and antibiotic resistance profiles of L. monocytogenes in RTE-associated foods and their antibiotic resistance profiles. Given the rapid increase in consumption of RTE foods of both animal and plant origin, it is imperative to know the prevalence deductive data focusing on how much of L. monocytogenes is present in RTE foods, which is critical for food safety managers and retailers to assess the possible risk posed to end-users. In addition, valuable insight and another angle to the depth of the problem, we conducted a systematic review and meta-analysis to synthesize available data regarding the prevalence of L. monocytogenes in RTE foods and antibiotic resistance profiles.Materials and Methods:We conducted a meta-analysis study of L. monocytogenes and antibiotic resistance to clinically relevant antibiotics to determine the extent of L. monocytogenes contamination in RTE foods and antibiotic resistance profiles. The primary search terms, also known as keywords used, were restricted to peer-reviewed and review articles, and databases, including Google Scholars, Science-Direct, and Scopus, were searched. The inclusion of articles meeting eligibility criteria published between 2010 and 2020 after title, abstract, and full article screening. Data analysis was performed at multiple stages using quantitative meta-analysis reviews.Results:L. monocytogenes pooled proportion/prevalence was highest in chicken products determined at (22%) followed by various but uncategorized RTE foods at 21%. Regarding antibiotic resistance, profiling’s highest pooled prevalence resistance was observed in penicillin at 80% resistance, followed by cephalosporin at 47%.Conclusion:Within its limitations, this study has attempted to provide insight into the pooled proportion/prevalence of L. monocytogenes in RTE foods and the antibiotic resistance profile at the global level. Determining the proportion/prevalence of L. monocytogenes in RTE foods across the globe and antibiotic resistance profile is essential for providing quality food and reducing public health problems due to unsuccessful treatment of foodborne illness. This study provides insight into the pooled prevalence of L. monocytogenes in RTE foods and the antibiotic resistance profile. The results of this study partly endeavored to help appropriate authorities strengthen their preventive measures on specific RTE foods that are most likely to be contaminated with L. monocytogenes and antibiotic resistance profiles.

A Systematic Review of Listeria Species and Listeria monocytogenes Prevalence, Persistence, and Diversity throughout the Fresh Produce Supply Chain.

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.

Prevalence and Distribution of Listeria monocytogenes in Three Commercial Tree Fruit Packinghouses.

A 2-year longitudinal study of three tree fruit packinghouses was conducted to determine the prevalence and distribution of Listeria monocytogenes. Samples were collected from 40 standardized non-food-contact surface locations six different times over two 11-month production seasons. Of the 1,437 samples collected, the overall prevalence of L. monocytogenes over the course of the study was 17.5%. Overall prevalence did not differ significantly (p > 0.05) between each year. However, values varied significantly (p ≤ 0.05) within each production season following packing activity levels; increasing in the fall, peaking in early winter, and then decreasing through spring. L. monocytogenes was most often found in the packing line areas, where moisture and fruit debris were commonly observed and less often in dry cold storage and packaging areas. Persistent contamination was attributed to the inability of water drainage systems to prevent moisture accumulation on floors and equipment during peak production times and uncontrolled employee and equipment traffic throughout the facility. This is the first multiyear longitudinal surveillance study to compare L. monocytogenes prevalence at standardized sample sites common to multiple tree fruit packinghouses. Recommendations based on our results will help packinghouse operators to identify critical areas for inclusion in their L. monocytogenes environmental monitoring programs.

Listeria monocytogenes Prevalence Varies More within Fields Than between Fields or over Time on Conventionally Farmed New York Produce Fields

Past studies have shown that the on-farm distribution of Listeria monocytogenes is affected by environmental factors (e.g., weather). However, most studies were conducted at large scales (e.g., across farms), whereas few studies examined drivers of L. monocytogenes prevalence at smaller scales (e.g., within a single field). This study was performed to address this knowledge gap by (i) tracking L. monocytogenes distribution in two fields on one farm over a growing season and (ii) identifying factors associated with L. monocytogenes isolation from drag swab, soil, and agricultural water samples. Overall, L. monocytogenes was detected in 78% (21 of 27), 19% (7 of 36), and 8% (37 of 486) of water, drag swab, and soil samples, respectively. All isolates were characterized by pulsed-field gel electrophoresis. Of the 43 types identified, 14 were isolated on multiple sampling visits and/or from multiple sample types, indicating persistence in or repeated introduction into the farm environment during the study. Our findings also suggest that L. monocytogenes prevalence, even at the small spatial scale studied here, (i) was not uniform and (ii) varied more within fields than between fields or over time. This is illustrated by plot (in-field variation), field (between-field variation), and sampling visit (time), accounting for 18, 2, and 3% of variance in odds of isolating L. monocytogenes, respectively. Moreover, according to random forest analysis, water-related factors were among the top-ranked factors associated with L. monocytogenes isolation from all sample types. For example, the likelihood of isolating L. monocytogenes from drag and soil samples increased monotonically as rainfall increased. Overall, findings from this single-farm study suggests that mitigation strategies for L. monocytogenes in produce fields should focus on water-associated risk factors (e.g., rain and distance to water) and be tailored to specific high-risk in-field areas.

