Association of Listeria monocytogenes LIPI-1 and LIPI-3 marker llsX with invasiveness

Listeria monocytogenes from Food Products and Food Associated Environments: Antimicrobial Resistance, Genetic Clustering and Biofilm Insights

Listeria monocytogenes, a foodborne pathogen, exhibits high adaptability to adverse environmental conditions and is common in the food industry, especially in ready-to-eat foods. L. monocytogenes strains pose food safety challenges due to their ability to form biofilms, increased resistance to disinfectants, and long-term persistence in the environment. The aim of this study was to evaluate the presence and genetic diversity of L. monocytogenes in food and related environmental products collected from 2014 to 2022 and assess antibiotic susceptibility and biofilm formation abilities. L. monocytogenes was identified in 13 out of the 227 (6%) of samples, 7 from food products (meat preparation, cheeses, and raw milk) and 6 from food-processing environments (slaughterhouse-floor and catering establishments). All isolates exhibited high biofilm-forming capacity and antibiotic susceptibility testing showed resistance to several classes of antibiotics, especially trimethoprim-sulfamethoxazole and erythromycin. Genotyping and core-genome clustering identified eight sequence types and a cluster of three very closely related ST3 isolates (all from food), suggesting a common contamination source. Whole-genome sequencing (WGS) analysis revealed resistance genes conferring resistance to fosfomycin (fosX), lincosamides (lin), fluoroquinolones (norB), and tetracycline (tetM). In addition, the qacJ gene was also detected, conferring resistance to disinfecting agents and antiseptics. Virulence gene profiling revealed the presence of 92 associated genes associated with pathogenicity, adherence, and persistence. These findings underscore the presence of L. monocytogenes strains in food products and food-associated environments, demonstrating a high virulence of these strains associated with resistance genes to antibiotics, but also to disinfectants and antiseptics. Moreover, they emphasize the need for continuous surveillance, effective risk assessment, and rigorous control measures to minimize the public health risks associated to severe infections, particularly listeriosis outbreaks. A better understanding of the complex dynamics of pathogens in food products and their associated environments can help improve overall food safety and develop more effective strategies to prevent severe health consequences and economic losses.

Genomic epidemiology of hypervirulent Listeria monocytogenes CC619: Population structure, phylodynamics and virulence

Listeria monocytogenes is a ubiquitous foodborne pathogen causing human and animal listeriosis with high mortality. Neurological and maternal-neonatal listeriosis outbreaks in Europe and the United States were frequently associated with clonal complexes CC1, CC2 and CC6 harboring Listeria Pathogenicity Island-1 (LIPI-1), as well as CC4 carrying both LIPI-1 and LIPI-4. However, human listeriosis in China was predominantly linked to CC87 and CC619 from serotype 1/2b. To understand the genetic evolution and distribution patterns of CC619, we characterized the epidemic history, population structure, and transmission feature of CC619 strains through analysis of 49,421 L. monocytogenes genomes globally. We found that CC619 was uniquely distributed in China, and closely related with perinatal infection. As CC619 strains were being mainly isolated from livestock and poultry products, we hypothesized that pigs and live chicken were the reservoirs of CC619. Importantly, all CC619 strains not only harbored the intact LIPI-1 and LIPI-4, but these also carried LIPI-3 that could facilitate host colonization and invasion. The deficiency of LIPI-3 or LIPI-4 markedly decreased L. monocytogenes colonization capacity in a model of intragastric infection in the mouse. Altogether, our findings suggest that the hypervirulent CC619 harboring three pathogenicity islands LIPI-1, LIPI-3 and LIPI-4 is a putatively persistent population in various foods, environment, and human population, warranting the further research for deciphering its pathogenicity and strengthening epidemiological surveillance.

