Multi-Province Listeriosis Outbreak Linked to Contaminated Deli Meat Consumed Primarily in Institutional Settings, Canada, 2008

Application of gelatin-based zinc oxide nanoparticles bionanocomposite coatings to control Listeria monocytogenes in Talaga cheese and camel meat during refrigerated storage

Listeria monocytogenes is a concerning foodborne pathogen incriminated in soft cheese and meat-related outbreaks, highlighting the significance of applying alternative techniques to control its growth in food. In the current study, eco-friendly zinc oxide nanoparticles (ZnO-NPs) were synthesized using Rosmarinus officinalis, Punica granatum, and Origanum marjoram extracts individually. The antimicrobial efficacy of the prepared ZnO-NPs against L. monocytogenes was assessed using the agar well diffusion technique. Data indicated that ZnO-NPs prepared using Origanum marjoram were the most effective; therefore, they were used for the preparation of gelatin-based bionanocomposite coatings. Furthermore, the antimicrobial efficacy of the prepared gelatin-based bionanocomposite coatings containing eco-friendly ZnO-NPs was evaluated against L. monocytogenes in Talaga cheese (an Egyptian soft cheese) and camel meat during refrigerated storage at 4 ± 1 oC. Talaga cheese and camel meat were inoculated with L. monocytogenes, then coated with gelatin (G), gelatin with ZnO-NPs 1% (G/ZnO-NPs 1%), and gelatin with ZnO-NPs 2% (G/ZnO-NPs 2%). Microbiological examination showed that the G/ZnO-NPs 2% coating reduced L. monocytogenes count in the coated Talaga cheese and camel meat by 2.76 ± 0.19 and 2.36 ± 0.51 log CFU/g, respectively, by the end of the storage period. Moreover, G/ZnO-NPs coatings controlled pH changes, reduced water losses, and improved the sensory characteristics of Talaga cheese and camel meat, thereby extending their shelf life. The obtained results from this study indicate that the application of gelatin/ZnO-NPs 2% bionanocomposite coating could be used in the food industry to control L. monocytogenes growth, improve quality, and extend the shelf life of Talaga cheese and camel meat.

Listeria monocytogenes in beef: a hidden risk

Listeria monocytogenes in beef receives less attention compared to other pathogens such as Salmonella and Escherichia coli. To address this gap, we conducted a literature review focusing on the presence of L. monocytogenes in beef. This review encompasses the pathogenic mechanisms, routes of contamination, prevalence rates, and the laws and regulations employed in various countries. Our findings reveal a prevalence of L. monocytogenes in beef and beef products ranging from 2.5% to 59.4%. Notably, serotype 4b was most frequently isolated in cases of beef contamination during food processing, with the skinning and evisceration stages identified as critical points of contamination.

Listeria monocytogenes prevalence and genomic diversity along the pig and pork production chain

The facultative intracellular bacterium Listeria monocytogenes (L. monocytogenes) is the causative agent of listeriosis, a severe invasive illness. This ubiquitous species is widely distributed in the environment, but infection occurs almost exclusively through ingestion of contaminated food. The pork production sector has been heavily affected by a series of L. monocytogenes-related foodborne outbreaks in the past around the world. Ready-to-eat (RTE) pork products represent one of the main food sources for strong-evidence listeriosis outbreaks. This pathogen is known to be present throughout the entire pig and pork production chain. Some studies hypothesized that the main source of contamination in final pork products was either living pigs or the food-processing environment. A detailed genomic picture of L. monocytogenes can provide a renewed understanding of the routes of contamination from pig farms to the final products. This review provides an overview of the prevalence, the genomic diversity and the genetic background linked to virulence of L. monocytogenes along the entire pig and pork production chain, from farm to fork.

A novel multiplex PCR based method for the detection of Listeria monocytogenes clonal complex 8

Listeria monocytogenes is an important foodborne pathogen worldwide, which could cause listeriosis with a 20-30 % fatality rate in immunocompromised individuals. Listeria monocytogenes MLST clonal complex (CC) 8 strain is a common clone in food and clinical cases. The aim of this study was to develop multiplex PCR (mPCR) and high-resolution melting (HRM) qPCR to simultaneously detect L. monocytogenes CC8 and the other L. monocytogenes strains based on pan-genome analysis. A novel multiplex PCR and HRM qPCR targeted for the genes LM5578_1180 (specific for CC8) and LM5578_2262 (for L. monocytogenes) were developed. The specificity of this multiplex PCR and HRM qPCR were verified with other CCs of L. monocytogenes and other species strains. The detection limit of this multiplex PCR and HRM qPCR is 2.1 × 103 CFU/mL and 2.1 × 100 CFU/mL, respectively. This multiplex PCR and HRM qPCR could accurately detect CC8 strains with the interference of different ratios of L. monocytogenes CC9, CC87, CC121, CC155, and L. innocua strains. Subsequently, the detection ability of mPCR and HRM qPCR were also evaluated in spiked samples. The mPCR method could successfully detect 6.2 × 103 CFU/mL of CC8 L. monocytogenes after 6 h enrichment while the multiplex HRM qPCR method could successfully detect 6.2 × 104 CFU/mL of CC8 L. monocytogenes after 3 h enrichment. The feasibility of these methods were satisfactory in terms of sensitivity, specificity, and efficiency after evaluating 12 mushroom samples and was consistent with that of the National Standard Detection Method (GB4789.30-2016). In conclusion, the developed assays could be applied for rapid screening and detection of L. monocytogenes CC8 strains both in food and food production environments, providing accurate results to adopt monitoring measures to improve microbiological safety.

Clinical Findings of Listeria monocytogenes Infections with a Special Focus on Bone Localizations

Listeria monocytogenes is a Gram-positive pathogenic bacterium which can be found in soil or water. Infection with the microorganism can occur after ingestion of contaminated food products. Small and large outbreaks of listeriosis have been described in the past. L. monocytogenes can cause a number of different clinical syndromes, most frequently sepsis, meningitis, and rhombencephalitis, particularly in immunocompromised hosts. L. monocytogenes systemic infections can develop following tissue penetration across the gastrointestinal tract or to hematogenous spread to sterile sites, possibly evolving towards bacteremia. L. monocytogenes only rarely causes bone or joint infections, usually in the context of prosthetic material that can provide a site for bacterial seeding. We describe here the clinical findings of invasive listeriosis, mainly focusing on the diagnosis, clinical management, and treatment of bone and vertebral infections occurring in the context of invasive listeriosis.

Persistence of microbiological hazards in food and feed production and processing environments

Listeria monocytogenes (in the meat, fish and seafood, dairy and fruit and vegetable sectors), Salmonella enterica (in the feed, meat, egg and low moisture food sectors) and Cronobacter sakazakii (in the low moisture food sector) were identified as the bacterial food safety hazards most relevant to public health that are associated with persistence in the food and feed processing environment (FFPE). There is a wide range of subtypes of these hazards involved in persistence in the FFPE. While some specific subtypes are more commonly reported as persistent, it is currently not possible to identify universal markers (i.e. genetic determinants) for this trait. Common risk factors for persistence in the FFPE are inadequate zoning and hygiene barriers; lack of hygienic design of equipment and machines; and inadequate cleaning and disinfection. A well-designed environmental sampling and testing programme is the most effective strategy to identify contamination sources and detect potentially persistent hazards. The establishment of hygienic barriers and measures within the food safety management system, during implementation of hazard analysis and critical control points, is key to prevent and/or control bacterial persistence in the FFPE. Once persistence is suspected in a plant, a 'seek-and-destroy' approach is frequently recommended, including intensified monitoring, the introduction of control measures and the continuation of the intensified monitoring. Successful actions triggered by persistence of L. monocytogenes are described, as well as interventions with direct bactericidal activity. These interventions could be efficient if properly validated, correctly applied and verified under industrial conditions. Perspectives are provided for performing a risk assessment for relevant combinations of hazard and food sector to assess the relative public health risk that can be associated with persistence, based on bottom-up and top-down approaches. Knowledge gaps related to bacterial food safety hazards associated with persistence in the FFPE and priorities for future research are provided.

