Listeria Monocytogenes Outbreak Research Articles

Oxford Nanopore's 2024 sequencing technology for Listeria monocytogenes outbreak detection and source attribution: progress and clone-specific challenges.

Whole genome sequencing is an essential cornerstone of pathogen surveillance and outbreak detection. Established sequencing technologies are currently being challenged by Oxford Nanopore Technologies (ONT), which offers an accessible and cost-effective alternative enabling gap-free assemblies of chromosomes and plasmids. Limited accuracy has hindered its use for investigating pathogen transmission, but recent technology updates have brought significant improvements. To evaluate its readiness for outbreak detection, we selected 78 Listeria monocytogenes isolates from diverse lineages or known epidemiological clusters for sequencing with ONT's V14 Rapid Barcoding Kit and R10.4.1 flow cells. The most accurate of several tested workflows generated assemblies with a median of one error (SNP or indel) per assembly. For 66 isolates, the cgMLST profiles from ONT-only assemblies were identical to those generated from Illumina data. Eight assemblies were of lower quality, with more than 20 erroneous sites each, primarily caused by methylations at the GAAGAC motif (5'-GAAG6mAC-3'/5'-GT4mCTTC-3'). This led to inaccurate clustering, failing to group isolates from a persistence-associated clone that carried the responsible restriction-modification system. Out of 50 methylation motifs detected among the 78 isolates, only the GAAGAC motif was linked to substantially increased error rates. Our study shows that most L. monocytogenes genomes assembled from ONT-only data are suitable for high-resolution genotyping, but further improvements of chemistries or basecallers are required for reliable routine use in outbreak and food safety investigations.

Antilisterial effect of alkyl polyglycosides biosurfactant and modes of action

Several outbreaks of Listeria monocytogenes originated mainly from contaminated contact surfaces. Thus, this study investigated the antilisterial effect of natural surfactants in terms of their use as a 2-in-1 sanitizing washer on a food contact surface and evaluated their modes of action. The antilisterial activity of alkyl polyglycosides (APGs), namely capryl glucoside (CA), coco glucoside (CG), and decyl glucoside (DG), was evaluated based on the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) using broth dilution assay. The results showed that CG had the strongest antilisterial activity. Therefore, CG was selected for further investigation. The time-kill assay showed a lethal effect of 0.5 % (w/w) CG by inactivating 4 Log reduction (99.99 %) of L. monocytogenes within 3 s. Furthermore, 1 % (w/w) CG with slight mechanical force in washing (by shaking) was efficient for sanitizing a stainless-steel coupon surface based on its ability to cause a total reduction of deposited L. monocytogenes (99.9 %) within 10 min. Scanning electron microscopy and applying Fourier-transform infrared spectroscopy revealed that CG chemically disrupted the cell wall and plasma membrane of L. monocytogenes within 5 min after a gentle wash. The results showed it had potent antimicrobial activity and was bactericidal against L. monocytogenes. Overall, our results supported the use of CG as a natural antibacterial surfactant to alter the chemical sanitizer and the possibility of its practical use in the food industry and for household use.

Outbreak of Listeria monocytogenes in hospital linked to a fava bean product, Finland, 2015 to 2019.

Listeria monocytogenes (Lm) is a bacterium widely distributed in the environment. Listeriosis is a severe disease associated with high hospitalisation and mortality rates. In April 2019, listeriosis was diagnosed in two hospital patients in Finland. We conducted a descriptive study to identify the source of the infection and defined a case as a person with a laboratory-confirmed Lm serogroup IIa sequence type (ST) 37. Six cases with Lm ST 37 were notified to the Finnish Infectious Diseases Registry between 2015 and 2019. Patient interviews and hospital menus were used to target traceback investigation of the implicated foods. In 2021 and 2022, similar Lm ST 37 was detected from samples of a ready-to-eat plant-based food product including fava beans. Inspections by the manufacturer and the local food control authority indicated that the food products were contaminated with Lm after pasteurisation. Our investigation highlights the importance that companies producing plant-based food are subject to similar controls as those producing food of animal origin. Hospital menus can be a useful source of information that is not dependent on patient recall.

