Multistate Outbreak of Listeriosis Associated with Packaged Leafy Green Salads, United States and Canada, 2015-2016

Detection of foodborne pathogens in contaminated food using nanomaterial-based electrochemical biosensors

Foodborne pathogens are a grave concern for the for food, medical, environmental, and economic sectors. Their ease of transmission and resistance to treatments, such as antimicrobial agents, make them an important challenge. Food tainted with these pathogens is swiftly rejected, and if ingested, can result in severe illnesses and even fatalities. This review provides and overview of the current status of various pathogens and their metabolites transmitted through food. Despite a plethora of studies on treatments to eradicate and inhibit these pathogens, their indiscriminate use can compromise the sensory properties of food and lead to contamination. Therefore, the study of detection methods such as electrochemical biosensors has been proposed, which are devices with advantages such as simplicity, fast response, and sensitivity. However, these biosensors may also present some limitations. In this regard, it has been reported that nanomaterials with high conductivity, surface-to-volume ratio, and robustness have been observed to improve the detection of foodborne pathogens or their metabolites. Therefore, in this work, we analyze the detection of pathogens transmitted through food and their metabolites using electrochemical biosensors based on nanomaterials.

Microbiological quality of irrigation water on highly diverse fresh produce smallholder farms: elucidating environmental routes of contamination

AIM

To evaluate the microbiological safety, potential multidrug-resistant bacterial presence and genetic relatedness (DNA fingerprints) of Escherichia coli isolated from the water-soil-plant nexus on highly diverse fresh produce smallholder farms.

METHODS AND RESULTS

Irrigation water (n = 44), soil (n = 85), and fresh produce (n = 95) samples from six smallholder farms with different production systems were analysed for hygiene indicator bacterial counts and the presence of shigatoxigenic E. coli and Salmonella spp. using standard microbiological methods. Identities of isolates were confirmed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and the genetic relatedness of the E. coli isolates determined using enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) analysis. Irrigation water E. coli levels ranged between 0 and 3.45 log MPN/100 ml-1 with five farms having acceptable levels according to the World Health Organization limit (3 log MPN/100 ml-1). Fresh produce samples on four farms (n = 65) harboured E. coli at low levels (<1 log CFU/g-1) except for one sample from kale, spring onion, green pepper, onion, and two tomato samples, which exceeded international acceptable limits (100 CFU/g-1). Only one baby carrot fresh produce sample tested positive for Salmonella spp. Of the 224 samples, E. coli isolates were identified in 40% (n = 90) of all water, soil, and fresh produce types after enrichment. Additionally, the DNA fingerprints of E. coli isolates from the water-soil-plant nexus of each respective farm clustered together at high similarity values (>90%), with all phenotypically characterized as multidrug-resistant.

CONCLUSIONS

The clustering of E. coli isolated throughout the water-soil-plant nexus, implicated irrigation water in fresh produce contamination. Highlighting the importance of complying with irrigation water microbiological quality guidelines to limit the spread of potential foodborne pathogens throughout the fresh produce supply chain.

Temporal, spatial and space-time distribution of infections caused by five major enteric pathogens, Ontario, Canada, 2010-2017

AIMS

In Canada, enteric diseases pose substantial health and economic burdens. The distribution of these diseases is uneven across both geography and time and understanding these patterns is therefore important for the prevention of future outbreaks. We evaluated temporal, spatial and space-time clustering of laboratory-confirmed cases of Campylobacter spp. (n = 28,728), non-typhoidal Salmonella spp. (n = 22,640), Shiga toxin-producing Escherichia coli (STEC; n = 1340), Yersinia spp. (n = 1674) and Listeria monocytogenes (n = 471) infections, reported between 2010 and 2017 inclusive in Ontario, the most populous province in Canada (population ~ 13,500,000 in 2016).

METHODS AND RESULTS

For each enteric pathogen, we calculated the mean incidence rates (IRs) for Ontario's 35 public health unit (PHU) areas and visualized them using choropleth maps. We identified temporal, spatial and space-time high infection rate clusters using retrospective Poisson scan statistics. Campylobacter and Salmonella infections had the highest IRs, while Listeria infections had the lowest. Campylobacter, Salmonella, STEC and Listeria mostly clustered temporally in the spring/summer and sometimes extended into fall, while Yersinia showed a less clear seasonal pattern. The IR visualizations and spatial and space-time scan statistics showed geographic heterogeneity of infection rates with high infection rate clusters detected mainly in PHUs across the southwestern and central-western regions of Ontario for Campylobacter, Salmonella and STEC infections, and mainly in PHUs located in the central-eastern regions for Yersinia and Listeria. A high proportion of cases in some of the significant Salmonella, STEC and Listeria infection clusters were linked to disease outbreaks.

CONCLUSIONS

Results from this study will inform heightened public health surveillance, and prevention and control programmes, in populations and regions of high infection rates. Further research is needed to determine the pathogen-specific socioeconomic, environmental and agricultural risk factors that may be related to the temporal and spatial disease patterns we observed in our study.

Comparing the susceptibility to sanitizers, biofilm-forming ability, and biofilm resistance to quaternary ammonium and chlorine dioxide of 43 Salmonella enterica and Listeria monocytogenes strains

This study determined the susceptibility to sanitizers and biofilm-forming ability on stainless steel of 43 Salmonella enterica and Listeria monocytogenes strains. Besides, the biofilm resistance to sanitizers of four bacterial pathogen strains was evaluated. Four sanitizers commonly used in the food industry were tested: peracetic acid (PAA), chlorine dioxide (ClO2), sodium hypochlorite (SH), and quaternary ammonium compound (QAC). The susceptibility to sanitizers varied widely among the strains of both pathogens. On the other hand, the number of biofilm-associated cells on the stainless-steel surface was >5 log CFU/cm2 for all of them. Only one Salmonella strain and two L. monocytogenes strains stood out as the least biofilm-forming. The resistance of biofilms to sanitizers also varied among strains of each pathogen. Biofilms of L. monocytogenes were more susceptible to the disinfection process with ClO2 and QAC than those of Salmonella. However, no correlation was observed between the ability to form denser biofilm and increased sanitizer resistance. In general, chlorine compounds were more effective than other sanitizers in inactivating planktonic cells and biofilms.

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.

Impact of High-Pressure Processing (HPP) on Listeria monocytogenes-An Overview of Challenges and Responses

High-pressure processing (HPP) is currently one of the leading methods of non-thermal food preservation as an alternative to traditional methods based on thermal processing. The application of HPP involves the simultaneous action of a combination of several factors-pressure values (100-600 MPa), time of operation (a few-several minutes), and temperature of operation (room temperature or lower)-using a liquid medium responsible for pressure transfer. The combination of these three factors results in the inactivation of microorganisms, thus extending food shelf life and improving the food's microbiological safety. HPP can provide high value for the sensory and quality characteristics of products and reduce the population of pathogenic microorganisms such as L. monocytogenes to the required safety level. Nevertheless, the technology is not without impact on the cellular response of pathogens. L. monocytogenes cells surviving the HPP treatment may have multiple damages, which may impact the activation of mechanisms involved in the repair of cellular damage, increased virulence, or antibiotic resistance, as well as an increased expression of genes encoding pathogenicity and antibiotic resistance. This review has demonstrated that HPP is a technology that can reduce L. monocytogenes cells to below detection levels, thus indicating the potential to provide the desired level of safety. However, problems have been noted related to the possibilities of cell recovery during storage and changes in virulence and antibiotic resistance due to the activation of gene expression mechanisms, and the lack of a sufficient number of studies explaining these changes has been reported.