Two Listeria monocytogenes outbreaks in a cancer centre: onsite food premises and their potential health risk to patients

BACKGROUND

This report describes two L. monocytogenes outbreak investigations that occurred in March and September of 2018 and that linked illness to a food premises located in an Ontario cancer centre. The cancer centre serves patients from across the province.

METHODS

In Ontario, local public health agencies follow up with all reported laboratory-confirmed cases of listeriosis to identify possible sources of disease acquisition and to carry out investigations, including at suspected food premises. The Canadian Food Inspection Agency (CFIA) is notified of any Listeria-positive food product collected in relation to a case. The CFIA traces Listeria-positive product through the food distribution system to identify the contamination source and ensure the implicated manufacturing facility implements corrective measures.

RESULTS

Outbreaks one and two each involved three outbreak-confirmed listeriosis cases. All six cases were considered genetically related by whole genome sequencing (WGS). In both outbreaks, outbreak-confirmed cases reported consuming meals at a food premises located in a cancer centre (food premises A) before illness onset. Various open deli meat samples and, in outbreak two, environmental swabs (primarily from the meat slicer) collected from food premises A were genetically related to the outbreak-confirmed cases. Food premises A closed as a result of the investigations.

CONCLUSIONS

When procuring on-site food premises, healthcare facilities and institutions serving individuals with immuno-compromising conditions should consider the potential health risk of foods available to their patient population.

Use of a taxon-specific reference database for accurate metagenomics-based pathogen detection of Listeria monocytogenes in turkey deli meat and spinach

BACKGROUND

The reliability of culture-independent pathogen detection in foods using metagenomics is contingent on the quality and composition of the reference database. The inclusion of microbial sequences from a diverse representation of taxonomies in universal reference databases is recommended to maximize classification precision for pathogen detection. However, these sizable databases have high memory requirements that may be out of reach for some users. In this study, we aimed to assess the performance of a foodborne pathogen (FBP)-specific reference database (taxon-specific) relative to a universal reference database (taxon-agnostic). We tested our FBP-specific reference database's performance for detecting Listeria monocytogenes in two complex food matrices-ready-to-eat (RTE) turkey deli meat and prepackaged spinach-using three popular read-based DNA-to-DNA metagenomic classifiers: Centrifuge, Kraken 2 and KrakenUniq.

RESULTS

In silico host sequence removal led to substantially fewer false positive (FP) classifications and higher classification precision in RTE turkey deli meat datasets using the FBP-specific reference database. No considerable improvement in classification precision was observed following host filtering for prepackaged spinach datasets and was likely a consequence of a higher microbe-to-host sequence ratio. All datasets classified with Centrifuge using the FBP-specific reference database had the lowest classification precision compared to Kraken 2 or KrakenUniq. When a confidence-scoring threshold was applied, a nearly equivalent precision to the universal reference database was achieved for Kraken 2 and KrakenUniq. Recall was high for both reference databases across all datasets and classifiers. Substantially fewer computational resources were required for metagenomics-based detection of L. monocytogenes using the FBP-specific reference database, especially when combined with Kraken 2.

CONCLUSIONS

A universal (taxon-agnostic) reference database is not essential for accurate and reliable metagenomics-based pathogen detection of L. monocytogenes in complex food matrices. Equivalent classification performance can be achieved using a taxon-specific reference database when the appropriate quality control measures, classification software, and analysis parameters are applied. This approach is less computationally demanding and more attainable for the broader scientific and food safety communities.

Human Listeriosis

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that can cause severe invasive infections upon ingestion with contaminated food. Clinically, listerial disease, or listeriosis, most often presents as bacteremia, meningitis or meningoencephalitis, and pregnancy-associated infections manifesting as miscarriage or neonatal sepsis. Invasive listeriosis is life-threatening and a main cause of foodborne illness leading to hospital admissions in Western countries. Sources of contamination can be identified through international surveillance systems for foodborne bacteria and strains' genetic data sharing. Large-scale whole genome studies have increased our knowledge on the diversity and evolution of L. monocytogenes, while recent pathophysiological investigations have improved our mechanistic understanding of listeriosis. In this article, we present an overview of human listeriosis with particular focus on relevant features of the causative bacterium, epidemiology, risk groups, pathogenesis, clinical manifestations, and treatment and prevention.

Recent Advances in the Detection of Listeria monocytogenes

Listeria monocytogenes is the third-most severe pathogen causing a yearly outbreak of food poisoning in the world that proliferates widely in the environment. Infants, pregnant mothers, and immuno-compromised people are at high risk. Its ability to grow in both biotic and abiotic environments leads to epidemics that infect 5 out of 10 people annually. Because of the epithelial adhesion (by E-cadherin binding), it can suppress immune cells and thrive in the gastrointestinal tract till the brain through blood flow (E-cadherin). Microbial culture is still used as a gold standard, but takes a long time and often yields false positive results due to incompetence and temperature variations. Therefore, in order to treat it rather than using broad spectrum antibiotics, a standardized time-saving and highly specific technology for early detection is very important. It has been observed that the production of a particular antibody is delaying (so does the detection process) as a result of the inadequate understanding of the pathophysiology of the bacteria. This book chapter provides a brief summary of a pathogen as well as the scientific advances that led to its identification more easily.

Wholegenome sequencing as the gold standard approach for control of Listeria monocytogenes in the food chain

Listeria monocytogenes has been implicated in numerous outbreaks and related deaths of listeriosis. In food production, L. monocytogenes occurs in raw food material and above all, through postprocessing contamination. The use of next-generation sequencing technologies such as whole-genome sequencing (WGS) facilitates foodborne outbreak investigations, pathogen source tracking and tracing geographic distributions of different clonal complexes, routine microbiological/epidemiological surveillance of listeriosis, and quantitative microbial risk assessment. WGS can also be used to predict various genetic traits related to virulence, stress, or antimicrobial resistance, which can be of great benefit for improving food safety management as well as public health.

Sugar Modification of Wall Teichoic Acids Determines Serotype-Dependent Strong Biofilm Production in Listeria monocytogenes

Biofilm production is responsible for persistent food contamination by Listeria monocytogenes, threatening food safety and public health. Human infection and food contamination with L. monocytogenes are caused primarily by serotypes 1/2a, 1/2b, and 4b. However, the association of biofilm production with phylogenic lineage and serotype has not yet been fully understood. In this study, we measured the levels of biofilm production in 98 clinical strains of L. monocytogenes at 37°C, 25°C, and 4°C. The phylogenetic clusters grouped by core genome multilocus sequence typing (cgMLST) exhibited association between biofilm production and phylogenetic lineage and serotype. Whereas clusters 1 and 3 consisting of serotype 4b strains exhibited weak biofilm production, clusters 2 (serotype 1/2b) and 4 (serotype 1/2a) were composed of strong biofilm formers. Particularly, cluster 2 (serotype 1/2b) strains exhibited the highest levels of biofilm production at 37°C, and the levels of biofilm production of cluster 4 (serotype 1/2a) strains were significantly elevated at all tested temperatures. Pan-genome analysis identified 22 genes unique to strong biofilm producers, most of which are related to the synthesis and modification of teichoic acids. Notably, a knockout mutation of the rml genes related to the modification of wall teichoic acids with l-rhamnose, which is specific to serogroup 1/2, significantly reduced the level of biofilm production by preventing biofilm maturation. Here, the results of our study show that biofilm production in L. monocytogenes is related to phylogeny and serotype and that the modification of wall teichoic acids with l-rhamnose is responsible for serotype-specific strong biofilm formation in L. monocytogenes. IMPORTANCE Biofilm formation on the surface of foods or food-processing facilities by L. monocytogenes is a serious food safety concern. Here, our data demonstrate that the level of biofilm production differs among serotypes 1/2a, 1/2b, and 4b depending on the temperature. Furthermore, sugar decoration of bacterial cell walls with l-rhamnose is responsible for strong biofilm production in serotypes 1/2a and 1/2b, commonly isolated from foods and listeriosis cases. The findings in this study improve our understanding of the association of biofilm production with phylogenetic lineage and serotype in L. monocytogenes.

