Bacterium Listeria Monocytogenes Research Articles

Interspecies Interaction of Bacteria Listeria monocytogenes, Yersinia pseudotuberculosis, and Marine Saprotrophs during Long-Term Culturing in Biofilms.

All bacterial strains studied retained the viability and ability to form both mono- and polycultural biofilms under conditions of long-term culturing in artificial seawater at 6°C and without addition of nutrients. Bacillus sp. and Pseudomonas japonica presumably stimulated the growth and reproduction of the pathogenic bacteria Listeria monocytogenes and Yersinia pseudotuberculosis. Preserved cell viability in a monoculture biofilm for a long period without adding a food source can indicate allolysis. At the same time, in a polycultural biofilm, the metabolites secreted by saprotrophic strains can stimulate the growth of L. monocytogenes and Y. pseudotuberculosis.

Ratanjot (Alkanna tinctoria L.) Root Extract, Rich in Antioxidants, Exhibits Strong Antimicrobial Activity against Foodborne Pathogens and Is a Potential Food Preservative.

Natural and sustainable plant-based antioxidants and antimicrobials are highly desirable for improving food quality and safety. The present investigation assessed the antimicrobial and antioxidant properties of active components from Alkanna tinctoria L. (herb) roots, also known as Ratanjot root. Two methods were used to extract active components: microwave-assisted hot water (MAHW) and ethanolic extraction. MAHW extract yielded 6.29%, while the ethanol extract yielded 18.27%, suggesting superior Ratanjot root extract powder (RRP) solubility in ethanol over water. The ethanol extract showed significantly higher antioxidant activity than the MAHW extract. Gas Chromatography-Mass Spectrometry analysis revealed three major phenolic compounds: butanoic acid, 3-hydroxy-3-methyl-; arnebin 7, and diisooctyl pthalate. The color attributes (L*, a*, b*, H°ab, C*ab) for the ethanolic and MAHW extracts revealed significant differences (p < 0.05) in all the above parameters for both types of extracts, except for yellowness (b*) and chroma (C*ab) values. The ethanol extract exhibited antimicrobial activity against 14 foodborne bacteria, with a significantly higher inhibitory effect against Gram-positive bacteria (Listeria monocytogenes and Staphylococcus aureus) than the Gram-negative bacteria (Salmonella enterica serovar Typhimurium and Escherichia coli). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were both 25 mg/mL for the Gram-negative bacteria, while the MIC and MBC concentrations varied for Gram-positive bacteria (0.049-0.098 mg/mL and 0.098-0.195 mg/mL) and the antimicrobial effect was bactericidal. The antimicrobial activities of RRP extract remained stable under broad temperature (37-100 °C) and pH (2-6) conditions, as well as during refrigerated storage for 30 days. Application of RRP at 1% (10 mg/g) and 2.5% (25 mg/g) levels in a cooked chicken meatball model system prevented lipid oxidation and improved sensory attributes and retarded microbial growth during refrigerated (4 °C) storage for 20 days. Furthermore, the RRP extract was non-toxic when tested with sheep erythrocytes and did not inhibit the growth of probiotics, Lacticaseibacillus casei, and Lactiplantibacillus plantarum. In conclusion, the study suggests that RRP possesses excellent antimicrobial and antioxidant activities, thus making it suitable for food preservation.

Invasive Listeriosis in End-Stage Kidney Disease (ESKD) Patients Receiving Long-Term Dialysis: A 21-Year Case Series.