Genomics for public health and international surveillance of antimicrobial resistance

Historically, epidemiological investigation and surveillance for bacterial antimicrobial resistance (AMR) has relied on low-resolution isolate-based phenotypic analyses undertaken at local and national reference laboratories. Genomic sequencing has the potential to provide a far more high-resolution picture of AMR evolution and transmission, and is already beginning to revolutionise how public health surveillance networks monitor and tackle bacterial AMR. However, the routine integration of genomics in surveillance pipelines still has considerable barriers to overcome. In 2022, a workshop series and online consultation brought together international experts in AMR and pathogen genomics to assess the status of genomic applications for AMR surveillance in a range of settings. Here we focus on discussions around the use of genomics for public health and international AMR surveillance, noting the potential advantages of, and barriers to, implementation, and proposing recommendations from the working group to help to drive the adoption of genomics in public health AMR surveillance. These recommendations include the need to build capacity for genome sequencing and analysis, harmonising and standardising surveillance systems, developing equitable data sharing and governance frameworks, and strengthening interactions and relationships among stakeholders at multiple levels.

Predicting Food Sources of Listeria monocytogenes Based on Genomic Profiling Using Random Forest Model

Listeria monocytogenes can cause severe foodborne illness, including miscarriage during pregnancy or death in newborn infants. When outbreaks of L. monocytogenes illness occur, it may be possible to determine the food source of the outbreak. However, most reported L. monocytogenes illnesses do not occur as part of a recognized outbreak and most of the time the food source of sporadic L. monocytogenes illness in people cannot be determined. In the United States, L. monocytogenes isolates from patients, foods, and environments are routinely sequenced and analyzed by whole genome multilocus sequence typing (wgMLST) for outbreak detection by PulseNet, the national molecular surveillance system for foodborne illnesses. We investigated whether machine learning approaches applied to wgMLST allele call data could assist in attribution analysis of food source of L. monocytogenes isolates. We compiled isolates with a known source from five food categories (dairy, fruit, meat, seafood, and vegetable) using the metadata of L. monocytogenes isolates in PulseNet, deduplicated closely genetically related isolates, and developed random forest models to predict the food sources of isolates. Prediction accuracy of the final model varied across the food categories; it was highest for meat (65%), followed by fruit (45%), vegetable (45%), dairy (44%), and seafood (37%); overall accuracy was 49%, compared with the naive prediction accuracy of 28%. Our results show that random forest can be used to capture genetically complex features of high-resolution wgMLST for attribution of isolates to their sources.

Microbiological hazards associated with the use of water in the post-harvest handling and processing operations of fresh and frozen fruits, vegetables and herbs (ffFVHs). Part 1 (outbreak data analysis, literature review and stakeholder questionnaire)

The contamination of water used in post-harvest handling and processing operations of fresh and frozen fruit, vegetables and herbs (ffFVHs) is a global concern. The most relevant microbial hazards associated with this water are: Listeria monocytogenes, Salmonella spp., human pathogenic Escherichia coli and enteric viruses, which have been linked to multiple outbreaks associated with ffFVHs in the European Union (EU). Contamination (i.e. the accumulation of microbiological hazards) of the process water during post-harvest handling and processing operations is affected by several factors including: the type and contamination of the FVHs being processed, duration of the operation and transfer of microorganisms from the product to the water and vice versa, etc. For food business operators (FBOp), it is important to maintain the microbiological quality of the process water to assure the safety of ffFVHs. Good manufacturing practices (GMP) and good hygienic practices (GHP) related to a water management plan and the implementation of a water management system are critical to maintain the microbiological quality of the process water. Identified hygienic practices include technical maintenance of infrastructure, training of staff and cooling of post-harvest process water. Intervention strategies (e.g. use of water disinfection treatments and water replenishment) have been suggested to maintain the microbiological quality of process water. Chlorine-based disinfectants and peroxyacetic acid have been reported as common water disinfection treatments. However, given current practices in the EU, evidence of their efficacy under industrial conditions is only available for chlorine-based disinfectants. The use of water disinfection treatments must be undertaken following an appropriate water management strategy including validation, operational monitoring and verification. During operational monitoring, real-time information on process parameters related to the process and product, as well as the water and water disinfection treatment(s) are necessary. More specific guidance for FBOp on the validation, operational monitoring and verification is needed.

Listeria monocytogenes an Emerging Pathogen: a Comprehensive Overview on Listeriosis, Virulence Determinants, Detection, and Anti-Listerial Interventions

Listeria monocytogenes, the third most deleterious zoonotic pathogen, is a major causative agent of animal and human listeriosis, an infection related to the consumption of contaminated food products. Even though, this pathogen has been responsible for the outbreaks of foodborne infections in the early 1980s, the major outbreaks have been reported during the past two decades. Listeriosis infection in the host is a rare but life-threatening disease with major public health and economic implications. Extensive reports on listeriosis outbreaks are associated with milk and milk products, meat and meat products, and fresh produce. This bacterium can adapt to any environmental and stress conditions, making it a prime causative agent for major foodborne diseases. The pathogen could survive an antibiotic treatment and persist in the host cell, thereby escaping the standard diagnostic practices. The current review strives to provide concise information on the epidemiology, serotypes, and pathogenesis of the L. monocytogenes to decipher the knowledge on the endurance of the pathogen inside the host and food products as a vehicle for Listeria contaminations. In addition, various detection methods for Listeria species from food samples and frontline regimens of L. monocytogenes treatment have also been discussed.

Mechanism of acid and alkali electrolyzed water on the elimination of Listeria monocytogenes biofilm based on proteomic analysis

Acidic electrolyzed water is a relatively mature bactericide, which has a certain inhibitory effect on a variety of microorganisms, and is widely used in the field of food processing for cleaning, sterilization and disinfection. This study investigated the deactivation mechanisms of Listeria monocytogenes by Tandem Mass Tags quantitative proteomics analysis. Samples were treated through A1S4 (Alkaline electrolytic water treatment for 1 min and Acid electrolytic water treatment for 4 min), S3A1S1 (Acid electrolyzed water treatment 3 min, Alkaline electrolyzed water treatment 1 min and Acid electrolyzed water treatment 1 min), S5 (Acid electrolytic water treatment for 5 min). Proteomic analysis showed that the mechanism of acid alkaline electrolyzed water treatment to eliminate the inactivation of the biofilm of L. monocytogenes was related to protein transcription and extension, RNA processing and synthesis, gene regulation, sugar and amino acid transport and metabolism, signal transduction and ATP binding. The study on the influence mechanism and action mechanism of the combination of acidic and alkaline electrolyzed water to remove L. monocytogenes biofilm is helpful to understand the development of the process of removing biofilm by electrolyzed water, and provides theoretical support for the treatment of other microbial contamination problems in food processing by electrolyzed water.

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.

Prioritization of vegetable-borne biological hazards in Argentina using a multicriteria decision analysis tool

Vegetables, especially those eaten raw, have been implicated in several foodborne disease outbreaks. Since multiple vegetable matrices and hazards are involved, risk managers have to prioritize those with the greatest impact on public health to design control strategies. In this study, a scientific-based risk ranking of foodborne pathogens transmitted by leafy green vegetables in Argentina was performed. The prioritization process included hazard identification, evaluation criteria identification and definition, criteria weighting, expert survey design and selection and call for experts, hazard score calculation, hazard ranking and variation coefficient, and result analysis. Regression tree analysis determined four risk clusters: high (Cryptosporidum spp., Toxoplasma gondii, Norovirus), moderate (Giardia spp., Listeria spp., Shigella sonnei), low (Shiga toxin-producing Escherichia coli, Ascaris spp., Entamoeba histolytica, Salmonella spp., Rotavirus, Enterovirus) and very low (Campylobacter jejuni, hepatitis A virus and Yersinia pseudotuberculosis). Diseases caused by Norovirus, Cryptosporidium spp. and T. gondii do not require mandatory notification. Neither viruses nor parasites are included as microbiological criteria for foodstuff. The lack of outbreak studies did not allow to accurately identify vegetables as a source of Norovirus disease. Information on listeriosis cases or outbreaks due to vegetable consumption was not available. Shigella spp. was the main responsible for bacterial diarrhea, but it has not been epidemiologically associated with vegetable consumption. The quality of the available information for all hazards studied was very low and low. The implementation of good practice guidelines throughout the entire vegetable production chain could prevent the presence of the identified hazards. The current study allowed the identification of vacancy areas and could help reinforce the need for performing epidemiological studies on foodborne diseases potentially associated with vegetable consumption in Argentina.