A subtractive proteomics and immunoinformatics approach towards designing a potential multi-epitope vaccine against pathogenic Listeriamonocytogenes

Listeria monocytogenes is the causative agent of listeriosis, which is dangerous for pregnant women, the elderly or individuals with a weakened immune system. Individuals with leukaemia, cancer, HIV/AIDS, kidney transplant and steroid therapy suffer from immunological damage are menaced. World Health Organization (WHO) reports that human listeriosis has a high mortality rate of 20-30% every year. To date, no vaccine is available to treat listeriosis. Thereby, it is high time to design novel vaccines against L. monocytogenes. Here, we present computational approaches to design an antigenic, stable and safe vaccine against the L. monocytogenes that could help to control the infections associated with the pathogen. Three vital pathogenic proteins of L. monocytogenes, such as Listeriolysin O (LLO), Phosphatidylinositol-specific phospholipase C (PI-PLC), and Actin polymerization protein (ActA), were selected using a subtractive proteomics approach to design the multi-epitope vaccine (MEV). A total of 5 Cytotoxic T-lymphocyte (CTL) and 9 Helper T-lymphocyte (HTL) epitopes were predicted from these selected proteins. To design the multi-epitope vaccine (MEV) from the selected proteins, CTL epitopes were joined with the AAY linker, and HTL epitopes were joined with the GPGPG linker. Additionally, a human β-defensin-3 (hBD-3) adjuvant was added to the N-terminal side of the final MEV construct to increase the immune response to the vaccine. The final MEV was predicted to be antigenic, non-allergen and non-toxic in nature. Physicochemical property analysis suggested that the MEV construct is stable and could be easily purified through the E. coli expression system. This in-silico study showed that MEV has a robust binding interaction with Toll-like receptor 2 (TLR2), a key player in the innate immune system. Current subtractive proteomics and immunoinformatics study provides a background for designing a suitable, safe and effective vaccine against pathogenic L. monocytogenes.

Lifestyle of Listeria monocytogenes and food safety: Emerging listericidal technologies in the food industry

Listeria monocytogenes, a causative agent of listeriosis, is a major foodborne pathogen. Among pathogens, L. monocytogenes stands out for its unique ecological and physiological characteristics. This distinct lifestyle of L. monocytogenes has a significant impact on food safety and public health, mainly through the ability of this pathogen to multiply at refrigeration temperature and to persist in the food processing environment. Due to a combination of these characteristics and emerging trends in consumer preference for ready-to-eat and minimally processed food, there is a need to develop effective and sustainable approaches to control contamination of food products with L. monocytogenes. Implementation of an efficient and reliable control strategy for L. monocytogenes must first address the problem of cross-contamination. Besides the preventive control strategies, cross-contamination may be addressed with the introduction of emerging post packaging non-thermal or thermal hurdles that can ensure delivery of a listericidal step in a packed product without interfering with the organoleptic characteristics of a food product. This review aims to present the most relevant findings underlying the distinct lifestyle of L. monocytogenes and its impact on food safety. We also discuss emerging food decontamination technologies that can be used to better control L. monocytogenes.

First Survey about Current Practices of Environmental Monitoring Programs within French Agri-Food Industries

Simple Summary

Environmental monitoring programs (EMP) have become essential levers of action to ensure food safety. EMPs are already implemented in some food plants; however, knowledge about monitoring practices remains poorly disseminated. The present survey collected information on the monitoring practices of manufacturing environments in several sectors of the French agri-food industry. We observed that EMP strategies were based on a risk management approach. Practices are codified and transcribed in the HACCP system of some food manufacturers, which include hazards to be monitored, zones to be identified, surfaces to be sampled, tools for sampling and analysis, the number of samples collected, the frequency of sampling, monitoring contamination trends in microbial ecology, and corrective action plans for non-compliant results. EMP strategies are strongly related to food plant characteristics, and there is a lack of guidance. Therefore, a balance must be found between the harmonization of monitoring practices and the specificities of each site.

Abstract

Food safety is a constant challenge for stakeholders in the food industry. To manage the likelihood of microbiological contamination, food safety management systems must be robust, including food and environmental testing. Environmental monitoring programs (EMP) have emerged this last decade aiming to validate cleaning–sanitation procedures and other environmental pathogen control programs. The need to monitor production environments has become evident because of recent foodborne outbreaks. However, the boundaries of environmental monitoring are not only limited to the management of pathogens but also extend to spoilage and hygiene indicators, microorganisms, allergens, and other hygiene monitoring. Surfaces in production environments can be a source of contamination, either through ineffective cleaning and disinfection procedures or through contamination during production by flows or operators. This study analyses the current practices of 37 French agri-food industries (small, medium, or large), reporting their objectives for EMPs, microbial targets, types, numbers and frequency of sampling, analysis of results, and types of corrective actions.

Challenge Test as Special Tool to Estimate the Dynamic of Listeria monocytogenes and Other Foodborne Pathogens

Over 23 million cases of foodborne disease (FBD) occur in Europe each year, with over 4700 deaths. Outbreaks of FBD have a significant impact on our society due to the high economic losses they cause (hospital treatment of affected patients and destruction of contaminated food). Among its health objectives, the European Union has set itself the goal of reducing the incidence of the main FBDs, approving various regulations that codify requirements in order to produce food that is “safe” for human consumption. Among these rules, Regulation 2005/2073 establishes precise food safety criteria for foods that are judged to be most at risk of causing episodes of FBD. The food business operator (FBO) must know their food better and know how to estimate whether a food can support the growth of food pathogens or if they are able to hinder it during the food’s shelf life. It is becoming crucial for each FBO to schedule specific laboratory tests (challenge tests) to establish the growth potential of individual pathogens and their maximum growth rate. In 2008 the European Union published the guidelines for programming the challenge tests for Listeria monocytogenes in RTE foods. These guidelines were further implemented in 2014 and again in 2019. In June 2019 the UNI EN ISO 20976-1 was published, which contains indications for setting up and carrying out challenge tests for all foodborne pathogens in all foods. In this article, we compare the three official documents to highlight their common aspects and differences, highlighting the advantages and disadvantages that each of them offers for those who have to set up a challenge test for the various foodborne pathogens. Our conclusion is that the challenge test is today the most effective tool to estimate the dynamics and growth potential of pathogenic microorganisms in food, if it is designed and implemented in a scrupulous way. It is important to develop a rational experimental design for each challenge test, and for each food, and this requires professionals who are experts in this specific field of study and who must be properly trained.

Consumption of High-Risk Foods in the Canadian Population, Foodbook Study, 2014 to 2015

ABSTRACT

Many foods have the potential to cause foodborne illness; however, some pose a higher risk. Data were collected through the Foodbook study, a population-based telephone survey conducted between 2014 and 2015 that assessed 10,942 Canadians' food exposures using a 7-day recall period. The 19 foods included in the survey were identified as high risk for common foodborne pathogens in Canada. Results were analyzed by age group, gender, region of residence, income, and education. Consumption proportions of high-risk foods ranged from 0.4% (raw oysters) to 49.3% (deli meats). Roughly 94% of the population reported consuming one or more high-risk food in the past week. Certain high-risk food behaviors were associated with demographic characteristics. High-risk adults such as those 65 years or older still report consuming high-risk foods of concern, including deli meats (41.8%), soft cheeses (13.7%), and smoked fish (6.3%). Consumption of certain foods differed between genders, with males consuming significantly more deli meats, hot dogs, and raw or undercooked eggs and females consuming significantly more prebagged mixed salad greens. The overall number of high-risk foods consumed was similar, with both genders most frequently consuming three to five high-risk foods. High-risk food consumption was seen to increase with increasing household income, with 14.2% of the highest income level consuming six-plus high-risk foods in the past week, compared with 7.1% of the lowest income level. If a respondent had heard of a risk of foodborne illness associated with a food, it did not affect whether it was consumed. Additional consumer food safety efforts put in place alongside current messaging may improve high-risk food consumption behaviors. Enhancing current messaging by using multifaceted communications (e.g., social media and information pamphlets) and highlighting the large incidence and severity of foodborne illnesses in Canada are important strategies to improve behavior change.