Listeria monocytogenes in ready-to-eat (RTE) delicatessen foods: Prevalence, genomic characterization of isolates and growth potential

This study investigated Listeria monocytogenes prevalence and count in 132 ready-to-eat (RTE) delicatessen samples belonging to different categories (starters with/without mayonnaise pasta/rice-based courses, meat/fish-based main courses) produced by an Italian industry. Whole Genome Sequencing characterized the isolates to map the pathogen circulation. Moreover, the growth potential of L. monocytogenes in the most contaminated product was investigated by a challenge test. L. monocytogenes was detected in 23 samples, giving an estimated prevalence of 17.4 %. Starters with mayonnaise showed a very high prevalence (56.7 %), showing the role of the sauce in the diffusion of the pathogen within the plant. A total of 49 isolates were obtained; they belonged to two different serogroups, IIb and IIa, and were related to two clonal complexes (CCs) and sequence types (STs) (CC288-ST330 and CC121-ST717), suggesting the possible persistence and circulation of the pathogen within the plant. The results of the challenge test showed a limited ability to grow in the selected product thanks to the presence of lactic microflora.

Listeria monocytogenes in ready to eat meat products from Zambia: phenotypical and genomic characterization of isolates

The contamination of ready to eat foods (RTE) products due to Listeria monocytogenes could compromise the products safety becoming a great risk for the consumers. The high presence of L. monocytogenes in RTE products has been described worldwide, but few data are available about these products from African countries. The aims of this study were to report the presence of L. monocytogenes in Zambian RTE products, providing genomic characterization and data on similarity with African circulating strains using whole genome sequencing (WGS). A total of 304 RTE products, produced by different Zambian manufacturers, were purchased at retail, from major supermarkets located in Lusaka, Zambia, comprising 130 dairy and 174 meat products. L. monocytogenes was detected only in 18 (10.3%) RTE meat products of the 174 samples tested. The MLST analysis grouped the 18 L. monocytogenes isolates in 7 clonal complexes (CCs): CC1 (n = 5), CC2 (n = 4), CC9 (n = 4), CC5 (n = 2), CC121 (n = 1), CC155 (n = 1), and CC3 (n = 1). According to the cgMLST results, several clusters were detected, in particular belonging to hyper-virulent clones CC1 and CC2. Regarding the virulence factors, a complete L. monocytogenes Pathogenicity Island 3 (LIPI-3) was present both in the CC1 and CC3, in addition to LIPI-1. Several resistance genes and mobile genetic elements were detected, including Stress Islands, the bcrABC cassette and Tn6188_qac transposon, plasmids and intact prophages. Despite being a first preliminary work with a limited number of samples and isolates, this study helped to increase existing knowledge on contaminated RTE products in Zambia, confirming the presence of hyper-virulent L. monocytogenes CCs, which could play an important role in human diseases, posing a public health concern for consumers.

Association of Virulence, Biofilm, and Antimicrobial Resistance Genes with Specific Clonal Complex Types of Listeria monocytogenes

Precise classification of foodborne pathogen Listeria monocytogenes is a necessity in efficient foodborne disease surveillance, outbreak detection, and source tracking throughout the food chain. In this study, a total of 150 L. monocytogenes isolates from various food products, food processing environments, and clinical sources were investigated for variations in virulence, biofilm formation, and the presence of antimicrobial resistance genes based on their Whole-Genome Sequences. Clonal complex (CC) determination based on Multi-Locus Sequence Typing (MLST) revealed twenty-eight CC-types including eight isolates representing novel CC-types. The eight isolates comprising the novel CC-types share the majority of the known (cold and acid) stress tolerance genes and are all genetic lineage II, serogroup 1/2a-3a. Pan-genome-wide association analysis by Scoary using Fisher's exact test identified eleven genes specifically associated with clinical isolates. Screening for the presence of antimicrobial and virulence genes using the ABRicate tool uncovered variations in the presence of Listeria Pathogenicity Islands (LIPIs) and other known virulence genes. Specifically, the distributions of actA, ecbA, inlF, inlJ, lapB, LIPI-3, and vip genes across isolates were found to be significantly CC-dependent while the presence of ami, inlF, inlJ, and LIPI-3 was associated with clinical isolates specifically. In addition, Roary-derived phylogenetic grouping based on Antimicrobial-Resistant Genes (AMRs) revealed that the thiol transferase (FosX) gene was present in all lineage I isolates, and the presence of the lincomycin resistance ABC-F-type ribosomal protection protein (lmo0919_fam) was also genetic-lineage-dependent. More importantly, the genes found to be specific to CC-type were consistent when a validation analysis was performed with fully assembled, high-quality complete L. monocytogenes genome sequences (n = 247) extracted from the National Centre for Biotechnology Information (NCBI) microbial genomes database. This work highlights the usefulness of MLST-based CC typing using the Whole-Genome Sequence as a tool in classifying isolates.