Listeriosis is caused by the facultative anaerobic bacterium Listeria monocytogenes. Infection from Listeria-contaminated food or water is the main etiology. If Listeria travels outside the intestines, it can cause invasive listeriosis, such as sepsis, meningitis, and meningoencephalitis. Invasive illness is especially dangerous for pregnant women and their newborns, elderly people, and people with compromised immune systems or medical conditions such as end-stage kidney disease (ESKD) patients receiving long-term dialysis. Describe the manifestations and hospital outcomes of invasive listeriosis and identify the risk factors for in-hospital and one-year mortality in ESKD patients receiving long-term dialysis. This retrospective observational study examined hospitalized patient records at a Taiwanese tertiary medical center from August 1, 2000, to August 31, 2021. ESKD patients on chronic dialysis were identified with invasive listeriosis by blood culture and discharge diagnosis. Over 21 years, we accurately recorded 26 cases. ESKD patients on chronic dialysis with invasive listeriosis have a poor prognosis. Only 53.8% of chronic dialysis patients with invasive listeriosis survived their first hospital episode. 42.3% of hospitalized ESKD patients with invasive listeriosis survived one year later. In univariate analysis, shock, tachypnea (RR ≥ 22), respiratory failure, qSOFA score ≥ 2, and lower initial platelet count were linked to greater in-hospital mortality rates. ESKD patients with invasive listeriosis have a grave prognosis. Our research reveals that an early blood sample for a bacterial culture may identify invasive listeriosis in chronic dialysis patients with fever, nausea or vomiting, confusion, and respiratory distress. This study is the first to identify a lower platelet count and qSOFA score ≥ 2 as markers of high-risk invasive listeriosis in ESKD patients.

Francisella tularensis Live Vaccine Strain training of murine alveolar and bone marrow-derived macrophages.

The discovery of non-specific "trained immunity" in monocytes has generated substantial excitement. However, to date, training has been studied with relatively few microbes (e.g., Mycobacterium bovis Bacille Calmette-Guérin, a live attenuated intracellular bacterium used as a vaccine) and microbial substances (e.g., LPS), and it remains unclear whether training during infection is common. We previously demonstrated that vaccination of mice with Francisella tularensis Live Vaccine Strain (LVS), another live attenuated intracellular bacterium, protected against challenge with the unrelated bacterium Listeria monocytogenes. The present study therefore tested whether LVS vaccination engenders trained macrophages that contributed to this protection. To do so, we used a previous in vitro co-culture approach with murine bone marrow-derived macrophages to expand and study lung alveolar macrophages. We demonstrated that alveolar macrophages can be productively infected and employed to characterize interactions with LVS-immune lymphocytes. However, we find no evidence that either bone marrow-derived or alveolar macrophages are trained by LVS vaccination.

Bioactives of the essential oil from the leaves of Eugenia pyriformis Cambess (Myrtaceae) on the effects of tobacco.

Lung cancer is the most commonly diagnosed and the main cause of cancer death, usually related to cigarette smoking. Furthermore, the microbiota of people exposed to cigarette smoke can be modified, making it difficult to eliminate opportunistic microorganisms. The leaves of Eugenia pyriformis are a by-product of fruit production and, to date, there have been no studies addressing the antiproliferative, anti-inflammatory, and antimicrobial activities. Investigate the antimicrobial, Nitric Oxide (NO)-production inhibition, and antiproliferative activities of the essential oil from E. pyriformis leaves and its possible effect on the treatment and prevention of damage caused by tobacco. The essential oil (EO) was obtained by hydrodistillation (3h). Its chemical composition was investigated by GC-MS. It was proposed to investigate antiproliferative activity against human tumor cell lines, namely, breast adenocarcinoma (MCF-7), lung (NCI-H460), cervical (HeLa), and hepatocellular (HepG2) carcinomas. A non-tumor primary culture from pig liver (PLP2) was also tested. The EO capacity to inhibit nitric oxide (NO) production was evaluated by a lipopolysaccharide stimulated murine macrophage cell line. Antibacterial and antifungal activities against opportunistic pathogens were investigated against seven strains of bacteria and eight fungi. The results indicated the presence of 23 compounds in the essential oil, the majority were spathulenol (45.63%) and β-caryophyllene oxide (12.72%). Leaf EO provided 50% inhibition of nitric oxide production at a concentration of 92.04µgmL-1. The EO also demonstrated antiproliferative activity against all human tumor cell lines studied, with GI50 values comprised between 270.86 and 337.25µgmL-1. The essential oil showed antimicrobial potential against the bacteria Listeria monocytogenes (Murray et al.) Pirie (NCTC 7973) and Salmonella Typhimurium ATCC 13311 (MIC 1870µgmL-1) and fungi Aspergillus versicolor ATCC 11730, Aspergillus ochraceus ATCC 12066, Penicillium ochrochloron ATCC 90288, Penicillium verrucosum var. cyclopium (Westling) Samson, Stolk & Hadlok (food isolate) (MIC 1870µgmL-1) and Trichoderma viride Pers. IAM 5061 (1,400µg mL-1). The demonstrated anti-inflammatory, antiproliferative, and antimicrobial activities in the leaves of E. pyriformis can add value to the production chain of this plant, being a possible option for preventing and combating cancer, including lung cancer.

