Phenotypic and genotypic antimicrobial resistance of Listeria spp. in Spain.

Listeriosis is a zoonotic disease caused by Listeria monocytogenes and Listeria ivanovii. The genus Listeria currently includes 27 recognized species and is found throughout the environment. The number of systematic studies on antimicrobial resistance in L. monocytogenes isolates from domestic farms using antimicrobial substances is limited. Importantly, dairy ruminant farms are reservoir of hypervirulent lineage I L. monocytogenes isolates, previously associated with human clinical cases. Considering that the classes of antibiotics used in food-producing domestic animals are frequently the same or closely related to those used in human medicine, studies about the impact of antibiotic use on the acquisition of antibiotic resistance in Listeria spp. in domestic animal farms are, therefore, of high importance. Here, susceptibility to 25 antibiotics was determined. Eighty-one animal-related, 35 food and 21 human pathogenic Listeria spp. isolates and 114 animal-related non-pathogenic Listeria spp. isolates were tested. Whole genome sequencing data was used for molecular characterization. Regarding L. monocytogenes, 2 strains from the clinical-associated linage I showed resistance to erythromycin, both related to dairy ruminants. Acquired resistance to one antibiotic was exhibited in 1.5% of L. monocytogenes isolates compared with 14% of non-pathogenic Listeria spp. isolates. Resistance to tetracycline (7.9%), doxycycline (7.9%), penicillin (4.4%), and ampicillin (4.4%) were the most frequently observed in non-pathogenic Listeria spp. While resistance to two or more antibiotics (5.6%) was most common in Listeria spp., isolates, resistance to one antibiotic was also observed (1.6%). The present results show that non-pathogenic Listeria spp. harbour antimicrobial resistance genes.

Isolation and engineering of a Listeria grayi bacteriophage.

The lack of bacteriophages capable of infecting the Listeria species, Listeria grayi, is academically intriguing and presents an obstacle to the development of bacteriophage-based technologies for Listeria. We describe the isolation and engineering of a novel L. grayi bacteriophage, LPJP1, isolated from farm silage. With a genome over 200,000 base pairs, LPJP1 is the first and only reported jumbo bacteriophage infecting the Listeria genus. Similar to other Gram-positive jumbo phages, LPJP1 appeared to contain modified base pairs, which complicated initial attempts to obtain genomic sequence using standard methods. Following successful sequencing with a modified approach, a recombinant of LPJP1 encoding the NanoLuc luciferase was engineered using homologous recombination. This luciferase reporter bacteriophage successfully detected 100 stationary phase colony forming units of both subspecies of L. grayi in four hours. A single log phase colony forming unit was also sufficient for positive detection in the same time period. The recombinant demonstrated complete specificity for this particular Listeria species and did not infect 150 non-L. grayi Listeria strains nor any other bacterial genus. LPJP1 is believed to be the first reported lytic bacteriophage of L. grayi as well as the only jumbo bacteriophage to be successfully engineered into a luciferase reporter.

Nationwide genomic atlas of soil-dwelling Listeria reveals effects of selection and population ecology on pangenome evolution.

Natural bacterial populations can display enormous genomic diversity, primarily in the form of gene content variation caused by the frequent exchange of DNA with the local environment. However, the ecological drivers of genomic variability and the role of selection remain controversial. Here, we address this gap by developing a nationwide atlas of 1,854 Listeria isolates, collected systematically from soils across the contiguous United States. We found that Listeria was present across a wide range of environmental parameters, being mainly controlled by soil moisture, molybdenum and salinity concentrations. Whole-genome data from 594 representative strains allowed us to decompose Listeria diversity into 12 phylogroups, each with large differences in habitat breadth and endemism. 'Cosmopolitan' phylogroups, prevalent across many different habitats, had more open pangenomes and displayed weaker linkage disequilibrium, reflecting higher rates of gene gain and loss, and allele exchange than phylogroups with narrow habitat ranges. Cosmopolitan phylogroups also had a large fraction of genes affected by positive selection. The effect of positive selection was more pronounced in the phylogroup-specific core genome, suggesting that lineage-specific core genes are important drivers of adaptation. These results indicate that genome flexibility and recombination are the consequence of selection to survive in variable environments.