HIGHLIGHTS

Use of an Ecosystem-Based Approach to Shed Light on the Heterogeneity of the Contamination Pattern of Listeria monocytogenes on Conveyor Belt Surfaces in a Swine Slaughterhouse in the Province of Quebec, Canada

The role of the accompanying microbiota in the presence of Listeria monocytogenes on meat processing surfaces is not yet understood, especially in industrial production conditions. In this study, 300 conveyor belt samples from the cutting room of a swine slaughterhouse were collected during production. The samples were subjected to the detection of L. monocytogenes. Recovered strains were characterized by serogrouping-PCR, InlA Sanger sequencing and for their ability to form biofilm. A selection of isolates was compared with core genome multi-locus sequence typing analysis (cgMLST). The sequencing of the V4 region of the 16S RNA gene of the microorganisms harvested from each sample was carried out in parallel using the Illumina MiSeq platform. Diversity analyses were performed and MaAsLin analysis was used to assess the link between L. monocytogenes detection and the surrounding bacteria. The 72 isolates collected showed a low genetic diversity and important persistence characteristics. L. monocytogenes isolates were not stochastically distributed on the surfaces: the isolates were detected on three out of six production lines, each associated with a specific meat cut: the half carcasses, the bostons and the picnics. MaAsLin biomarker analysis identified the taxa Veillonella (p ≤ 0.0397) as a bacterial determinant of the presence of L. monocytogenes on processing surfaces. The results of this study revealed a heterogenous contamination pattern of the processing surfaces by L. monocytogenes and targeted a bacterial indicator of the presence of the pathogen. These results could lead to a better risk assessment of the contamination of meat products.

Healthcare-associated foodborne outbreaks in high-income countries: a literature review and surveillance study, 16 OECD countries, 2001 to 2019

BackgroundHealthcare-associated foodborne outbreaks (HA-FBO) may have severe consequences, especially in vulnerable groups.AimThe aim was to describe the current state of HA-FBO and propose public health recommendations for prevention.MethodsWe searched PubMed, the Outbreak Database (Charité, University Medicine Berlin), and hand-searched reference lists for HA-FBO with outbreak onset between 2001 and 2018 from Organisation for Economic Co-operation and Development (OECD) countries and HA-FBO (2012-2018) from the German surveillance system. Additionally, data from the European Food Safety Authority were analysed.ResultsThe literature search retrieved 57 HA-FBO from 16 OECD countries, primarily in the US (n = 11), Germany (n = 11) and the United Kingdom (n = 9). In addition, 28 HA-FBO were retrieved from the German surveillance system. Based on the number of outbreaks, the top three pathogens associated with the overall 85 HA-FBO were Salmonella (n = 24), norovirus (n = 22) and Listeria monocytogenes (n = 19). Based on the number of deaths, L. monocytogenes was the main pathogen causing HA-FBO. Frequently reported implicated foods were 'mixed foods' (n = 16), 'vegetables and fruits' (n = 15) and 'meat and meat products' (n = 10). Consumption of high-risk food by vulnerable patients, inadequate time-temperature control, insufficient kitchen hygiene and food hygiene and carriers of pathogens among food handlers were reported as reasons for HA-FBO.ConclusionTo prevent HA-FBO, the supply of high-risk food to vulnerable people should be avoided. Well working outbreak surveillance facilitates early detection and requires close interdisciplinary collaboration and exchange of information between hospitals, food safety and public health authorities.

Listeriosis associated with pre-prepared sandwich consumption in hospital in England, 2017

A case of listeriosis occurred in a hospitalised patient in England in July 2017. Analysis by whole genome sequencing of the Listeria monocytogenes from the patient's blood culture was identified as clonal complex (CC) 121. This culture was indistinguishable to isolates from sandwiches, salads and the maufacturing environment of Company X which supplied these products widely to the National Health Service. Whilst an inpatient, the case was served sandwiches produced by this company on 12 occasions. No other cases infected by this type were detected in the UK between 2016 and 2020. Between 2016 and 2020, more than 3000 samples of food, food ingredients and environmental swabs from this company were tested. Listeria monocytogenes contamination rates declined after July 2017 from 31% to 0.3% for salads and 3% to 0% for sandwiches. A monophyletic group of 127 L. monocytogenes CC121 isolates was recovered during 2016-2019 and was used to estimate the time of the most recent common ancestor as 2014 (95% CI of between 2012 and 2016). These results represent persistent contamination of equipment, food contact surfaces and foods at a food manufacturer by a single L. monocytogenes strain. Colonisation and persistent contamination of food and production environments are risks for public health.

Combined impact of high-pressure processing and slightly acidic electrolysed water on Listeria monocytogenes proteomes

Slightly acidic electrolysed water (SAEW) and high-pressure processing (HPP) are well-established non-thermal preservation technologies. This study investigated the deactivation mechanisms of Listeria monocytogenes by label-free quantitative proteomics analysis. Samples were treated through HPP (300 MPa for 3 min), SAEW (20 ppm available chlorine concentration), and their combinations. The KEGG pathway analysis found SAEW + HPP induced differentially expressed proteins (DEPs) associated to biofunctions of ribosomes, secondary metabolite biosynthesis, microbial metabolism in diverse environments, carbon metabolism, and biosynthesis of amino acid and aminoacyl-transfer RNA. The results showed these non-thermal treatments were able to induce the shifting of ribosome biogenesis to initiate translation in L. monocytogenes. During protein translation, the initiation stage was upregulated. However, subsequent elongation, termination, and recycling of used ribosomes were retarded. Comparing various treatments, the combination of hurdles showed greater deactivation of L. monocytogenes than any single one. The approaches developed in this study provided crucial information for minimally processing in the food industries on the application of foodborne listeriosis prevention.

Genomic Markers for Quaternary Ammonium Compound Resistance as a Persistence Indicator for Listeria monocytogenes Contamination in Food Manufacturing Environments

ABSTRACT

Persistent contamination of food manufacturing environments by Listeria monocytogenes is an important public health risk, because such contamination events defy standard sanitization protocols, for example, the application of quaternary ammonium compounds such as benzalkonium chloride (BC), providing a source for prolonged dissemination of the bacteria in food products. We performed whole genome sequencing analyses of 1,279 well-characterized L. monocytogenes isolates from various foods and food manufacturing environments and identified the bcrABC gene cassette associated with BC resistance in 531 (41.5%) isolates. The bcrABC cassette was significantly associated with L. monocytogenes isolates belonging to clonal complex (CC) 321, CC155, CC204, and CC199, which are among the 10 most prevalent genotypes recovered from foods and food production environments. All but 1 of the 177 CC321 isolates harbored the bcrABC cassette. In addition, 384 (38.6%) of the 994 isolates recovered from foods representing 67 different CCs and 119 (59.2%) of isolates from food manufacturing environmental samples representing 26 different CCs were found to harbor the intact bcrABC cassette. A representative set of 69 isolates with and without bcrABC was assayed for the ability to grow in the presence of BC, and 34 of 35 isolates harboring the bcrABC cassette exhibited MICs of ≥10 μg/mL BC. Determination of bcrABC in isolates could be achieved using both PCR and whole genome sequencing techniques, providing food testing laboratories with options for the characterization of isolates. The ability to determine markers of quaternary ammonium compound resistance such as bcrABC and epidemiologic lineage may provide risk managers with a tool to assess the potential for persistent contamination of the food manufacturing environment and the need for more targeted surveillance to ensure the efficacy of mitigation actions.