Safety and quality of different domestic manufacturers and determination of its falsification

At the current stage, the dairy industry in Ukraine is at a fairly high level, although in comparison with world standards, it does not meet the world level in a number of indicators. One of the main tasks for Ukraine as a member of the WTO and in connection with the prospect of its accession to the EU is the harmonization of national regulatory and legal requirements with international ones in the field of food safety and quality. The purpose of the study is to evaluate the safety and quality of sour cream obtained from various domestic manufacturers, as well as to determine its adulteration according to generally accepted methods and developed patented express methods. Analytical, organoleptic, physico-chemical, microbiological, toxicological and statistical methods of research were used to implement the research goal. Sour cream produced by Ukrainian dairy enterprises according to organoleptic indicators (appearance, color, consistency, smell, taste) and physicochemical indicators (mass fraction of fat, titrated acidity, phosphatase, temperature during storage) met the requirements of the current national standard of Ukraine - DSTU 4418:2005. With the exception of sour cream of samples No. 1 and No. 5) - the fat content is reduced, and respectively 8.72±0.07% and 9.10±0.95% (according to the standards of 15−40%) and increased titrated acidity (sample No. 1) − 109.0±1.43 °T (according to standards of 60–100 °T). According to the microbiological tests of sour cream, the content of viable lactic acid bacteria was significantly lower - from (1.16±0.21)x102 to (1.42±0.21)x103 CFU/g compared to the normative indicators (1.0x107 CFU/g), which indicated a significant reduction in the contamination of the product by microorganisms as a result of compliance with sanitary and hygienic requirements for sour cream production. The content of coliform bacteria, Salmonella bacteria, Listeria monocytogenes bacteria, Staphylococcus aureus bacteria, yeast, mold fungi in sour cream met the regulatory requirements of the current national standard of Ukraine - DSTU 4418:2005. During the determination of product falsification, the presence of impurities of starch, sodium hydrogen carbonate, alkaline detergents, hydrogen peroxide, gelatin, and vegetable fats in the sour cream of the producers (samples No. 1 and No. 5) was found; no impurities were detected in the sour cream of other producers. The content of toxic elements (heavy metals), mycotoxins, antibiotics and hormonal drugs in sour cream did not exceed the maximum permissible level (MRL). Express and optimized methods for determining adulteration of sour cream have been developed. Key words: dairy industry, food product, sour cream, organoleptic, physicochemical, microbiological, toxicological indicators, safety, quality, consumer.

In vitro bioactivity of biodegradable films based on chitosan/quince seed mucilage reinforced with ZnO-nanoparticle

In this study, biodegradable active films were designed by adding ZnO-NPs to the quince seed mucilage/chitosan matrix. The films were investigated for characterization and in vitro bioactivity. According to the results, a significant decrease in moisture content, water holding capacity and light (L*) occurred with the addition of ZnO-NP. (p < 0.05). FT-IR spectra showed the interaction between ZnO-NPs and N-H quince seed mucilage and chitosan groups. Nanocomposite films containing ZnO-NP showed improved thermal stability. The developed bionanocomposite films were easily buried in soil and subjected to degradation. The minimum degradation of the film in soil after 20 days was 62.02%. The maximum cell viability (%) of C/ZnO-NP and C/QSM/ZnO-NP films were determined as 86.81% and 91.22%, respectively, and the films were found to be non-toxic. Moreover, while the quince seed mucilage film did not show antibacterial performance, chitosan and ZnO NPs showed antibacterial effects against the tested bacteria Listeria monocytogenes (ATCC 7644) and Escherichia coli O157:H7 (ATCC 35,150). In this context, the design bionanocomposite films can be used as an active food packaging material for food preservation by controlling food-borne pathogens. In addition, the developed films do not pose a threat to the environment and therefore have great potential for the sustainable food packaging industry.

