Listeria Monocytogenes Research Articles

Listeria Rhombencephalitis: A Case of an Immunocompetent Adult

Listeriosis is one of the most important foodborne diseases, caused by a Gram-positive facultative anaerobic intracellular bacterium found in food and the environment, Listeria monocytogenes. It causes one of the most life-threatening bacterial infections of the central nervous system (CNS). Meningoencephalitis and rhomboencephalitis are the most common forms and immunosuppression represents the main risk factor. In this article, we report a case of severe, invasive Listeria monocytogenes rhombencephalitis in a healthy middle-aged man, admitted to our hospital with meningeal syndrome associated with left VI nerve palsy. No apparent abnormality was found in a head CT and brain magnetic resonance imaging. Following the preliminary LP results, a diagnosis of bacterial meningitis was suspected and empirical antibiotic and antiviral therapy was initiated. Because of the lack of any significant improvement in his clinical status, on day 2 of his admission, a genetic identification of CSF pathogens by high-throughput genome sequencing was performed and identified L. monocytogenes. The Clinical status improved with complete recovery after appropriate antibiotic treatment with sulfamethoxazole-trimethoprim. In conclusion, in an infectious context, pontine involvement should systematically evoke the diagnosis of listeriosis.

Clinical Characteristics and Fatality Risk Factors for Patients with Listeria monocytogenes Infection: A 12-Year Hospital-Based Study in Xi'an, China.

Listeriosis is a severe food-borne disease caused by Listeria monocytogenes infection. The data of listeriosis in Xi'an population are limited. The aim of this study is to evaluate the clinical features and fatality risk factors for listeriosis in three tertiary-care hospitals in Xi'an, China METHODS: The characteristics of demographic data, underlying diseases, clinical manifestations, laboratory indicators, cranial imaging examination, antibiotics therapeutic schemes, and clinical outcomes were collected between 2011 and 2023. Logistic regression analysis was performed. Seventy-one etiologically confirmed listeriosis patients were enrolled, including 12 neonatal and 59 non-neonatal cases. The majority of neonatal listeriosis presented as preterm (50%) and fetal distress (75%). The main clinical manifestations of non-neonatal listeriosis included fever (88%), headache (32%), disorder of consciousness (25%), vomiting (17%), abdominal pain (12%), and convulsions (8%). The fatality rate in neonatal cases was higher than in non-neonatal listeriosis (42 vs. 17%). Although no deaths were reported in maternal listeriosis, only two of 23 patients had an uneventful obstetrical outcome. Five maternal listeriosis delivered culture-positive neonates, three of whom decreased within 1week post-gestation due to severe complications. Twenty-eight cases were neurolisteriosis and 43 cases were bacteremia. Neurolisteriosis had a higher fatality rate compared with bacteremia listeriosis (36 vs. 12%). The main neuroradiological images were cerebral edema/hydrocephalus, intracranial infection, and cerebral hernia. Listeria monocytogenes showed extremely low resistance to ampicillin (two isolates) and penicillin (one isolate). The fatality risk factors were the involvement of the central nervous system, hyperbilirubinemia, and hyponatremia for all enrolled subjects. Hyperuricemia contributed to the elevation of fatality risk in non-neonatal listeriosis. When the patients suffered with symptoms of fever and central nervous system infection, they should be alert to the possibility of listeriosis. Early administration of ampicillin- or penicillin-based therapy might be beneficial for recovery of listeriosis.

Unraveling the antimicrobial activity of nutmeg and turmeric essential oils against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella spp.

The consumer demand for a reduction in the use of synthetic additives in food has been providing a greater search and incentive for the food industries to use new alternatives for food preservation. Among them, there is the initiative to use essential oils (EOs) due to their antimicrobial properties, coming from specific compounds in their compositions. However, in view of limitations related to the use of EOs, as well as their susceptibility to oxidation and degradation, the possibility arises of employing protection methods such as microencapsulation to minimize the impairment of the benefits associated with the application of EOs. This study aimed to examine the antimicrobial effect of turmeric and nutmeg EOs against microbial strains of Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella spp., as well as the microparticles of the EOs involved. Analyses of the minimum inhibitory concentration (MIC), the minimum bactericidal concentration (MBC), and the developed microparticles, as well as the verification of the synergistic inhibitory action between these oils, were carried out. For free oils, antimicrobial action was evidenced against the vast majority of microorganisms tested, with free nutmeg EO having a better antimicrobial effect than free turmeric oil. In contrast, for encapsulated oils, only antimicrobial action was noted against strains of Listeria. Furthermore, the synergism of free oils did not potentiate the antimicrobial action. Regarding the alternative of microencapsulation of EOs, it was obtained that the results in which chitosan was used as wall material were more promising than when gelatin was used as wall material.

