Evaluation of environmental sampling methods and rapid detection assays for recovery and identification of Listeria spp. from meat processing facilities

European survey and evaluation of sampling methods recommended by the standard EN ISO 18593 for the detection of Listeria monocytogenes and Pseudomonas fluorescens on industrial surfaces

The ready-to-eat products can be contaminated during processing by pathogen or spoilage bacteria, which persist in the industrial environment. Some bacterial species are able to form biofilms which protect them from environmental conditions. To check the bacterial contamination of the surfaces in the food industries, the professionals must regularly use surface sampling methods to detect the pathogen such as Listeria monocytogenes or the spoilage such as Pseudomonas fluorescens. In 2010, we designed and carried out a European survey to collect surface sampling information to detect or enumerate L. monocytogenes in food processing plants. A total of 137 questionnaires from 14 European Union Member States were returned. The outcome of this survey showed that the professionals preferred friction sampling methods with gauze pad, swab and sponges versus contact sampling methods. After this survey, we compared the effectiveness of these three friction sampling methods and the contact plates, as recommended in the standard EN ISO 18593 that was revised in 2018, on the recovery of L. monocytogenes and of P. fluorescens in mono-specie biofilms. This study showed no significant difference between the effectiveness of the four sampling methods to detach the viable and culturable bacterial population of theses mono-specie biofilms.

Prevalence of Listeria spp. in produce handling and processing facilities in the Pacific Northwest

Listeria monocytogenes is a significant concern for the produce industry; however, there is limited information to support the practical decision-making to mitigate this risk. This study investigated the prevalence of Listeria spp. and L. monocytogenes in seven produce handling and processing (PHP) facilities in the Pacific Northwest. PHP facilities were defined as facilities that receive raw agricultural commodities and further handle, pack, wash, or process prior to distribution into the retail sector. Environmental swabs (n = 50/facility) were collected in high-risk areas (e.g., near raw product entry points) from seven PHP facilities over two visits. Listeria spp. were isolated using modified ISO 11290-1 method and speciated with Microgen® Listeria-ID. Listeria spp., including L. monocytogenes, were found in 5/7 PHP. Prevalence of Listeria spp. ranged from 2% to 26% in these five facilities. Drains, entry areas, and portable equipment consistently tested positive for Listeria spp. during active production. Two additional sampling rounds (n = 50/round) were conducted in the highest prevalence facility (Facility #1). Overall, Listeria spp. were detected in 44/150 (29.3%) swabs collected from Facility #1. This study demonstrated the high prevalence of Listeria spp. near raw product entry points across PHP facilities.

Design Elements of Listeria Environmental Monitoring Programs in Food Processing Facilities: A Scoping Review of Research and Guidance Materials

Occurrence of Listeria monocytogenes (Lm), the causative agent of listeriosis, in food processing facilities presents considerable challenges to food producers and food safety authorities. Design of an effective, risk-based environmental monitoring (EM) program is essential for finding and eliminating Lm from the processing environment to prevent product contamination. A scoping review was conducted to collate and synthesize available research and guidance materials on Listeria EM in food processing facilities. An exhaustive search was performed to identify all available research, industry and regulatory documents, and search results were screened for relevance based on eligibility criteria. After screening, 198 references were subjected to an in-depth review and categorized according to objectives for conducting Listeria sampling in food processing facilities and food sector. Mapping of the literature revealed research and guidance gaps by food sector, as fresh produce was the focus in only 10 references, compared to 72 on meat, 52 on fish and seafood, and 50 on dairy. Review of reported practices and guidance highlighted key design elements of EM, including the number, location, timing and frequency of sampling, as well as methods of detection and confirmation, and record-keeping. While utilization of molecular subtyping methods is a trend that will continue to advance understanding of Listeria contamination risks, improved study design and reporting standards by researchers will be essential to assist the food industry optimize their EM design and decision-making. The comprehensive collection of documents identified and synthesized in this review aids continued efforts to minimize the risk of Lm contaminated foods.

Tracking cross-contamination transfer dynamics at a mock retail deli market using GloGerm

Ready-to-eat (RTE) deli meats are considered a food at high risk for causing foodborne illness. Deli meats are listed as the highest risk RTE food vehicle for Listeria monocytogenes. Cross-contamination in the retail deli market may contribute to spread of pathogens to deli meats. Understanding potential cross-contamination pathways is essential for reducing the risk of contaminating various products. The objective of this study was to track cross-contamination pathways through a mock retail deli market using an abiotic surrogate, GloGerm, to visually represent how pathogens may spread through the deli environment via direct contact with food surfaces. Six contamination origination sites (slicer blade, meat chub, floor drain, preparation table, employee's glove, and employee's hands) were evaluated separately. Each site was inoculated with 20 ml of GloGerm, and a series of standard deli operations were completed (approximately 10 min of work). Photographs were then taken under UV illumination to visualize spread of GloGerm throughout the deli. A sensory panel evaluated the levels of contamination on the resulting contaminated surfaces. Five of the six contamination origination sites were associated with transfer of GloGerm to the deli case door handle, slicer blade, meat chub, preparation table, and the employee's gloves. Additional locations became contaminated (i.e., deli case shelf, prep table sink, and glove box), but this contamination was not consistent across all trials. Contamination did not spread from the floor drain to any food contact surfaces. The findings of this study reinforce the need for consistent equipment cleaning and food safety practices among deli workers to minimize cross-contamination.

