Growth Of Listeria Monocytogenes Research Articles

Listeria monocytogenes Challenge Testing of Ready-to-Eat Uncured Vacuum-Packed Pork Bars with Dried Plasma

Newly developed formulas of ready-to-eat (RTE) products, despite conforming to the latest nutritional trends involving low-processed and high-protein products, may pose a risk of promoting the growth of Listeria monocytogenes during shelf life. Food safety experts recommend challenge tests to assess the growth potential of L. monocytogenes, which will ultimately provide microbiological evidence to determine the food safety limit. The present study evaluated whether RTE uncured vacuum-packed pork bars with dried plasma met the 100 CFU/g safety level at the end of shelf life under certain storage conditions and aimed to develop predictive models for the growth of L. monocytogenes in the above product. The bars were artificially inoculated with a mixture of three strains of L. monocytogenes at two different inoculum densities of 2 log CFU/g and 5 log CFU/g and stored at three different temperatures (2, 4, and 6 °C) and then subjected to microbiological evaluation at specific time intervals up to 21 storage days. The growth potential (Δ-value) for RTE pork bars contaminated with 2 log CFU/g L. monocytogenes inoculum was 0.36, 0.14, and 0.91 log CFU/g at 2, 4, and 6 °C, respectively, while for bars contaminated with 5 log CFU/g inoculum, they were −0.36, −0.40, and 0.64 at 2, 4, and 6 °C, respectively. Statistically higher growth potential (p < 0.05) was detected for RTE bars contaminated with 2 log CFU/g inoculum than with 5 log CFU/g. The results indicate that this type of product must be classified as a food category: “Ready-to-eat foods able to support the growth of L. monocytogenes, other than those intended for infants and for special medical purposes” (Category 1.2. according to EU Regulation 2073/2005). The newly created models can also describe L. monocytogenes growth in an environment where factors, such as temperature, pH, and aw, change with time. The results showed that a higher inoculum density statistically reduced the growth potential values of L. monocytogenes compared to a lower density.

Microbial Growth, Survival, and Cryotolerance in Plant-Based Milk Alternatives: A Study with Listeria monocytogenes.

The increasing popularity of plant-based milk products as an alternative to traditional bovine milk has sparked concerns about their safety and nutritional impact. This study focuses on the growth, survival, and cryotolerance behavior of Listeria monocytogenes (strains: ATCC 19115 and RS1) in various plant-based milk substitutes. Samples of almond milk, oat milk, soy milk, and bovine milk, all subjected to ultra-high temperature treatment, were evaluated for their influence on L. monocytogenes growth at 4°C and survival through repeated freezing and thawing cycles. Despite the nutritional differences, the growth rates of two L. monocytogenes strains at 4°C in plant-based milk alternatives and bovine milk displayed similarity (p > 0.05). Both strains of L. monocytogenes demonstrated similar biofilm formation abilities in plant-based milk alternatives and bovine milk. However, L. monocytogenes exhibited different levels of tolerance to repeated freezing and thawing cycles depending on plant-based milk alternatives in which they were grown at 4°C (p < 0.05). In the case of L. monocytogenes ATCC19115, cells cultured in almond milk at 4°C showed a significant reduction in their freezing and thawing tolerance (2.80 log reduction), followed by cells grown in soy milk (2.09 log reduction) when compared with oat and bovine milk (p < 0.05). A parallel trend of tolerance was evident in L. monocytogenes RS1 (2.82 and 3.22 log reduction in almond milk and soy milk, respectively). These findings underscore the need for comprehensive assessments of microbial behavior in emerging food products like plant-based milk alternatives. As these alternatives continue to gain traction, ensuring their safety and stability remains important. With insights into L. monocytogenes growth and survival in milk alternatives, this study will contribute to the evolving understanding of microbial dynamics in response to changing dietary trends.

Combined stochastic modelling of pathogenic and spoilage microorganisms.