Comparison of recombinant and synthetic listeriolysin- O peptide- based indirect ELISA vis-à-vis cultural isolation for detection of listeriosis in caprine and ovine species.

The present study evaluated the comparative serodiagnostic efficacy of recombinant listeriolysin-O (rLLO) and synthetic LLO- 2 peptide-based indirect ELISA vis-à-vis cultural isolation using samples (n = 1326; blood, sera, vaginal swabs, and rectal swabs) collected from caprines (n = 350) and ovines (n = 50) having reproductive and/or nervous system disorders and/or healthy animals. On screening the test sera by rLLO- based ELISA, the antibodies against LLO (ALLO) were observed in 17.71% of the caprines and 2% of the ovines, respectively, while synthetic LLO-2- based ELISA revealed ALLO in 6.86% of caprines and not in ovines. Moreover, the adsorption of positive test sera with streptolysin-O (SLO) resulted in a significant reduction (7.43%; p < 0.05) in the seropositivity with rLLO- based ELISA, whereas LLO-2- based ELISA revealed marginal reduction (4.29%; p > 0.05) in the seropositivity. Overall, the seropositivity with LLO-2 synthetic peptide revealed comparatively less cross-reactivity in comparison to rLLO. The cultural isolation yielded five pathogenic L. monocytogenes isolates and three non-pathogenic Listeria spp. from caprine samples; however, Listeria spp. could not be recovered from any of the ovine samples. Further, on comparing seropositivity with the isolation study results, it was found that two out of the five animals from which pathogenic L. monocytogenes isolated were also found seropositive in both the ELISAs even after adsorption with SLO. Interestingly, rLLO- based ELISA detected antibodies against unadsorbed caprine sera even in those samples from which non-pathogenic Listeria spp. were isolated, whereas antibodies were not detected in LLO-2 peptide-based ELISA. In conclusion, it could be inferred that the synthetic LLO-2 peptide serves as a non- cross-reactive, ideal diagnostic antigen in serodiagnosis of capro-ovine listeriosis.

The prevalence of Listeria species in different food items of animal and plant origin in Ethiopia: a systematic review and meta-analysis.

BACKGROUND: Listeriosis is one of the important emerging zoonotic disease affecting human health following the consumption of contaminated food of animal origin. It results in serious clinical complications in humans with a high case facility rate. Therefore, this systematic review and meta-analysis aimed to estimate the pooled prevalence of Listeria species in Ethiopia. METHODS: A systematic search was conducted on PubMed, Web of Science, EMBASE, Google Scholar and the Cochrane Library. All identified observational studies reporting the prevalence of Listeria species in different food items of animal and plant origin in Ethiopia were included. Three authors independently extracted data and analyzed them using STATA Version 13 statistical software. A random effects model was computed to estimate the pooled prevalence of Listeria species in Ethiopia. RESULTS: After reviewing 122 studies, five studies fulfilled the inclusion criteria were included in the meta-analysis. The findings from the five studies revealed that the pooled prevalence of Listeria species in different food items of animal and plant origin in Ethiopia was 27% (95% CI 25, 29). The highest prevalence of Listeria species was reported in beef meat followed by ice cream with prevalence rates of 62% (95% CI 50, 75) and 43% (95% CI 33, 53), respectively. CONCLUSION: The presence of Listeria species in different food items of animal and plant origin in Ethiopia is an indicator of the presence of public health hazards to the consumer, particularly to the high-risk groups. Hence, awareness creation on food safety and implementation of regulations is strongly recommended.

Genomic analysis of high copy-number sequences for the targeted detection of Listeria species using a flow-through surveillance system.

The bacterial foodborne pathogen Listeria monocytogenes has been implicated in fresh produce outbreaks with a significant economic impact. Given that L. monocytogenes is widespread in the environment, food production facilities constantly monitor for the presence of Listeria species. To develop a surveillance platform for food processing facilities, this study conducted a comparative genomic analysis for the identification of conserved high copy sequences in the ribosomal RNA of Listeria species. Simulated folding was performed to assess RNA accessibility in the identified genomic regions targeted for detection, and the developed singleplex assay accurately detected cell amounts lower than 5 cells, while no signals were detected for non-targeted bacteria. The singleplex assay was subsequently tested with a flow-through system, consisting of a DNA aptamer-capture step, followed by sample concentration and mechanical lysis for the detection of Listeria species. Validation experiments indicated the continuous flow-through system accurately detected Listeria species at low cell concentrations.