Accumulation of Lipid Droplets Induced by Listeria monocytogenes in Macrophages: Implications for Survival and Evasion of Innate Immunity.

Listeriosis, caused by Listeria monocytogenes (L.m.), poses a significant public health concern as one of the most severe foodborne diseases. The pathogenesis of L.m. involves critical steps such as phagosome rupture and escape upon internalization. Throughout infection, L.m. influences various host processes, including lipid metabolism pathways, yet the role of lipid droplets (LDs) remains unclear. Here, we reported a rapid, time-dependent increase in LD formation in macrophages induced by L.m. LD biogenesis was found to be dependent on L.m. viability and virulence genes, particularly on the activity of the pore-forming protein listeriolysin O (LLO). The prevention of LD formation by inhibiting diacylglycerol O-acyltransferase 1 (DGAT1) and cytosolic phospholipase A2 (cPLA2) significantly reduced intracellular bacterial survival, impaired prostaglandin E2 (PGE2) synthesis, and decreased IL-10 production. Additionally, inhibiting LD formation led to increased levels of TNF-α and IFN-β. Collectively, our data suggest a role for LDs in promoting L.m. cell survival and evasion within macrophages.

The mitochondrial carboxylase PCCA interacts with Listeria monocytogenes phospholipase PlcB to modulate bacterial survival.

Mitochondria represent attractive targets for pathogenic bacteria seeking to modulate host cellular processes to promote their survival and replication. Our current study has uncovered mitochondrial carboxylase propionyl-coenzyme A carboxylase (PCCA) as a novel host cell protein that interacts with L. monocytogenes PlcB. The results demonstrate that PCCA plays a negative regulatory role in L. monocytogenes infection, as heightened PCCA levels are associated with reduced bacterial survival and persistence. However, L. monocytogenes may exploit the PlcB-PCCA interaction to maintain stable PCCA expression and establish a favorable intracellular milieu for bacterial infection. Our findings shed new light on the intricate interplay between bacterial pathogens and host cell mitochondria, while also highlighting the potential of mitochondrial metabolic enzymes as antimicrobial agents.

Lactic Acid Bacteria and Bacillus subtilis as Potential Protective Cultures for Biopreservation in the Food Industry

The use of bacteria and/or their compounds is an alternative to the use of positive-list additives that the food industry is using as a tool to meet consumer demands for more natural, long-shelf-life, and healthy products, in short, to offer clean label foods. The aim of this study is to investigate the suitability of cell-free supernatants (CFSs) from Qualified Presumption of Safety strains as bioprotective cultures. Out of an initial screening panel of about 200 isolates, strains Pediococcus acidilactici CNTA 1059, Lactiplantibacillus plantarum CNTA 600, Levilactobacillus brevis CNTA 1374, and Bacillus subtilis CNTA 517 demonstrated strong antimicrobial activity against, especially, Gram-positive bacteria. The CFSs of these four strains showed minimum inhibitory concentration values between 0.15% and 5% against Listeria monocytogenes and Lentilactobacillus parabuchneri. None of the four selected strains exhibited acquired resistance to target antibiotics, and the non-toxigenicity of all the CFSs was demonstrated. In the case of the three lactic acid bacteria, the presence of bacteriocin-like inhibitory substances was confirmed following the decline in antimicrobial activity due to treatment with proteases. Regarding B. subtilis, biosynthetic gene clusters for different bacteriocin-like substances, including protease-resistant lipoproteins, were found via whole-genome sequencing. In addition, all of the CFSs exhibited stable antimicrobial activity at a wide range of temperatures (70–121 °C) used for the pasteurization and sterilization of food products, with a loss of antimicrobial activity ranging from 3% to 28%. These results point to the possibility that CFSs from these strains could be used in the food industry as a biocontrol tool to develop new products.