Quantitative microbiological risk assessment (QMRA) of pathogens in food safety is well established, but steps are being taken to expand this methodology to food spoilage. Parallels can be drawn between the steps involved in a QMRA for pathogens and its application to specific spoilage organisms (SSO). During hazard characterisation for pathogens, the appropriate dose-response model is used to link the hazard level to the health outcome by estimating the probability of illness, resulting from the ingestion of a certain dose of the hazard. The dose-response model, in the case of food spoilage, may be translated into a spoilage-response relationship linking the spoilage-level with the probability the consumer will discard the food and not consume it. Such models are developed with sensory testing, assessing consumers sensitivity to microbial spoilage quality defects and correlating them to the SSO concentration. Ignoring food spoilage before the stated expiration date can lead to the final health risk being overestimated, since cases in which the food item poses a real risk to the consumer but is not consumed due to perceived spoilage are not excluded. Plenty of risk assessments have been carried out for pathogens in different RTE foods. What is missing is the integration of the two approaches into a single model that can estimate the risk of illness, factoring in the variability of consumer responses to spoilage. The spoilage-response relationship was combined with a stochastic modelling approach for lactic acid bacteria (LAB) and Listeria monocytogenes growth, also taking into account microbial interaction between LAB and L. monocytogenes (Jameson effect) to increase accuracy. The comparison of results between the 'Baseline' and the 'Spoilage-informed' approach showed significant difference in listeriosis cases, both for consumers under and over 65 years old. These results may suggest, that the hypothesis about overestimation of listeriosis risk in case of not taking into account product spoilage is correct. The combined QMRA model developed in the present study can be a useful tool for risk management decisions in the meat industry.

Assessing Listeria monocytogenes Growth in Artificially Inoculated Sea-Farmed Product—Raw Sea Bass (Dicentrarchus labrax) Fillet, Produced in Greece

Listeria monocytogenes (Lm) is responsible for listeriosis, a serious foodborne disease, with high hospitalization and mortality rates worldwide. The main cause of listeriosis in humans is the consumption of ready-to-eat (RTE) foods; Commission Regulation (EC) No 2073/2005 establishes microbiological criteria for Lm in RTE foods. Raw fish products are widely consumed, e.g., in sushi and various seafood recipes (e.g., carpaccio, sashimi, maki, nigiri, tartare, etc.), but are not subjected to RTE food safety criteria. The aim of our study was to assess the growth potential of Lm in raw sea bass fillets obtained from a leading aquaculture company in Greece. In order to assess the growth of Lm in raw sea bass fillets, we applied the “challenge test”, a scientific experiment designed to assess the growth of Lm within a specific food product under controlled conditions. According to our results, and taking into consideration the health risk for the listeriosis-vulnerable population, raw fish products utilized in the preparation of RTE foods, including sushi and an array of seafood dishes, should be incorporated in the Category of Safety Criteria of Regulation (EC) No 2073/2005 “Ready-to-eat food able to support the growth of Listeria monocytogenes”.

Effect of Nitrite-Embedded Packaging Film on Growth of Listeria monocytogenes in Nitrite-free and Conventionally-cured Bologna Sausage

Listeria monocytogenes is a pathogen frequently associated with ready-to-eat (RTE) meat and poultry products. Nitrite is a key antimicrobial additive that can offer some degree of protection against L. monocytogenes when included in meat product formulations. The objectives of this study were to determine the potential of nitrite-embedded film to affect the growth of L. monocytogenes following postthermal processing of conventionally-cured and nitrite-free bologna. Two bologna treatment formulations, a conventionally-cured control formulation (CON) and a nitrite-free formulation (UCC), were manufactured, packaged in conventional (CF) or nitrite-embedded (NEF) film, inoculated with 3.5 log CFU/cm2 of a cocktail of L. monocytogenes strains, and stored at 10 ± 1 °C. CON-NEF and UCC-NEF treatments had significantly slower (P < 0.05) growth of L. monocytogenes than CON-CF and UCC-CF, with populations in UCC-CF (which contained no nitrite) increasing by 3.4 logs after 10 d of storage in UCC-CF and 3.6 logs after 50 d in CON-CF (which had formulated nitrite only), while in the NEF-packaged samples, with or without formulated nitrite, they did not exceed the inoculum level until after day 40. Initial (day 0) residual nitrite was significantly greater (P < 0.05) in the control formulation. Packaging in NEF, however, resulted in an increase of 27–28 ppm by day 3, regardless of formulation, after which it decreased rapidly. Results suggest NEF can be used as a post-lethality antimicrobial intervention in food safety intervention strategies, in both cured and uncured processed meat products.