Listeria monocytogenes loss of cultivability on carrot is associated with the formation of mesosome-like structures

Raw carrot is known to have antimicrobial activity against Listeria monocytogenes, but the mechanism of action has not been fully elucidated. In this study, we examined carrot antilisterial activity against several strains of Listeria species (including L. grayi, L. innocua, L. seeligeri, and L. welshimeri) and L. monocytogenes. A representative strain of L. monocytogenes was subsequently used for further characterizing carrot antilisterial activity. Exposure to fresh-cut carrot for 15 min resulted in a similar loss of cultivability, ranging from 2.5 to 4.7 log units, across all Listeria strains evaluated. L. monocytogenes recovered from the fresh-cut surface of different raw carrots was 1.6 to 4.1 log lower than levels obtained from paired boiled carrot samples with abolished antilisterial activity. L. monocytogenes levels recovered from fresh-cut carrot were 2.8 to 3.1 log lower when enumerated by culture-dependent methods than by the culture-independent method of PMAxx-qPCR, a qPCR assay that is performed using DNA pre-treated to selectively sequester DNA from cells with injured membranes. These results suggested that L. monocytogenes loss of cultivability on fresh-cut carrot was not associated with a loss of L. monocytogenes cell membrane integrity and putative cell viability. Transmission electron microscopy imaging revealed that L. monocytogenes rapidly formed mesosome-like structures upon exposure to carrot fresh-cut surface but not upon exposure to boiled carrot surface, suggesting there may be an association between the formation of these mesosome-like structures and a loss of cultivability in L. monocytogenes. However, further research is necessary to conclude the causality of this association.

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.

Fresh Produce as a Potential Vector and Reservoir for Human Bacterial Pathogens: Revealing the Ambiguity of Interaction and Transmission

The consumer demand for fresh produce (vegetables and fruits) has considerably increased since the 1980s for more nutritious foods and healthier life practices, particularly in developed countries. Currently, several foodborne outbreaks have been linked to fresh produce. The global rise in fresh produce associated with human infections may be due to the use of wastewater or any contaminated water for the cultivation of fruits and vegetables, the firm attachment of the foodborne pathogens on the plant surface, and the internalization of these agents deep inside the tissue of the plant, poor disinfection practices and human consumption of raw fresh produce. Several investigations have been established related to the human microbial pathogens (HMPs) interaction, their internalization, and survival on/within plant tissue. Previous studies have displayed that HMPs are comprised of several cellular constituents to attach and adapt to the plant’s intracellular niches. In addition, there are several plant-associated factors, such as surface morphology, nutrient content, and plant–HMP interactions, that determine the internalization and subsequent transmission to humans. Based on documented findings, the internalized HMPs are not susceptible to sanitation or decontaminants applied on the surface of the fresh produce. Therefore, the contamination of fresh produce by HMPs could pose significant food safety hazards. This review provides a comprehensive overview of the interaction between fresh produce and HMPs and reveals the ambiguity of interaction and transmission of the agents to humans.

Molecular investigation of ready-to-eat salads for Giardia duodenalis and Cryptosporidium spp. in Portugal

Foodborne outbreaks are often associated with the consumption of salads. However, published studies on the detection of foodborne pathogens in ready-to-eat salads are scarce. The aim of this study was to detect Giardia duodenalis and Cryptosporidium DNA in ready-to-eat salads, by applying techniques of molecular biology to study the frequency of contamination in salads. A total of 100 packages of ready-to-eat salads containing assorted leafy green vegetables were randomly purchased from hypermarkets located in central regions of Portugal (Coimbra and Viseu). Nested-PCR and qPCR methods were used to detect G. duodenalis and Cryptosporidium DNA. Species and assemblages of the parasites were identified by sequence analysis and PCR. Eighteen of the 100 samples (18%) were positive for G. duodenalis and twelve were sequenced and identified as assemblage A. Cryptosporidium spp. were not detected in any salads. Overall, pre-harvest and post-harvest preventive measures may be need for G. duodenalis control throughout the food production industry, from the field to consumers.

Growth and inactivation of Listeria monocytogenes in sterile extracts of fruits and vegetables: Impact of the intrinsic factors pH, sugar and organic acid content

Intrinsic characteristics of fresh produce, such as pH, water activity, acid content and nutrient availability are critical factors in determining the survival and growth of Listeria monocytogenes (Lm). In this study, sterile fresh produce juice was used to analyze Lm growth potential among 14 different commodities and to identify physicochemical characteristics in those juices that affect Lm growth. Significant growth of Lm was observed in juices with pH ≥5.6 and low acidity (0.04-0.07 % titratable acidity (TA)) (cantaloupe, carrot, celery, green pepper, parsley, and romaine lettuce), slight reduction of Lm was observed in juices with pH 4.1 (tomato) and pH 3.9 (mango), and no Lm counts were recovered from juices with pH ≤3.8 and high acidity (0.28-1.17 % TA) (apple, blueberry, grape, peach, and pineapple). Although these acidic fruit juices possessed a high sugar content, the pH and acidity of produce juice seemed to be the primary determinants for Lm growth. The neutralization of acidic juices (i.e., Fuji and Gala apple, blueberry, grape, mango, pineapple, peach, and tomato) enabled Lm growth at 37 °C in all juices except for Gala apple and peach. Strong decline in Lm populations in Gala apple, grape and peach juices might be linked to sensitivity to organic acids, such as malic acid. Furthermore, Lm populations significantly decreased in pH-neutral (7.6) cauliflower juice, suggesting that potential antilisterial substances may play a role in Lm decline in cauliflower juice.

Listeria monocytogenes Illness and Deaths Associated With Ongoing Contamination of a Multiregional Brand of Ice Cream Products, United States, 2010-2015

BACKGROUND

Frozen foods have rarely been linked to Listeria monocytogenes illness. We describe an outbreak investigation prompted by both hospital clustering of illnesses and product testing.

METHODS

We identified outbreak-associated listeriosis cases using whole-genome sequencing (WGS), product testing results, and epidemiologic linkage to cases in the same Kansas hospital. We reviewed hospital medical and dietary records, product invoices, and molecular subtyping results. Federal and state officials tested product and environmental samples for L. monocytogenes.

RESULTS

Kansas officials were investigating 5 cases of listeriosis at a single hospital when, simultaneously, unrelated sampling for a study in South Carolina identified L. monocytogenes in Company A ice cream products made in Texas. Isolates from 4 patients and Company A products were closely related by WGS, and the 4 patients with known exposures had consumed milkshakes made with Company A ice cream while hospitalized. Further testing identified L. monocytogenes in ice cream produced in a second Company A production facility in Oklahoma; these isolates were closely related by WGS to those from 5 patients in 3 other states. These 10 illnesses, involving 3 deaths, occurred from 2010 through 2015. Company A ultimately recalled all products.