Listeria cossartiae sp. nov., Listeria farberi sp. nov., Listeria immobilis sp. nov., Listeria portnoyi sp. nov. and Listeria rustica sp. nov., isolated from agricultural water and natural environments.

A total of 27 Listeria isolates that could not be classified to the species level were obtained from soil samples from different locations in the contiguous United States and an agricultural water sample from New York. Whole-genome sequence-based average nucleotide identity blast (ANIb) showed that the 27 isolates form five distinct clusters; for each cluster, all draft genomes showed ANI values of <95 % similarity to each other and any currently described Listeria species, indicating that each cluster represents a novel species. Of the five novel species, three cluster with the Listeria sensu stricto clade and two cluster with sensu lato. One of the novel sensu stricto species, designated L. cossartiae sp. nov., contains two subclusters with an average ANI similarity of 94.9%, which were designated as subspecies. The proposed three novel sensu stricto species (including two subspecies) are Listeria farberi sp. nov. (type strain FSL L7-0091T=CCUG 74668T=LMG 31917T; maximum ANI 91.9 % to L. innocua), Listeria immobilis sp. nov. (type strain FSL L7-1519T=CCUG 74666T=LMG 31920T; maximum ANI 87.4 % to L. ivanovii subsp. londoniensis) and Listeria cossartiae sp. nov. [subsp. cossartiae (type strain FSL L7-1447T=CCUG 74667T=LMG 31919T; maximum ANI 93.4 % to L. marthii) and subsp. cayugensis (type strain FSL L7-0993T=CCUG 74670T=LMG 31918T; maximum ANI 94.7 % to L. marthii). The two proposed novel sensu lato species are Listeria portnoyi sp. nov. (type strain FSL L7-1582T=CCUG 74671T=LMG 31921T; maximum ANI value of 88.9 % to L. cornellensis and 89.2 % to L. newyorkensis) and Listeria rustica sp. nov. (type strain FSL W9-0585T=CCUG 74665T=LMG 31922T; maximum ANI value of 88.7 % to L. cornellensis and 88.9 % to L. newyorkensis). L. immobilis is the first sensu stricto species isolated to date that is non-motile. All five of the novel species are non-haemolytic and negative for phosphatidylinositol-specific phospholipase C activity; the draft genomes lack the virulence genes found in Listeria pathogenicity island 1 (LIPI-1), and the internalin genes inlA and inlB, indicating that they are non-pathogenic.

Prevalence of Listeria Species on Food Contact Surfaces in Washington State Apple Packinghouses.

The 2014 caramel apple listeriosis outbreak was traced back to cross-contamination between food contact surfaces (FCS) of equipment used for packing and fresh apples. For Washington state, the leading apple producer in the United States with 79% of its total production directed to the fresh market, managing the risk of apple contamination with Listeria monocytogenes within the packing environment is crucial. The objectives of this study were to determine the prevalence of Listeria spp. on FCS in Washington state apple packinghouses over two packing seasons and to identify those FCS types with the greatest likelihood to harbor Listeria spp. Five commercial apple packinghouses were visited quarterly over two consecutive year-long packing seasons. A range of 27 to 50 FCS were swabbed at each facility to detect Listeria spp. at two sample times, (i) postsanitation and (ii) in-process (3 h of packinghouse operation), following a modified protocol of the FDA's Bacteriological Analytical Manual method. Among 2,988 samples tested, 4.6% (n = 136) were positive for Listeria spp. Wax coating was the unit operation from which Listeria spp. were most frequently isolated. The FCS that showed the greatest prevalence of Listeria spp. were polishing brushes, stainless steel dividers and brushes under fans/blowers, and dryer rollers. The prevalence of Listeria spp. on FCS increased throughout apple storage time. The results of this study will aid apple packers in controlling for contamination and harborage of L. monocytogenes and improving cleaning and practices for sanitation of the FCS on which Listeria spp. are the most prevalent.IMPORTANCE Since 2014, fresh apples have been linked to outbreaks and recalls associated with postharvest cross-contamination with the foodborne pathogen L. monocytogenes These situations drive both public health burden and economic loss and underscore the need for continued scrutiny of packinghouse management to eliminate potential Listeria niches. This research assesses the prevalence of Listeria spp. on FCS in apple packinghouses and identifies those FCS most likely to harbor Listeria spp. Such findings are essential for the apple-packing industry striving to further understand and exhaustively mitigate the risk of contamination with L. monocytogenes to prevent future listeriosis outbreaks and recalls.