Rapid detection of the source of a Listeria monocytogenes outbreak in Switzerland through routine interviewing of patients and whole-genome sequencing.

Listeriosis is a notifiable disease in Switzerland. In summer 2022, the Swiss Federal Office of Public Health noticed an increase in reports of listeriosis cases, indicating a possible ongoing outbreak. Here we present the approaches applied for rapidly confirming the outbreak, detecting the underlying source of infection and the measures put in place to eliminate it and contain the outbreak. For close surveillance and early detection of outbreak situations with their possible sources, listeriosis patients in Switzerland are systematically interviewed about risk behaviours and foods consumed prior to the infection.Listeria monocytogenesisolates derived from patients in medical laboratories are sent to the National Reference Laboratory for Enteropathogenic Bacteria and Listeria, where they routinely undergo whole-genome sequencing. Interview and whole-genome sequencing data are continuously linked for comparison and analysis. In summer 2022, 20 patient-derivedL. monocytogenesserotype 4b sequence type 388 strains were found to belong to an outbreak cluster (≤10 different alleles between neighbouring isolates) based on core genome multilocus sequence typing analysis. Geographically, 18 of 20 outbreak cases occurred in northeastern Switzerland. The median age of patients was 77.4 years (range: 58.1-89.7), with both sexes equally affected. Rolling analysis of the interview data revealed smoked trout from a local producer as a suspected infection source, triggering an on-site investigation of the production facility and sampling of the suspected products by the responsible cantonal food inspection team on 15 July 2022. Seven of ten samples tested positive forL. monocytogenesand the respective cantonal authority ordered a ban on production and distribution as well as a product recall. The Federal Food Safety and Veterinary Office released a nationwide public alert covering the smoked fish products concerned. Whole-genome sequencing analysis confirmed the interrelatedness of theL. monocytogenessmoked trout product isolates and the patient-derived isolates. Following the ban on production and distribution and the product recall, reporting of new outbreak-related cases rapidly dropped to zero. This listeriosis outbreak could be contained within a relatively short time thanks to identification of the source of contamination through the established combined approach of timely interviewing of every listeriosis patient or a representative and continuous molecular analysis of the patient- and food-derivedL. monocytogenesisolates. These findings highlight the effectiveness of this well-established, joint approach involving the federal and cantonal authorities and the research institutions mandated to contain listeriosis outbreaks in Switzerland.

Unveiling a Listeria monocytogenes Outbreak in a Rabbit Farm: Clinical Manifestation, Antimicrobial Resistance, Genomic Insights and Environmental Investigation.

Listeria monocytogenes poses a threat to both human and animal health. This work describes an L. monocytogenes outbreak in a Portuguese rabbit farm, detailing the isolates' clinical manifestations, necropsy findings, and phenotypic and genomic profiles. Clinical signs, exclusively observed in does, included lethargy and reproductive signs. Post-mortem examination of does revealed splenomegaly, hepatomegaly with a reticular pattern, pulmonary congestion, and haemorrhagic lesions in the uterus, with thickening of the uterine wall and purulent greyish exudates. Positive L. monocytogenes samples were identified in fattening and maternity units across different samples, encompassing does and environmental samples. Core-genome Multi Locus Sequence Typing (cgMLST) analysis confirmed the outbreak, with the 16 sequenced isolates (lineage II, CC31, and ST325) clustering within a ≤2 allelic difference (AD) threshold. Antimicrobial susceptibility testing for five antibiotics revealed that 15 out of 19 outbreak isolates were resistant to sulfamethoxazole-trimethoprim (SXT). Concordantly, all SXT-resistant sequenced isolates were found to exclusively harbour a plasmid containing a trimethoprim-resistance gene (dfrD), along with loci linked to resistance to lincosamides (lnuG), macrolides (mphB), and polyether ionophores (NarAB operon). All sequenced outbreak isolates carried the antibiotic resistance-related genes tetM, fosX, lin, norB, lmrB, sul, and mprF. The outbreak cluster comprises isolates from does and the environment, which underscores the ubiquitous presence of L. monocytogenes and emphasizes the importance of biosecurity measures. Despite limited data on listeriosis in rabbit farming, this outbreak reveals its significant impact on animal welfare and production.