CONCLUSIONS

In this US outbreak of listeriosis linked to a widely distributed brand of ice cream, WGS and product sampling helped link cases spanning 5 years to 2 production facilities, indicating longstanding contamination. Comprehensive sanitation controls and environmental and product testing for L. monocytogenes with regulatory oversight should be implemented for ice cream production.

Genomic Surveillance of Listeria monocytogenes in Taiwan, 2014 to 2019

Listeria monocytogenes is a life-threatening foodborne pathogen. Here, we report the genomic characterization of a nationwide dataset of 411 clinical and 82 food isolates collected in Taiwan between 2014 and 2019. The observed incidence of listeriosis increased from 0.83 to 7 cases per million population upon implementation of mandatory notification in 2018. Pregnancy-associated cases accounted for 2.8% of human listeriosis and all-cause 7-day mortality was of 11.9% in nonmaternal-neonatal listeriosis. L. monocytogenes was isolated from 90% of raw pork and 34% of chicken products collected in supermarkets. Sublineages SL87, SL5, and SL378 accounted for the majority (65%) of clinical cases. SL87 and SL378 were also predominant (57%) in food products. Five cgMLST clusters accounted for 57% clinical cases, suggesting unnoticed outbreaks spanning up to 6 years. Mandatory notification allowed identifying the magnitude of listeriosis in Taiwan. Continuous real-time genomic surveillance will allow reducing contaminating sources and disease burden. IMPORTANCE Understanding the phylogenetic relationship between clinical and food isolates is important to identify the transmission routes of foodborne diseases. Here, we performed a nationwide study between 2014 and 2019 of both clinical and food Listeria monocytogenes isolates and sequenced their genomes. We show a 9-fold increase in listeriosis reporting upon implementation of mandatory notification. We found that sublineages SL87 and SL378 predominated among both clinical (50%) and food (57%) isolates, and identified five cgMLST clusters accounting for 57% of clinical cases, suggestive of potential protracted sources of contamination over up to 6 years in Taiwan. These findings highlight that mandatory declaration is critical in identifying the burden of listeriosis, and the importance of genome sequencing for a detailed characterization of the pathogenic L. monocytogenes genotypes circulating in Asia.

Microbiological Quality of Ready-to-Eat Salad Products Collected from Retail and Catering Settings in England during 2020 to 2021

ABSTRACT

Salad and other fresh produce were collected in England from retail and catering businesses during 2020 to 2021 and were tested for Salmonella, Shiga toxin-producing Escherichia coli (STEC), Listeria, Bacillus cereus, and E. coli. Of the 604 samples collected, 57% were from retail settings and 43% were from catering settings; 61% were either salad leaves or salad leaves mixed with other products. Equal numbers of samples were prepacked or loose, and 50% were refrigerated at the time of sampling. Combining results for all microbiological parameters, 84% were interpreted as satisfactory, 12% were interpreted as borderline, and 4% were interpreted as unsatisfactory. One sample (prepacked leaves, cucumber, and tomato from a caterer) was categorized as unacceptable and potentially injurious because of detection of STEC O76; no STEC from human infections in the United Kingdom matched this isolate. No Salmonella enterica was detected, but Listeria monocytogenes was recovered from 11 samples: 1 at 20 CFU/g and the remainder at <20 CFU/g. B. cereus was detected at borderline levels (103 to ≤105 CFU/g) in 9% of samples and at an unsatisfactory level (>105 CFU/g) in one sample. E. coli was detected in 3% of samples at borderline levels (20 to ≤102 CFU/g) and in 4% at unsatisfactory levels (>102 CFU/g). There was a significant association between detection of L. monocytogenes and borderline or unsatisfactory levels of E. coli. There were no specific risk profiles associated with products with the higher levels of B. cereus, STEC, or Listeria, but elevated levels of E. coli were predominantly confined to loose products from the United Kingdom collected from caterers in summer or autumn 2021 and may have resulted from relaxation of COVID-19 restrictions. Among the L. monocytogenes isolates, only one matched those from human cases and was recovered from a prepacked mixed salad from a catering business in 2021. This isolate was the same strain as that responsible for a multicountry outbreak (2015 to 2018) associated with Hungarian-produced frozen sweet corn; no link to the outbreak food chain was established.

HIGHLIGHTS

Cultivation Conditions of Spinach and Rocket Influence Epiphytic Growth of Listeria monocytogenes

Leafy vegetables are associated with Listeriosis outbreaks due to contamination with Listeria monocytogenes. To date, contradictory findings were reported on spinach, rocket, and kale, where some studies reported growth of L. monocytogenes, while others did not. Thus, the current study investigated the reason for conflicting findings by producing leafy vegetables, where cultivation factors were known for growth potential studies. Of all polytunnel produce, kale Nero di Toscana demonstrated the highest growth potential (2.56 log cfu g−1), followed by spinach F1 Cello (1.84 log cfu g−1), rocket Buzz (1.41 log cfu g−1), spinach F1 Trumpet (1.37 log cfu g−1), and finally rocket Esmee (1.23 log cfu g−1). Thus, plant species and variety influenced L. monocytogenes growth potentials. Moreover, significantly lower growth potentials of 0.3 log cfu g−1 were identified when rocket Buzz was cultivated in open fields (1.11 log cfu g−1) instead of a polytunnel. The opposite effect was observed for spinach F1 Trumpet, where growth potentials increased significantly by 0.84 log cfu g−1 when cultivated in open fields (2.21 log cfu g−1). Furthermore, a significant seasonality effect between batches was found (p < 0.05). This study revealed that spinach and rocket cultivation conditions are at least co-factors in the reporting of differing growth potentials of L. monocytogenes across literature and should be considered when conducting future growth potential studies.

Listeria monocytogenes Pathogenesis: The Role of Stress Adaptation

Adaptive stress tolerance responses are the driving force behind the survival ability of Listeria monocytogenes in different environmental niches, within foods, and ultimately, the ability to cause human infections. Although the bacterial stress adaptive responses are primarily a necessity for survival in foods and the environment, some aspects of the stress responses are linked to bacterial pathogenesis. Food stress-induced adaptive tolerance responses to acid and osmotic stresses can protect the pathogen against similar stresses in the gastrointestinal tract (GIT) and, thus, directly aid its virulence potential. Moreover, once in the GIT, the reprogramming of gene expression from the stress survival-related genes to virulence-related genes allows L. monocytogenes to switch from an avirulent to a virulent state. This transition is controlled by two overlapping and interlinked transcriptional networks for general stress response (regulated by Sigma factor B, (SigB)) and virulence (regulated by the positive regulatory factor A (PrfA)). This review explores the current knowledge on the molecular basis of the connection between stress tolerance responses and the pathogenesis of L. monocytogenes. The review gives a detailed background on the currently known mechanisms of pathogenesis and stress adaptation. Furthermore, the paper looks at the current literature and theories on the overlaps and connections between the regulatory networks for SigB and PrfA.

Listeria monocytogenes in Irrigation Water: An Assessment of Outbreaks, Sources, Prevalence, and Persistence

As more fresh fruits and vegetables are needed to meet the demands of a growing population, growers may need to start depending on more varied sources of water, including environmental, recycled, and reclaimed waters. Some of these sources might be susceptible to contamination with microbial pathogens, such as Listeria monocytogenes. Surveys have found this pathogen in water, soil, vegetation, and farm animal feces around the world. The frequency at which this pathogen is present in water sources is dependent on multiple factors, including the season, surrounding land use, presence of animals, and physicochemical water parameters. Understanding the survival duration of L. monocytogenes in specific water sources is important, but studies are limited concerning this environment and the impact of these highly variable factors. Understanding the pathogen’s ability to remain infectious is key to understanding how L. monocytogenes impacts produce outbreaks and, ultimately, consumers’ health.