Prevalence and transmission characteristics of Listeria species from ruminants in farm and slaughtering environments in China.

Listeria monocytogenes is an important foodborne pathogen, and is ubiquitously distributed in the natural environment. Cattle and sheep, as natural hosts, can transmit L. monocytogenes to related meat and dairy products. In this study, the prevalence, distribution, and transmission characteristics of Listeria were analysed by investigating 5214 samples of cattle and sheep in farm and slaughtering environments in China. A low contamination incidence of L. monocytogenes (0.5%, 20/4430) was observed in farm environment, but there was a high contamination incidence in slaughtering environment (9.4%, 74/784). The incidence of L. innocua in cattle and sheep farm and slaughtering environments is more common and significantly higher (9.7%, 508/5214) than that of L. monocytogenes (1.8%, 94/5214). The distinct molecular and genetic characteristics of Listeria by PFGE and MLST indicated that L. monocytogenes and L. innocua were gradually transmitted from the farm and slaughtering environments to end products, such as beef and mutton along the slaughtering chain. The ST7, ST9, ST91, and ST155 found in our study were associated with the human listeriosis cases in China. In addition, the findings of virulence markers (inlC, inlJ, LIPI-3, LIPI-4, and ECIII) concerned with the pathogenesis of human listeriosis and antibiotics resistance of L. monocytogenes in this study implies a potential public health risk. This study fills the gap in the epidemiology of beef cattle and sheep that carry Listeria in farm and slaughtering environments in major cattle and sheep producing areas in China.

Listeria spp. Isolated from Tonsils of Wild Deer and Boars: Genomic Characterization.

Listeria monocytogenes is a major human and animal foodborne pathogen. However, data from environmental reservoirs remain scarce. Here, we used whole-genome sequencing to characterize Listeria species isolates recovered over 1 year from wild animals in their natural habitats in Spain. Three different Listeria spp. (L. monocytogenes [n = 19], Listeria ivanovii subsp. londoniensis [n = 4], and Listeria innocua [n = 3]) were detected in 23 animal tonsils (9 deer, 14 wild boars) and 2 feeding troughs. No Listeria species was detected in feces. L. monocytogenes was detected in tonsils of 44.4% (8 out of 18) of deer and 40.7% (11 out of 27) of wild boars. L. monocytogenes isolates belonged to 3 different core genome multilocus sequence typing (cgMLST) types (CTs) of 3 distinct sublineages (SL1, SL387, and SL155) from lineages I and II. While cgMLST type L1-SL1-ST1-CT5279 (IVb; clonal complex 1 [CC1]) occurred only in one animal, types L1-SL387-ST388-CT5239 (IVb; CC388) and L2-SL155-ST155-CT1170 (IIa; CC155) were retrieved from multiple animals. In addition, L1-SL387-ST388-CT5239 (IVb; CC388) isolates were collected 1 year apart, revealing their long-term occurrence within the animal population and/or environmental reservoir. The presence of identical L. monocytogenes strains in deer and wild boars suggests contamination from a common food or environmental source, although interhost transmission cannot be excluded. Pathogenicity islands LIPI-1, LIPI-3, and LIPI-4 were present in 100%, 5%, and 79% of the L. monocytogenes isolates, respectively, and all L. monocytogenes lineage II isolates (n = 3) carried SSI-1 stress islands. This study highlights the need for monitoring L. monocytogenes environmental contamination and the importance of tonsils as a possible L. monocytogenes intrahost reservoir.IMPORTANCEListeria monocytogenes is a foodborne bacterial pathogen responsible for listeriosis. Whole-genome sequencing has been extensively used in public health and food industries to characterize circulating Listeria isolates, but genomic data on isolates occurring in natural environments and wild animals are still scarce. Here, we show that wild animals carry pathogenic Listeria and that the same genotypes can be found at different time points in different host species. This work highlights the need of Listeria species monitoring of environmental contamination and the importance of tonsils as a possible L. monocytogenes intrahost reservoir.