Genomic and pathogenicity islands of Listeria monocytogenes-overview of selected aspects

Listeria monocytogenes causes listeriosis, a disease characterized by a high mortality rate (up to 30%). Since the pathogen is highly tolerant to changing conditions (high and low temperature, wide pH range, low availability of nutrients), it is widespread in the environment, e.g., water, soil, or food. L. monocytogenes possess a number of genes that determine its high virulence potential, i.e., genes involved in the intracellular cycle (e.g., prfA, hly, plcA, plcB, inlA, inlB), response to stress conditions (e.g., sigB, gadA, caspD, clpB, lmo1138), biofilm formation (e.g., agr, luxS), or resistance to disinfectants (e.g., emrELm, bcrABC, mdrL). Some genes are organized into genomic and pathogenicity islands. The islands LIPI-1 and LIPI-3 contain genes related to the infectious life cycle and survival in the food processing environment, while LGI-1 and LGI-2 potentially ensure survival and durability in the production environment. Researchers constantly have been searching for new genes determining the virulence of L. monocytogenes. Understanding the virulence potential of L. monocytogenes is an important element of public health protection, as highly pathogenic strains may be associated with outbreaks and the severity of listeriosis. This review summarizes the selected aspects of L. monocytogenes genomic and pathogenicity islands, and the importance of whole genome sequencing for epidemiological purposes.

Genetic Characterization of Listeria from Food of Non-Animal Origin Products and from Producing and Processing Companies in Bavaria, Germany

Reported cases of listeriosis from food of non-animal origin (FNAO) are increasing. In order to assess the risk of exposure to Listeria monocytogenes from FNAO, the genetic characterization of the pathogen in FNAO products and in primary production and processing plants needs to be investigated. For this, 123 samples of fresh and frozen soft fruit and 407 samples of 39 plants in Bavaria, Germany that produce and process FNAO were investigated for Listeria contamination. As a result, 64 Listeria spp. isolates were detected using ISO 11290-1:2017. Environmental swabs and water and food samples were investigated. L. seeligeri (36/64, 56.25%) was the most frequently identified species, followed by L. monocytogenes (8/64, 12.50%), L. innocua (8/64, 12.50%), L. ivanovii (6/64, 9.38%), L. newyorkensis (5/64, 7.81%), and L. grayi (1/64, 1.56%). Those isolates were subsequently sequenced by whole-genome sequencing and subjected to pangenome analysis to retrieve data on the genotype, serotype, antimicrobial resistance (AMR), and virulence markers. Eight out of sixty-four Listeria spp. isolates were identified as L. monocytogenes. The serogroup analysis detected that 62.5% of the L. monocytogenes isolates belonged to serogroup IIa (1/2a and 3a) and 37.5% to serogroup IVb (4b, 4d, and 4e). Furthermore, the MLST (multilocus sequence typing) analysis of the eight detected L. monocytogenes isolates identified seven different sequence types (STs) and clonal complexes (CCs), i.e., ST1/CC1, ST2/CC2, ST6/CC6, ST7/CC7, ST21/CC21, ST504/CC475, and ST1413/CC739. The core genome MLST analysis also showed high allelic differences and suggests plant-specific isolates. Regarding the AMR, we detected phenotypic resistance against benzylpenicillin, fosfomycin, and moxifloxacin in all eight L. monocytogenes isolates. Moreover, virulence factors, such as prfA, hly, plcA, plcB, hpt, actA, inlA, inlB, and mpl, were identified in pathogenic and nonpathogenic Listeria species. The significance of L. monocytogenes in FNAO is growing and should receive increasing levels of attention.