Combining Whole Genome Sequencing Data from Human and Non-Human Sources: Tackling Listeria monocytogenes Outbreaks.

Listeria monocytogenes (Lm) is ubiquitous in nature and known for its ability to contaminate foods during production processes. Near real-time monitoring of whole genome sequences from food and human isolates, complemented with epidemiological data, has been used in the Netherlands since 2019 to increase the speed and success rate of source finding in the case of (active) clusters. Nine clusters with 4 to 19 human cases investigated between January 2019 and May 2023 are described. Fish production sites were most often linked to outbreaks of listeriosis (six clusters), though other types of food businesses can face similar Lm problems, as the production processes and procedures determine risk. The results showed that low levels of Lm in food samples can still be linked to disease. Therefore, the investigation of a cluster of cases and deployment of the precautionary principle helps to focus on safe food and to prevent further cases. Good practice of environmental monitoring within a food business allows early detection of potential issues with food safety and helps food businesses to take appropriate measures such as cleaning to prevent regrowth of Lm and thus future outbreaks.

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

BackgroundThis 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.MethodsIn 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.ResultsOutbreaks 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.ConclusionsWhen 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.

Effect of antimicrobial treatments applied individually and in combination on the growth of Listeria monocytogenes in Queso Fresco at 3 different temperatures

Queso fresco (QF), a fresh soft cheese, is one of the most popular Hispanic cheeses in the United States and is frequently associated with Listeria monocytogenes outbreaks. Listeria monocytogenes can grow and thrive at room temperature as well as refrigeration temperatures. A combination of antimicrobial agents provides a larger spectrum of listeriostatic and listeriocidal activity resulting in a more effective approach toward the control of L. monocytogenes. In this study, we evaluated the efficacy of 3 Food and Drug Administration-approved generally recognized as safe (GRAS) antimicrobials, nisin (NIS), lauric arginate ethyl ester (LAE), and ε-polylysine (EPL), and the endolysin PlyP100 individually and in combination for control of L. monocytogenes in QF at 4°C, 7°C, and 10°C. Additionally, growth curves of L. monocytogenes were obtained in BHI broth and QF at these temperatures. In order for an antimicrobial to be considered a postlethality treatment for L. monocytogenes, it should not allow an increase of more than 2-log over the product's shelf life. Three treatments, PlyP100, PlyP100 + NIS, and EPL + LAE, effectively kept the pathogen below the 2 log growth threshold at 4°C. However, at 7°C and 10°C, none of the antimicrobial treatments could inhibit L. monocytogenes growth (i.e., <2 log). Overall, our results suggest the importance of considering the effect of cold storage temperatures above 4°C on the antilisterial efficacy of antimicrobial treatments in QF.

Prevalence of Listeria monocytogenes and indicator microorganisms in Florida cantaloupe packinghouses, 2013–2014

Prior to the 2013 cantaloupe season, the US Food and Drug Administration notified the industry that inspections of a subset of packinghouses would commence that year in response to the 2011 Listeria monocytogenes outbreak associated with cantaloupe. In May 2013, five Florida cantaloupe packinghouses participated in an environmental monitoring survey to evaluate their sanitary conditions prior to a potential FDA inspection. Two facilities participated again in 2014. Surface swabs (n = 374) were collected in each facility and included up to 60 food contact and non-food contact surfaces, including water. Samples were enumerated for total plate counts (TPC), generic Escherichia coli, and coliforms, and enriched for Listeria. Listeria were confirmed and speciated by sequencing of the partial sigB gene, and further characterized by pulsed field gel electrophoresis (AscI and Apal). In 2013, two zone 1 surfaces in same facility, were positive for L. monocytogenes (2/233). No L. monocytogenes was detected (n = 103) in the two facilities sampled the following year, including the previously L. monocytogenes-positive facility. Prevalence of L. monocytogenes in FL cantaloupe packinghouses was generally low (2/374), compared to other food environments. TPC, coliforms, E. coli and Listeria spp. were poor indicators of L. monocytogenes contamination in Florida packinghouses.