Bovine Lactoferrin can Decrease the In Vitro Biofilm Production and Show Synergy with Antibiotics Against Listeria and Escherichia coli Isolates.

BACKGROUND: Bovine Lactoferrin (bLf) has been reported as antimicrobial, antiviral, immunomodulatory and anticancer protein. Escherichia coli and Listeria spp. are food-borne bacteria that can produce illness in human being and mammals, the emergent antimicrobial drug resistance has been reported in these pathogens. OBJECTIVE: The aim for this study was to evaluate the bLf effect on in vitro biofilm production and the synergic effect of antibiotics on E. coli and Listeria isolates. METHODS: E. coli and Listeria specimens were isolated from bovine carcasses and slaughterhouses surfaces, respectively. Biofilm formation was analyzed with or without bLf, incubated for 48 h and spectrophotometry, cell viability was analyzed by colony-forming unit (CFU) and the synergistic effect of bLf with ampicillin, oxytetracycline, and streptomycin was evaluated through the fractional concentration index (FCI). RESULTS: Our results show that a low bLf concentration (0.8 µM) can diminish the in vitro biofilm production in Listeria isolates; also improves the in vitro oxytetracycline and streptomycin activity against E. coli, and ampicillin activity against Listeria isolates. CONCLUSION: bLf can affect the biofilm production in Listeria isolates from slaughterhouses surfaces and shown synergic effect with ampicillin. Also has a synergic effect with oxytetracycline and streptomycin against E. coli isolates from bovine carcasses.

Microbiological quality and safety of minimally processed parsley (Petroselinum crispum) sold in food markets, southeastern Brazil.

AIMS: This study evaluated the microbiological quality and safety of minimally processed parsley sold in southeastern Brazilian food markets. METHODS AND RESULTS: One hundred samples were submitted to the enumeration of Enterobacteriaceae by plating on MacConkey agar. Colonies of Enterobacteriaceae were randomly selected and identified by MALDI-TOF MS. Samples were also tested for Listeria monocytogenes and Salmonella sp. The mean count of Enterobacteriaceae was 6·0 ± 1·0 log CFU per gram, while 18 genera (including 30 species) of bacteria belonging to this family were identified. Salmonella and L. monocytogenes were not detected, while L. innocua was found in two samples and L. fleischmannii was found in one sample. Moreover generic Escherichia coli was found in three samples, all from different brands of minimally processed parsley. CONCLUSIONS: Even though microbial pathogens were not isolated, a variety of indicator micro-organisms were identified, including vegetable spoilers and species capable of causing human opportunistic infections. These results suggest hygienic failures and/or lack of temperature control during processing and storage of these ready-to-eat products. SIGNIFICANCE AND IMPACT OF STUDY: This study highlights the need for control measures during the production chain of minimally processed parsley in order to reduce microbial contamination and the risks of foodborne diseases.

Listeria valentina sp. nov., isolated from a water trough and the faeces of healthy sheep.

In the context of a study on the occurrence of Listeria species in an animal farm environment in Valencia, Spain, six Listeria-like isolates could not be assigned to any known species. Phylogenetic analysis based on the 16S rRNA gene and on 231 Listeria core genes grouped these isolates in a monophyletic clade within the genus Listeria, with highest similarity to Listeria thailandensis. Whole-genome sequence analyses based on in silico DNA-DNA hybridization, the average nucleotide blast and the pairwise amino acid identities against all currently known Listeria species confirmed that these isolates constituted a new taxon within the genus Listeria. Phenotypically, these isolates differed from other Listeria species mainly by the production of acid from inositol, the absence of acidification in presence of methyl α-d-glucoside, and the absence of α-mannosidase and nitrate reductase activities. The name Listeria valentina sp. nov. is proposed for this novel species, and the type strain is CLIP 2019/00642T (=CIP 111799T=DSM 110544T).