A Comprehensive Virulence and Resistance Characteristics of Listeria monocytogenes Isolated from Fish and the Fish Industry Environment

Listeria monocytogenes is an important pathogen, often associated with fish, that can adapt and survive in products and food processing plants, where it can persist for many years. It is a species characterized by diverse genotypic and phenotypic characteristics. Therefore, in this study, a total of 17 L. monocytogenes strains from fish and fish-processing environments in Poland were characterized for their relatedness, virulence profiles, and resistance genes. The Core Genome Multilocus Sequence Typing (cgMLST) analysis revealed that the most frequent serogroups were IIa and IIb; sequence types (ST) were ST6 and ST121; and clonal complexes (CC) were CC6 and CC121. Core genome multilocus sequence typing (cgMLST) analysis was applied to compare the present isolates with the publicly available genomes of L. monocytogenes strains recovered in Europe from humans with listeriosis. Despite differential genotypic subtypes, most strains had similar antimicrobial resistance profiles; however, some of genes were located on mobile genetic elements that could be transferred to commensal or pathogenic bacteria. The results of this study showed that molecular clones of tested strains were characteristic for L. monocytogenes isolated from similar sources. Nevertheless, it is worth emphasizing that they could present a major public health risk due to their close relation with strains isolated from human listeriosis.

Pathometagenomics reveals susceptibility to intestinal infection by Morganella to be mediated by the blood group-related B4galnt2 gene in wild mice

Infectious disease is widely considered to be a major driver of evolution. A preponderance of signatures of balancing selection at blood group-related genes is thought to be driven by inherent trade-offs in susceptibility to disease. B4galnt2 is subject to long-term balancing selection in house mice, where two divergent allele classes direct alternative tissue-specific expression of a glycosyltransferase in the intestine versus blood vessels. The blood vessel allele class leads to prolonged bleeding times similar to von Willebrand disease in humans, yet has been maintained for millions of years. Based on in vivo functional studies in inbred lab strains, it is hypothesized that the cost of prolonged bleeding times may be offset by an evolutionary trade-off involving susceptibility to a yet unknown pathogen(s). To identify candidate pathogens for which resistance could be mediated by B4galnt2 genotype, we here employed a novel "pathometagenomic" approach in a wild mouse population, which combines bacterial 16S rRNA gene-based community profiling with histopathology of gut tissue. Through subsequent isolation, genome sequencing and controlled experiments in lab mice, we show that the presence of the blood vessel allele is associated with resistance to a newly identified subspecies of Morganella morganii, a clinically important opportunistic pathogen. Given the increasing importance of zoonotic events, the approach outlined here may find useful application in the detection of emerging diseases in wild animal populations.

Resistome and virulome diversity of foodborne pathogens isolated from artisanal food production chain of animal origin in the Mediterranean region

The aim of the present study was to investigate the resistome and virulome diversity of 43 isolates of Listeria monocytogenes, Salmonella enterica and S. aureus collected from artisanal fermented meat and dairy products and their production environments in Portugal, Spain, Italy and Morocco. After DNA extraction, genomes were sequenced, and de novo assembled. Genetic relationships among genomes were investigated by SNP calling and in silico 7- loci MLST. Genomes of the same species belonged to different ST-types demonstrating the circulation of different clones in in the same artisanal production plant. One specific clone included genomes of S. Paratyphi B belonging to ST43 and repeatedly isolated for more than a year in an artisanal sausage production plant. No genomes but three (belonging to Salmonella enterica), were predicted as multiresistant to different antimicrobials classes. Regarding virulence, genomes of L. monocytogenes belonging to ST1, ST3 and ST489, as well as genomes of S.enterica enterica (ST43, ST33, ST314, ST3667, ST1818, ST198) and ST121 S. aureus were predicted as virulent and hypervirulent. The occurrence of virulent and hypervirulent L. monocytogenes, Salmonella enterica and S. aureus strains in artisanal fermented meat and dairy productions as well as in their finished products suggests the need for a specific focus on prevention and control measures able to reduce the risk of these biological hazards in artisanal food productions.

