Infrastructure, sanitation, and management practices impact Listeria monocytogenes prevalence in retail grocery produce environments

Developing an Agent-Based Model that Predicts Listeria spp. Transmission to Assess Listeria Control Strategies in Retail Stores

Contamination of fresh produce with Listeria monocytogenes can occur throughout the supply chain, including at retail, where Listeria spp., including L. monocytogenes, may be introduced and spread via various routes. However, limited tools are available for retailers to assess practices that can enhance control of Listeria transmission to fresh produce. Therefore, we developed an agent-based model that can simulate Listeria transmission in retail produce sections to optimize environmental sampling programs and evaluate control strategies. A single retail store was used as a model environment, in which various routes of Listeria introduction into and transmission between environmental surfaces were modeled. Model prediction (i.e., Listeria prevalence) was validated using a published longitudinal study for all surfaces that were included in both the model and the validation data. Sensitivity analysis using the Partial Rank Correlation Coefficient showed that (i) initial Listeria concentration from incoming produce, (ii) transfer coefficient from produce to employee's hands, and (iii) transfer coefficient from consumer to produce were the top three parameters that were significantly (p < 0.0018) associated with the mean Listeria prevalence across all agents, suggesting that the accuracy of these parameters are important for prediction of overall Listeria prevalence at retail. Cluster analysis grouped agents with similar contamination patterns into six unique clusters; this information can be used to optimize the sampling plans for retail environments. Scenario analysis suggested that (i) more stringent supplier control as well as (ii) practices reducing Listeria transmission via consumer's hands may have the largest impact on reducing finished product contamination. Overall, we show that an agent-based model can serve as a foundational tool to help with decision-making on Listeria control strategies at retail.

Food Safety and Management System Audits in Food Retail Chain Stores in Greece

The present study aimed to assess the performance of food safety management systems in food retail stores via audits to reveal potential areas of improvement and to find out possible corrective actions to suggest to the top management. Two cycles of on-site audits took place in 106 stores to assess the requirements and hygiene conditions. After the first cycle of audits, improvements were suggested to the top management, and a second cycle of audits took place after a reasonable time. In the checklist, we recorded the temperatures of retail refrigerators and the scores from the inspection of hygiene and HACCP documentation. In the A' audit, the percentage of stores that had higher temperatures than the critical limits was equal to 51%, and those temperatures occurred in the refrigerators for salads, followed by the refrigerators for deli meat, yogurts and desserts. In the B' audit, only the refrigerators for salads exhibited percentages that were statistically significant lower (p-value < 0.05), and the stores were improved after the audit. High percentages of high-scoring stores were observed in the A' and B' audit in the inspection of HACCP documentation, although there was not a statistically significant improvement observed (p-value > 0.05). In the hygiene inspection, statistically significant improvement with 95% confidence appeared for "Refrigerator's products appearance", "Storage cleanliness", and "Grocery shelf cleanliness". The highest number of non-conformities without statistically significant improvement was found for "Checking temperatures of the receiving products" and "Labeling of fruit store products", with the percentages being lower than 15% in both of the audit cycles. Many employees of the stores did not check and record the temperatures of receiving products from suppliers. In addition, the storage of spoiled products beneath fresh products for selling in the same refrigerator is not a good practice. Greater efforts must be made by top management and employees to maintain and distribute food products in the best and safest possible hygiene conditions.

Insight into the Postbiotic Potential of the Autochthonous Bacteriocin-Producing Enterococcus faecium BGZLM1-5 in the Reduction in the Abundance of Listeria monocytogenes ATCC19111 in a Milk Model

This study aimed to explore the probiogenomic characteristics of artisanal bacteriocin-producing Enterococcus faecium BGZLM1-5 and its potential application in reducing Listeria monocytogenes in a milk model. The BGZLM1-5 strain was isolated from raw cow's milk from households in the Zlatar Mountain region. The whole genome sequencing approach and bioinformatics analyses reveal that the strain BGZLM1-5 is non-pathogenic to humans. Bacteriocin-containing supernatant was thermally stable and antimicrobial activity retained 75% of the initial activity compared with that of the control after treatment at 90 °C for 30 min. Antimicrobial activity maintained relative stability at pH 3-11 and retained 62.5% of the initial activity compared with that of the control after treatment at pH 1, 2, and 12. The highest activity of the partially purified bacteriocin was obtained after precipitation at 40% saturation with ammonium sulfate and further purification by mixing with chloroform. Applying 3% and 5% (v/v) of the bacteriocin-containing supernatant and 0.5% (v/v) of the partially purified bacteriocin decreased the viable number of L. monocytogenes ATCC19111 after three days of milk storage by 23.5%, 63.5%, and 58.9%, respectively.