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

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

Designing a Multiepitope Vaccine against the Foodborne Pathogenic Bacteria Listeria monocytogenes Using Subtractive Immunoinformatics Approaches

Designing a Multiepitope Vaccine against the Foodborne Pathogenic Bacteria Listeria monocytogenes Using Subtractive Immunoinformatics Approaches

Microbiological Assessment of Dairy Products Produced by Small-Scale Dairy Producers in Serbia

The microbiological quality of dairy products from small-scale producers in Serbia was analysed. A total of 302 dairy products [raw (n = 111) and pasteurized milk cheeses (n = 79) and kajmak (n = 112)], were collected and tested for the presence of pathogens, Listeria monocytogenes and Salmonella spp., and enumerated for Coagulase-positive staphylococci (CPS), Escherichia coli, and yeasts and moulds. None of the samples tested positive for Salmonella spp., while L. monocytogenes was recovered from one raw milk cheese and five kajmak samples. Raw milk cheese and kajmak also had higher levels of indicator microorganisms, namely E. coli and yeast and moulds. Molecular serotyping grouped L. monocytogenes isolates into serogroups 1 (1/2a and 3a) and 3 (1/2b, 3b, and 7). When exposed to eight antibiotics, L. monocytogenes isolates were mostly sensitive, with the exception of oxacillin and reduced susceptibility to clindamycin, penicillin G, and trimethoprim/sulfamethoxazole, emphasizing the importance of continuous surveillance for antimicrobial resistance. Samples that tested positive for Listeria spp. also had higher loads of indicator microorganisms, namely E. coli and yeast and moulds, suggesting lapses in hygiene practices during production. Collectively, these data emphasize the need for improved food safety and hygiene practices among small-scale dairy producers. This is crucial to reduce the microbial contamination and improve both the quality and safety of dairy products in the Serbian market.

Virulence and Antimicrobial Resistance of Listeria monocytogenes Isolated from Ready-to-Eat Food Products in Romania

Listeria monocytogenes (L. monocytogenes) poses a significant threat to food safety due to its ability to cause severe human illness and its resistance to various antibiotics and environmental conditions. This study investigated the prevalence, serotype distribution, virulence gene profiles, and antimicrobial resistance patterns of L. monocytogenes in ready-to-eat (RTE) food products from Romania. A total of 8151 samples were analyzed, including various processed dairy, bovine, poultry, pork, and fish products. Bacterial isolation was conducted using the classical standard method, followed by confirmation through biochemical and molecular testing. Among the isolated strains, serotypes 1/2a, 1/2b, and 1/2c were identified, with a prevalence of 75% for serotype 1/2a. Additionally, virulence genes specific to listeriolysin O (hlyA) and regulatory factor A (prfA) were detected in all isolates. Antimicrobial susceptibility testing revealed varying resistance patterns among the L. monocytogenes strains. Trimethoprim-sulfamethoxazole and oxacillin showed the highest prevalence of resistance at 26.92% and 23.07%, respectively. However, all strains remained susceptible to ciprofloxacin, levofloxacin, and moxifloxacin. Notably, 23.07% of the isolates exhibited multidrug resistance, with the most common pattern being resistance to oxacillin, penicillin, and tetracycline. Analysis of antimicrobial resistance genes identified tetracycline resistance genes, particularly tet(C), tet(M), and tet(K), in a significant proportion of isolates. The presence of ampC and dfrD genes was also notable, indicating potential mechanisms of resistance. These results emphasize the necessity for ongoing surveillance of L. monocytogenes in RTE foods and emphasize the importance of thorough monitoring of antimicrobial resistance to guide public health strategies within the European Union.

Inactivation of Listeria monocytogenes on a laboratory medium and enoki mushrooms using organic acid and essential oil vapors