Multi-functional copper oxide nanoparticles synthesized using Lagerstroemia indica leaf extracts and their applications

Developing multifunctional nanomaterials through environmentally friendly and efficient approaches is a pivotal focus in nanotechnology. This study aimed to employ a biogenic method to synthesize multifunctional copper oxide nanoparticles (LI-CuO NPs) with diverse capabilities, including antibacterial, antioxidant, and seed priming properties, as well as photocatalytic organic dye degradation and wastewater treatment potentials using Lagerstroemia indica leaf extract. The synthesized LI-CuO NPs were extensively characterized using UV–vis spectroscopy, dynamic light scattering (DLS), X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform-infrared spectroscopy (FT-IR). The colloid displayed surface plasmon resonance peaks at 320 nm, characteristic of LI-CuO NPs. DLS analysis revealed an average particle size of 93.5 nm and a negative zeta potential of −20.3 mV. FTIR and XPS analyses demonstrated that LI-CuO NPs possessed abundant functional groups that acted as stabilizing agents. XRD analysis indicated pure crystalline and spherical LI-CuO NPs measuring 36 nm in size. Antibacterial tests exhibited significant differential activity of LI-CuO NPs against both gram-negative (Escherichia coli, Salmonella typhimurium) and gram-positive (Staphylococcus aureus and Listeria monocytogenes) bacteria. In antioxidant tests, the LI-CuO NPs demonstrated a remarkable radical scavenging activity of 97.6 % at a concentration of 400 μg mL−1. These nanoparticles were also found to enhance mustard seed germination at low concentrations. With a remarkable reusability, LI-CuO NPs exhibited excellent photocatalytic performance, with a degradation efficiency of 97.6 % at 150 μg/mL as well as a 95.6 % reduction in turbidity when applied to wastewater treatment. In conclusion, this study presents environmentally friendly method for the facile synthesis of LI-CuO NPs that could potentially offer promising applications in biomedicine, agriculture, and environmental remediation due to their multifunctional properties.

Melittin—The principal toxin of honeybee venom—Is also produced in the honeybee fat body

Melittin is a powerful toxin present in honeybee venom that is active in a wide range of animals, from insects to humans. Melittin exerts numerous biological, toxicological, and pharmacological effects, the most important of which is destruction of the cell membrane. The phospholipase activity of melittin and its ability to activate phospholipases in the venom contribute to these actions. Using analytical methods, we discovered that the honeybee Apis mellifera produces melittin not only in the venom gland but also in its fat body cells, which remain resistant to this toxin's effects. We suggest that melittin acts as an anti-bacterial agent, since its gene expression is significantly upregulated when honeybees are infected with Escherichia coli and Listeria monocytogenes bacteria; additionally, melittin effectively kills these bacteria in the disc diffusion test. We hypothesize that the chemical and physicochemical properties of the melittin molecule (hydrophilicity, lipophilicity, and capacity to form tetramers) in combination with reactive conditions (melittin concentration, salt concentration, pH, and temperature) are responsible for the targeted destruction of bacterial cells and apparent tolerance towards own tissue cells. Considering that melittin is an important current and, importantly, potential broad-spectrum medication, a thorough understanding of the observed phenomena may significantly increase its use in clinical practice.

Developing a novel, low-cost, antimicrobial, and biodegradable pectin/HEC/ZnO biofilm for edible food packaging applications