Antioxidant and antimicrobial emulsions with amphiphilic olive extract, nanocellulose-stabilized thyme oil and common salts for active paper-based packaging

Anionic cellulose nanofibers (CNFs) were used to stabilize emulsions that combined water-soluble (and oil-soluble), strongly antioxidant extracts with a water-immiscible, notably antimicrobial essential oil. Specifically, the radical scavenging activity was primarily provided by aqueous extracts from olive fruit (Olea europaea L.), while the antimicrobial effects owed eminently to thyme oil (Thymus vulgaris L.). The resulting emulsions were highly viscous at low shear rate (4.4 Pa·s) and displayed yield stress. The addition of edible salts decreased the yield stress, the apparent viscosity and the droplet size, to the detriment of stability at ionic strengths above 50 mM. Once characterized, the antioxidant and antimicrobial emulsions were applied on packaging-grade paper. Coated paper sheets inhibited the growth of Listeria monocytogenes, a common foodborne pathogen, and acted as antioxidant emitters. In this sense, the release to food simulants A (ethanol 10 vol%), B (acetic acid 3 wt%), and C (ethanol 20 vol%) was assessed. A 24-hour exposure of 0.01 m2 of coated paper to 0.1 L of these hydrophilic simulants achieved inhibition levels of the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) in the 15–29 % range. All considered, the bioactive properties of thyme essential oil towards lipophilic food products can be complemented with the antioxidant activity of aqueous olive extracts towards hydrophilic systems, resulting in a versatile combination for active food packaging.

Lactobacillus plantarum derived nanoparticles deliver class IIa bacteriocin as a potential natural food preservatives

In recent years, the growing concern over human health risks associated with chemical preservatives in food has sparked increased interest in utilizing natural biopreservatives derived from probiotics. Bacteriocins, which are antibacterial peptides that have been deemed safe for human consumption and have been applied to food preservation. Several studies have emphasized that nanoparticles derived from edible plants can modulate microbes’ metabolic processes. In this study, we discovered that Lactobacillus plantarum LPL-1 can produce extracellular nanoparticles (LPL-NPs) containing a specific class IIa bacteriocin known as plantaricin LPL-1. LPL-NPs effectively suppressed the growth of Listeria monocytogenes 54002 by gradually disrupting their cell membranes. Intriguingly, we have also demonstrated that the ginger derived exosome-like NPs (GELNPs) enhance the antibacterial activity of LPL-NPs by enriching plantaricin LPL-1 within them through activation of a quorum sensing system component. Furthermore, GELNPs-treated LPL-NPs (GLPL-NPs) can effectively extend the storage period of sturgeon at 4 °C by mitigating pathogenic bacterial growth, preserving sensory quality, and reducing the levels of total volatile basic nitrogen (TVB-N), K value, trichloroacetic acid (TCA)-soluble peptides, and thiobarbituric acid reactive substances (TBARS). This study provides insight into a strategy for application of LPL-NPs as a natural biopreservative for food preservation.

Growth of Listeria monocytogenes in fresh vegetables and vegetable salad products: An update on influencing intrinsic and extrinsic factors.