The aim of this study was to determine the antimicrobial activity of organic acid (OA) and essential oil (EO) vapors against Listeria monocytogenes on a laboratory medium and enoki mushrooms. Among 14 OA and 8 EO vapors tested, 3 OA vapors (acetic, formic, and propionic acid) and 3 EO vapors (cinnamon bark, citronella, and lemongrass) showed relatively strong antilisterial activity. On tryptic soy agar (TSA), all three OA vapors had a minimum inhibitory concentration (MIC) of 12.5 mg/L, while the minimum lethal concentration (MLC) of formic acid vapor was the lowest, at 50 mg/L, followed by acetic acid vapor (200 mg/L) and propionic acid vapor (400 mg/L). The MIC values of lemongrass, cinnamon bark, and citronella EO vapors were 25, 100, and 100 mg/L, respectively. The MLC of lemongrass EO vapor was 100 mg/L and MLCs of other EO vapors were >400 mg/L. Formic acid and lemongrass EO vapors showed a partial synergism on TSA (fractional inhibitory concentration index of 0.7500). For L. monocytogenes inoculated on enoki mushrooms, formic acid vapor at a concentration of ≥50 mg/L, as well as formic acid and lemongrass vapors in combination (1:2 vol ratio) at ≥ 75 mg/L, inactivated L. monocytogenes. These results indicate that formic acid vapor is effective at controlling the growth of L. monocytogenes on enoki mushrooms.

Listeria brain abscess: a therapeutically challenging rare presentation of listeriosis

We report a very rare case of Listeria multiple brain abscesses manifested as delirium, which represented diagnostic and therapeutic challenges overcome only by the close cooperation between Infectious Diseases and Neuroradiology, without which a satisfactory outcome would not be achieved.An elderly man presented with confusion and drowsiness with a background of type-II diabetes mellitus. Although computed tomography of the brain only showed frontal lobe oedema, contrast magnetic resonance (MR) imaging showed numerous irregular rim-enhancing lesions containing central diffusion restriction, suggesting multiple pyogenic cerebral abscesses of unclear aetiology. Thereafter, Listeria monocytogenes was isolated from blood cultures, suggesting this as the causative organism. Deemed unsuitable for neurosurgical drainage, the patient received medical management with a protracted course of antibiotics. This case was extremely challenging, due to 1) the impossibility of source control, 2) the small number of effective antibiotics available to treat this condition, and 3) the inevitable antibiotic side-effects, derived from long-term exposure. A successful outcome was only possible thanks to strict close multidisciplinary follow up, requiring frequent MR imaging and a judicious antibiotic choice, including monitoring of their side-effects. Due to the rarity of this condition, there is lack of guidance on its management, hence the importance of multidisciplinary involvement with very close imaging and antibiotic monitoring.

Antibacterial Activity and Mechanism of Action of Osthole against Listeria monocytogenes.

The purpose of this study was to investigate the antibacterial activity and mechanism of action of osthole against Listeria monocytogenes. The antibacterial activity of osthole was evaluated by determining the minimum inhibitory concentration (MIC) and growth curve. Cell morphology, membrane permeability, membrane integrity, bacterial physiology, and metabolism were explored using different methods to elucidate the mechanism of action of osthole. It was shown that the MIC of osthole against L. monocytogenes was 62.5 μg/mL and it inhibited the growth of L. monocytogenes effectively in a concentration-dependent manner. Scanning electron microscopy (SEM) images demonstrated morphology changes of L. monocytogenes, including rough surface, cell shrinkage, and rupture. It was found that extracellular conductivity and macromolecule content were increased significantly in the presence of osthole, indicating the disruption of cell membrane integrity and permeability. Laser confocal microscopy results supported the conclusion that osthole caused severe damage to the cell membrane. It was also noticed that osthole depleted intracellular adenosine triphosphate (ATP), inhibited Na+-K+-ATPase and Ca2+-Mg2+-ATPase activity, and promoted the accumulation of intracellular reactive oxygen species (ROS), leading to cell death. This study suggests that osthole is a promising antibacterial agent candidate against L. monocytogenes, and it shows potential in the prevention and control of foodborne pathogens.

Endophytic fungi-assisted biomass synthesis of eco-friendly formulated silver nanoparticles for enhanced antibacterial, antioxidant, and antidiabetic activities

