Reassessing the role of internalin B in Listeria monocytogenes virulence using the epidemic strain F2365

Listeria monocytogenes: possible mechanism of infection of goat uterus and its effects on uterine autophagy and cell apoptosis

Listeriosis is highly prevalent in the animal farming industry, with Listeria monocytogenes as the causative pathogen. To identify potential therapeutic targets for LM infection, we investigated the mechanisms of LM infection in goat uteri. We inoculated a group of goats with LM via jugular vein injection, isolated and raised them, and subsequently collected sterile samples of their uterine tissue after they exhibited clinical symptoms of LM infection. We used Giemsa staining, immunohistochemical staining, real-time qPCR, and Western blotting as experimental methods.First, we investigated the mechanism of Listeria monocytogenes (LM) infection in the goat uterus by examining the expression levels of listeriolysin O, E-cadherin, and tyrosine kinase c-Met in the uterus.Furthermore, we investigated the impact of LM infection on uterine autophagy and cell apoptosis. The results indicate that the injection of LM into the goats' jugular veins leads to LM infection in the goats' uteri. During LM survival inside the goat uterine cells, there is a significant increase in the expression levels of LLO, E-cadherin, and c-Met in the host uterine tissue. This suggests that LM may potentially infect goat uteri through the InlA/E-cadherin and InlB/c-Met pathways. Furthermore, LM infection increases the levels of apoptosis and autophagy in goat uteri. Apoptosis genes Bcl-2 and Bax, as well as autophagy-related genes LC3B, PINK1, and Parkin, exhibit varying degrees of changes in localization and expression in goat uteri, mediating the occurrence of apoptotic and autophagic responses.

High Prevalence of Virulence-Associated Genes and Length Polymorphism in actA and inlB Genes Identified in Listeria monocytogenes Isolates from Meat Products and Meat-Processing Environments in Poland

Listeria monocytogenes is a human pathogen that has the ability to cause listeriosis, a disease with possible fatal outcomes. The typical route of infection is ingestion of the bacteria with contaminated food. In this study, 13 virulence-associated genes were examined with PCR in the genomes of 153 L. monocytogenes isolates collected from meat products and processing environments in Poland. All isolates possessed genes from LIPI-1-hly, actA, plcA, plcB and mpl-as well as four internalins: inlA, inlB, inlC, inlJ. Invasion-associated protein iap, as well as genes prfA and sigB, encoding regulatory proteins, were also detected in all isolates. Gene flaA, encoding flagellin, was detected in 113 (74%) isolates. This was the only gene that was not detected in all isolates, as its presence is serotype-dependent. Gene actA showed polymorphism with longer and shorter variants in PCR amplicons. Two isolates were characterized by truncated inlB genes, lacking 141 bp in their sequence, which was confirmed by gene sequencing. All isolates were positive in hemolysis assays, proving the synthesis of functional PrfA and Hly proteins. Four genotypes of L. monocytogenes based on actA polymorphism and two genotypes based on inlB polymorphism were distinguished within the isolates' collection.

Cell-surface anchoring of Listeria adhesion protein on L. monocytogenes is fastened by internalin B for pathogenesis

Listeria adhesion protein (LAP) is a secreted acetaldehyde alcohol dehydrogenase (AdhE) that anchors to an unknown molecule on the Listeria monocytogenes (Lm) surface, which is critical for its intestinal epithelium crossing. In the present work, immunoprecipitation and mass spectrometry identify internalin B (InlB) as the primary ligand of LAP (K_D ∼ 42 nM). InlB-deleted and naturally InlB-deficient Lm strains show reduced LAP-InlB interaction and LAP-mediated pathology in the murine intestine and brain invasion. InlB-overexpressing non-pathogenic Listeria innocua also displays LAP-InlB interplay. In silico predictions reveal that a pocket region in the C-terminal domain of tetrameric LAP is the binding site for InlB. LAP variants containing mutations in negatively charged (E₅₂₃S, E₆₂₁S) amino acids in the C terminus confirm altered binding conformations and weaker affinity for InlB. InlB transforms the housekeeping enzyme, AdhE (LAP), into a moonlighting pathogenic factor by fastening on the cell surface.