The ability of foodborne pathogens to grow in food products increases the associated food safety risks. Listeria monocytogenes(Lm) is a highly adaptable pathogen that can survive and grow under a wide range of environmental circumstances, including otherwise inhibitory conditions, such as restrictive cold temperatures. It can also survive long periods under adverse environmental conditions. This review examines the experimental evidence available for the survival and growth of Lm on fresh vegetables and ready-to-eat vegetable salads. Published data indicate that, depending on certain intrinsic (e.g., nutrient composition) and extrinsic factors (e.g., storage temperature, packaging atmosphere), Lm can survive on and in a wide variety of vegetables and fresh-cut minimally processed vegetable salads. Studies have shown that temperature, modified atmosphere packaging, relative humidity, pH, water activity, background microbiota of vegetables, microbial strain peculiarities, and nutrient type and availability can significantly impact the fate of Lm in vegetables and vegetable salads. The influence of these factors can either promote its growth or decline. For example, some studies have shown that background microbiota inhibit the growth of Lm in vegetables and minimally processed vegetable salads, but others have reported a promoting, neutral, or insignificant effect on the growth of Lm. A review of relevant literature also indicated that the impact of most influencing factors is related to or interacts with other intrinsic or extrinsic factors. This literature synthesis contributes to the body of knowledge on possible strategies for improving food safety measures to minimize the risk of Lm-associated foodborne outbreaks involving vegetables and vegetable salads.

Comparative growth kinetics of Listeria monocytogenes and Salmonella enterica on dehydrated enoki and wood ear mushrooms during rehydration and storage.

Specialty mushrooms have been implicated in foodborne illness outbreaks in the U.S. in recent years. These mushrooms are available to consumers in both their fresh and dried states. Dehydrating mushrooms is a convenient way to increase shelf life. The dehydration process results in a lowered water activity (aw) of the commodity, creating an environment where both spoilage and pathogenic bacteria cannot proliferate. Prior to food preparation and consumption, these mushrooms are typically rehydrated and possibly stored for later use which could lead to increased levels of pathogens. This study examined the survival and growth of Listeria monocytogenes and Salmonella enterica on dehydrated enoki and wood ear mushrooms during rehydration and subsequent storage. Mushrooms were heat dehydrated, inoculated at 3 log CFU/g, and rehydrated at either 5 or 25°C for 2 h. Rehydrated mushrooms were stored at 5, 10, or 25°C for up to 14 d. L. monocytogenes and S. enterica survived on enoki and wood ear mushroom types during rehydration at 5 and 25°C, with populations often <2.39 log CFU/g. During subsequent storage, no growth was observed on wood ear mushrooms, regardless of the rehydration or storage temperature, with populations remaining <2.39 log CFU/g for both pathogens. When stored at 5°C, no growth was observed for either pathogen on enoki mushrooms. During storage at 10 and 25°C, pathogen growth rates and populations after 14 d were generally significantly higher on the enoki mushrooms rehydrated at 25°C; the highest growth rate (3.56 ± 0.75 log CFU/g/d) and population (9.48 ± 0.62 log CFU/g) after 14 d for either pathogen was observed by S. enterica at 25°C storage temperature. Results indicate a marked difference in pathogen survival and proliferation on the two specialty mushrooms examined in this study and highlight the need for individual product assessments. Data can be used to assist in informing guidelines for time and temperature control for the safety of rehydrated mushrooms.

Modelling the Growth of Listeria monocytogenes on Fresh-Cut Cucumbers at Various Storage Temperatures

The primary objective of this study was to investigate the behavior of Listeria monocytogenes (L. monocytogenes) on fresh-cut cucumbers. Fresh-cut cucumber samples were inoculated with a mixture of six strains of L. monocytogenes. The inoculated samples were stored at 5, 10, 15, 20, 25, 30, and 35 °C. The results demonstrated that L. monocytogenes was able to grow on fresh-cut cucumbers at all the evaluated temperatures, although its growth decreased but was not inhibited at 5 °C. An extreme storage temperature of 35 °C considerably reduced the lag time. L. monocytogenes growth on fresh-cut cucumbers was controlled for several days by storage at a low temperature, mainly at 5 °C. Thus, this product should only be stored at low temperatures. The growth process was fitted by the Baranyi model, with the specific growth rates equally well-fitted to the Ratkowsky square-root model. The R-square and mean square error values for the corresponding Ratkowsky square-root models were 0.97 (R2 &gt; 0.95) and 0.02, respectively. The Baranyi and Ratkowsky square-root models exhibited good relevancy. The predictive models developed in this study can be used to estimate the risk assessment of L. monocytogenes on fresh-cut cucumber.