Fungi-mediated biosynthesis of silver nanoparticles is one of the promising nanomanufacturing processes. Using endophytic fungi isolated from potential medicinal plants has emerged as a novel approach for producing several metal oxide nanoparticles in a green and cost-effective manner. The present study validates the biomimetic synthesis of silver nanoparticles of endophytic fungus (Phyllosticta capitalensis Henn.) (Phyllo-AgNPs) isolated from the leaves of Annona muricata and the effect of process variables, i.e., reductant concentration, ratio of AgNO3 to reductant concentration, reaction time and reaction pH to achieve maximum efficiency using the factorial design approach. The nanoparticle formation was confirmed by absorption peaks between 400 nm and 500 nm, followed by their characterization by UV–visible spectroscopy, TEM, SEM-EDX, XRD, particle size, and zeta potential analysis. The in-vitro antioxidant, antidiabetic and antimicrobial potential (agar well dfiffusion and minimum inhibitory concentration) of Phyllo-AgNPs at various concentrations were assessed. The Phyllo-AgNPs scavenged the 2,2-diphenyl-1-picrylhydrazyl radical and inhibited the activity of α-amylase and α-glucosidase enzymes at an IC50 of 31.75 ± 0.70, 39.32 ± 1.12 and 28.56 ± 1.08 μg/mL, respectively. The antimicrobial potential was determined against Listeria monocytogenes, Staphylococcus aureus, Escherichia coli and, Salmonella typhimurium. The study revealed the therapeutic potential of Phyllo-AgNPs against pathogenic microorganisms. Additionally, the in-vitro antioxidant and antidiabetic activities showed improved results compared to the standard (ascorbic acid and acarbose). By taking note of this, Phyllo-AgNPs can be further studied for pre-clinical trials, which would be beneficial in developing novel medicines with no adverse effects for the benefit of mankind.

Laboratory investigation of causes of bovine abortion and stillbirth in the Republic of Korea, 2014-2020.

Bovine abortion is a critical problem in the cattle industry. Identifying causes of abortion is key to establishing appropriate herd management and prevention strategies. We used pathology examinations, detection of etiologic agents, and serology to determine the cause of bovine abortions in Korea. We analyzed 360 abortion and stillbirth cases submitted to the Animal and Plant Quarantine Agency from December 2014 to January 2020. The putative cause of abortion was identified in 140 of 360 (38.9%) cases; 124 of the 140 (88.6%) cases were attributed to infections. The most common etiologic agents detected were bovine viral diarrhea virus (65 of 360; 18.1%), Coxiella burnetii (19 of 360; 5.3%), Leptospira spp. (13 of 360; 3.6%), Listeria monocytogenes (9 of 360; 2.5%), and Neospora caninum (8 of 360; 2.2%). Minor abortifacient pathogens included Brucella abortus (2 of 360; 0.6%), bovine alphaherpesvirus 1 (2 of 360; 0.6%), Akabane virus (2 of 360, 0.6%), and bovine ephemeral fever virus (1 of 360; 0.3%). Non-infectious conditions included congenital anomalies (7 of 360; 1.9%), goiter (7 of 360; 1.9%), and vitamin A deficiency (2 of 360; 0.6%). Our diagnostic rate in cases with placenta submitted (42 of 86; 48.8%) was significantly higher than in cases without placenta (98 of 274; 35.8%), which highlights the value of submitting placentas. Our results confirm the status of the large variety of causative agents associated with abortions in cattle in Korea.

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

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

Increased incidence and mortality from Listeria monocytogenes infection in Spain

Background:Listeria monocytogenes (LM) is a health treat worldwide given its high mortality and the growing of high-risk susceptible populations.Methods: All hospitalizations with a diagnosis of LM in the National Registry of Hospital Discharges were examined in Spain from 2000 to 2021.Results: A total of 8,152 hospital admissions with LM were identified. The mean age was 59.5 years and 48% were immunosuppressed (IS).The rate of LM hospitalizations increased from 5 per 1 million population in 2000 to 8.9 in 2021 (p<0.001). A foodborne outbreak in Andalusia determined a sharp increase of admissions with LM during 2019. The COVID-19 pandemic and lockdowns were associated with a fall in LM admissions.The overall in-hospital mortality was 16.7%. The number of deaths in patients hospitalized with LM rose from 7.8 per 100,000 deceased in 2000 to 18 in 2021 (p<0.001). After adjustment, age >65 years-old (Odds ratio [OR]=2.16), sepsis (OR=2.60), meningoencephalitis (OR=1.72), endocarditis (OR=2.0), neonatal listeriosis (OR=2.10) and IS (OR=2.09) were associated with mortality.Conclusions: The number of patients hospitalized with LM in Spain has risen significantly from 2000 to 2021. The increase in the rate of admissions and deaths was largely driven by the growing proportion of elderly and of immunosuppressed patients.