Nonsynonymous Mutations in fepR Are Associated with Adaptation of Listeria monocytogenes and Other Listeria spp. to Low Concentrations of Benzalkonium Chloride but Do Not Increase Survival of L. monocytogenes and Other Listeria spp. after Exposure to Benzalkonium Chloride Concentrations Recommended for Use in Food Processing Environments

Selection for Listeria monocytogenes strains that are tolerant to quaternary ammonium compounds (such as benzalkonium chloride [BC]) is a concern across the food industry, including in fresh produce processing environments. This study evaluated the ability of 67 strains of produce-associated L. monocytogenes and other Listeria spp. (“parent strains”) to show enhanced BC tolerance after serial passaging in increasing BC concentrations and to maintain this tolerance after substreaking in the absence of BC. After serial passaging in BC, 62/67 “BC passaged cultures” showed higher MICs (4 to 20 mg/L) than parent strains (2 to 6 mg/L). After the substreaking of two isolates from BC passaged cultures for each parent strain, 105/134 “adapted isolates” maintained MICs (4 to 6 mg/L) higher than parent strain MICs. These results suggested that adapted isolates acquired heritable adaptations that confer BC tolerance. Whole-genome sequencing and Sanger sequencing of fepR, a local repressor of the MATE family efflux pump FepA, identified nonsynonymous fepR mutations in 48/67 adapted isolates. The mean inactivation of adapted isolates after exposure to use-level concentrations of BC (300 mg/L) was 4.48 log, which was not significantly different from inactivation observed in parent strains. Serial passaging of cocultures of L. monocytogenes strains containing bcrABC or qacH did not yield adapted isolates that showed enhanced BC tolerance in comparison to that of monocultures. These results suggest that horizontal gene transfer either did not occur or did not yield isolates with enhanced BC tolerance. Overall, this study provides new insights into selection of BC tolerance among L. monocytogenes and other Listeria spp.

IMPORTANCEListeria monocytogenes tolerance to quaternary ammonium compounds has been raised as a concern with regard to L. monocytogenes persistence in food processing environments, including in fresh produce packing and processing environments. Persistence of L. monocytogenes can increase the risk of product contamination, food recalls, and foodborne illness outbreaks. Our study shows that strains of L. monocytogenes and other Listeria spp. can acquire heritable adaptations that confer enhanced tolerance to low concentrations of benzalkonium chloride, but these adaptations do not increase survival of L. monocytogenes and other Listeria spp. when exposed to concentrations of benzalkonium chloride used for food contact surface sanitation (300 mg/L). Overall, these findings suggest that the emergence of benzalkonium chloride-tolerant Listeria strains in food processing environments is of limited concern, as even strains adapted to gain higher MICs in vitro maintain full sensitivity to the concentrations of benzalkonium chloride used for food contact surface sanitation.

The Microbial Metagenome of Eluates Obtained From the Surface of Broccoli Heads Subjected to Different Light Treatments

Foodborne illnesses present a major threat to public health and are frequently attributed to foodborne pathogens present on fresh produce. Some opportunistic pathogens of broccoli are also responsible for causing head rot. Three different light treatments, UV-C, red LED (50 μml/m²/s), and UV-C + LED were used to treat broccoli prior to or during storage. Following the light treatments, microorganisms present in eluates obtained from the surface of broccoli heads were characterized using a metagenomic approach. Metagenomic DNA libraries were subjected to high-throughput sequencing on an Illumina Hiseq platform. Results indicated that the combined treatment of LED red light and UV-C provided the best sensory preservation of broccoli, followed by LED red light and then UV-C. The bacterial communities in the eluates obtained from the surface of broccoli heads in all three light treatments were primarily represented at the phylum level by Proteobacteria and Firmicutes, while fungal communities were primarily represented by Ascomycota and Basidiomycota. Further analysis indicated that the all three light treatments reduced the presence of foodborne pathogens and bacterial taxa responsible for broccoli spoilage. While UV-C had a significant inhibitory effect on Botrytis cinerea, the light treatments increased the relative abundance of Pseudomonas fluorescens. Results indicate that a metagenomic approach can be used to detect pathogenic bacteria and fungi on fresh vegetables and assess the impact of management practices, such as light treatments, designed to maintain postharvest quality, on the composition of the microbiome present on the surface of harvested produce.

Prevalence and Clonal Diversity of over 1,200 Listeria monocytogenes Isolates Collected from Public Access Waters near Produce Production Areas on the Central California Coast during 2011 to 2016

A 5-year survey of public access surface waters in an agricultural region of the Central California Coast was done to assess the prevalence of the foodborne pathogen Listeria monocytogenes. In nature, L. monocytogenes lives as a saprophyte in soil and water, which are reservoirs for contamination of preharvest produce. Moore swabs were deployed biweekly in lakes, ponds, streams, and rivers during 2011 to 2016. L. monocytogenes was recovered in 1,224 of 2,922 samples, resulting in 41.9% prevalence. Multiple subtypes were isolated from 97 samples, resulting in 1,323 L. monocytogenes isolates. Prevalence was higher in winter and spring and after rain events in some waterways. Over 84% of the isolates were serotype 4b. Whole-genome sequencing was done on 1,248 isolates, and in silico multilocus sequence typing revealed 74 different sequence types (STs) and 39 clonal complexes (CCs). The clones most isolated, CC639, CC183, and CC1, made up 27%, 19%, and 13%, respectively, of the sequenced isolates. Other types were CC663, CC6, CC842, CC4, CC2, CC5, and CC217. All sequenced isolates contained intact copies of core L. monocytogenes virulence genes, and pathogenicity islands LIPI-3 and LIPI-4 were identified in 73% and 63%, respectively, of the sequenced isolates. The virulence factor internalin A was predicted to be intact in all but four isolates, while genes important for sanitizer and heavy metal resistance were found in <5% of the isolates. These waters are not used for crop irrigation directly, but they are available to wildlife and can flood fields during heavy rains. IMPORTANCE Listeria monocytogenes serotype 4b and 1/2a strains are implicated in most listeriosis, and hypervirulent listeriosis stems from strains containing pathogenicity islands LIPI-3 and LIPI-4. The waters and sediments in the Central California Coast agricultural region contain widespread and diverse L. monocytogenes populations, and all the isolates contain intact virulence genes. Emerging clones CC183 and CC639 were the most abundant clones, and major clones CC1, CC4, and CC6 were well represented. CC183 was responsible for three produce-related outbreaks in the last 7 years. Most of the isolates in the survey differ from those of lesser virulence that are often isolated from foods and food processing plants because they contain genes encoding an intact virulence factor, internalin A, and most did not contain genes for sanitizer and heavy metal resistance. This isolate collection is important for understanding L. monocytogenes populations in agricultural and natural regions.

Evaluation of the Persistence and Characterization of Listeria monocytogenes in Foodservice Operations

Listeria monocytogenes is a major foodborne pathogen that can contaminate food products and colonize food-producing facilities. Foodservice operations (FSOp) are frequently responsible for foodborne outbreaks due to food safety practices failures. We investigated the presence of and characterized L. monocytogenes from two FSOp (cafeterias) distributing ready-to-eat meals and verified FSOp’s compliance with good manufacturing practices (GMP). Two facilities (FSOp-A and FSOp-B) were visited three times each over 5 months. We sampled foods, ingredients, and surfaces for microbiological analysis, and L. monocytogenes isolates were characterized by phylogenetic analyses and phenotypic characteristics. GMP audits were performed in the first and third visits. A ready-to-eat salad (FSOp-A) and a frozen ingredient (FSOp-B) were contaminated with L. monocytogenes, which was also detected on Zone 3 surfaces (floor, drains, and a boot cover). The phylogenetic analysis demonstrated that FSOp-B had persistent L. monocytogenes strains, but environmental isolates were not closely related to food or ingredient isolates. GMP audits showed that both operations worked under “fair” conditions, and “facilities and equipment” was the section with the least compliances. The presence of L. monocytogenes in the environment and GMP failures could promote food contamination with this pathogen, presenting a risk to consumers.