Isoflavone glucoside genistin, an inhibitor targeting Sortase A and Listeriolysin O, attenuates the virulence of Listeria monocytogenes in vivo and in vitro

As a common intracellular facultative anaerobic Gram-positive bacterium, Listeria monocytogenes (L. monocytogenes) exhibits strong resistance to extreme environments, such as low temperature and a wide range of pH values, causing contamination in food production and processing. Sortase A (SrtA) and listeriolysin O (LLO), two crucial virulence factors of L. monocytogenes, are widely recognized as potential targets for the development of anti-L. monocytogenes infection drugs. In this study, we found that genistin simultaneously inhibits the peptidase activity of SrtA and the hemolytic activity of LLO without affecting the growth of L. monocytogenes, alleviating concerns about developing resistance. Furthermore, we demonstrated that genistin reduces L. monocytogenes biofilm formation and invasion of human colorectal cancer (Caco-2) cells. Subsequent mechanistic studies revealed that genistin inhibited LLO-mediated Caco-2 cell damage by blocking LLO oligomerization. Fluorescence quenching assay revealed the potential binding mode of SrtA and LLO to genistin. Genistin might bind to the active pocket of SrtA through residues Leu33, Asn29, and Met40, interacting with D1 domain of LLO involved in oligomerization and pore formation through residues Asn259. Studies in infection models revealed that genistin reduces mortality and pathological damage in mice infected with L. monocytogenes. These results indicate that genistin is a promising anti-virulence agent that could be considered an alternative candidate for the treatment of L. monocytogenes infection.

Listeria monocytogenes-How This Pathogen Uses Its Virulence Mechanisms to Infect the Hosts

Listeriosis is a serious food-borne illness, especially in susceptible populations, including children, pregnant women, and elderlies. The disease can occur in two forms: non-invasive febrile gastroenteritis and severe invasive listeriosis with septicemia, meningoencephalitis, perinatal infections, and abortion. Expression of each symptom depends on various bacterial virulence factors, immunological status of the infected person, and the number of ingested bacteria. Internalins, mainly InlA and InlB, invasins (invasin A, LAP), and other surface adhesion proteins (InlP1, InlP4) are responsible for epithelial cell binding, whereas internalin C (InlC) and actin assembly-inducing protein (ActA) are involved in cell-to-cell bacterial spread. L. monocytogenes is able to disseminate through the blood and invade diverse host organs. In persons with impaired immunity, the elderly, and pregnant women, the pathogen can also cross the blood-brain and placental barriers, which results in the invasion of the central nervous system and fetus infection, respectively. The aim of this comprehensive review is to summarize the current knowledge on the epidemiology of listeriosis and L. monocytogenes virulence mechanisms that are involved in host infection, with a special focus on their molecular and cellular aspects. We believe that all this information is crucial for a better understanding of the pathogenesis of L. monocytogenes infection.

Prevalence and Population Diversity of Listeria monocytogenes Isolated from Dairy Cattle Farms in the Cantabria Region of Spain

Simple Summary

The origin and prevalence of Listeria monocytogenes was studied in dairy cattle farms in order to examine its diversity and determine its possible persistence in manure. The utilization of manure for agricultural purposes is common in many countries. While properly treated and managed manure is an effective and safe fertilizer, foodborne illness outbreaks can occur, as many of the most prominent foodborne pathogens are carried by healthy livestock. It is, therefore, necessary to study the origin and persistence of zoonotic agents in general and of L. monocytogenes in particular, in order to avoid recirculation in farms and reduce risk for human populations.

Abstract

Listeria monocytogenes is an opportunistic pathogen that is widely distributed in the environment. Here we show the prevalence and transmission of L. monocytogenes in dairy farms in the Cantabria region, on the northern coast of Spain. A total of 424 samples was collected from 14 dairy farms (5 organic and 9 conventional) and 211 L. monocytogenes isolates were recovered following conventional microbiological methods. There were no statistically significant differences in antimicrobial resistance ratios between organic and conventional farms. A clonal relationship among the isolates was assessed by pulsed field gel electrophoresis (PFGE) analysis and 64 different pulsotypes were obtained. Most isolates (89%, n = 187) were classified as PCR serogroup IVb by using a multiplex PCR assay. In this case, 45 isolates of PCR serogroup IVb were whole genome-sequenced to perform a further analysis at genomic level. In silico MLST analysis showed the presence of 12 sequence types (ST), of which ST1, ST54 and ST666 were the most common. Our data indicate that the environment of cattle farms retains a high incidence of L. monocytogenes, including subtypes involved in human listeriosis reports and outbreaks. This pathogen is shed in the feces and could easily colonize dairy products, as a result of fecal contamination. Effective herd and manure management are needed in order to prevent possible outbreaks.