AbstractThe purpose of this study was to investigate the potential of pectin extracted from orange waste by acid hydrolysis and prepared Pectin/ hydroxyethyl cellulose (HEC)/ZnO nanoparticles (ZnO-NPs) biofilm for food packaging applications. The pectin/HEC/ZnO biofilms were prepared in an aqueous solution at room temperature using solvent casting method and characterized by different techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM). Also, thermal gravimetric analysis (TGA), mechanical properties, and water vapor permeability-WVP were evaluated. Moreover, its antimicrobial activity against Gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa, and Salmonella enterica Typhimiurium) and two Gram positive bacteria (Listeria monocytogenes and Staphylococcus aureus), and also has antifungal activity against Candida albicans was assessed. The obtained results display that the water vapor permeability (WVP) indicated a reduction in permeability with increased ZnO concentration, with WVPs ranging from 2.55 × 10−12 to 4.28 × 10−12 gm/pas.m2, which indicates that our pectin/HEC/ZnO bionanocomposite biofilm could efficiently decrease moisture transfer, thereby potentially extending the shelf-life of packaged food products. Furthermore, the results showed enhanced tensile strength and flexibility in the biofilms with the addition of 1% ZnO nanoparticles from 1.2 to 2.6 MPa and 4.5 to 13 MPa respectively. The WVP indicated a reduction in permeability with increased ZnO concentration, with WVPs ranging from 2.55 × 10−12 to 4.28 × 10−12 gm/pas.m2. The antimicrobial activity against pathogens such as Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica Typhimurium, Listeria monocytogenes, Staphylococcus aureus, and Candida albicans was significant, with a 99.96% reduction in E. coli counts at a biofilm concentration of 200 mg/mL. Furthermore, the current study revealed that the synthesized bionanocomposite biofilms had excellent qualities such as transparency, flexibility, low cost, and being environmentally friendly. The pectin/HEC/ZnO bionanocomposite was found to be an ideal biofilm for food packaging due to its safety and affordability, which is able to prolong food shelf-life.

Cross-regulation of Listeria monocytogenes and the host ubiquitin system in listeriosis

The facultative intracellular bacterium Listeria (L.) monocytogenes may cause severe diseases in humans and animals. The control of listeriosis/L. monocytogenes requires the concerted action of cells of the innate and adaptive immune systems. In this regard, cell-intrinsic immunity of infected cells, activated by the immune responses, is crucial for the control and elimination intracellular L. monocytogenes. Both the immune response against L. monocytogenes and cell intrinsic pathogen control are critically regulated by post-translational modifications exerted by the host ubiquitin system and ubiquitin-like modifiers (Ubls). In this review, we discuss our current understanding of the role of the ubiquitin system and Ubls in listeriosis, as well as future directions of research.

Sanitizing of stainless steel surfaces in the food industry: Effect of gaseous ozone against pathogens and filamentous fungi

AbstractThe aim of this work was to evaluate the resistance of two pathogenic bacteria (Listeria monocytogenes and Salmonella enterica subsp. enterica serotype Senftenberg), and three airborne food‐spoiling filamentous fungi (Hyphopichia burtonii, Penicillium nordicum, and Aspergillus brasiliensis ATCC 16404) to gaseous ozone on stainless steel. Tests were carried out by exposing inoculated tiles to gaseous ozone in a laboratorial chamber at concentrations up to 50 mg/L and at times up to 180 min (bacteria) or 300 min (filamentous fungi). For bacteria, the resistance to gaseous ozone of L. monocytogenes proved markedly higher than that of S. enterica. Their D‐values increased by seven times (from 27.3 to 200.7 min for the strain of L. monocytogenes studied; from 7.3 to 48.0 min for the Salmonella species studied) when the ozone concentration were reduced from 12 to 4 mg/L. For filamentous fungi, a substantial effect was observed only at 50 mg/L on single‐layered inocula: at these conditions, A. brasiliensis ATCC 16404 proved the most resistant strain to gaseous ozone, its D‐value (134.4 min) being higher than those registered for the tested strains of H. burtonii (9.9 min) and P. nordicum (17.1 min). The results demonstrated that the use of gaseous ozone as a sanitizing agent for environments and working surfaces seems to be a potential alternative to chemical sanitizers against the two pathogens studied, whereas it seemed effective against the three filamentous fungi studied only in limited circumstances.

Synthesis and in vitro Antibacterial Evaluation of N‐(4‐methoxy‐2‐nitrophenyl)‐β‐alanine Derivatives

AbstractIn this study a series of N‐(4‐methoxy‐2‐nitrophenyl)‐β‐alanine derivatives were prepared, characterized by the NMR and IR spectroscopic and microanalysis techniques and evaluated for their antibacterial potency against Gram‐positive Staphylococcus aureus and Listeria monocytogenes bacteria strains as well Gram‐negative Escherichia coli and Salmonella enteritidis. The assessment was carried out using the in vitro methodologies. According to the results, the best antibacterial properties were shown by hydrazones with the incorporated thien‐2‐yl and dimethylaminophenyl fragments. According to the data, almost all compounds except N‐alkylated dimethylaminophenyl‐having hydrazone are regarded as bactericidal agents for the used bacteria. The obtained data demonstrate that the above‐mentioned hydrazones could be further selectively explored for the development of antibacterial candidates targeting Gram‐positive and Gram‐negative bacteria.