Genetic Diversity and Potential Virulence of Listeria monocytogenes Isolates Originating from Polish Artisanal Cheeses

Artisanal cheeses can be sources of Listeria monocytogenes and cause disease in humans. This bacterial pathogen is a species of diverse genotypic and phenotypic characteristics. The aim of the study was to characterize 32 isolates of L. monocytogenes isolated in 2014-2018 from artisanal cheeses. The isolates were characterized using whole genome sequencing and bioinformatics analysis. The artisanal cheese isolates resolved to four molecular groups: 46.9% of them to IIa (1/2a-3a), 31.2% to IVb (4ab-4b-4d-4e), 12.5% to IIc (1/2c-3c), and 9.4% to IIb (1/2b-3b-7). Two evolutionary lineages emerged: lineage II having 59.4% of the isolates and lineage I having 40.6%. The sequence types (ST) totaled 18: ST6 (15.6% of the isolates), ST2, ST20, ST26, and ST199 (each 9.4%), ST7 and ST9 (each 6.3%), and ST1, ST3, ST8, ST16, ST87, ST91, ST121, ST122, ST195, ST217, and ST580 (each 3.1%). There were 15 detected clonal complexes (CC): CC6 (15.6% of isolates), CC9 (12.5%), CC2, CC20, CC26, and CC199 (each 9.4%), CC7 and CC8 (each 6.3%), and CC1, CC3, CC14, CC87, CC121, CC195, and CC217 (each 3.1%). The isolates were varied in their virulence genes and the differences concerned: inl, actA, LIPI-3, ami, gtcA, aut, vip, and lntA.

Review of CRISPR-Cas Systems in Listeria Species: Current Knowledge and Perspectives

Listeria spp. are pathogens widely distributed in the environment and Listeria monocytogenes is associated with food-borne illness in humans. Food facilities represent an adverse environment for this bacterium, mainly due to the disinfection and cleaning processes included in good hygiene practices, and its virulence is related to stress responses. One of the recently described stress-response systems is CRISPR-Cas. Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (cas) genes have been found in several bacteria. CRISPR-Cas has revolutionized biotechnology since it acts as an adaptive immune system of bacteria, which also helps in the evasion of the host immune response. There are three CRISPR systems described on Listeria species. Type II is present in many pathogenic bacteria and characterized by the presence of cas9 that becomes the main target of some anti-CRISPR proteins, such as AcrIIA1, encoded on Listeria phages. The presence of Cas9, either alone or in combination with anti-CRISPR proteins, suggests having a main role on the virulence of bacteria. In this review, we describe the most recent information on CRISPR-Cas systems in Listeria spp., particularly in L. monocytogenes, and their relationship with the virulence and pathogenicity of those bacteria. Besides, some applications of CRISPR systems and future challenges in the food processing industry, bacterial vaccination, antimicrobial resistance, pathogens biocontrol by phage therapy, and regulation of gene expression have been explored.

Whole-Genome Sequencing Characterization of Virulence Profiles of Listeria monocytogenes Food and Human Isolates and In Vitro Adhesion/Invasion Assessment

Listeria monocytogenes (Lm) is the causative agent of human listeriosis. Lm strains have different virulence potential. For this reason, we preliminarily characterised via Whole-Genome Sequencing (WGS) some Lm strains for their key genomic features and virulence-associated determinants, assigning the clonal complex (CC). Moreover, the ability of the same strains to adhere to and invade human colon carcinoma cell line Caco-2, evaluating the possible correspondence with their genetic virulence profile, was also assessed. The clinical strains typed belonged to clonal complex (CC)1, CC31, and CC101 and showed a very low invasiveness. The Lm strains isolated from food were assigned to CC1, CC7, CC9, and CC121. All CC1 carried the hypervirulence pathogenicity island LIPI-3 in addition to LIPI-1. Premature stop codons in the inlA gene were found only in Lm of food origin belonging to CC9 and CC121. The presence of LIPI2_inlII was observed in all the CCs except CC1. The CC7 strain, belonging to an epidemic cluster, also carried the internalin genes inlG and inlL and showed the highest level of invasion. In contrast, the human CC31 strain lacked the lapB and vip genes and presented the lowest level of invasiveness. In Lm, the genetic determinants of hypo- or hypervirulence are not necessarily predictive of a cell adhesion and/or invasion ability in vitro. Moreover, since listeriosis results from the interplay between host and virulence features of the pathogen, even hypovirulent clones are able to cause infection in immunocompromised people.