Dynamics of Listeria monocytogenes and the microbiome on fresh-cut cantaloupe and romaine lettuce during storage at refrigerated and abusive temperatures

Listeria monocytogenes (Lm) outbreaks and recalls associated with fresh produce in recent years have heightened concerns and demands from industry and consumers to more effectively mitigate the contamination risk of this foodborne pathogen on fresh produce. In this study, the growth of Lm and indigenous bacteria on fresh-cut cantaloupe and romaine lettuce held at refrigerated (4 °C) and abusive (10-24 °C) temperatures was determined by both culture dependent and independent methods. Composition and dynamics of bacterial communities on Lm inoculated and non-inoculated samples were analyzed by 16S rRNA high-throughput sequencing. Fresh-cut cantaloupe provided favorable growth conditions for Lm proliferation (1.7 and >6 log increase at refrigerated and abusive temperatures, respectively) to overtake indigenous bacteria. The Lm population also increased on fresh-cut lettuce, but the growth rate was lower than that of the total mesophilic bacteria, resulting in 0.4 and >2 log increase at refrigerated and abusive temperatures. Microbial diversity of fresh-cut cantaloupe was significantly lower than that of fresh-cut romaine lettuce. The Shannon index of microbial communities on cantaloupe declined after storage, but it was not significantly changed on lettuce samples. Shifts in the bacterial microbiome on cantaloupe were mainly affected by Lm inoculation, while both inoculation and storage temperature played significant roles on lettuce bacterial communities. Multiple indigenous bacteria, including Leuconostoc and Weissella spp., were negatively correlated to Lm abundance on romaine lettuce, and were determined by bioassay as potential anti-listerial species. Data derived from this study contribute to better understanding of the relationship between Lm and indigenous microbiota on fresh-cut produce during storage.

Assessment of Reference Method Selective Broth and Plating Media with 19 Listeria Species Highlights the Importance of Including Diverse Species in Listeria Method Evaluations

ABSTRACT

Reference methods developed for detection of Listeria monocytogenes are commonly used for detection of Listeria at the genus level. Improved method performance data are needed because this genus has expanded from 6 to 26 species and now includes several Listeria sensu lato species, which can have phenotypes distinct from those of Listeria sensu stricto. We evaluated growth of 19 Listeria species, including 12 recently described Listeria sensu lato species, using the media specified by (i) the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual, (ii) the U.S. Department of Agriculture (USDA) Microbiology Laboratory Guidebook, and (iii) the International Organization for Standardization (ISO). The FDA broth enrichment procedure allowed all species to grow to detectable levels (≥4 log CFU/mL), yielded the highest mean growth (7.58 log CFU/mL), and was the only procedure with which no Listeria sensu lato species yielded significantly higher growth than did a comparison Listeria sensu stricto species. With the USDA and ISO broth enrichment procedures, several Listeria sensu lato species yielded significantly higher growth than did either Listeria seeligeri or Listeria ivanovii, suggesting that these two Listeria sensu stricto species could be outgrown by Listeria sensu lato species. On selective and differential agar media, L. seeligeri, L. ivanovii, and Listeria grayi produced colonies with atypical morphology and/or growth of these species was inhibited (which may lead to incorrect classification of a sample as negative), whereas several newly described Listeria sensu lato species grew to high levels and produced colonies with typical morphology. Overall, our study results indicate that the ability to detect various Listeria species can be impacted by the specific broth and selective and differential agar used. Our data can help guide selection of appropriate media and detection methods for environmental Listeria monitoring programs and methods that are most likely to detect the targeted Listeria groups (e.g., Listeria sensu stricto, which appear to be the most appropriate index organisms for the pathogen L. monocytogenes).

HIGHLIGHTS

Listerial Spontaneous Bacterial Peritonitis

Spontaneous bacterial peritonitis (SBP) is a severe complication of ascites often seen in advanced hepatic disease that is most commonly caused by Gram-negative bacilli. Here, we report a rare case of Listeria monocytogenes SBP, diagnosed by peritoneal fluid culture and responsive to ampicillin, in a patient with portal hypertension secondary to nodular regenerative hyperplasia. Because Listeria species are resistant to empiric SBP therapies and delays in treatment have been associated with increased mortality, they must be considered in high-risk patients.

Incidence, Demographic, and Seasonal Risk Factors of Infections Caused by Five Major Enteric Pathogens, Ontario, Canada, 2010-2017

In Canada, enteric infections cause significant health and economic burden. We evaluated the individual characteristics of laboratory-confirmed cases of Campylobacter spp. (n = 28,728), non-typhoidal Salmonella spp. (n = 22,640), Yersinia spp. (n = 1674), Verotoxin-producing Escherichia coli (VTEC; n = 1340), and Listeria monocytogenes (n = 471), reported between 2010 and 2017 inclusive, in Ontario, Canada (population ∼13,500,000). We calculated overall and pathogen-specific annual and mean incidence rates (IRs) for Ontario. We used multivariable Poisson and negative binomial regression models to estimate incidence rate ratios (IRRs) for years, seasons, age groups, and sexes, and we included two-way age and sex interaction terms in the models. Campylobacter and Salmonella infections had the highest IRs whereas Listeria infections had the lowest IRs. None of the infections showed long-term trends over the 8-year study period; however, rates of all five infections were elevated in the summer. More Salmonella, VTEC, and Listeria infections were linked to disease outbreaks than were Campylobacter and Yersinia infections. Overall, mean IRs of Campylobacter, Salmonella, Yersinia, and VTEC infections were highest in children 0-4 years old, whereas Listeria IRs peaked in adults 60 years and older. Higher mean IRs of Campylobacter were observed in males. No other differences by sex were statistically significant. The same mean rate was observed in both sexes for Listeria. Adjusting for all other factors, significant age- and sex-specific differences in IRs were observed in Campylobacter, Salmonella, and VTEC infection rates. No significant interactions of age and sex were found for Yersinia and Listeria infections. Future research should focus on the pathogen-specific socioeconomic, environmental, or agricultural risk factors that might be responsible for these infections.

Microbiological safety of spinach throughout commercial supply chains in Gauteng Province, South Africa and characterization of isolated multidrug-resistant Escherichia coli

AIM

To investigate the microbiological quality, potential foodborne pathogen presence, and to phenotypically (antimicrobial resistance [AMR] profiles) and genotypically (DNA fingerprints and diarrhoeagenic genes) characterize Escherichia coli isolated throughout spinach production systems from farm-to-sale.

METHODS AND RESULTS

Samples (n = 288) were collected from two commercial supply chains using either river or borehole irrigation water. E. coli was enumerated throughout the chain where river water was directly used for overhead irrigation at levels between 0.00 and 3.22 log colony forming unit (CFU) g^-1 . Following enrichment, isolation and matrix-assisted laser desorption ionization time-of-flight mass spectrometry identification, E. coli was isolated from 22.57% (n = 65/288) of all samples. Salmonella spp. were isolated from 3% (n = 9/288) of river and irrigation water samples on one farm, and no Listeria monocytogenes was detected throughout the study. Of the 80 characterized E. coli isolates, one harboured the stx2 virulence gene, while 43.75% (n = 35) were multidrug resistant. Overall, 26.30% of the multidrug-resistant E. coli isolates were from production scenario one that used river irrigation water, and 17.50% from the second production scenario that used borehole irrigation water. A greater percentage of resistance phenotypes were from water E. coli isolates (52.50%), than isolates from spinach (37.50%). E. coli isolates from spinach and irrigation water clustered together at high similarity values (>90%) using enterobacterial repetitive intergenic consensus-polymerase chan reaction analysis.