Межвидовое взаимодействие бактерий Listeria monocytogenes, Yersinia pseudotuberculosis и морских сапротрофов при долговременном культивировании в биоплёнках

Межвидовое взаимодействие бактерий Listeria monocytogenes, Yersinia pseudotuberculosis и морских сапротрофов при долговременном культивировании в биоплёнках

Defect-Passivated Photosensor Based on Cesium Lead Bromide (CsPbBr3) Perovskite Quantum Dots for Microbial Detection.

A defect-passivated photosensor based on cesium lead bromide (CsPbBr3) perovskite quantum dots (QD) was fabricated using parylene films, and the photosensor was applied for the microbial detection. The CsPbBr3 perovskite QDs were synthesized to be homogeneous in size under thermodynamic control, and the perovskite QD-based photosensor was fabricated using MoS2 flakes as the electron transfer layer. In this work, a parylene film with functional groups was deposited on a photosensor for physical protection (waterproof) and defect (halide vacancy) passivation of the perovskite QD. As the first effect of the parylene film, the physical protection of the perovskite QD from water was estimated by comparing the photosensor performance after incubation in water. As the second effect of the parylene, the interaction between the functional groups of the parylene film and the halide vacancies of the perovskite QDs was investigated through the bandgap, crystal structure, and trap-state density analysis. Additionally, density functional theory analysis on Mulliken charges, lattice parameters, and Gibbs free energy demonstrated the effect of the defect passivation by parylene films. Finally, the parylene-passivated QD-based photosensor was applied to the detection of two kinds of food-poisoning and gastroduodenal disease bacteria (Listeria monocytogenes and Helicobacter pylori).

Improving the technology for the production of raw dried beef products

The relevance of this work lies in the need to reduce the negative impact on human health of sodium nitrite (food additive E250), which is added to meat products, in particular to raw dried sausages, in order to accelerate their maturation and give them the shades familiar to consumers. The aim of the work is to improve the technology for the production of raw dried beef products based on the use of modern biotechnological approaches, sea salt and the natural colouring agent betanin, and beetroot juice as a substitute for sodium nitrite. This goal was achieved through the implementation of a mixed salting method, whereby the surface of the meat semi-product was rubbed with a reduced amount of salt, including 0.0005 kilograms of sodium nitrite per kilogram of meat weight, compared to standard technology, and the rest of the salting mixture, which contained 0.0045 sodium nitrite, was injected deep into the semi-product as an aqueous solution. The source of nitrite was beetroot juice rich in nitrate ion, 0.03 dm3 of which contained 0.0052 kilograms of sodium nitrate, sufficient to synthesize 0.0045 kilograms of nitrite ion per kilogram of meat raw material. The chosen salting method reduced the amount of sodium nitrite from 0.015 to 0.005 kilograms per kilogram of meat product compared to the classical method, and the addition of beetroot juice made it possible to give the product a uniform colour throughout. Contamination of the product with dangerous microflora was prevented by adding a preparation containing bacteria of the Pediococcus acidilactici and Staphylococcus carnosus strains to the syringe solution. A positive effect of Pediococcus acidilactici was found, which was achieved by accelerating the pH of the meat mass to 5.0÷5.5, which stopped the growth of most dangerous microorganisms, including Shigella spp., Salmonella spp., Clostridium difficile and Escherichia coli. The product was protected from the development of Listeria monocytogenes bacteria by bacteria of the Staphylococcus carnosus strain. The proposed technology can be used in the food industry in the manufacture of raw meat products, which will significantly reduce the negative impact of sodium nitrite on human health

Structural basis for the unique molecular properties of broad-range phospholipase C from Listeria monocytogenes

Listeriosis is one of the most serious foodborne diseases caused by the intracellular bacterium Listeria monocytogenes. Its two major virulence factors, broad-range phospholipase C (LmPC-PLC) and the pore-forming toxin listeriolysin O (LLO), enable the bacterium to spread in the host by destroying cell membranes. Here, we determine the crystal structure of LmPC-PLC and complement it with the functional analysis of this enzyme. This reveals that LmPC-PLC has evolved several structural features to regulate its activity, including the invariant position of the N-terminal tryptophan (W1), the structurally plastic active site, Zn2+-dependent activity, and the tendency to form oligomers with impaired enzymatic activity. We demonstrate that the enzymatic activity of LmPC-PLC can be specifically inhibited by its propeptide added in trans. Furthermore, we show that the phospholipase activity of LmPC-PLC facilitates the pore-forming activity of LLO and affects the morphology of LLO oligomerization on lipid membranes, revealing the multifaceted synergy of the two virulence factors.