HIGHLIGHTS

Identification of Listeria monocytogenes Contamination in a Ready-to-Eat Meat Processing Plant in China

Listeria monocytogenes is the etiologic agent of listeriosis, which remains a significant public health concern in many countries due to its high case-fatality rate. The constant risk of L. monocytogenes transmission to consumers remains a central challenge in the food production industry. At present, there is very little known about L. monocytogenes contamination in ready-to-eat (RTE) processing plants in China. In this study, L. monocytogenes in an RTE meat processing plant in Shanghai municipality was characterized using pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS). Furthermore, the biofilm formation ability of the pathogen was also tested. Results revealed that L. monocytogenes isolates were present in 12 samples out of the 48 samples investigated. Most of them (66.7%, 8/12) were identified from the processing facilities irrespective of observed hygiene levels of aerobic plate count (APC) and coliforms. Coliforms were present in only one processing area. ST5 (1/2b) isolates were predominant (83.3%, 10/12) and were identified in two dominant pulsotypes (PTs) (three in PT3 and seven in PT4, respectively). Results of the core-genome multi-locus sequence typing (cgMLST) showed that ST5 in three PTs (PT1, PT3, and PT4) had 0-8 alleles, which confirmed that clonal transmission occurred in the RTE meat processing facilities. In addition, the biofilm formation test confirmed that the isolates from the processing facilities could form biofilms, which helped them colonize and facilitate persistence in the environment. These results indicated that common sanitation procedures regularly applied in the processing environment were efficient but not sufficient to remove L. monocytogenes isolates, especially biofilm of L. monocytogenes. Furthermore, the ST5 isolates in this study exhibited 12 alleles with one ST5 clinical isolate, which contributes to the understanding of the potential pathogenic risk that L. monocytogenes in RTE meat processing equipment posed to consumers. Therefore, strong hygienic measures, especially sanitation procedures for biofilms eradication, should be implemented to ensure the safety of raw materials. Meanwhile, continuous surveillance might be vital for the prevention and control of listeriosis caused by L. monocytogenes.

10-Year Molecular Surveillance of Listeria monocytogenes Using Whole-Genome Sequencing in Shanghai, China, 2009-2019

Listeria monocytogenes is an etiologic agent of listeriosis, and has emerged as an important foodborne pathogen worldwide. In this study, the molecular characteristics of 155 L. monocytogenes isolates from seven food groups in Shanghai, the biggest city in China, were identified using whole-genome sequencing (WGS). Most L. monocytogenes isolates (79.3%) were obtained between May and October from 2009 to 2019. The serogroups and clonal complexes (CCs) of L. monocytogenes were found useful for identifying potential health risks linked to foods. Differences in distributions of serogroups and CCs among different food groups were analyzed using t-test. The results showed that the IIa and IVb serogroups were identified among most of food groups. However, the prevalence of serogroup IIb was significantly higher in ready-to-eat (RTE) food and raw seafood than in other food groups, similar to group IIc in raw meat and raw poultry than others. Meanwhile, the prevalence of CC9 in raw meat and raw poultry, CC8 in raw poultry, and CC87 in raw seafood significantly exceeded that of in other food groups. Specially, CC87 was the predominant CC in foodborne and clinical isolates in China, indicating that raw seafood may induce a high-risk to food safety. Also, hypervirulence pathogenicity islands LIPI-3 and LIPI-4 were found in CC3, CC1, and CC87, respectively. The clonal group CC619 carried LIPI-3 and LIPI-4, as previously reported in China. Core genome multilocus sequence typing (cgMLST) analysis suggested that CC87 isolates from the same food groups in different years had no allelic differences, indicating that L. monocytogenes could persist over years. These 10-year results in Shanghai underscore the significance of molecular epidemiological surveillance of L. monocytogenes in foodborne products in assessing the potential risk of this pathogen, and further address food safety issues in China.

Listeria monocytogenes in Cooked Chicken: Detection of an Outbreak in the United Kingdom (2016 to 2017) and Analysis of L. monocytogenes from Unrelated Monitoring of Foods (2013 to 2017)

ABSTRACT

In England and Wales, Public Health England applies whole genome sequencing to cultures of Listeria monocytogenes recovered from human cases of listeriosis, foods, and food production environments. Following the routine inspection of a small retailer in February and March 2016, two unopened packs of cooked chicken produced by the same manufacturer were found to be contaminated with L. monocytogenes at levels of 340 and 20 CFU/g. A public recall of this product was issued in March 2016. Early in 2017, a less than five single-nucleotide polymorphism single-linkage cluster was detected between the L. monocytogenes isolates from the two cooked chicken products and cultures from five cases of human listeriosis in England and Scotland with onsets of illness between March 2016 and February 2017. Epidemiological data provided further supportive evidence that this cluster was an outbreak linked to a manufacturer of cooked chicken whose products were supplied to the small retailer that initiated the outbreak investigation. Unrelated to this outbreak, 34 L. monocytogenes isolates recovered from routine food monitoring of 2,007 samples of cooked chicken during 2013 to 2017 were analyzed by whole genome sequencing. Previously undetected fewer than five single-nucleotide polymorphism single-linkage clusters were identified between cultures from cooked chicken and with those from two clusters and two sporadic cases of human listeriosis that were consistent with foodborne transmission. This analysis identified linkage of L. monocytogenes clusters within specific food chains more readily than traditional manual tracing. Linking of data associated with L. monocytogenes cultures from cases of listeriosis with those from unrelated food testing is a unique source of information for communicable disease risk assessment, epidemiological studies, and disease prevention and control. This report provides further evidence that should act as a reminder of the association between cooked chicken consumption and human listeriosis.

HIGHLIGHTS

Human foodborne listeriosis in England and Wales, 1981 to 2015

Almost all cases of human listeriosis are foodborne, however the proportion where specific exposures are identified is small. Between 1981 and 2015, 5252 human listeriosis cases were reported in England and Wales. The purpose of this study was to summarise data where consumption of specific foods was identified with transmission and these comprised 11 sporadic cases and 17 outbreaks. There was a single outbreak in the community of 378 cases (7% of the total) which was associated with pâté consumption and 112 cases (2% of the total) attributed to specific foods in all the other incidents. The proportion of food-attributed cases increased during this study with improvements in typing methods for Listeria monocytogenes. Ten incidents (one sporadic case and nine outbreaks of 2-9 cases over 4 days to 32 months) occurred in hospitals: all were associated with the consumption of pre-prepared sandwiches. The 18 community incidents comprised eight outbreaks (seven of between 3 and 17 cases) and 10 sporadic cases: food of animal origin was implicated in 16 of the incidents (sliced or potted meats, pork pies, pâté, liver, chicken, crab-meat, butter and soft cheese) and food of non-animal origin in the remaining two (olives and vegetable rennet).

Persistent and sporadic Listeria monocytogenes strains do not differ when growing at 37 °C, in planktonic state, under different food associated stresses or energy sources

Background

The foodborne pathogen Listeria monocytogenes causes the potentially lethal disease listeriosis. Within food-associated environments, L. monocytogenes can persist for long periods and increase the risk of contamination by continued presence in processing facilities or other food-associated environments. Most research on phenotyping of persistent L. monocytogenes’ has explored biofilm formation and sanitizer resistance, with less data examining persistent L. monocytogenes’ phenotypic responses to extrinsic factors, such as variations in osmotic pressure, pH, and energy source availability. It was hypothesized that isolates of persistent strains are able to grow, and grow faster, under a broader range of intrinsic and extrinsic factors compared to closely related isolates of sporadic strains.

Results

To test this hypothesis, 95 isolates (representing 74 isolates of 20 persistent strains and 21 isolates of sporadic strains) from a series of previous studies in retail delis, were grown at 37 °C, in (i) stress conditions: salt (0, 5, and 10% NaCl), pH (5.2, 7.2, and 9.2), and sanitizer (benzalkonium chloride, 0, 2, and 5 μg/mL) and (ii) energy sources: 25 mM glucose, cellobiose, glycogen, fructose, lactose, and sucrose; the original goal was to follow up with low temperature experiments for treatments where significant differences were observed. Growth rate and the ability to grow of 95 isolates were determined using high-throughput, OD₆₀₀, growth curves. All stress conditions reduced growth rates in isolates compared to control (p < 0.05). In addition, growth varied by the tested energy sources. In chemically defined, minimal media there was a trend toward more isolates showing growth in all replicates using cellobiose (p = 0.052) compared to the control (glucose) and fewer isolates able to grow in glycogen (p = 0.02), lactose (p = 2.2 × 10^− 16), and sucrose (p = 2.2 × 10^− 16). Still, at least one isolate was able to consistently grow in every replicate for each energy source.