Hyper-Virulent Listeria monocytogenes Strains Associated With Respiratory Infections in Central Italy

Listeria monocytogenes (Lm) is a foodborne pathogen causing listeriosis. Invasive forms of the disease mainly manifest as septicaemia, meningitis and maternal-neonatal infections. Lm-associated respiratory infections are very rare and little known. We reported two Lm respiratory infection cases occurred in Central Italy during the summer of 2020, in the midst of the SARS-CoV2 pandemic. In addition to collect the epidemiological and clinical characteristics of the patients, we used Whole Genome Sequencing to study the genomes of the Lm isolates investigating their virulence and antimicrobial profiles and the presence of genetic mobile elements. Both the strains belonged to hypervirulent MLST clonal complexes (CC). In addition to the Listeria Pathogenicity Island 1 (LIPI-1), the CC1 strain also carried LIPI-3 and the CC4 both LIPI-3 and LIPI-4. Genetic determinants for antimicrobial and disinfectants resistance were found. The CC1 genome presented prophage sequences but they did not interrupt the comK gene, involved in the phagosomal escape of Lm. None of the strains carried plasmids. Lm is an important, although rare, opportunistic pathogen for respiratory tract and lung infections. To avoid dangerous diagnostic delays of these severe clinical forms, it is important to sensitize hospital laboratories to this rare manifestation of listeriosis considering Lm in the differential diagnosis of respiratory infections.

Application of Whole Genome Sequencing to Understand Diversity and Presence of Genes Associated with Sanitizer Tolerance in Listeria monocytogenes from Produce Handling Sources

Recent listeriosis outbreaks linked to fresh produce suggest the need to better understand and mitigate L. monocytogenes contamination in packing and processing environments. Using whole genome sequencing (WGS) and phenotype screening assays for sanitizer tolerance, we characterized 48 L. monocytogenes isolates previously recovered from environmental samples in five produce handling facilities. Within the studied population there were 10 sequence types (STs) and 16 cgMLST types (CTs). Pairwise single nucleotide polymorphisms (SNPs) ranged from 0 to 3047 SNPs within a CT, revealing closely and distantly related isolates indicative of both sporadic and continuous contamination events within the facility. Within Facility 1, we identified a closely related cluster (0-2 SNPs) of isolates belonging to clonal complex 37 (CC37; CT9492), with isolates recovered during sampling events 1-year apart and in various locations inside and outside the facility. The accessory genome of these CC37 isolates varied from 94 to 210 genes. Notable genetic elements and mutations amongst the isolates included the bcrABC cassette (2/48), associated with QAC tolerance; mutations in the actA gene on the Listeria pathogenicity island (LIPI) 1 (20/48); presence of LIPI-3 (21/48) and LIPI-4 (23/48). This work highlights the potential use of WGS in tracing the pathogen within a facility and understanding properties of L. monocytogenes in produce settings.

Conditions of In Vitro Biofilm Formation by Serogroups of Listeria monocytogenes Isolated from Hass Avocados Sold at Markets in Mexico

Listeria monocytogenes is an important pathogen that has been implicated in foodborne illnesses and the recall of products such as fruit and vegetables. This study determines the prevalence of virulence-associated genes and serogroups and evaluates the effects of different growth media and environmental conditions on biofilm formation by L. monocytogenes. Eighteen L. monocytogenes isolates from Hass avocados sold at markets in Guadalajara, Mexico, were characterized by virulence-associated genes and serogroup detection with PCR. All isolates harbored 88.8% actA, 88.8% plcA, 83.3% mpl, 77.7% inlB, 77.7% hly, 66.6% prfA, 55.5% plcB, and 33.3% inlA. The results showed that 38.8% of isolates harbored virulence genes belonging to Listeria pathogenicity island 1 (LIPI-1). PCR revealed that the most prevalent serogroup was serogroup III (1/2b, 3b, and 7 (n = 18, 66.65%)), followed by serogroup IV (4b, 4d-4e (n = 5, 27.7%)) and serogroup I (1/2a-3a (n = 1, 5.5%)). The assessment of the ability to develop biofilms using a crystal violet staining method revealed that L. monocytogenes responded to supplement medium TSBA, 1/10 diluted TSBA, and TSB in comparison with 1/10 diluted TSB (p < 0.05) on polystyrene at 240 h (p < 0.05). In particular, the biofilm formation by L. monocytogenes (7.78 ± 0.03-8.82 ± 0.03 log₁₀ CFU/cm²) was significantly different in terms of TSBA on polypropylene type B (PP) (p < 0.05). In addition, visualization by epifluorescence microscopy, scanning electron microscopy (SEM), and treatment (DNase I and proteinase K) revealed the metabolically active cells and extracellular polymeric substances of biofilms on PP. L. monocytogenes has the ability to develop biofilms that harbor virulence-associated genes, which represent a serious threat to human health and food safety.