CONCLUSIONS

This study reported the presence of multidrug-resistant environmental E. coli throughout spinach production from farm, during processing and up to retail. Furthermore, the similarity of multi-drug resistant E. coli isolates suggests transfer from irrigation water to spinach in both scenarios, reiterating that irrigation water for vegetables consumed raw, should comply with standardized microbiological safety guidelines.

SIGNIFICANCE AND IMPACT OF STUDY

Multidrug-resistant E. coli presence throughout spinach production emphasizes the necessity of increased surveillance of AMR in fresh produce and the production environment within a One Health paradigm to develop AMR mitigation strategies.

Genomic Determinants of Pathogenicity and Antimicrobial Resistance for 60 Global Listeria monocytogenes Isolates Responsible for Invasive Infections

Listeria monocytogenes remains a significant public health threat, causing invasive listeriosis manifested as septicemia, meningitis, and abortion, with up to 30% of cases having a fatal outcome. Tracking the spread of invasive listeriosis requires an updated knowledge for virulence factors (VFs) and antimicrobial resistance features, which is an essential step toward its clinical diagnosis and treatment. Taking advantage of high-throughput genomic sequencing, we proposed that the differential genes based on the pathogenomic composition could be used to evaluate clinical observations and therapeutic options for listeriosis. Here, we performed the comparative genomic analysis of 60 strains from five continents with a diverse range of sources, representing serotypes 1/2a, 1/2b, 1/2c, and 4b, comprising lineage I and lineage II and including 13 newly contributed Chinese isolates from clinical cases. These strains were associated with globally distributed clonal groups linked with confirmed foodborne listeriosis outbreak and sporadic cases. We found that L. monocytogenes strains from clonal complex (CC) CC8, CC7, CC9, and CC415 carried most of the adherence and invasive genes. Conversely, CC1, CC2, CC4, and CC6 have the least number of adherence and invasive genes. Additionally, Listeria pathogenicity island-1 (LIPI-1), LIPI-2, intracellular survival, surface anchoring, and bile salt resistance genes were detected in all isolates. Importantly, LIPI-3 genes were harbored in CC3, CC224, and ST619 of the Chinese isolates and in CC1, CC4, and CC6 of other worldwide isolates. Notably, Chinese isolates belonging to CC14 carried antibiotic resistance genes (ARGs) against β-lactams (blaTEM-101, blaTEM-105) and macrolide (ermC-15), whereas CC7 and CC8 isolates harbored ARGs against aminoglycoside (aadA10_2, aadA6_1), which may pose a threat to therapeutic efficacy. Phylogenomic analysis showed that CC8, CC7, and CC5 of Chinese isolates, CC8 (Swiss and Italian isolates), and CC5 and CC7 (Canadian isolates) are closely clustered together and belonged to the same CC. Additionally, CC381 and CC29 of Chinese isolates shared the same genomic pattern as CC26 of Swiss isolate and CC37 of Canadian isolate, respectively, indicating strong phylogenomic relation between these isolates. Collectively, this study highlights considerable clonal diversity with well-recognized virulence and antimicrobial-resistant determinants among Chinese and worldwide isolates that stress to design improved strategies for clinical therapies.

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.

Estimating case fatality risk of severe Yellow Fever cases: systematic literature review and meta-analysis

BACKGROUND

Case fatality risk (CFR), commonly referred to as a case fatality ratio or rate, represents the probability of a disease case being fatal. It is often estimated for various diseases through analysis of surveillance data, case reports, or record examinations. Reported CFR values for Yellow Fever vary, offering wide ranges. Estimates have not been found through systematic literature review, which has been used to estimate CFR of other diseases. This study aims to estimate the case fatality risk of severe Yellow Fever cases through a systematic literature review and meta-analysis.

METHODS

A search strategy was implemented in PubMed and Ovid Medline in June 2019 and updated in March 2021, seeking reported severe case counts, defined by fever and either jaundice or hemorrhaging, and the number of those that were fatal. The searches yielded 1,133 studies, and title/abstract review followed by full text review produced 14 articles reporting 32 proportions of fatal cases, 26 of which were suitable for meta-analysis. Four studies with one proportion each were added to include clinical case data from the recent outbreak in Brazil. Data were analyzed through an intercept-only logistic meta-regression with random effects for study. Values of the I2 statistic measured heterogeneity across studies.

RESULTS

The estimated CFR was 39 % (95 % CI: 31 %, 47 %). Stratifying by continent showed that South America observed a higher CFR than Africa, though fewer studies reported estimates for South America. No difference was seen between studies reporting surveillance data and studies investigating outbreaks, and no difference was seen among different symptom definitions. High heterogeneity was observed across studies.

CONCLUSIONS

Approximately 39 % of severe Yellow Fever cases are estimated to be fatal. This study provides the first systematic literature review to estimate the CFR of Yellow Fever, which can provide insight into outbreak preparedness and estimating underreporting.

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

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

Big Data Impacting Dynamic Food Safety Risk Management in the Food Chain

Foodborne pathogens are a major contributor to foodborne illness worldwide. The adaptation of a more quantitative risk-based approach, with metrics such as Food safety Objectives (FSO) and Performance Objectives (PO) necessitates quantitative inputs from all stages of the food value chain. The potential exists for utilization of big data, generated through digital transformational technologies, as inputs to a dynamic risk management concept for food safety microbiology. The industrial revolution in Internet of Things (IoT) will leverage data inputs from precision agriculture, connected factories/logistics, precision healthcare, and precision food safety, to improve the dynamism of microbial risk management. Furthermore, interconnectivity of public health databases, social media, and e-commerce tools as well as technologies such as blockchain will enhance traceability for retrospective and real-time management of foodborne cases. Despite the enormous potential of data volume and velocity, some challenges remain, including data ownership, interoperability, and accessibility. This paper gives insight to the prospective use of big data for dynamic risk management from a microbiological safety perspective in the context of the International Commission on Microbiological Specifications for Foods (ICMSF) conceptual equation, and describes examples of how a dynamic risk management system (DRMS) could be used in real-time to identify hazards and control Shiga toxin-producing Escherichia coli risks related to leafy greens.

Anti-listerial properties of chemical constituents of Eruca sativa (rocket salad): From industrial observation to in vitro activity

The frequency of foodborne outbreaks epidemiologically associated with Listeria monocytogenes in fresh produce has increased in recent years. Although L. monocytogenes may be transferred from the environment to vegetables during farming, contamination of food products most commonly occurs in food processing facilities, where L. monocytogenes has the ability to establish and persist on processing equipment. The current study was undertaken to collect data on the occurrence of L. monocytogenes and the identity of the endogenous microbiota in a fresh produce processing facility, for which information has remained scarce. L. monocytogenes was not detected in the facility. Experiments simulating conditions in the processing environment were performed, including examination of bacterial growth in nutrients based on vegetables (salad juice) compared to in other types of nutrients (fish, meat). Results showed that the endogenous microbiota (dominated by Pseudomonas) grew well in iceberg lettuce and rocket salad juice at low temperatures, while growth inhibition of L. monocytogenes was observed, particularly in rocket salad juice. The anti-listerial activity in rocket salad juice was retained in a polar chromatographic fraction containing several metabolites. Characterization of this active fraction, using LC-MS/MS, led to identification of 19 compounds including nucleosides and amino acids. Further work is necessary to determine the molecular mechanism responsible for the inhibitory activity of rocket salad constituents. The study nevertheless suggests that the available nutrients, as well as a low temperature (3 °C) and the in-house bacterial flora, may influence the prevalence of L. monocytogenes in fresh produce processing facilities.