Impact of processing method on recovery of bacteria from wipes used in biological surface sampling

Environmental sampling for microbiological contaminants is a key component of hygiene monitoring and risk characterization practices utilized across diverse fields of application. However, confidence in surface sampling results, both in the field and in controlled laboratory studies, has been undermined by large variation in sampling performance results. Sources of variation include controlled parameters, such as sampling materials and processing methods, which often differ among studies, as well as random and systematic errors; however, the relative contributions of these factors remain unclear. The objective of this study was to determine the relative impacts of sample processing methods, including extraction solution and physical dissociation method (vortexing and sonication), on recovery of Gram-positive (Bacillus cereus) and Gram-negative (Burkholderia thailandensis and Escherichia coli) bacteria from directly inoculated wipes. This work showed that target organism had the largest impact on extraction efficiency and recovery precision, as measured by traditional colony counts. The physical dissociation method (PDM) had negligible impact, while the effect of the extraction solution was organism dependent. Overall, however, extraction of organisms from wipes using phosphate-buffered saline with 0.04% Tween 80 (PBST) resulted in the highest mean recovery across all three organisms. The results from this study contribute to a better understanding of the factors that influence sampling performance, which is critical to the development of efficient and reliable sampling methodologies relevant to public health and biodefense.

Comparison of sampling procedures for recovery of Listeria monocytogenes from stainless steel food contact surfaces

A number of techniques exist for microbiological sampling of food processing environments in food industries. In the present study the efficacies of nine sampling procedures for the recovery of Listeria monocytogenes from food contact surfaces, including a new sampling device consisting of a miniroller, were evaluated and compared. A stainless steel table was inoculated with L. monocytogenes strain 935 (serovar 4b, human origin) and L. monocytogenes strain 437/07 (serovar 1/2b, food origin), at 10(5) CFU/100 cm(2). L. monocytogenes strain 935 was best recovered with the minirollers (recovery of up to 6.27%), while poor recoveries (<0.30%) were obtained with the towel (one-ply composite tissue), alginate swab, metallic swab, and Petrifilm methods. In the case of L. monocytogenes strain 437/07 the replicate organism detection and counting (RODAC) ALOA contact plates yielded the best recoveries (4.15%), followed by the minirollers (up to 1.52%). Overall, recovery percentages with the minirollers were higher with stomacher homogenization than with Vibromatic agitation. The recovery percentages obtained for the Listeria strain of human origin were higher than those obtained with the food strain for all sampling procedures except Petrifilm and RODAC ALOA. With the miniroller device coated with wool fiber, the recovery of L. monocytogenes can be improved from 2 to 17 times over recoveries obtained with the sponge and cotton swab. This is the first report of a miniroller device for microbiological sampling in the available literature. The novel sampling procedure is convenient to apply on surfaces, is cost-effective, and results in better recovery of L. monocytogenes than do the conventional methods.

Occurrence and distribution of listeria species in facilities producing ready-to-eat foods in British Columbia, Canada

In British Columbia (BC), Canada, food processing facilities licensed under provincial authority are not required to sample for Listeria monocytogenes in food products or processing environments. In 2009, we conducted a survey of dairy, fish, and meat facilities under BC authority to estimate the prevalence of Listeria spp. and L. monocytogenes in ready-to-eat (RTE) foods and production environments. From August to October, 250 RTE food samples and 258 swabs from the food processing environments of 43 facilities were collected. Standard culture methods were applied to both food samples and swabs. Of swabs collected from all 258 environmental surfaces, 15% were positive for Listeria spp. Significantly (P, 0.001) more fish facilities than dairy and meat facilities had food contact surfaces contaminated with Listeria spp. L. monocytogenes was found in RTE foods from fish facilities alone (5 of 12); in all five of the fish facilities with contaminated product, one or more environmental swabs were also positive for L. monocytogenes. The results suggest that while control of L. monocytogenes in BC-inspected dairy and meat facilities is effective in limiting food contamination, there is a need for provincial inspectors to initiate improved monitoring and management of contamination by L. monocytogenes in RTE fish processing facilities.

Detection, isolation, and incidence of Listeria spp. in small-scale artisan cheese processing facilities: a methods comparison

Environmental sampling, focused on environmental sites with a high probability of contamination, was conducted in eight artisan cheese processing facilities. Samples (n = 236) from 86 food contact surfaces and 150 non-food contact surfaces were examined for the presence of Listeria spp. by comparing the efficacy of three different primary enrichment media used in five detection and isolation methods. University of Vermont broth was the most sensitive primary enrichment medium for the detection of Listeria spp., including Listeria monocytogenes. These results, however, did not differ significantly from those obtained with Listeria repair broth or Oxoid 24 Listeria enrichment broth. When full methods were considered, the use of dual enrichment methods identified the most Listeria spp.-positive samples, whereas the BAX System PCR Assay for the Genus Listeria 24E provided the most rapid results (approximately 30 h). Cultural results from the direct plating of secondary enrichment broths were generally in agreement with PCR results when compared within methods. Despite minor differences in efficacy, all five methods were in agreement with one another. Overall, 24 (10.7%) of the 236 environmental samples were positive for Listeria spp., all of which were collected from non-food contact surfaces. Nine of these sites were also positive in previous sampling events, suggesting that these sites serve as Listeria niches and that certain ribotypes are particularly persistent, inhabiting environments and specific sites for over 2 years. Overall, our results suggest that the extent of Listeria spp. contamination, notably L. monocytogenes, in small-scale artisan cheese processing environments is low.