Conclusions

The central hypothesis was rejected, as there was not a significant difference in growth rate or ability to grow for retail deli isolates of persistent strains compared to sporadic strains for any treatments at 37 °C. Therefore, these data suggest that persistence is likely not determined by a phenotype unique to persistent strains grown at 37 °C and exposed to extrinsic stresses or variation in energy sources.

Outbreak of Escherichia coli O157:H7 Infections Linked to Mechanically Tenderized Beef and the Largest Beef Recall in Canada, 2012

Contaminated beef is a known vehicle of Escherichia coli O157:H7 infection, although more attention is given to the control of E. coli O157:H7 in ground, rather than whole-cut, beef products. In September 2012, an investigation was initiated at an Alberta, Canada, beef plant after the detection of E. coli O157:H7 in two samples of trim cut from beef originating from this plant. Later in September 2012, Alberta Health Services identified five laboratory-confirmed infections of E. coli O157:H7, and case patients reported eating needle-tenderized beef steaks purchased at a store in Edmonton, Alberta, produced with beef from the Alberta plant. In total, 18 laboratory-confirmed illnesses in Canada in September and October 2012 were linked to beef from the Alberta plant, including the five individuals who ate needle-tenderized steaks purchased at the Edmonton store. A unique strain of E. coli O157:H7, defined by molecular subtyping and whole genome sequencing, was detected in clinical isolates, four samples of leftover beef from case patient homes, and eight samples of Alberta plant beef tested by industry and food safety partners. Investigators identified several deficiencies in the control of E. coli O157:H7 at the plant; in particular, the evaluation of, and response to, the detection of E. coli O157 in beef samples during routine testing were inadequate. To control the outbreak, 4,000 tons of beef products were recalled, making it the largest beef recall in Canadian history. This outbreak, in combination with similar outbreaks in the United States and research demonstrating that mechanical tenderization can transfer foodborne pathogens present on the surface into the interior of beef cuts, prompted amendments to Canada's Food and Drug Regulations requiring mechanically tenderized beef to be labeled as such and to provide safe cooking instructions to consumers. A detailed review of this event also led to recommendations and action to improve the safety of Canada's beef supply.

Listeria monocytogenes Associated with Pasteurized Chocolate Milk, Ontario, Canada

In an investigation of a listeriosis outbreak in Ontario, Canada, during November 2015–June 2016, pasteurized chocolate milk was identified as the source. Because listeriosis outbreaks associated with pasteurized milk are rare in North America, these findings highlight that dairy products can be contaminated after pasteurization.

Changes detected in the genome sequences of Escherichia coli, Listeria monocytogenes, Vibrio parahaemolyticus, and Salmonella enterica after serial subculturing

Whole genome sequencing (WGS) is rapidly replacing other molecular techniques for identifying and subtyping bacterial isolates. The resolution or discrimination offered by WGS is significantly higher than that offered by other molecular techniques, and WGS readily allows infrequent differences that occur between 2 closely related strains to be found. In this investigation, WGS was used to identify the changes that occurred in the genomes of 13 strains of bacterial foodborne pathogens after 100 serial subcultures. Pure cultures of Shiga-toxin-producing Escherichia coli, Salmonella enterica, Listeria monocytogenes, and Vibrio parahaemolyticus were subcultured daily for 100 successive days. The 1st and 100th subcultures were whole-genome sequenced using short-read sequencing. Single nucleotide polymorphisms (SNPs) were identified between the 1st and final culture using 2 different approaches, and multilocus sequence typing of the whole genome was also performed to detect any changes at the allelic level. The number of observed genomic changes varied by strain, species, and the SNP caller used. This study provides insight into the genomic variation that can be detected using next-generation sequencing and analysis methods after repeated subculturing of 4 important bacterial pathogens.

Epidemiology and Clinical Manifestations of Listeria monocytogenes Infection

Listeria monocytogenes is a Gram-positive pathogenic bacterium which can be found in soil or water. Infection with the organism can develop after ingestion of contaminated food products. Small and large outbreaks of listeriosis have been described. Listeria monocytogenes can cause a number of clinical syndromes, most frequently sepsis, meningitis, and rhombencephalitis, particularly in immunocompromised hosts. The latter syndrome mimics the veterinary infection in ruminants called "circling disease". Neonatal infection can occur as a result of maternal chorioamnionitis ("early onset" sepsis) or through passage through a birth canal colonized with Listeria from the gastrointestinal tract. ("late onset" meningitis). Treatment of listeriosis is usually with a combination of ampicillin and an aminoglycoside but other regimens have been used. The mortality rate is high, reflecting the combination of an immunocompromised host and an often delayed diagnosis.

EnABLe: An agent-based model to understand Listeria dynamics in food processing facilities

Detection of pathogens in food processing facilities by routine environmental monitoring (EM) is essential to reduce the risk of foodborne illness but is complicated by the complexity of equipment and environment surfaces. To optimize design of EM programs, we developed EnABLe ("Environmental monitoring with an Agent-Based Model of Listeria"), a detailed and customizable agent-based simulation of a built environment. EnABLe is presented here in a model system, tracing Listeria spp. (LS) (an indicator for conditions that allow the presence of the foodborne pathogen Listeria monocytogenes) on equipment and environment surfaces in a cold-smoked salmon facility. EnABLe was parameterized by existing literature and expert elicitation and validated with historical data. Simulations revealed different contamination dynamics and risks among equipment surfaces in terms of the presence, level and persistence of LS. Grouping of surfaces by their LS contamination dynamics identified connectivity and sanitary design as predictors of contamination, indicating that these features should be considered in the design of EM programs to detect LS. The EnABLe modeling approach is particularly timely for the frozen food industry, seeking science-based recommendations for EM, and may also be relevant to other complex environments where pathogen contamination presents risks for direct or indirect human exposure.

Shared genome analyses of notable listeriosis outbreaks, highlighting the critical importance of epidemiological evidence, input datasets and interpretation criteria

The persuasiveness of genomic evidence has pressured scientific agencies to supplement or replace well-established methodologies to inform public health and food safety decision-making. This study of 52 epidemiologically defined Listeria monocytogenes isolates, collected between 1981 and 2011, including nine outbreaks, was undertaken (1) to characterize their phylogenetic relationship at finished genome-level resolution, (2) to elucidate the underlying genetic diversity within an endemic subtype, CC8, and (3) to re-evaluate the genetic relationship and epidemiology of a CC8-delimited outbreak in Canada in 2008. Genomes representing Canadian Listeria outbreaks between 1981 and 2010 were closed and manually annotated. Single nucleotide variants (SNVs) and horizontally acquired traits were used to generate phylogenomic models. Phylogenomic relationships were congruent with classical subtyping and epidemiology, except for CC8 outbreaks, wherein the distribution of SNV and prophages revealed multiple co-evolving lineages. Chronophyletic reconstruction of CC8 evolution indicates that prophage-related genetic changes among CC8 strains manifest as PFGE subtype reversions, obscuring the relationship between CC8 isolates, and complicating the public health interpretation of subtyping data, even at maximum genome resolution. The size of the shared genome interrogated did not change the genetic relationship measured between highly related isolates near the tips of the phylogenetic tree, illustrating the robustness of these approaches for routine public health applications where the focus is recent ancestry. The possibility exists for temporally and epidemiologically distinct events to appear related even at maximum genome resolution, highlighting the continued importance of epidemiological evidence.

