Enhanced detection of Listeria spp. in farmstead cheese processing environments through dual primary enrichment, PCR, and molecular subtyping

Isolation and characterization of halophilic Kocuria salsicia strains from cheese brine

Kocuria salsicia can survive in extreme environments and cause infections, including catheter-related bacteremia, in humans. Here, we investigated and evaluated the characteristics of nine K. salsicia strains (KS1–KS9) isolated from cheese brine from a farmstead cheese-manufacturing plant in Korea from June to December, 2020. Staphylococcus aureus American Type Culture Collection (ATCC) 29213 was used as a positive control in the growth curve analysis and biofilm-formation assays. All K. salsicia isolates showed growth at 15% salt concentration and temperatures of 15°C, 25°C, 30°C, 37°C, and 42°C. KS6 and KS8 showed growth at 5°C, suggesting that they are potential psychrotrophs. In the biofilm-formation analysis via crystal violet staining, KS6 exhibited the highest biofilm-forming ability at various temperatures and media [phosphate buffered saline, nutrient broth (NB), and NB containing 15% sodium chloride]. At 25°C and 30°C, KS3, KS6, and KS8 showed higher biofilm-forming ability than S. aureus ATCC 29213. The antimicrobial resistance of the isolates was evaluated using the VITEK^® 2 system; most isolates were resistant to marbofloxacin and nitrofurantoin (both 9/9, 100%), followed by enrofloxacin (7/9, 77.8%). Five of the nine isolates (5/9, 55.6%) showed multidrug resistance. Our study reports the abilities of K. salsicia to grow in the presence of high salt concentrations and at relatively low temperatures, along with its multidrug resistance and tendency to form biofilms.

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.

Human microbiome versus food-borne pathogens: friend or foe

As food safety advances, there is a great need to maintain, distribute, and provide high-quality food to a much broader consumer base. There is also an ever-growing "arms race" between pathogens and humans as food manufacturers. The human microbiome is a collective organ of microbes that have found community niches while associating with their host and other microorganisms. Humans play an important role in modifying the environment of these organisms through their life choices, especially through individual diet. The composition of an individual's diet influences the digestive system-an ecosystem with the greatest number and largest diversity of organisms currently known. Organisms living on and within food have the potential to be either friends or foes to the consumer. Maintenance of this system can have multiple benefits, but lack of maintenance can lead to a host of chronic and preventable diseases. Overall, this dynamic system is influenced by intense competition from food-borne pathogens, lifestyle, overall diet, and presiding host-associated microbiota.

Occurrence of Listeria monocytogenes in Ready-to-Eat Meat Products and Meat Processing Plants in Spain

The aim of this work was to study the occurrence of Listeria monocytogenes in several types of ready-to-eat (RTE) meat products and in the environment of meat processing plants. A total of 129 samples of RTE meat products and 110 samples from work surfaces and equipment were analyzed. L. monocytogenes was detected in 6 out of 35 cooked products (17.14%), 21 out of 57 raw-cured products (36.84%), and 9 out of 37 dry-cured, salted products (24.32%). The number of sample units that exceeded the food safety limit of 100 cfu/g decreased from the manufacture date to half shelf life, and then it was further reduced at the end of shelf life. L. monocytogenes was detected in 25 out of 110 (22.72%) food contact surfaces. The number of positive and negative results from both food and environmental samples were cross-tabulated and the calculated Cohen's kappa coefficient (κ) was 0.3233, indicating a fair agreement in terms of Listeria contamination. L.monocytogenes was recovered after cleaning and disinfection procedures in four plants, highlighting the importance of thorough cleaning and disinfection.

Is the exoproteome important for bacterial pathogenesis? Lessons learned from interstrain exoprotein diversity in Listeria monocytogenes grown at different temperatures

Bacterial exoproteomes vary in composition and quantity among species and within each species, depending on the environmental conditions to which the cells are exposed. This article critically reviews the literature available on exoproteins synthesized by the foodborne pathogenic bacterium Listeria monocytogenes grown at different temperatures. The main challenges posed for exoproteome analyses and the strategies that are being used to overcome these constraints are discussed. Over thirty exoproteins from L. monocytogenes are considered, and the multifunctionality of some of them is discussed. Thus, at the host temperature of 37°C, good examples are provided by Lmo0443, a potential marker for low virulence, and by the virulence factors internalin C (InlC) and listeriolysin O (LLO). Based on the reported LLO-induced mucin exocytosis, a model is proposed for the involvement of extracellular LLO in optimizing the conditions for InlC intervention in the invasion of intestinal epithelial cells. At lower growth temperatures, exoproteins such as flagellin (FlaA) and oligopeptide permease (OppA) may explain the persistence of particular strains in the food industry environment, eventually allowing the development of new tools to eradicate L. monocytogenes, a major concern for public health.