Guidance on date marking and related food information: part 1 (date marking)

A risk-based approach was developed to be followed by food business operators (FBO) when deciding on the type of date marking (i.e. 'best before' date or 'use by' date), setting of shelf-life (i.e. time) and the related information on the label to ensure food safety. The decision on the type of date marking needs to be taken on a product-by-product basis, considering the relevant hazards, product characteristics, processing and storage conditions. The hazard identification is food product-specific and should consider pathogenic microorganisms capable of growing in prepacked temperature-controlled foods under reasonably foreseeable conditions. The intrinsic (e.g. pH and aw), extrinsic (e.g. temperature and gas atmosphere) and implicit (e.g. interactions with competing background microbiota) factors of the food determine which pathogenic and spoilage microorganisms can grow in the food during storage until consumption. A decision tree was developed to assist FBOs in deciding the type of date marking for a certain food product. When setting the shelf-life, the FBO needs to consider reasonably foreseeable conditions of distribution, storage and use of the food. Key steps of a case-by-case procedure to determine and validate the shelf-life period are: (i) identification of the relevant pathogenic/spoilage microorganism and its initial level, (ii) characterisation of the factors of the food affecting the growth behaviour and (iii) assessment of the growth behaviour of the pathogenic/spoilage microorganism in the food product during storage until consumption. Due to the variability between food products and consumer habits, it was not appropriate to present indicative time limits for food donated or marketed past the 'best before' date. Recommendations were provided relating to training activities and support, using 'reasonably foreseeable conditions', collecting time-temperature data during distribution, retail and domestic storage of foods and developing Appropriate Levels of Protection and/or Food Safety Objectives for food-pathogen combinations.

Effectiveness of Phage-Based Inhibition of Listeria monocytogenes in Food Products and Food Processing Environments

Providing safe products and compliance of legal requirements is still a great challenge for food manufacturers regarding microbiological safety, especially in the context of Listeria monocytogenes food contamination. L. monocytogenes is a human pathogen, which, due to the ability of survival and proliferation in preservation conditions such as high salinity, acidity and refrigeration temperatures, is a significant threat to the food industry. Novel methods of elimination of the bacterial pathogen in food products and food processing environments are required. Among emerging technologies, one of the very promising solutions is using bacteriophages as natural control agents. This review focus on the major aspects of phage-based inhibition of L. monocytogenes in aspects of food safety. We describe an overview of foods and technological factors influencing the efficacy of phage use in biocontrol of L. monocytogenes. The most noteworthy are food matrix properties, phage concentration and stability, the time of phage application and product storage temperature. The combined methods, phage immobilization (active packing), pathogen resistance to phages and legislation aspects of antilisterial bacteriophage use in the food industry are also discussed.

Planar Interdigitated Aptasensor for Flow-Through Detection of Listeria spp. in Hydroponic Lettuce Growth Media

Irrigation water is a primary source of fresh produce contamination by bacteria during the preharvest, particularly in hydroponic systems where the control of pests and pathogens is a major challenge. In this work, we demonstrate the development of a Listeria biosensor using platinum interdigitated microelectrodes (Pt-IME). The sensor is incorporated into a particle/sediment trap for the real-time analysis of irrigation water in a hydroponic lettuce system. We demonstrate the application of this system using a smartphone-based potentiostat for rapid on-site analysis of water quality. A detailed characterization of the electrochemical behavior was conducted in the presence/absence of DNA and Listeria spp., which was followed by calibration in various solutions with and without flow. In flow conditions (100 mL samples), the aptasensor had a sensitivity of 3.37 ± 0.21 k log-CFU-1 mL, and the LOD was 48 ± 12 CFU mL-1 with a linear range of 102 to 104 CFU mL-1. In stagnant solution with no flow, the aptasensor performance was significantly improved in buffer, vegetable broth, and hydroponic media. Sensor hysteresis ranged from 2 to 16% after rinsing in a strong basic solution (direct reuse) and was insignificant after removing the aptamer via washing in Piranha solution (reuse after adsorption with fresh aptamer). This is the first demonstration of an aptasensor used to monitor microbial water quality for hydroponic lettuce in real time using a smartphone-based acquisition system for volumes that conform with the regulatory standards. The aptasensor demonstrated a recovery of 90% and may be reused a limited number of times with minor washing steps.

Inhibition of Listeria monocytogenes by the Staphylococcus capitis - derived bacteriocin capidermicin

Natural methods to control food pathogens are required and bacteriocins have received much interest in this regard. The aim of this study was to investigate the ability of the novel bacteriocin capidermicin to inhibit Listeria monocytogenes. Agar-based deferred antagonism assays were carried out with the capidermicin producer against 17 L. monocytogenes strains and large zones of inhibition were observed for 12 strains. Minimal inhibitory concentration assays performed with purified capidermicin peptide revealed MIC values between 680 nM and 11 μM. Biofilm assays were performed with five L. monocytogenes strains. Addition of capidermicin prevented biofilm formation by one strain and could remove pre-established biofilms of all five strains. Broth based growth experiments demonstrated that addition of capidermicin resulted in an extended lag phase of both L. monocytogenes strains tested. Kill-curve experiments showed that capidermicin was able to potentiate the anti-Listeria effects of the lantibiotic nisin. This enhanced killing by the combination of both peptides was also observed in model food systems (cottage cheese and chocolate milk). In summary, we show that capidermicin can inhibit L. monocytogenes and warrants further investigation as a potential natural agent for the control of this pathogen.

Survival of Salmonella enterica subsp. enterica serovar Javiana and Listeria monocytogenes is dependent on type of soil-free microgreen cultivation matrix

AIMS

This study measured the survival of Listeria monocytogenes and Salmonella enterica subsp. enterica serovar Javiana over a 10-day period on four soil-free cultivation matrix (SFCM) types in the absence of microgreens and fertilizers.

METHODS AND RESULTS

Coco coir (CC), a Sphagnum peat/vermiculite mix, Biostrate^® and hemp mat samples were inoculated with 3 × 10⁶  CFU per ml bacteria, incubated at room temperature, and analysed on day 0, 1, 3, 6, and 10. Statistically significant differences in pathogen survival were observed across multiple time points for hemp and Biostrate compared to CC, peat and bacteria in phosphate buffered saline (PBS) (P < 0·05). S. Javiana showed greater overall survival compared to Listeria (P < 0·0002). By day 10, S. Javiana persisted at the initial inoculum concentration for hemp and Biostrate while declining by 1-2 log CFU per ml in CC, peat and PBS. Listeria also persisted at the initial concentration in hemp and Biostrate but decreased to 1 log CFU per ml in peat and below the detection limit in CC and PBS.

CONCLUSIONS

Overall, there are survival differences between bacterial pathogens in SFCM used in microgreen production systems. To our knowledge, this is the first comparison of survival among SFCM involving a S. enterica serovar and L. monocytogenes, and the first study comparing CC, Biostrate and hemp.

SIGNIFICANCE AND IMPACT OF THE STUDY

Microgreens production systems predominantly utilize soil alternatives, and it is not well-understood how pathogen transmission risk may be affected by the type of SFCM. The results of this study impact the microgreen industry as media selection may be used to reduce the risk of bacterial pathogen proliferation and transmission to the plant potentially resulting in potential foodborne illness.