Quantitative live imaging reveals a direct interaction between CD44v6 and MET in membrane domains upon activation with both MET ligands, HGF and internalin B

Deregulation of the receptor tyrosine kinase MET/hepatocyte growth factor (HGF) pathway results in several pathological processes involved in tumor progression and metastasis. In a different context, MET can serve as an entry point for the bacterium Listeria monocytogenes, when activated by the internalin B (InlB) protein during infection of non-phagocytic cells. We have previously demonstrated that MET requires CD44v6 for its ligand-induced activation. However, the stoichiometry and the steps required for the formation of this complex, are still unknown. In this work, we studied the dynamics of the ligand-induced interaction of CD44v6 with MET at the plasma membrane. Using Förster resonance energy transfer-based fluorescence lifetime imaging microscopy in T-47D cells, we evidenced a direct interaction between MET and CD44v6 promoted by HGF and InlB in live cells. In the absence of MET, fluorescence correlation spectroscopy experiments further showed the dimerization of CD44v6 and the increase of its diffusion induced by HGF and InlB. In the presence of MET, stimulation of the cells by HGF or InlB significantly decreased the diffusion of CD44v6, in line with the formation of a ternary complex of MET with CD44v6 and HGF/InlB. Finally, similarly to HGF/InlB, disruption of liquid-ordered domains (Lo) by methyl-β-cyclodextrin increased CD44v6 mobility suggesting that these factors induce the exit of CD44v6 from the Lo domains. Our data led us to propose a model for MET activation, where CD44v6 dimerizes and diffuses rapidly out of Lo domains to form an oligomeric MET/ligand/CD44v6 complex that is instrumental for MET activation.

Raising a Bacterium to the Rank of a Model System: The Listeria Paradigm.

My scientific career has resulted from key decisions and reorientations, sometimes taken rapidly but not always, guided by discussions or collaborations with amazing individuals from whom I learnt a lot scientifically and humanly. I had never anticipated that I would accomplish so much in what appeared as terra incognita when I started to interrogate the mechanisms underlying the virulence of the bacterium Listeria monocytogenes. All this has been possible thanks to a number of talented team members who ultimately became friends.

Environmental persistence of Listeria monocytogenes and its implications in dairy processing plants.

Listeriosis, an invasive illness with a fatality rate between 20% and 30%, is caused by the ubiquitous bacterium Listeria monocytogenes. Human listeriosis has long been associated with foods. This is because the ubiquitous nature of the bacteria renders it a common food contaminant, posing a significant risk to the food processingsector. Although several sophisticated stress coping mechanisms have been identified as significant contributing factors toward the pathogen's persistence, a complete understanding of the mechanisms underlying persistence across various strains remains limited. Moreover, aside from genetic aspects that promote the ability to cope with stress, various environmental factors that exist in food manufacturing plants could also contribute to the persistence of thepathogen. The objective of this review is to provide insight into the challenges faced by the dairy industry because of the pathogens' environmental persistence. Additionally, it also aims to emphasize the diverse adaptation and response mechanisms utilized by L. monocytogenes in food manufacturing plants to evade environmental stressors. The persistence of L. monocytogenes in the food processing environment poses a serious threat to food safety and public health. The emergence of areas with high levels of L. monocytogenes contamination could facilitate Listeria transmission through aerosols, potentially leading to the recontamination of food, particularly from floors and drains, when sanitation is implemented alongside product manufacturing. Hence, to produce safe dairy products and reduce the frequency of outbreaks of listeriosis, it is crucial to understand the factors that contribute to the persistence of this pathogen and to implement efficient control strategies.