Mozzarella cheese in Italy: Characteristics and occurrence of Listeria monocytogenes and coagulase-positive staphylococci at retail

Mozzarella cheese is a popular type of fresh cheese, originating from Mediterranean countries and worldwide consumed. As for other soft cheeses, its characteristics might support the growth of Listeria monocytogenes; therefore, the research's aim was to determine the occurrence of L. monocytogenes strains and Listeria spp. on mozzarella cheese at the time of purchase (T0) and at the end of shelf life (Tf). Given the relevance in dairy products, occurrence of coagulase-positive staphylococci was also explored. Retail batches (n = 106) collected in Italy, in supermarkets, discounts and small retailers, were analysed for pH and to detect L. monocytogenes, other Listeria spp. and coagulase-positive staphylococci. Three batches were positive for L. monocytogenes (2.8%; 3/106) and nine (9/106) for other species of Listeria spp. with an occurrence of 10.4% for Listeria spp. Coagulase-positive staphylococci were never detected. Mozzarella cheese showed variability in terms of pH (from 4.30 to 6.24 at T0) and residual shelf life (from 3 to 22 days). This research confirms that L. monocytogenes can be found in mozzarella cheese at retail. However, a low concentration of the pathogen (below the limit of quantification of 10 cfu g−1) was found in the contaminated products at the time of purchase and/or at the end of shelf life. This evidence is relevant since mozzarella cheese is not undergoing further treatment before consumption therefore thus represent the level of contamination to which the consumer might be exposed. Considering the technological steps of mozzarella production, preventing food contamination in food-processing and retail-handling environments is crucial to reduce the level of exposure to the consumer.

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.

Antilisterial activity of olive-derived polyphenols: an experimental study on meat preparations

Pork meat and processed pork products have been linked to multiple listeriosis outbreaks worldwide during the past years. Specifically, it has been highlighted that minced pork meat is easily perishable and may increase the growth of Listeria monocytogenes, which could be harmful to the general public's health. This study aimed to investigate the potential application of olive oil mill wastewater polyphenolic and red beet extracts as natural antimicrobial agents for L. monocytogenes growth control in burgers. The minced pork meat was mixed with the extracts and experimentally inoculated with L. monocytogenes, then molded into vacuum-packaged and cold-stored (4±1°C) burgers kept under alternating exposure to fluorescent light. The L. monocytogenes enumeration was performed on burgers at 0, 2, 5, and 10 days of shelf life. In uninoculated burgers, physicochemical (pH, water activity, color) and sensory determination (descriptive sensory analysis) were also conducted. At the end of storage, the samples treated with olive-derived extract showed the lowest value of L. monocytogenes (approximately 1.3 Log CFU/g). The physicochemical and sensory traits of burgers have benefited from the addition of both olive-derived and red beet extracts. Results suggest that olive mill wastewater polyphenolic extracts could be added to minced pork meat products to act as a natural antimicrobial agent.

Inactivation efficacy of four commercial post-process treatments against Listeria monocytogenes and impact on the commercial quality of leafy greens

The problem of product contamination with human pathogenic microorganisms is still unsolved. Although prevention through the implementation of good agricultural practices and good manufacturing practices is the gold standard, product decontamination strategies can be used to complement preventive measures. Different bioprotective treatments have been suggested to reduce the risk of listeriosis in fresh produce, but more information is needed before industrial implementation. This study focused on the efficacy of four commercial treatments against Listeria monocytogenes growth and their effect on the organoleptic quality of baby spinach, cut romaine, cut iceberg, and shredded cabbage. The treatments included SafePro® (CHR Hansen, DK) and Holdbac® (DowDuPont, US), based on the use of lactic acid bacteria (LAB) cultures as well as two different bacteriophage solutions, ListShield (Intralytix, US) and PhageGuard Listex™ (PhageGuard, US). The selected treatments were tested under simulated commercial conditions. The application was performed after processing and before packaging using a fine mist spray. In all the trials, Listex™ showed the best results in reducing L. monocytogenes growth during shelf life in the four leafy greens chosen. Microbial reductions were close to 2 log units. L. monocytogenes reductions were observed 1 day after Listex™ application and the efficacy was maintained during storage (15 days at 7 °C). Organoleptic quality, including flavor, texture, browning/yellowing, decay, and visual appearance of the four leafy greens was not significantly affected by the application of Listex™ when compared to the untreated products. Post-process treatment with Listex™ based on bacteriophages effectively reduced L. monocytogenes and can be recommended as a control tool to reduce the risks for the presence of L. monocytogenes in leafy greens.