Microbiological Quality and Safety Issues in Cheesemaking

As the manufacture of cheese relies in part on the select outgrowth of microorganisms, such conditions can also allow for the multiplication of unwanted contaminants. Milk ultimately becomes contaminated with microorganisms originating from infection, the farm environment, and feedstuffs, as well as milking and processing equipment. Thus, poor sanitation, improper milk handling, and animal health issues can result in not only decreased yield and poor quality but also sporadic cases and outbreaks of dairy-related disease. The entry, establishment, and persistence of food-borne pathogens in dairy processing environments also present a considerable risk to products postprocessing. Food safety management systems coupled with regulatory policies and microbiological standards for milk and milk products currently implemented in various nations work to reduce risk while improving the quality and safety of cheese and other dairy products. With that, cheese has enjoyed an excellent food safety record with relatively few outbreaks of food-borne disease considering the amount of cheese produced and consumed worldwide. However, as cheese production and consumption continue to grow, we must remain vigilant in ensuring the continued production of safe, high-quality cheese.

Comparison of polymerase chain reaction methods and plating for analysis of enriched cultures of Listeria monocytogenes when using the ISO11290-1 method

Analysis for Listeria monocytogenes by ISO11290-1 is time-consuming, entailing two enrichment steps and subsequent plating on agar plates, taking five days without isolate confirmation. The aim of this study was to determine if a polymerase chain reaction (PCR) assay could be used for analysis of the first and second enrichment broths, saving four or two days, respectively. In a comprehensive approach involving six European laboratories, PCR and traditional plating of both enrichment broths from the ISO11290-1 method were compared for the detection of L. monocytogenes in 872 food, raw material and processing environment samples from 13 different dairy and meat food chains. After the first and second enrichments, total DNA was extracted from the enriched cultures and analysed for the presence of L. monocytogenes DNA by PCR. DNA extraction by chaotropic solid-phase extraction (spin column-based silica) combined with real-time PCR (RTi-PCR) was required as it was shown that crude DNA extraction applying sonication lysis and boiling followed by traditional gel-based PCR resulted in fewer positive results than plating. The RTi-PCR results were compared to plating, as defined by the ISO11290-1 method. For first and second enrichments, 90% of the samples gave the same results by RTi-PCR and plating, whatever the RTi-PCR method used. For the samples that gave different results, plating was significantly more accurate for detection of positive samples than RTi-PCR from the first enrichment, but RTi-PCR detected a greater number of positive samples than plating from the second enrichment, regardless of the RTi-PCR method used. RTi-PCR was more accurate for non-food contact surface and food contact surface samples than for food and raw material samples especially from the first enrichment, probably because of sample matrix interference. Even though RTi-PCR analysis of the first enrichment showed less positive results than plating, in outbreak scenarios where a rapid result is required, RTi-PCR could be an efficient way to get a preliminary result to be then confirmed by plating. Using DNA extraction from the second enrichment broth followed by RTi-PCR was reliable and a confirmed result could be obtained in three days, as against seven days by ISO11290-1.

Incidence of Listeria monocytogenes and Listeria spp. in a small-scale mushroom production facility

Listeria monocytogenes is a foodborne pathogen of significant concern to the agricultural and food processing industry because of its ability to grow and persist in cool and moist environments and its association with listeriosis, a disease with a very high mortality rate. Although there have been no listeriosis outbreaks attributed to fresh mushrooms in the United States, retail surveys and recalls are evidence that L. monocytogenes contamination of mushrooms (Agaricus bisporus) can occur. The objective of this study was to determine the prevalence of Listeria spp., including L. monocytogenes, in a small-scale mushroom production facility on the campus of the Pennsylvania State University in the United States. Of 184 samples taken from five production zones within the facility, 29 (15.8%) samples were positive for Listeria spp. Among the Listeria spp. isolates, L. innocua was most prevalent (10.3%) followed by L. welshimeri (3.3%), L. monocytogenes (1.6%), and L. grayi (0.5%). L. monocytogenes was recovered only from the phase I raw material composting area. Isolates of L. monocytogenes were confirmed and serotyped by multiplex PCR. The epidemiological relatedness of the three L. monocytogenes isolates to those serotypes or lineages frequently encountered in listeriosis infections was determined by multi-virulence-locus sequence typing using six virulence genes, namely, prfA, inlB, inlC, dal, clpP, and lisR. The phylogenetic positions of the three isolates in the dendrogram prepared with data from other isolates of L. monocytogenes showed that all isolates were grouped with serotype 4a, lineage IIIA. To date, this serotype has rarely been reported in foodborne disease outbreaks.

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.