Intensive Environmental Surveillance Plan for Listeria monocytogenes in Food Producing Plants and Retail Stores of Central Italy: Prevalence and Genetic Diversity

Listeria monocytogenes (Lm) can persist in food processing environments (FPEs), surviving environmental stresses and disinfectants. We described an intensive environmental monitoring plan performed in Central Italy and involving food producing plants (FPPs) and retail grocery stores (RSs). The aim of the study was to provide a snapshot of the Lm circulation in different FPEs during a severe listeriosis outbreak, using whole genome sequencing (WGS) to investigate the genetic diversity of the Lm isolated, evaluating their virulence and stress resistance profiles. A total of 1217 samples were collected in 86 FPEs with 12.0% of positive surfaces at FPPs level and 7.5% at RSs level; 133 Lm isolates were typed by multilocus sequencing typing (MLST) and core genome MLST (cgMLST). Clonal complex (CC) 121 (25.6%), CC9 (22.6%), CC1 (11.3%), CC3 (10.5%), CC191 (4.5%), CC7 (4.5%) and CC31 (3.8%) were the most frequent MLST clones. Among the 26 cgMLST clusters obtained, 5 of them persisted after sanitization and were re-isolated during the follow-up sampling. All the CC121 harboured the Tn6188_qac gene for tolerance to benzalkonium chloride and the stress survival islet SSI-2. The CC3, CC7, CC9, CC31 and CC191 carried the SSI-1. All the CC9 and CC121 strains presented a premature stop codon in the inlA gene. In addition to the Lm Pathogenicity Island 1 (LIPI-1), CC1, CC3 and CC191 harboured the LIPI-3. The application of intensive environmental sampling plans for the detection and WGS analysis of Lm isolates could improve surveillance and early detection of outbreaks.

Hypo- and Hyper-Virulent Listeria monocytogenes Clones Persisting in Two Different Food Processing Plants of Central Italy

A total of 66 Listeria monocytogenes (Lm) isolated from 2013 to 2018 in a small-scale meat processing plant and a dairy facility of Central Italy were studied. Whole Genome Sequencing and bioinformatics analysis were used to assess the genetic relationships between the strains and investigate persistence and virulence abilities. The biofilm forming-ability was assessed in vitro. Cluster analysis grouped the Lm from the meat plant into three main clusters: two of them, both belonging to CC9, persisted for years in the plant and one (CC121) was isolated in the last year of sampling. In the dairy facility, all the strains grouped in a CC2 four-year persistent cluster. All the studied strains carried multidrug efflux-pumps genetic determinants (sugE, mdrl, lde, norM, mepA). CC121 also harbored the Tn6188 specific for tolerance to Benzalkonium Chloride. Only CC9 and CC121 carried a Stress Survival Islet and presented high-level cadmium resistance genes (cadA1C1) carried by different plasmids. They showed a greater biofilm production when compared with CC2. All the CC2 carried a full-length inlA while CC9 and CC121 presented a Premature Stop Codon mutation correlated with less virulence. The hypo-virulent clones CC9 and CC121 appeared the most adapted to food-processing environments; however, even the hyper-virulent clone CC2 warningly persisted for a long time. The identification of the main mechanisms promoting Lm persistence in a specific food processing plant is important to provide recommendations to Food Business Operators (FBOs) in order to remove or reduce resident Lm.