Extension of the gamma concept to handle changing environment during shelf-life. Applied to an example with Listeria monocytogenes in salads with changing pH.

Prediction of microbial growth is the main topic within the area of predictive microbiology. A commonly used framework is the so-called gamma concept which is to view the bacterial growth rate as a product of a bacteria- and medium specific maximum instantaneous factor, and several environmental factors. Traditionally environmental factors are assumed to be constant, leading to exponential growth. In the current study, we expand the gamma concept to include changing dynamic environmental factors, exemplified by pH, and show how this might affect estimates for Listeria monocytogenes growth rates and thereby predicted shelf-life. The study shows how substantial environmental changes might lead to large biases for the estimated growth and shelf-life, if not accounted for in the model. Finally, the study shed some light on how accuracy for the growth rate estimates might be improved by allocating more weight to observations prone to favorable than unfavorable environmental conditions.

Characterization of Antimicrobial Activities of Bifidobacterium lactis BB-12 and Their Inhibitory Effect Against Some Foodborne Pathogens.

Bifidobacterium animalis subsp. lactis BB-12, a probiotic, has shown potential to promote health benefits and control pathogens. This study aimed to investigate the effectiveness of BB-12 and its cell-free supernatant (CFS) in inhibiting the growth of Listeria monocytogenes and Salmonella enterica serovar Typhimurium. To assess the antimicrobial activity of BB-12, agar well diffusion, disk diffusion, and minimum inhibitory concentration (MIC) tests were conducted. The bicinchoninic acid (BCA) assay was performed to measure the protein concentration in CFS. The study's results indicated that the BB-12 strain inhibited the pathogens' growth. The disk diffusion test using BB-12 showed inhibitory results ranging from 11 to 14 mm for both bacteria. The agar well diffusion test reported the zone of inhibition ranging from 11.6 to 16 mm for both bacteria. The MIC test was conducted as a confirmatory test, which demonstrated the highest inhibitory zone using 2 McFarland (6 × 108 CFU/mL) concentrations of probiotics on L. monocytogenes (44.98%) and S. Typhimurium (66.41%). The disk diffusion test revealed that the probiotic CFS had a significant inhibitory impact on S. Typhimurium with a 16.6 mm zone of inhibition. The BCA test findings indicated that the 24- and 48-h CFSs exhibited inhibitory properties against infections. Notably, the 24-h CFS, including a protein level of 78.47 μg/mL, demonstrated a more pronounced inhibitory impact on both pathogens. The findings highlight that utilizing the BB-12 strain and its CFS can serve as a viable approach to battle infections, enhancing food safety and public health.

Lymph node stromal cells vary in susceptibility to infection but can support the intracellular growth of Listeria monocytogenes.

Lymph node stromal cells (LNSC) are an often overlooked component of the immune system, but play a crucial role in maintaining tissue homeostasis and orchestrating immune responses. Our understanding of the functions these cells serve in the context of bacterial infections remains limited. We previously showed that Listeria monocytogenes, a facultative intracellular foodborne bacterial pathogen, must replicate within an as-yet-unidentified cell type in the mesenteric lymph node (MLN) to spread systemically. Here, we show that L. monocytogenes could invade, escape from the vacuole, replicate exponentially, and induce a type I IFN response in the cytosol of two LNSC populations infected in vitro, fibroblastic reticular cells (FRC) and blood endothelial cells (BEC). Infected FRC and BEC also produced a significant chemokine and pro-inflammatory cytokine response after in vitro infection. Flow cytometric analysis confirmed that GFP+ L. monocytogenes were associated with a small percentage of MLN stromal cells in vivo following foodborne infection of mice. Using fluorescent microscopy, we showed that these cell-associated bacteria were intracellular L. monocytogenes and the number of infected FRC and BEC changed over the course of a three-day infection in mice. Ex vivo culturing of these infected LNSC populations revealed viable, replicating bacteria that grew on agar plates. These results highlight the unexplored potential of FRC and BEC to serve as suitable growth niches for L. monocytogenes during foodborne infection and to contribute to the pro-inflammatory environment within the MLN that promotes clearance of listeriosis.