Phage Display-Derived Monoclonal Antibodies Against Internalins A and B Allow Specific Detection of Listeria monocytogenes

Listeria monocytogenes is the causative agent of listeriosis, a highly lethal disease initiated after the ingestion of Listeria-contaminated food. This species comprises different serovars, from which 4b, 1/2a, and 1/2b cause most of the infections. Among the different proteins involved in pathogenesis, the internalins A (InlA) and B (InlB) are the best characterized, since they play a major role in the enterocyte entry of Listeria cells during early infection. Due to their covalent attachment to the cell wall and location on the bacterial surface, along with their exclusive presence in the pathogenic L. monocytogenes, these proteins are also used as detection targets for this species. Even though huge advancements were achieved in the enrichment steps for subsequent Listeria detection, few studies have focused on the improvement of the antibodies for immunodetection. In the present study, recombinant InlA and InlB produced in Escherichia coli were used as targets to generate antibodies via phage display using the human naïve antibody libraries HAL9 and HAL10. A set of five recombinant antibodies (four against InlA, and one against InlB) were produced in scFv-Fc format and tested in indirect ELISA against a panel of 19 Listeria strains (17 species; including the three main serovars of L. monocytogenes) and 16 non-Listeria species. All five antibodies were able to recognize L. monocytogenes with 100% sensitivity (CI 29.24–100.0) and specificity (CI 88.78–100.0) in all three analyzed antibody concentrations. These findings show that phage display-derived antibodies can improve the biological tools to develop better immunodiagnostics for L. monocytogenes.

The combination of thymol and cinnamaldehyde reduces the survival and virulence of Listeria monocytogenes on autoclaved chicken breast

AIMS

To reveal the antibacterial mechanism of the combination of thymol and cinnamaldehyde to Listeria monocytogenes ATCC 19115 on autoclaved chicken breast.

METHODS AND RESULTS

In this study, Listeria monocytogenes ATCC 19115 on autoclaved chicken breast was exposed to the stress of 125 μg/mL thymol and 125 μg/mL cinnamaldehyde, and transcriptome analysis was used to reveal the crucial antibacterial mechanism. According to the results, 1303 significantly differentially expressed genes (DEGs) were identified. Treated by thymol and cinnamaldehyde in combination, pyrimidine and branched-chain amino acids biosynthesis of L. monocytogenes were thwarted which impairs its nucleic acid biosynthesis and intracellular metabolism. The up-regulated DEGs involved in membrane composition and function contributed to membrane repair. Besides, pyruvate catabolism and TCA cycle were restrained which brought about the disturbance of amino acid metabolism. ABC transporters were also perturbed, for instance, the uptake of cysteine, D-methionine and betaine was activated, while the uptake of vitamin, iron and carnitine was repressed. Thus, L. monocytogenes tended to activate PTS, glycolysis, glycerol catabolism, and pentose phosphate pathways to obtain energy to adapt to the hostile condition. Noticeably, DEGs involved in virulence factors were totally down-regulated, including genes devoted to encoding flagella, chemotaxis, biofilm formation, internalin as well as virulence gene clusters.

CONCLUSIONS

The combination of thymol and cinnamaldehyde is effective to reduce the survival and potential virulence of L. monocytogenes on autoclaved chicken breast.

SIGNIFICANCE AND IMPACT OF STUDY

This work contributes to providing theoretical information for the application and optimization of thymol and cinnamaldehyde in ready-to-eat meat products to inhibit L. monocytogenes.

Pathogenicity and virulence of Listeria monocytogenes: A trip from environmental to medical microbiology

Listeria monocytogenes is a saprophytic gram-positive bacterium, and an opportunistic foodborne pathogen that can produce listeriosis in humans and animals. It has evolved an exceptional ability to adapt to stress conditions encountered in different environments, resulting in a ubiquitous distribution. Because some food preservation methods and disinfection protocols in food-processing environments cannot efficiently prevent contaminations, L. monocytogenes constitutes a threat to human health and a challenge to food safety. In the host, Listeria colonizes the gastrointestinal tract, crosses the intestinal barrier, and disseminates through the blood to target organs. In immunocompromised individuals, the elderly, and pregnant women, the pathogen can cross the blood-brain and placental barriers, leading to neurolisteriosis and materno-fetal listeriosis. Molecular and cell biology studies of infection have proven L. monocytogenes to be a versatile pathogen that deploys unique strategies to invade different cell types, survive and move inside the eukaryotic host cell, and spread from cell to cell. Here, we present the multifaceted Listeria life cycle from a comprehensive perspective. We discuss genetic features of pathogenic Listeria species, analyze factors involved in food contamination, and review bacterial strategies to tolerate stresses encountered both during food processing and along the host's gastrointestinal tract. Then we dissect host-pathogen interactions underlying listerial pathogenesis in mammals from a cell biology and systemic point of view. Finally, we summarize the epidemiology, pathophysiology, and clinical features of listeriosis in humans and animals. This work aims to gather information from different fields crucial for a comprehensive understanding of the pathogenesis of L. monocytogenes.