Backtracking and forward checking of human listeriosis clusters identified a multiclonal outbreak linked to Listeria monocytogenes in meat products of a single producer

Due to its high case fatality rate, foodborne listeriosis is considered a major public health concern worldwide. We describe one of the largest listeriosis outbreaks in Germany with 83 cases of invasive listeriosis between 2013 and 2018. As part of the outbreak investigation, we identified a highly diverse Listeria monocytogenes population at a single producer of ready-to-eat meat products. Strikingly, the extensive sampling after identification of a first match between a cluster of clinical isolates and a food isolate allowed for a linkage between this producer and a second, previously unmatched cluster of clinical isolates. Bacterial persistence in the processing plant and indications of cross-contamination events explained long-term contamination of food that led to the protracted outbreak. Based on screening for virulence factors, a pathogenic phenotype could not be ruled out for other strains circulating in the plant, suggesting that the outbreak could have been even larger. As most isolates were sensitive to common biocides used in the plant, hard to clean niches in the production line may have played a major role in the consolidation of the contamination. Our study demonstrates how important it is to search for the origin of infection when cases of illness have occurred (backtracking), but also clearly highlights that it is equally important to check whether a contamination at food or production level has caused disease (forward checking). Only through this two-sided control strategy, foodborne disease outbreaks such as listeriosis can be minimized, which could be a real improvement for public health.

Listeriosis outbreak likely due to contaminated liver pâté consumed in a tavern, Austria, December 2018

In late December 2018, an outbreak of listeriosis occurred after a group of 32 individuals celebrated in a tavern in Styria, Austria; traditional Austrian food (e.g. meat, meat products and cheese) was served. After the celebration, 11 individuals developed gastrointestinal symptoms, including one case with severe sepsis. Cases had consumed mixed platters with several meat products and pâtés originating from a local production facility (company X). Human, food and environmental samples taken from the tavern and company X were tested for L. monocytogenes. Whole genome sequence-based typing detected a novel L. monocytogenes strain of serotype IVb, sequence type 4 and CT7652 in 15 samples; 12 human, two food and one environmental sample from company X with an allelic difference of 0 to 1. Active case finding identified two further cases who had not visited the tavern but tested positive for the outbreak strain. In total, 13 cases (seven females and six males; age range: 4–84 years) were identified. Liver pâté produced by company X was identified as the likely source of the outbreak. Control measures were implemented and since the end of December 2018, no more cases were detected.

Interference of the acid stress on the expression of llsX by Listeria monocytogenes pathogenic island 3 (LIPI-3) variants

Listeria monocytogenes harbor different virulence factors, with a highly heterogeneous distribution between distinct lineages and serotypes. The Listeria Pathogenicity Island 3 (LIPI-3), mainly described in lineage I, encodes for Listeriolysin S (LLS), a virulence factor expressed by L. monocytogenes in the gastrointestinal tract during in vivo infections. The aim of this study was to carry out a comparative genotypic analysis of LIPI-3 identified in L. monocytogenes isolates obtained in Brazil and subjected to whole genomic sequencing (WGS). In addition, transcription of llsX expression under different acid stress conditions was evaluated by RT-PCR. Homologues of the eight LIPI-3 genes (llsAGHXBYDP) were identified in 15 isolates (all from lineage I) representative of different sequence types: ST1 (n = 3), ST3 (n = 6), ST218 (n = 5) and ST288 (n = 1). Single nucleotide polymorphism (SNP) analysis revealed that genetic variation resulted in modification of the final peptide LLS for ST218 (serogroup IVb-v1) and ST288 (serogroup IIb). Selected strains from ST3 and ST288 were subjected to acid stress conditions and the expression of llsX, a LIPI-3 gene, was observed: only F2365 (4b/ST1) presented llsX expression after six hours of acid stress, indicating relevant differences when compared to isolates IIb (ST3 and 288). The results highlight the presence of genomic variations on LIPI-3 and llsX expression under acid stress conditions, demanding further studies to evaluate if these mutations have an impact on L. monocytogenes virulence in vivo.