Occurrence of Listeria and Escherichia coli in frozen fruit and vegetables collected from retail and catering premises in England 2018-2019.

Frozen vegetables have previously been associated with outbreaks of listeriosis in both the USA and Europe. An outbreak of Listeria monocytogenes serogroup 4 caused 53 cases in five European countries between 2015 and 2018. Whole genome sequencing (WGS) indicated that frozen sweet corn from a producer in Hungary was the source of illness. However, limited data is available on the prevalence of Listeria in frozen produce. A study of frozen fruit and vegetables from catering and retail premises in England was therefore carried out to assess their microbiological quality with respect to Listeria and Escherichia coli. Between December 2018 and April 2019, 1050 frozen fruit and vegetable samples were collected. Of these, 99% were of a satisfactory or borderline microbiological quality. Eleven samples (1%) contained ≥100 cfu/g of Escherichia coli (considered unsatisfactory in products labelled as ready-to-eat). Listeria monocytogenes or other Listeria species were detected in six samples (2%) of fruit compared to 167 samples (24%) of vegetables and six samples (26%) of fruit and vegetable mixes, but none at a level of ≥100 cfu/g. Characterisation by WGS of 74 L. monocytogenes isolates identified ten genetic clusters indicating a common source. For 8 of the 10 clusters, the isolates came from homogenous food types: four were sweet corn, and there was one cluster each for beans, peas, peppers and broccoli. There were five genetic associations between isolates from frozen vegetables and from clinical cases of listeriosis, including two cultures from frozen beans that were indistinguishable from the 2015-2018 sweet corn outbreak strain. This study indicates that L. monocytogenes was present in 10% of frozen vegetables and even though products are generally not ready-to-eat and are intended to be cooked prior to consumption, these have the potential to cause illness. Clear cooking and handling instructions are therefore required on these products to ensure that the health of consumers is not put at risk, and appropriate Good Manufacturing Practice measures should be followed by all fruit and vegetable freezing plants in order to reduce contamination with Listeria during processing.

Laboratory-based surveillance of invasive listeriosis in Northern Italy over a fourteen-year period: epidemiological and clinical results.

INTRODUCTION: Invasive listeriosis is a rare foodborne disease with a significant impact on public health worldwide, because of the severity of its clinical manifestations and high fatality rate. In this study, we provide a snapshot of epidemiology of listeriosis in Lombardy Region, Northern Italy, reviewing enhanced surveillance data collected over fourteen years, after the implementation of a voluntary laboratory-based surveillance system for the referral of clinical isolates of Listeria monocytogenes to a regional reference laboratory, since 2005. METHODS: Invasive listeriosis cases data from 2005 to 2018 were extracted from the regional laboratory-based surveillance system database and compared with the regional mandatory notification disease system data. RESULTS: Over the fourteen-year period under study, 533 Listeria monocytogenes isolates were detected by the laboratory surveillance system, 55 of which from pregnancy-related cases. The median age of non-pregnancy-associated patients was 71 years, with 64.6% of cases observed in the elderly. Cases with underlying medical risk conditions accounted for 92.1%, and the fatality rate was 26.2%. By integrating data from the mandatory notification system and the laboratory-based surveillance system, a total of 935 cases were recorded. The collection of data through the laboratory surveillance system allowed to increase the surveillance sensitivity by 18%. CONCLUSIONS: Our results documented the growing epidemiological relevance of listeriosis through the analysis of two information sources, the regional mandatory notification system and the regional laboratory-based surveillance system. The data we obtained were consistent with the literature, except for pregnancy-related cases, which are often underdiagnosed. This study highlighted the importance of laboratory-based surveillance system, which led to a significant increase in the sensitivity of the mandatory notification system.

Prevalence of Listeria species and L. monocytogenes in ready-to-eat foods in the West Pomeranian region of Poland: Correlations between the contamination level, serogroups, ingredients, and producers.