Determination of Temperature Dependent Growth Parameters in Psychrotrophic Pathogen Bacteria and Tentative Use of Mean Kinetic Temperature for the Microbiological Control of Food

Temperature is the main factor to control the microbial growth in perishable foods. The psychrotrophic pathogen bacteria are microorganisms of concern for food products with extended shelf life in chilling conditions. The aims of this work were two. Firstly, to evaluate growth behavior of Aeromonas hydrophila DSM-30187, Listeria monocytogenes DSM-20600, and Yersinia enterocolitica DSM-27689 strains, at different temperatures (4, 7, 10, 15, 25, and 30°C) and starting cell concentrations (10 and 106 CFU/mL), in order to determine the activation energies (E a) of the relevant lag phases and growth rates. Secondly, to investigate if Mean Kinetic Temperature (MKT) might be applied in recording temperature devices to alert a thermal abuse in a management control system for food safety. As expected, lag phase and growth rate proved to be heavily affected by temperature whereas the inoculum size did not. The E a values involved in the duration of latent periods, calculated on the basis of the Arrhenius model, were comparable for A. hydrophila and L. monocytogenes strains (from 21.3 to 24.4 kcal/mol), while significantly differed for Y. enterocolitica (16.6 kcal/mol). The E a values of growth rates were similar for A. hydrophila and L. monocytogenes strains (from 20.9 to 21.1 kcal/mol), while were considerably lower for Y. enterocolitica (from 14.2 to 16.7 kcal/mol). The use of MKT is widespread and well-accepted in pharmaceutical field as convenient method for estimating drugs degradation in relation to storage temperature. The E a value of the lag phase found for L. monocytogenes (23.9 ± 1.2 kcal/mol) was included in the MKT formula. In this work, the air temperature of two chilling rooms was monitored during the normal operating activity in a catering company for a period of 8 months. The MKT profiles were then compared with those of mean temperatures in different conditions (short or prolonged events of thermal abuse) with the purpose to evaluate if it may be applicable to reduce false alarms without lowering the safety level of stored food.

Efficacy of Ozonated Water, Chlorine, Chlorine Dioxide, Quaternary Ammonium Compounds and Peroxyacetic Acid Against Listeria monocytogenes Biofilm on Polystyrene Surfaces

Listeria monocytogenes contaminated processing equipment and the general packing environment have been implicated in deadly foodborne listeriosis outbreaks, highlighting the significance of proper sanitization and disinfection of food contact surfaces. This study aims to comprehensively evaluate antimicrobial efficacy of commercially available, economical sanitizers at practical concentrations against L. monocytogenes biofilm formed on polystyrene surfaces under different conditions. Ozonated water 1-min treatment at 1.0, 2.0, and 4.0 ppm resulted in ∼0.9, 3.4, and 4.1 log reduction of L. monocytogenes single strain biofilm grown on polystyrene surfaces, respectively. However, its efficacy was dramatically diminished in multi-strain L. monocytogenes biofilm and was further compromised by aged biofilm and in the presence of organic matter. Quaternary ammonium compounds (QAC) at 100/400 ppm, chlorine at 100/200 ppm, chlorine dioxide at 2.5/5.0 ppm and peroxyacetic acid (PAA) at 80/160 ppm resulted in 2.4/3.6, 2.0/3.1, 2.4/3.8, and 3.6/4.8 log reduction of L. monocytogenes single strain biofilm, respectively. Antimicrobial efficacies of all tested sanitizers against 7-day-old biofilm were much lower when compared to 2-day-old biofilm, with PAA being the least influenced by the age of the biofilm. Organic matter conditioning with diluted milk or apple juice dramatically impacted the antimicrobial efficacy of all sanitizers. PAA treatment of 1 min at 160-200 ppm resulted in a 3.2-3.5 log reduction against 7-day-old biofilm in the presence of organic matter, thus showing its effectiveness in eradicating L. monocytogenes biofilm on polystyrene surface. Collectively, data highlight the importance of timely and thoroughly cleaning food contact surfaces before disinfection and provides practical information and guidance for the food industry in selecting the most effective sanitizer in their sanitizing regimes to eliminate L. monocytogenes biofilm.

An outbreak of listeriosis linked to turkey meat products in the Czech Republic, 2012-2016

Since 2012-2016 an increased number of listeriosis cases, especially from one region of the Czech Republic, were observed. Most of them were caused by strains of serotype 1/2a, clonal complex 8, indistinguishable by pulsed-field gel electrophoresis. Twenty-six human cases were reported, including two neonatal cases in twins. Three cases were fatal. The typing of Listeria monocytogenes isolates from food enabled to confirm a turkey meat delicatessen as the vehicle of infection for this local outbreak in the Moravian-Silesian Region. The food strains belonging to identical pulsotype were isolated from ready-to-eat turkey meat products packaged by the same producer between 2012 and 2016. This fact confirms that the described L. monocytogenes outbreak strain probably persisted in the environment of the aforementioned food-processing plant over several years. Whole-genome sequencing confirmed a very close relationship (zero to seven different alleles) between isolates from humans, foods and swabs from the environment of the food-processing plant under investigation.

Listeriosis in Pregnancy: Practitioners' Food Safety Counselling Practices to Pregnant Women

OBJECTIVE

The relative risk of invasive listeriosis in pregnant women is approximately 20 times greater than the general population, and listeriosis during pregnancy can have negative consequences for pregnant women, their fetuses, and their newborns. Health care providers are valuable sources of information, but published data suggest that most providers are unaware of the risk factors for listeriosis or its propensity for pregnant women, and they do not counsel their pregnant patients about risks. The objective of this study was to determine knowledge and practices of Canadian perinatal care providers on food safety counselling to pregnant women.

METHODS

An anonymous bilingual online questionnaire that sought information about awareness, knowledge of risk factors, practices for counselling pregnant women, and practitioners' learning needs with regard to listeriosis was sent to 3199 nurses, midwives, family physicians, and obstetrician/gynaecologists in Canada, with a response rate of 24.4%.

RESULTS

Most respondents had heard of listeriosis, provided prenatal care, and attended deliveries. Rates of awareness of listeriosis were the same among professions and were independent of years in practice, whether practice was urban or rural, and province. One third of the respondents (35.7%) were aware that listeriosis was more common in pregnant women; a minority (18.7%) correctly identified the incubation period for listeriosis and the stage in pregnancy in which women are at highest risk (30.4%). Those respondents who did not counsel women about the risks of listeriosis during pregnancy reported a lack of information or knowledge as the main reason.

CONCLUSION

Advising pregnant women about behaviours and lifestyle habits to prevent infectious diseases remains important, and information about preventive practices needs to be complete and adequate. The health care providers who participated in this study did express a clear need for information related to food safety during pregnancy and listeriosis, as supported by their lack of knowledge in some areas. If that lack is remedied, the knowledge gained could improve counselling practices.

Implicated Food Products for Listeriosis and Changes in Serovars of Listeria monocytogenes Affecting Humans in Recent Decades

Listeriosis is a foodborne disease with a high fatality rate, and infection is mostly transmitted through ready-to-eat (RTE) foods contaminated with Listeria monocytogenes, such as gravad/smoked fish, soft cheeses, and sliced processed delicatessen (deli) meat. Food products/dishes stored in vacuum or in modified atmospheres and with extended refrigerator shelf lives provide an opportunity for L. monocytogenes to multiply to large numbers toward the end of the shelf life. Elderly, pregnant women, neonates, and immunocompromised individuals are particularly susceptible to L. monocytogenes. Listeriosis in humans manifests primarily as septicemia, meningitis, encephalitis, gastrointestinal infection, and abortion. In the mid 1990s and early 2000s a shift from L. monocytogenes serovar 4b to serovar 1/2a causing human listeriosis occurred, and serovar 1/2a is becoming more frequently linked to outbreaks of listeriosis, particularly in Europe and Northern America. Consumer lifestyle has changed, and less time is available for food preparation. Modern lifestyle has markedly changed eating habits worldwide, with a consequent increased demand for RTE foods; therefore, more RTE and take away foods are consumed. There is a concern that many Listeria outbreaks are reported from hospitals. Therefore, it is vitally important that foods (especially cooked and chilled) delivered to hospitals and residential homes for senior citizens and elderly people are reheated to at least 72°C: cold food, such as turkey deli meat and cold-smoked and gravad salmon should be free from L. monocytogenes. Several countries have zero tolerance for RTE foods that support the growth of Listeria.