The effect of crisping, misting, and storage temperature on the survival or growth of Listeria monocytogenes and natural psychrotrophic bacteria on romaine lettuce

L. monocytogenes has been linked to fresh produce and detected in the retail environment. This study simulated the retail practices (crisping, misting, and storage) of unbagged whole heads of romaine lettuce to determine the growth of L. monocytogenes and natural psychrotrophic microflora. Three nalidixic acid-resistant strains of L. monocytogenes strains were inoculated to each head of lettuce (≈5 log10 CFU/g). For crisping, 24 heads of romaine lettuce were immersed in tap water or electrolyzed water (EW; free chlorine: 55 ppm) for 5 min, followed by holding at 5 °C for 2 h. The water-crisped (WC), EW crisped (EWC), or non-crisped (NC) lettuces were placed in a commercial refrigerated cabinet for misting at 5 °C. After 24-h misting, heads of lettuce were placed in perforated drain boxes with cover at 5 °C or 15 °C. The tap water and EW crisping achieved 1.3 and 2.9 log10 CFU/g reduction of L. monocytogenes, respectively. Approximately 1 log additional reduction of L. monocytogenes in the non-crisped lettuce was shown after misting (p < 0.05), but no significant effect of misting on the population of L. monocytogenes was observed on WC or EWC lettuces (p > 0.05). Regardless of the storage temperature or misting, L. monocytogenes populations remained significantly (p < 0.05) lower on EWC lettuce than NC and WC lettuce. On days 4 and 7 of storage, the natural psychrotrophic bacteria on lettuce stored at 5 °C was significantly lower than stored at 15 °C, and its population was not affected by crisping and misting. These provide insight into the influence of retail lettuce handling practices on the risk of L. monocytogenes.

A review of Canadian and international food safety systems: Issues and recommendations for the future

In January 2019, the Safe Food for Canadians Act/Safe Food for Canadians regulations (heretofore identified as SFCR) came into force across Canada and brought a more streamlined process to food safety practice in Canada. Food trade and production processes have evolved rapidly in recent decades, as Canada imports and exports food products; therefore it is critically important to remain aware of the latest advances responding to a range of challenges and opportunities in the food safety value chain. Looking through the optics of the recent SFCR framework, this paper places the spotlight on leading domestic and international research and practices to help strengthen food safety policies of the future. By shedding some light on new research, we also draw attention to international developments that are noteworthy, and place those in context as to how new Canadian food safety policy and regulation can be further advanced. The paper will benchmark Canada through a review study of food safety best practices by juxtaposing (i) stated aspirations with, (ii) actual performance in leading Organization for Economic Cooperation and Development (OECD) jurisdictions.

Lytic Capacity Survey of Commercial Listeria Phage Against Listeria spp. with Varied Genotypic and Phenotypic Characteristics

Listeria monocytogenes is regularly isolated from food processing environments and is endemic in some facilities. Bacteriophage have potential as biocontrol strategies for L. monocytogenes. In this study, the lytic capacity of a commercial Listeria phage cocktail was evaluated against a library of 475 Listeria spp. isolates (426 L. monocytogenes and 49 other Listeria spp.) with varied genotypic and phenotypic characteristics. The lytic capacity of the Listeria phages was measured by spot assays where lysis was scored on a scale of 0-3 (0 = no lysis; 1 = slight lysis; 2 = moderate lysis; 3 = confluent lysis). Only 5% of all tested Listeria spp. isolates, including L. monocytogenes, were either moderately or highly susceptible (score 2 or 3) to lysis by Listeria phage when scores were averaged across temperature and phage concentration; 155 of 5700 treatment (multiplicity of infection [MOI] and temperature) and characteristic (genotype, sanitizer tolerance, and attachment capacity) combinations resulted in confluent lysis (score = 3). Odds ratios for susceptibility to lysis were calculated using multinomial logistic regression. The odds of susceptibility to lysis by phage decreased (p < 0.05) if the L. monocytogenes isolate was previously found to persist or if the phage-bacteria culture was incubated at 30°C; neither isolate persistence or temperature was significant (p ≥ 0.05) when all factors were considered. In addition, lytic efficacy varied (p < 0.05) among pulse field gel electrophoresis (PFGE) pulsotypes and may be affected by host MOI (p < 0.05). There was no effect (p > 0.05) of attachment capacity or sanitizer tolerance on phage susceptibility. This study underscores the complexity of using Listeria phage as a biocontrol for Listeria spp. in food processing facilities and highlights that phage susceptibility is most greatly impacted by genotype. Further studies are needed to evaluate these findings within a processing environment.

Determining the Potential Food Safety Risks Associated with Dropped Produce on Floor Surfaces in Grocery Stores

ABSTRACT

Grocery stores handle fresh produce in large quantities daily. According to the Food and Drug Administration Food Code, food is to be stored at least 15 cm above the floor, and all foods shall be protected from any source of contamination or otherwise discarded. It is reported in the literature that dropped produce could be a potential source of microbial contamination. Both consumers and employees often drop produce on the floor and then place it back into a display case or bin, which could potentially serve as a source of contamination. This study aims to determine the bacterial transfer rate on different produce types when dropped for various contact times onto floor surfaces contaminated with Listeria monocytogenes. Apples, peaches, and romaine lettuce were dropped separately onto carpet and tile surfaces from a distance of 1 m and held for 5 s, 1 min, 10 min, 1 h, and 4 h. Results showed that transfer from all produce types occurred from both the carpet (10.56%) and tile (3.65%) surfaces. Still, percent transfer was not statistically significant among different times used in this study (P > 0.05). Dropped romaine lettuce had the most transfer (28.97%) from both the surfaces combined, followed by apples (8.80%) and peaches (7.32%) with minimal transfer. Even with a low transfer level, grocery stores should include signage to alert consumers not to pick up dropped produce and should train their employees accordingly.

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