Poland is one of the largest food producers in Europe, and the West Pomeranian region of Poland is a large producer of RTE food. Thus, the objective of this study was to determine the prevalence of Listeria sp. and L. monocytogenes (LM) in RTE foods manufactured by 13 selected Polish food producers whose processing plants are located in this region. In total, 650 samples of RTE foods, and 263 ingredients of salads and desserts were analyzed. Almost 18% of the RTE foods failed to meet the zero tolerance limit for Listeria, which means they should not be allowed for retail. LM was isolated from 13.5% of the samples, with counts of 10-100 CFU/g noted in half of them. Products with meat and dairy ingredients, and fish products, sandwiches, sprouts and sushi, were at the highest statistically significant risk of LM contamination. Four serogroups were identified among the LM isolated from RTE foods, of which the 4b-4d-4e serogroup was predominating. The samples most heavily contaminated with LM contained even 2 serogroups. Results were subjected to the cluster analysis and principal component analysis to determine correlations between food groups, food ingredients, producers, contamination level, and serogroups of LM.

Evaluation of MALDI-TOF MS as a tool for detection of Listeria spp. directly from selective enrichment broth from food and stool samples.

We evaluated the detection of Listeria spp. using MALDI-TOF MS directly in enrichment broths, without isolated colonies, with naturally contaminated food and stool samples. The success rate was 77%. Considering the reduced time for diagnosis and the success rate, this is a promising screening tool, but more tests are needed to determine its viability.

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

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

Effect of pulsed light treatment on Listeria inactivation, sensory quality and oxidation in two varieties of Spanish dry-cured ham.

The efficacy of pulsed light (PL) for the surface decontamination of ready-to-eat dry-cured ham was studied in two Spanish varieties, Serrano and Iberian. Listeriainnocua was inoculated on the surface of ham slices that were vacuum-packaged and flashed with 2.1, 4.2 and 8.4 J/cm2. Survivors were enumerated immediately after treatment. Peroxide values, sensory analysis and volatile profile were investigated during storage at 4 and 20 °C. Inactivation of Listeria was higher in Iberian (ca. 2 log cfu/cm2) than in Serrano ham (ca. 1 log cfu/cm2) with 8.4 J/cm2. PL did not increase the peroxide values above the usual levels reported in dry-cured ham, and no rancid notes were observed in the sensory analysis. PL-treated samples showed an increase in the concentration of some volatile compounds, such as methional, dimethyl disulfide and 1-octen-3-one, which imparted slight sulfur and metallic notes, although they disappeared during storage.

Prevalence and antimicrobial resistance of Listeria species and molecular characterization of Listeria monocytogenes isolated from retail ready-to-eat foods.

A wide variety of foods can be contaminated with Listeria species, especially L. monocytogenes. Ready-to-eat (RTE) foods are predominantly associated with human listeriosis caused by L. monocytogenes. Therefore, this study aimed to assess the presence of Listeria species in RTE foods and to characterize L. monocytogenes isolates by means of detection of virulence markers, serotypes and genetic relatedness. Of the 300 RTE food samples, 59 (19.7%) were positive for Listeria species: L. innocua (13.3%), L. monocytogenes (5%), L. welshimerii (2.3%), L. grayi subsp. murrayi (1.3%), L. grayi (1%), L. ivanovii (1%) and L. ivanovi subsp. londoniensis (0.3%). All L. monocytogenes isolates identified were positive for the actA, iap, inlA, inlB, inlC, inlJ, plcA and prfA virulence genes and biofilm. The isolates were serotyped as 1/2c (33.3%), 4b (26.7%), 1/2a (26.7%), 1/2b (6.7%) and 3c (6.7%) by the multiplex-PCR and agglutination methods. PCR-restriction fragment length polymorphism with AluI and MluCI resulted in three and two profiles, respectively. Pulsed-field gel electrophoresis differentiated the L. monocytogenes isolates into 15 ApaI and 12 AscI patterns. Antimicrobial resistance of all Listeria isolates was determined by the disk diffusion method. Most L. monocytogenes isolates were sensitive to antimicrobials used in the treatment of listeriosis. This study shows the presence of potential pathogenic and antimicrobial-resistant L. monocytogenes in RTE foods that may lead to consumer health risks.