Fast WGS source attribution of Listeria monocytogenes outbreak in a sheep flock in Abruzzo region

Abstract Background Listeriosis is a life-threatening disease in human as well as animals, cows and sheep are the most sensible to the disease. Correlation to feed is well documented (silage). Some clonal complexes (CCs) are more virulent than others and frequently involved in animal and human listeriosis. Whole genome sequencing (WGS) and in silico CCs identification and core genome multilocus sequence typing (cgMLST) determination are the best way to characterize isolates and confirm connection between clinical strains and source of contamination. This work aimed to demonstrate the advantages of using WGS to find the source of Listeria monocytogenes (Lm), causing an outbreak in an ovine farm in Abruzzo region. Methods Lm was detected according to ISO 11290-1:2017. Serogroup was determined by multiplex PCR. WGS data were obtained using Illumina platform. Sequences were used to assess CCs and cgMLST according to BIGSdb Pasteur platform. Two brain samples and 1 lymph node from 2 sheep, one sample of silage (15 analytical portion), and 1 sample of hay were tested. Results Lm was detected in all animal specimens and in 2 analytical portions of feed (silage) tested. Out of 35 colonies detected 28 were identified as Lm (27 serogoup IVb and 1 sample of silage serogroup IIa). Five colonies were selected for WGS (one from each animal brain, one from the lymph node and one from each positive analytical portion of silage), among them only one colony from the silage showed the same CC of the strains isolated from sheep (CC1). cgMLST revealed no allelic distances between these strains. Conclusions CC1 is the main virulent clone among Lm isolates often involved in human and animal outbreak. Feed may be a vehicle for Lm and could be the outbreak source. Cases ceased after removing the silage. Use of WGS is a definitive help in source attribution when feed is available and the sampling is done in a correct manner. Key messages Silage can be cause of listeriosis in livestock. WGS can improve source attribution of outbreaks detecting the relatedness of the strains and improving the epidemiological investigation in case of outbreak.

Identification of the source of a Listeria monocytogenes outbreak by investigational tracing

The number of identified listeriosis outbreaks has increased since the sequence typing of Listeria monocytogenes isolates was established in Germany. Due to the nature of the disease, listeriosis outbreaks are difficult to solve. We present investigational tracing as a simple and rapid method to conduct outbreak investigations. The method was applied in 2019 to stop a prolonged listeriosis outbreak in Germany. The starting point for the investigational tracing was nine health care facilities (HCF). Single cases developed listeriosis while they were staying at the nine facilities. Data were collected from companies that delivered foods to HCF and from ready-to-eat (RTE) foods that were consumed there. Following a step-wise approach, data analysis identified similarities in the food supply of the HCF. Food data were heterogeneous and needed to be standardised. Own brands and changing article numbers were challenging aspects during the identification of manufacturers. The analysis of the delivering companies revealed no similarities. Detailed information about the consumed risk foods for Listeria contamination became available for six HCF. All facilities served a wide variety of cold cut meat products to their in-patients. Investigational tracing revealed that only meat products from one out of 29 food business operators had been consumed in all six HCF. Further activities of the authorities enabled the identification of the outbreak strain on food products and in the processing environment of this company. A product recall and the measures taken stopped the listeriosis outbreak. Thus, investigational tracing can be crucial for the clarification of listeriosis outbreaks.

Food-borne outbreak of Listeria monocytogenes in school students in Seoul, Korea

In September 2018, an outbreak of Listeriosis cases in Korea was traced to food involved, using retrospective cohort studies and PFGE analyses. This study aimed to describe the first L.monocytogenes outbreak identified in Korea. We confirmed the presence of Serovar (4C) and virulence genes, and evaluated the genetic correlation between isolates by restriction digestion patterns of ApaI and AscI. Based on the epidemiological association, it is presumed that the seasoned crab meat with bean sprouts are contaminated by cross contamination during the bean sprouts washing (relative risk was 1.24; p-value: 0.0021 and they possessed virulence genes. Therefore, active laboratory surveillance is necessary to recognize the risk of L. monocytogenes in Korea.