Molecular characterization of Salmonella spp. and Listeria monocytogenes strains from biofilms in cattle and poultry slaughterhouses located in the federal District and State of Goiás, Brazil

Listeria monocytogenes and Salmonella spp. are considered important foodborne pathogens that are commonly associated with foods of animal origin. The aim of this study was to perform molecular characterization of L. monocytogenes and Salmonella spp. isolated from biofilms of cattle and poultry slaughterhouses located in the Federal District and State of Goiás, Brazil. Fourteen L. monocytogenes isolates and one Salmonella sp. were detected in poultry slaughterhouses. No isolates were detected in cattle slaughterhouses. All L. monocytogenes isolates belonged to lineage II, and 11 different pulsotypes were detected. Pulsed-field gel electrophoresis analysis revealed the dissemination of two strains within one plant, in addition to the regional dissemination of one of them. The Salmonella isolate was identified via whole genome sequencing as Salmonella enterica serovar Minnesota ST548. In the sequence analysis, no premature stop codons were detected in the inlA gene of Listeria. All isolates demonstrated the ability to adhere to Caco-2 cells, while 50% were capable of invading them. Antimicrobial resistance was detected in 57.1% of the L. monocytogenes isolates, and resistance to sulfonamide was the most common feature. The tetC, ermB, and tetM genes were detected, and four isolates were classified as multidrug-resistant. Salmonella sp. was resistant to nine antimicrobials and was classified as multidrug-resistant. Resistance genes qnrB19, blaCMY-2, aac(6')-Iaa, sul2, and tetA, and a mutation in the parC gene were detected. The majority (78.5%) of the L. monocytogenes isolates were capable of forming biofilms after incubation at 37°C for 24 h, and 64.3% were capable of forming biofilms after incubation at 12°C for 168 h. There was no statistical difference in the biofilm-forming capacity under the different evaluated conditions. Salmonella sp. was capable of forming biofilms at both tested temperatures. Biofilm characterization was confirmed by collecting the samples consistently, at the same sampling points, and by assessing biofilm formation in vitro. These results highlight the potential risk of cross-contamination in poultry slaughterhouses and the importance of surveillance and pathogen control maintenance programs within the meat production industry.

Listeria monocytogenes: review of pathogenesis and virulence determinants-targeted immunological assays

Listeria monocytogenes is one of the most invasive foodborne pathogens and is responsible for numerous outbreaks worldwide. Most of the methods to detect this bacterium in food require selective enrichment using traditional bacterial culture techniques that can be time-consuming and labour-intensive. Moreover, molecular methods are expensive and need specific technical knowledge. In contrast, immunological approaches are faster, simpler, and user-friendly alternatives and have been developed for the detection of L. monocytogenes in food, environmental, and clinical samples. These techniques are dependent on the constitutive expression of L. monocytogenes antigens and the specificity of the antibodies used. Here, updated knowledge on pathogenesis and the key immunogenic virulence determinants of L. monocytogenes that are used for the generation of monoclonal and polyclonal antibodies for the serological assay development are summarised. In addition, immunological approaches based on enzyme-linked immunosorbent assay, immunofluorescence, lateral flow immunochromatographic assays, and immunosensors with relevant improvements are highlighted. Though the sensitivity and specificity of the assays were improved significantly, methods still face many challenges that require further validation before use.

Proteomic Exploration of Listeria monocytogenes for the Purpose of Vaccine Designing Using a Reverse Vaccinology Approach

Listeriosis is a major foodborne infection provoked by a bacterium known as Listeria monocytogenes. It is one of the predominant causes of death in pregnant women, infants, and immunocompromised persons. Despite such fatal effects, until now there is no proper medication or drug available for such a serious foodborne infection. One of the most promising ways to deal with this challenge is vaccination. This present study aims at the prediction of B cell epitopes for subunit vaccine designing against Listeria monocytogenes using a reverse vaccinology approach. Among screened out 299 epitopes of strain F2365 of Listeria monocytogenes, based on the VaxiJen score, the top 20 epitopes were selected. 3D modeling of epitopes and alleles was generated by PEPstrMOD and Swiss Model respectively. Molecular docking reveals 4 epitopes viz., MKFLFPLKL, CEETFGIRL, FLKIDPPIL, and VRHHGGGHK based on binding energy. All 4 epitopes were investigated for non-toxicity, binding affinity, and population coverage. After vigorous investigation, epitope FLKIDPPIL was anticipated as the best vaccine contender. The stability of the FLKIDPPIL-HLA DRB1 _0101 complex was proved by performing the simulation. Here, predicted peptide through the Insilico approach may become a potential remedy against listeriosis, after the wet-lab approach and clinical trials.