The absence of N-acetylglucosamine in wall teichoic acids of Listeria monocytogenes modifies biofilm architecture and tolerance to rinsing and cleaning procedures

The wall teichoic acid (WTA) is the major carbohydrate found within the extracellular matrix of the Listeria monocytogenes biofilm. We first addressed the frequency of spontaneous mutations in two genes (lmo2549 and lmo2550) responsible for the GlcNAcylation in 93 serotype 1/2a strains that were mainly isolated from seafood industries. We studied the impact of mutations in lmo2549 or lmo2550 genes on biofilm formation by using one mutant carrying a natural mutation inactivating the lmo2550 gene (DSS 1130 BFA2 strain) and two EGD-e mutants that lack respective genes by in-frame deletion of lmo2549 or lmo2550 using splicing-by-overlap-extension PCR, followed by allelic exchange mutagenesis. The lmo2550 gene mutation, occurring in around 50% isolates, caused a decrease in bacterial adhesion to stainless steel compared to wild-type EGD-e strain during the adhesion step. On the other hand, bacterial population weren't significantly different after 24h-biofilm formation. The biofilm architecture was different between the wild-type strain and the two mutants inactivated for lmo2549 or lmo2550 genes respectively with the presence of bacterial micro-colonies for mutants which were not observed in the wild-type EGD-e strain biofilm. These differences might account for the stronger hydrophilic surface exhibited by the mutant cells. Upon a water flow or to a cleaning procedure at a shear stress of 0.16 Pa, the mutant biofilms showed the higher detachment rate compared to wild-type strain. Meanwhile, an increase in the amount of residual viable but non-culturable population on stainless steel was recorded in two mutants. Our data suggests that the GlcNAc residue of WTA played a role in adhesion and biofilm formation of Listeria monocyctogenes.

Listeria monocytogenes in Food-Processing Facilities, Food Contamination, and Human Listeriosis: The Brazilian Scenario

Listeria monocytogenes is a foodborne pathogen that contaminates food-processing environments and persists within biofilms on equipment, utensils, floors, and drains, ultimately reaching final products by cross-contamination. This pathogen grows even under high salt conditions or refrigeration temperatures, remaining viable in various food products until the end of their shelf life. While the estimated incidence of listeriosis is lower than other enteric illnesses, infections caused by L. monocytogenes are more likely to lead to hospitalizations and fatalities. Despite the description of L. monocytogenes occurrence in Brazilian food-processing facilities and foods, there is a lack of consistent data regarding listeriosis cases and outbreaks directly associated with food consumption. Listeriosis requires rapid treatment with antibiotics and most drugs suitable for Gram-positive bacteria are effective against L. monocytogenes. Only a minority of clinical antibiotic-resistant L. monocytogenes strains have been described so far; whereas many strains recovered from food-processing facilities and foods exhibited resistance to antimicrobials not suitable against listeriosis. L. monocytogenes control in food industries is a challenge, demanding proper cleaning and application of sanitization procedures to eliminate this foodborne pathogen from the food-processing environment and ensure food safety. This review focuses on presenting the L. monocytogenes distribution in food-processing environment, food contamination, and control in the food industry, as well as the consequences of listeriosis to human health, providing a comparison of the current Brazilian situation with the international scenario.

Identification and classification of sampling sites for pathogen environmental monitoring programs for Listeria monocytogenes: Results from an expert elicitation

Pathogen Environmental Monitoring (PEM) programs for Listeria are important to reduce the contamination risk for exposed Ready-To-Eat (RTE) food products with L. monocytogenes. Specific guidance to identify appropriate sampling sites in individual facilities, including equipment and other sites, will facilitate effective L. monocytogenes control and PEM programs. Key goals of Listeria PEM programs are to (i) identify and eliminate niches that allow for Listeria growth and survival and (ii) verify and validate preventive controls such as sanitation programs and sanitation standard operating procedures (SSOPs), sanitary equipment and facility design. Here, an initial list of 77 sampling sites covering Zones 1-4 was assembled based on current literature and guidance documents with initial classification of sites into (i) Zones 1, 2, 3, and 4; (ii) likely niches or transfer sites, and (iii) verification sites or indicator sites. An expert elicitation that included responses from 16 food safety professionals was used to (i) refine sampling site descriptions and identify 6 new sampling sites that were not included in the original list, (ii) refine classification of sites (e.g., into niches versus transfer sites), and (iii) rank sites on level of importance from 1 to 5. The final sample site list includes sampling sites classified by zone and type of site as well as relative importance of site based on reviewer feedback. This document thus provides an initial set of sites that can be used by industry to help in the development or refinement of Listeria PEM programs. The availability of this ranked list of sampling sites should reduce barriers to development of science based Listeria PEM programs.

Serotype to genotype: The changing landscape of listeriosis outbreak investigations

The classical definition of a disease outbreak is the occurrence of cases of disease in excess of what would normally be expected in a community, geographical area or time period. The establishment of an outbreak then starts with the identification of an incidence of cases above the normally expected threshold during a given time period. Subsequently, the cases are examined using a variety of subtyping methods to identify potential linkages. As listeriosis disease has a long incubation period, relating a single source or multiple sources of contaminated food to clinical disease is challenging and time consuming. The vast majority of human listeriosis cases are caused by three serotypes, 1/2a, 1/2b, and 4b. Thus serotyping of isolates from suspected foods and clinical samples, although useful for eliminating some food sources, has a very limited discriminatory power. The advent of faster and more affordable sequencing technology, coupled with increased computational power, has permitted comparisons of whole Listeria genome sequences from isolates recovered from clinical, food, and environmental sources. These analyses made it possible to identify outbreaks and the source much more accurately and faster, thus leading to a reduction in number of illnesses as well as a reduction in economic losses. Initial DNA sequence information also facilitated the development of a simple molecular serotype protocol which allowed for the identification of major disease causing serotypes of L. monocytogenes, including a clade of 4b variant (4bV) strains of L. monocytogenes involved in at least 3 more recent listeriosis outbreaks in the US. Furthermore, data generated using whole genome sequence (WGS) analyses was successfully utilized to develop a pan-genomic DNA microarray as well as a single nucleotide polymorphism (SNP) based analysis. Herein, we present and compare, the two recently developed sub-typing technologies and discuss how these methods are not only important in outbreak investigations, but could also shed light on possible adaptations to different foods and environments.

Stochastic and Differential Activation of σB and PrfA in Listeria monocytogenes at the Single Cell Level under Different Environmental Stress Conditions

During host infection, the foodborne pathogen Listeria monocytogenes must sense and respond to rapidly changing environmental conditions. Two transcriptional regulators, the alternative sigma factor B (σ^B) and the Positive Regulatory Factor A (PrfA), are key contributors to the transcriptomic responses that enable bacterial survival in the host gastrointestinal tract and invasion of host duodenal cells. Increases in temperature and osmolarity induce activity of these proteins; such conditions may be encountered in food matrices as well as within the host gastrointestinal tract. Differences in PrfA and σ^B activity between individual cells might affect the fate of a cell during host invasion, therefore, we hypothesized that PrfA and σ^B activities differ among individual cells under heat and salt stress. We used fluorescent reporter fusions to determine the relative proportions of cells with active σ^B or PrfA following exposure to 45°C heat or 4% NaCl. Activities of both PrfA and σ^B were induced stochastically, with fluorescence levels ranging from below detection to high among individual cells. The proportion of cells with active PrfA was significantly higher than the proportion with active σ^B under all tested conditions; under some conditions, nearly all cells had active PrfA. Our findings further support the growing body of evidence illustrating the stochastic nature of bacterial gene expression under conditions that are relevant for host invasion via food-borne, oral infection.

1926-2016: 90 Years of listeriology

ISOPOL - for "International Symposium on Problems of Listeria and Listeriosis" - meetings gather every three years since 1957 participants from all over the world and allow exchange and update on a wide array of topics concerning Listeria and listeriosis, ranging from epidemiology, diagnostic and typing methods, to genomics, post-genomics, fundamental microbiology, cell biology and pathogenesis. The XIXth ISOPOL meeting took place in Paris from June 14th to 17th, 2016 at Institut Pasteur. We provide here a report of the talks that were given during the meeting, which represents an up-to-date overview of ongoing research on this important pathogen and biological model.