Evaluation of the effectiveness of different preservation techniques on the inactivation of Listeria monocytogenes by using challenge testing protocol in the fresh, soft cheese - paneer

Paneer is a fresh, soft, unripened cheese, falls under the category of ready to eat product. From 2010 to 2015, because of consumption of soft cheese, several multistate outbreaks of Listeria monocytogenes happened in the USA. In the meantime, recalls of soft cheese happened in Australia and Canada due to association of soft cheese with L. monocytogenes. Therefore, this research was undertaken to study the growth potential of L. monocytogenes in this product by challenge testing with three different contamination modes and evaluate the effectiveness of different preservation techniques in inhibiting the growth of L. monocytogenes in this product. Results showed that paneer cheese supports the growth of L. monocytogenes to more than 2 logs (100 cfu/g) during the shelf life. It was found that the none of the preservation techniques evaluated inhibited the growth of L. monocytogenes to less than 1 log cycle during the shelf life. This study provides the scientific basis of assessing the growth potential of L. monocytogenes by challenge testing and mandates the implementation of regulatory guidelines while manufacturing, distribution, storage and importation of this product with the recommendation of use of hurdle technologies to inhibit the growth of L. monocytogenes in this product.

In vitro and in vivo characterisation of Listeria monocytogenes outbreak isolates

Listeriosis is an important food-borne disease responsible for high rates of morbidity and mortality. L. monocytogenes has been the cause of several foodborne outbreaks and its ability to adapt and survive in a wide range of environmental conditions makes eradication difficult. Many L. monocytogenes strains are avirulent but have the ability to increase their virulence if exposed to environmental stresses. The aim of this study was to explain the observed increase in virulence of outbreak L. monocytogenes isolates by using phenotypic assays and whole genome sequencing. Four L. monocytogenes isolates from sweetcorn and one isolate from a raw milk (control) were sequenced and characterised using a range of phenotypic assays. The four L. monocytogenes sweetcorn isolates displayed a significant increase for in vitro adhesion and invasion of epithelial cells compared to the control isolate. They also showed a higher level of colonisation of the liver and spleen in vivo. In addition, the four L. monocytogenes isolates displayed an increased ability to form biofilms, resist heat stress and resist a combination of antimicrobials. Investigation of the genomes of the four L. monocytogenes sweet corn isolates identified Single Nucleotide Polymorphisms (SNPs) in genes, which may have a role in the observed phenotypes characteristic of these strains, particularly in response to survival properties within the environment or in terms of virulence. We highlight the importance of combining whole genomic sequencing with phenotypic characterisation as a key element in the investigation of outbreaks of foodborne pathogens.

A Comprehensive Review on Molecular Characteristics and Food-Borne Outbreaks of Listeria monocytogenes

Listeria monocytogenes is an important foodborne pathogen which causes serious invasive illness, and affects mostly elderly and immune-compromised people, pregnant women, newborns and infants leading to listeriosis. L. monocytogenes can cause vast outbreaks due to consumption of contaminated food products, and has a significant role in public health. The pathogen has been isolated from food, human and animal samples world-wide. Neonatal listeriosis is most commonly reported incase of humans, where as in animal populations, spontaneous abortions, meningoencephalitis and endometritis are the most common. The purpose of this review is to enumerate Listeria epidemiology world-wide by using publicly available data from CDC, FDA and ProMED and by describing the details such as countries involved, source, suspected and confirmed case counts etc. to understand its public health importance. This review also offers a description of bacteriological characteristics, taxonomy, virulence determinants, typing methods, a detailed account of listeriosis in human and in animals and an up-to-date information of the recent outbreaks of L. monocytogenes. We specifically aimed at the prevalence and epidemiology of L. monocytogenes globally, since it is a major food-borne pathogen and is the third leading cause of death due to food poisoning. This review paper provides information on L. monocytogenes to understand the better management of the infection, the source of infection and route of transmission of the disease. Most of the listeriosis cases were linked with the consumption of contaminated food and it is important to identify the type of food materials to mitigate the risk of Listeriosis in the high-risk populations.