Virulence potential of Listeria monocytogenes strains recovered from pigs in Spain

BACKGROUND

Listeria monocytogenes is a foodborne bacterial pathogen that causes listeriosis, an infectious disease in animals and people, with pigs acting as asymptomatic reservoirs. In August 2019 an outbreak associated with the consumption of pork meat caused 222 human cases of listeriosis in Spain. Determining the diversity as well as the virulence potential of strains from pigs is important to public health.

METHODS

The behaviour of 23 L monocytogenes strains recovered from pig tonsils, meat and skin was compared by studying (1) internalin A, internalin B, listeriolysin O, actin assembly-inducing protein and PrfA expression levels, and (2) their invasion and intracellular growth in eukaryotic cells.

RESULTS

Marked differences were found in the expression of the selected virulence factors and the invasion and intracellular replication phenotypes of L monocytogenes strains. Strains obtained from meat samples and belonging to serotype 1/2a did not have internalin A anchored to the peptidoglycan. Some strains expressed higher levels of the studied virulence factors and invaded and replicated intracellularly more efficiently than an epidemic L monocytogenes reference strain (F2365).

CONCLUSION

This study demonstrates the presence of virulent L monocytogenes strains with virulent potential in pigs, with valuable implications in veterinary medicine and food safety.

Listeria monocytogenes Virulence, Antimicrobial Resistance and Environmental Persistence: A Review

Listeria monocytogenes is a ubiquitous opportunistic pathogen responsible for the well-known listeriosis disease. This bacterium has become a common contaminant of food, threatening the food processing industry. Once consumed, the pathogen is capable of traversing epithelial barriers, cellular invasion, and intracellular replication through the modulation of virulence factors such as internalins and haemolysins. Mobile genetic elements (plasmids and transposons) and other sophisticated mechanisms are thought to contribute to the increasing antimicrobial resistance of L. monocytogenes. The environmental persistence of the pathogen is aided by its ability to withstand environmental stresses such as acidity, cold stress, osmotic stress, and oxidative stress. This review seeks to give an insight into L. monocytogenes biology, with emphasis on its virulence factors, antimicrobial resistance, and adaptations to environmental stresses.

Listeria monocytogenes: cell biology of invasion and intracellular growth

The Gram-positive pathogen Listeria monocytogenes is able to promote its entry into a diverse range of mammalian host cells by triggering plasma membrane remodeling, leading to bacterial engulfment. Upon cell invasion, L. monocytogenes disrupts its internalization vacuole and translocates to the cytoplasm, where bacterial replication takes place. Subsequently, L. monocytogenes uses an actin-based motility system that allows bacterial cytoplasmic movement and cell-to-cell spread. L. monocytogenes therefore subverts host cell receptors, organelles and the cytoskeleton at different infection steps, manipulating diverse cellular functions that include ion transport, membrane trafficking, post-translational modifications, phosphoinositide production, innate immune responses as well as gene expression and DNA stability.

Listeriolysin O-dependent host surfaceome remodeling modulates Listeria monocytogenes invasion

Listeria monocytogenes is a pathogenic bacterium that invades epithelial cells by activating host signaling cascades, which promote bacterial engulfment within a phagosome. The pore-forming toxin listeriolysin O (LLO), which is required for bacteria phagosomal escape, has also been associated with the activation of several signaling pathways when secreted by extracellular bacteria, including Ca2+ influx and promotion of L. monocytogenes entry. Quantitative host surfaceome analysis revealed significant quantitative remodeling of a defined set of cell surface glycoproteins upon LLO treatment, including a subset previously identified to play a role in the L. monocytogenes infection process. Our data further shows that the lysosomal-associated membrane proteins LAMP-1 and LAMP-2 are translocated to the cellular surface and those LLO-induced Ca2+ fluxes are required to trigger the surface relocalization of LAMP-1. Finally, we identify late endosomes/lysosomes as the major donor compartments of LAMP-1 upon LLO treatment and by perturbing their function, we suggest that these organelles participate in L. monocytogenes invasion.