Interference of gastrointestinal barriers with antibiotic susceptibility of foodborne pathogens: an in vitro case study of ciprofloxacin and tetracycline against Salmonella enterica and Listeria monocytogenes

Minimum inhibitory concentrations (MIC) assays are often questioned for their representativeness. Especially when foodborne pathogens are tested, it is of crucial importance to also consider parameters of the human digestive system. Hence, the current study aimed to assess the inhibitory capacity of two antibiotics, ciprofloxacin and tetracycline, against Salmonella enterica and Listeria monocytogenes, under representative environmental conditions. More specifically, aspects of the harsh environment of the human gastrointestinal tract (GIT) were gradually added to the experimental conditions starting from simple aerobic lab conditions into an in vitro simulation of the GIT. In this way, the effects of parameters including the anoxic environment, physicochemical conditions of the GIT (low gastric pH, digestive enzymes, bile acids) and the gut microbiota were evaluated. The latter was simulated by including a representative consortium of selected gut bacteria species. In this study, the MIC of the two antibiotics against the relevant foodborne pathogens were established, under the previously mentioned environmental conditions. The results of S. enterica highlighted the importance of the anaerobic environment when conducting such studies, since the pathogen thrived under such conditions. Inclusion of physicochemical barriers led to exactly opposite results for S. enterica and L. monocytogenes since the former became more susceptible to ciprofloxacin while the latter showed lower susceptibility towards tetracycline. Finally, the inclusion of gut bacteria had a bactericidal effect against L. monocytogenes even in the absence of antibiotics, while gut bacteria protected S. enterica from the effect of ciprofloxacin.

Inactivation of Salmonella typhimurium and Listeria monocytogenes in dairy systems: Effect of fat and food matrix structure under radio frequency heating

The effect of two food intrinsic factors (fat content, matrix structure) on the radio frequency (RF) inactivation of Salmonella Typhimurium and Listeria monocytogenes was investigated in dairy model systems: i.e., liquids with 0.8% and 5.9% fat and gels with 0.8% and 5.9% fat. In the liquid, higher fat content resulted in higher inactivation for both microorganisms. In gels, inactivation rate was higher with the lower fat content, while opposite behaviour occurred for L. monocytogenes above 70 °C. A gel matrix resulted in higher inactivation of S. typhimurium, while complex temperature-dependent behaviour was present for L. monocytogenes. Sublethal injury was most significant for L. monocytogenes at 5.9% fat content and high temperatures. Overall, fat content and matrix structure impacted the microbial inactivation during RF heating and should be taken into account when designing novel RF heating food decontamination strategies. Industrial relevanceRadio frequency (RF) heating as a food processing technology has seen increased industrial application in recent years. The technology allows a more homogeneous heating of food products and also enables the treatment of low-moisture foods. The increased knowledge on the influence of fat content and food structure on RF thermal inactivation will lead to the development of improved and more efficient treatments.

Evaluation of the performance of a three-strains lactic acid bacteria cocktail for the control of Listeria monocytogenes on marinated lean pork

The aim of this study was to evaluate the addition of a cocktail of three lactic acid bacteria (LAB) (Lactococcus lactis, Lacticaseibacillus paracasei and Lactiplantibacillus plantarum) as a protective culture into marinated pork. The pork was artificially inoculated with two Listeria monocytogenes strains and stored for 12 days. Two packagings were used: vacuum or modified atmosphere packaging (MAP). LAB, L. monocytogenes, psychrotrophic bacteria, pH, aw, color, the metataxonomic profile and the sensorial quality of the product were evaluated. The growth of L. monocytogenes under vacuum and MAP was reduced with the use of the LAB up to 0.8 and 0.7 log10 CFU/g, respectively. LAB counts gradually increased, which was accompanied by a slight decrease in pH. In LAB samples, psychrotrophic bacteria showed a reduction at day 12 as compared to non-inoculated samples. Some minor differences were also observed among samples for color and sensory parameters. Regardless of the type of packaging, the microbiota of the marinated pork was dominated initially by Photobacterium and subsequently during storage by a diversity of LAB. The application of LAB could help to obtain a safe product, although further evaluation would be required to optimize the application of the LAB cocktail in real-scale commercial scenarios.