Changing epidemiology of Listeria monocytogenes outbreaks, sporadic cases, and recalls globally: A review of ProMED reports from 1996 to 2018

BackgroundThe purpose of this study was to identify global trends in Listeria monocytogenes epidemiology using ProMED reports. ProMED is a publicly available, global outbreak reporting system that uses both informal and formal sources. In the context of Listeria, ProMED reports on atypical findings such as higher than average case counts, events from unusual sources, and multinational outbreaks. MethodsKeywords “Listeria” and “listeriosis” were utilized in the ProMED search engine covering the years 1996–2018. Issue date, countries involved, source, suspected and confirmed case counts, and fatalities were extracted. Data unique to each event, including commentary by content experts, were evaluated. When multiple reports regarding the same outbreak or recall were obtained, the last report pertaining to that outbreak was utilized. Rates of Listeria events over time were compared using a normal approximation to the Poisson distribution; p < 0.05 was considered to be statistically significant. ResultsFrom 1996 through 2018, 123 Listeria events were identified in the ProMED database. Eighty-one events (65%) were associated with two or more human cases (outbreak events), 13 events (11%) were associated with only one human case (sporadic cases), and 29 events (24%) were precautionary food product recalls due to the presence of bacterial contamination without associated human cases. The implicated food vehicle was identified in 69 (85%) outbreak events and in 10 (77%) sporadic case events. Listeria contaminated foods were identified in all precautionary recall events. Overall, 28 events (23%) implicated novel food vehicles/sources. Events associated with novel food vehicles increased over the study period (p < 0.02), as did international events with more than one country involved (p < 0.02). Ten reports (8%) described hospital-acquired events. ConclusionsThis study demonstrates the use of publicly available data to document Listeria epidemiological trends, particularly in settings where foodborne disease surveillance is weak or non-existent. Over the last decade, an increasing number of events have been associated with foods not traditionally recognized as vehicles for Listeria transmission, and a rise in international events was noted. Informing high-risk individuals such as pregnant women and immunocompromised individuals of safe food handling practices is warranted. To ensure timely recall of contaminated food products, open data sharing and communication across borders is critical. Changes in food production and distribution, and improved diagnostics may have contributed to the observed changes.

Microbial analysis of commercially available US Queso Fresco

Queso Fresco (QF), a fresh Hispanic-style cheese, is often associated with Listeria monocytogenes outbreaks and recalls. Queso Fresco's susceptibility to bacterial contamination is partially due to its high pH and moisture content as well as Listeria's tolerance for the salt content typical for QF. Nine different brands of US QF, 2 packages from 4 different lots (to account for temporal variability), were sampled. The pH, salt content, and moisture content were analyzed in addition to microbial testing including yeasts and molds, coliforms, lactic acid bacteria enumeration, and L. monocytogenes counts. The cheeses were also inoculated with a cocktail of 5 food and human isolates of food-borne outbreak-associated Listeria monocytogenes strains to evaluate how the differences between brands influenced Listeria growth. Three of the cheeses underwent additional genus-level microbial analysis using extracted 16S rDNA, allowing for phylogenetic analysis between bacterial taxa including diversity and relative abundance. We found little variation between the sampled QF pH (range = 6.62-6.86), salt content (1.53-2.01%), and moisture content (43.90-54.50%). Yeasts and molds were below the detection limit of enumeration in all of the cheeses and coliforms were below the detection limit across the first 3 lots, but were detected at varying levels in the fourth lot (>3.0 most probable number/g) for 3 of the brands. Listeria monocytogenes was not isolated after enrichment in any of the samples. All cheeses tested positive for the presence of lactic acid bacteria, with only 1 of the cheeses being labeled as produced with added cultures having substantial counts. Fourteen days after inoculation with L. monocytogenes, at least 2.5 log10 cfu/g of growth was found for all QF brands stored at 4°C. Microbial genus analysis showed that, among the 3 brands, the microbial community was more similar within brand than when compared with the other 2 brands. Thermus, Anoxybacillus, and Streptococcus accounted for the dominant genera of brands A, B, and C, respectively. These variations within the microbial community may account for sensory differences and help manufacturers determine quality control consistency more readily than culture-based methods.