Listeria monocytogenes is prevalent in retail produce environments but Salmonella enterica is rare

The purpose of this study was to determine the prevalence of Listeria monocytogenes and Salmonella enterica in retail produce environments and to elucidate possible ecological niches. Thirty environmental samples per store were collected during daily operations monthly for six months in 30 retail produce departments across seven states. Selected samples were serially diluted and plated to determine aerobic plate count. Each sample was tested for L. monocytogenes and S. enterica using ROKA Atlas LmG2 and SEN assays, respectively. A total of 5,112 samples were tested for each pathogen. S. enterica was found during one sampling event in a single store; less than 0.1% of samples were positive overall. A total of 4.4% environmental samples tested positive for L. monocytogenes. L. monocytogenes was present on 8.1% of non-food contact surfaces and 1.6% of food contact surfaces tested; L. monocytogenes prevalence was highly variable among stores. Most of the positive L. monocytogenes samples were found in drains, floors, squeegees, or standing water. Genetically similar L. monocytogenes clones were found in multiple stores across multiple states. The odds of detecting L. monocytogenes increased 1.8-fold for every 1-log increase in APC (p < 0.0001). This is the first study to investigate prevalence and persistence of L. monocytogenes and S. enterica in retail produce environments. Our data suggest that some, but not all retail produce environments have high L. monocytogenes prevalence, which may cross-contaminate produce. Sites heavily contaminated with L. monocytogenes indicate potential targets for sanitation operating procedures and food safety management strategies. However, S. enterica prevalence is very low and likely due to transient contamination. Further, APC may be a cost-effective environmental monitoring tool that could indicate an environment capable of harboring L. monocytogenes.

Predictive risk models combined with employee- and management-implemented SSOPs identified and reduced Listeria monocytogenes prevalence in retail delis

Ready-to-eat (RTE) deli meats sliced at retail are predicted to cause 83% of deli meat-associated listeriosis cases annually. While Listeria monocytogenes is commonly found in delis, environmental prevalence varies by store (0–40%). A deep clean sanitation standard operating procedure (SSOP) executed by a third-party cleaning service immediately reduced L. monocytogenes prevalence in delis, but reductions were not sustained over time. The purpose of this study was to assess the efficacy of a L. monocytogenes predictive risk model and a subsequent deep-clean SSOP (deep clean) conducted by store employees and management complemented with training and facilities improvements all aimed to reduce L. monocytogenes prevalence in stores with known high L. monocytogenes prevalence and evidence of persistence. Fifty delis among six states were screened using a predictive logistic regression model that estimates the probability of high L. monocytogenes prevalence in a deli. The model identified 13 stores with potentially high L. monocytogenes prevalence; seven stores were confirmed and enrolled for further study. Retail employees executed deep clean; additional interventions (e.g., facilities improvements, training) were incorporated in stores. Environmental samples (n = 20) were collected immediately before and after, and for six months post-deep clean. Deep cleans immediately reduced L. monocytogenes prevalence in six of seven stores tested. A total of 21/138 (15.2%) samples before and 8/139 (5.8%) samples after deep-cleaning were positive for L. monocytogenes, with a marginal 16.0% decrease on non-food-contact surfaces (NFCS) immediately after deep clean (p = 0.0309, αadj = 0.0125) and a marginal 10.8% on NFCS during follow-up (p = 0.0337, αadj = 0.0125). Employee executed deep cleans with training, education, and maintenance programs can reduce environmental L. monocytogenes prevalence in retail delis, a pivotal part of preventing subsequent cross-contamination to RTE deli meats.

The prevalence of Listeria monocytogenes in meat products in China: A systematic literature review and novel meta-analysis approach

Meat products are commonly regarded as one of the main sources of human listeriosis caused by Listeria monocytogenes. The objective of this study was to estimate the prevalence of L. monocytogenes in a range of meat products from 24 different Chinese regions by using meta-analysis of literature data and a novel sensitivity analysis approach. A total of 112 publications from five databases, published between 1 January 2007 and 31 December 2017, were systematically selected for relevance and covered meat products sampled between 2000 and 2016. Estimated by the random-effects model, the pooled prevalence of L. monocytogenes was 8.5% (95% CI: 7.1%–10.3%) in raw meats and 3.2% (95% CI: 2.7%–3.9%) in ready-to-eat (RTE) meats. The prevalence differed from high to low among raw meats including prefabricated raw meats 12.6% (95% CI: 6.9%–21.7%), fresh pork 11.4% (95% CI: 8.6%–14.9%), fresh beef 9.1% (95% CI: 6.3%–13.0%), fresh poultry 7.2% (95% CI:4.9%–10.4%), frozen raw meats 7.2% (95% CI: 5.7%–9.0%), and fresh mutton 5.4% (95% CI: 2.5%–11.0%). A higher L. monocytogenes prevalence level was shown in the meat products from central and northeastern China provincial regions. The entropy-based sensitivity analysis utilized in the meta-analysis indicated that the sampling period and location were two critical factors influencing the prevalence level of L. monocytogenes in meat products. A better understanding of differences in prevalence levels per geographic region and between meat product sources may allow the competent authorities, industry, and other relevant stakeholders to tailor their interventions to control the occurrence of L. monocytogenes in meat products effectively.