Comparative Analysis of Growth, Survival, and Virulence Characteristics of Listeria monocytogenes Isolated from Imported Meat.

Listeria monocytogenes is an important foodborne pathogen with worldwide prevalence. Understanding the variability in the potential pathogenicity among strains of different subtypes is crucial for risk assessment. In this study, the growth, survival, and virulence characteristics of 16 L. monocytogenes strains isolated from imported meat in China (2018-2020) were investigated. The maximum specific growth rate (μmax) and lag phase (λ) were evaluated using the time-to-detection (TTD) method and the Baranyi model at different temperatures (25, 30, and 37 °C). Survival characteristics were determined by D-values and population reduction after exposure to heat (60, 62.5, and 65 °C) and acid (HCl, pH = 2.5, 3.5, and 4.5). The potential virulence was evaluated via adhesion and invasion to Caco-2 cells, motility, and lethality to Galleria mellonella. The potential pathogenicity was compared among strains of different lineages and subtypes. The results indicate that the lineage I strains exhibited a higher growth rate than the lineage II strains at three growth temperatures, particularly serotype 4b within lineage I. At all temperatures tested, serotypes 1/2a and 1/2b consistently demonstrated higher heat resistance than the other subtypes. No significant differences in the log reduction were observed between the lineage I and lineage II strains at pH 2.5, 3.5, and 4.5. However, the serotype 1/2c strains exhibited significantly low acid resistance at pH 2.5. In terms of virulence, the lineage I strains outperformed the lineage II strains. The invasion rate to Caco-2 cells and lethality to G. mellonella exhibited by the serotype 4b strains were higher than those observed in the other serotypes. This study provides meaningful insights into the growth, survival, and virulence of L. monocytogenes, offering valuable information for understanding the correlation between the pathogenicity and subtypes of L. monocytogenes.

The inhibitory effect of probiotic Lactococcus lactis on the growth and invasion of Listeria monocytogenes in Caco-2 cell line

The inhibitory effect of probiotic Lactococcus lactis on the growth and invasion of Listeria monocytogenes in Caco-2 cell line

Growth Control of Listeria monocytogenes in Raw Sausage via Bacteriocin-Producing Leuconostoc carnosum DH25.

The current study addresses the critical issue of Listeria monocytogenes growth in raw sausage/meat products leading to human infections, most commonly listeriosis, which is known for its high fatality rate. This research focuses on the isolation, identification, and screening of lactic acid bacteria from various meat and fish products in Switzerland. In total, 274 lactic acid bacteria strains were isolated from 30 different products and were screened for their ability to inhibit Listeria monocytogenes growth, with 51 isolates demonstrating anti-Listeria activity at 8 °C, 15 °C, 25 °C, and 37 °C. Further experiments, using a meat model and a raw sausage challenge test, demonstrated that Leuconostoc carnosum DH25 significantly inhibited Listeria monocytogenes growth during the ripening and storage of the tested meat/sausage. This inhibitory effect was found to be attributed to the bacteriocins produced by Leuconostoc carnosum DH25 rather than factors like pH or water activity. The stability of the anti-Listeria substances was examined, revealing their resistance to temperature and pH changes, making Leuconostoc carnosum DH25 a promising protective culture for raw sausages. The genome sequencing of this strain confirms its safety, with no antibiotic resistance genes or virulence factors detected, and reveals the presence of the structural genes for the production of the bacteriocin LeucocinB-Ta11a. This study underscores the potential of LAB strains and their bacteriocins as effective tools for enhancing food safety and preventing Listeria monocytogenes growth in meat products, offering valuable insights into biocontrol strategies in the food industry.