Listeria monocytogenes outbreak in Europe – updates in 2018

Listeria monocytogenes outbreak in Europe – updates in 2018

Multi‐country outbreak of Listeria monocytogenes serogroup IVb, multi‐locus sequence type 6, infections probably linked to frozen corn

An outbreak of invasive Listeria monocytogenes (L. monocytogenes) infections defined by whole‐genome sequencing (WGS) and probably linked to frozen corn has been ongoing in five EU Member States (Austria, Denmark, Finland, Sweden and the United Kingdom) since 2015. As of 8 March 2018, 32 cases have been reported and six patients have died due to or with the infection. WGS analysis of six non‐human L. monocytogenes isolates detected from 2016 to January 2018 in Austria, Finland, France and Sweden found these isolates closely related to the multi‐country cluster of L. monocytogenes serogroup IVb, multi‐locus sequence type 6 (ST6). The non‐human isolates were detected in two different samples from mixed frozen vegetables; three samples from frozen corn, and one sample from a surface where various vegetables could have been processed. The only common food item in all non‐human samples was corn. The WGS analysis provides a strong microbiological link between the human and the non‐human isolates and is suggestive of a potential contaminated food source related to frozen corn persisting in the food chain at least since 2016. Traceability information for the three frozen corn samples pointed to frozen corn products packed in Poland and processed/produced in Hungary. Two additional non‐human strains isolated in Austria from frozen vegetable mixes with corn as an ingredient were traced back to the same common origin in Hungary. Further investigations are needed to verify the point of contamination in the food chain. Consumption of frozen corn has been confirmed by two patients, one in Finland and one in Sweden. In addition, a Danish patient reported consumption of mixed frozen vegetables, which could have included corn. The Finnish patient confirmed consumption of frozen corn of one suspected brand, supporting an epidemiological link between the outbreak cases and frozen corn. However, no traceability and microbiological information was available for the corn consumed by the Finnish and the Swedish patients. Food business operators in Estonia, Finland, Poland and Sweden have withdrawn and recalled the implicated frozen corn products from the market. These measures are likely to significantly reduce the risk of human infections in these countries. However, new invasive listeriosis cases may be identified due to the long incubation period (1‐70 days), long shelf‐lives of frozen corn products and potential consumption of frozen corn bought by the customers before the recalls and eaten without being properly cooked. Furthermore, until the root source of contamination is established and control measures implemented, new cases may occur.

Hygienic Shortcomings of Frozen Dessert Freezing Equipment and Fate of Listeria monocytogenes on Ice Cream–Soiled Stainless Steel

Although frozen dairy desserts have a strong record of safety, recent outbreaks of foodborne disease linked to ice creams have brought new attention to this industry. There is concern that small-scale frozen dessert equipment may not comply with or be reviewed against published comprehensive design and construction sanitation specifications (National Sanitation Foundation or 3-A sanitary standards). Equipment sanitary design issues may result in reduced efficacy of cleaning and sanitation, thus increasing the likelihood of postprocess contamination with pathogenic bacteria. In this context, and given that Listeria monocytogenes outbreaks are of great concern for the frozen dessert industry, a complementary study was conducted to evaluate the fate of L. monocytogenes in ice cream mix on a stainless steel surface. Our results showed that L. monocytogenes survived for up to 6 weeks at room temperature and 9 weeks at 4°C in contaminated ice cream on a stainless steel surface. Furthermore, chlorine- and acid-based surface sanitizers had no detrimental effect on the L. monocytogenes when used at a concentration and contact time (1 min) recommended by the manufacturer; significant reduction in CFU required 5 to 20 min of contact time.