Significance and Characteristics of Listeria monocytogenes in Poultry Products

Microscopic and metabolomics analysis of the anti-Listeria activity of natural and engineered cruzioseptins

Listeria monocytogenes is a human opportunistic foodborne pathogen that produces life-threatening infections with a high mortality rate. The control of Listeria in the food production environment and effective clinical management of human listeriosis are challenging due to the emergence of antibiotic resistance. Hence we evaluate the in vitro anti-Listeria activity of two synthetic cruzioseptins reproducing their natural sequences CZS-9, and CZS-12, and one engineered sequence based on CZS-1, named [K4K15]CZS-1. The assessment of the in vitro potential of cruzioseptins, highlighted the promising antibacterial effect of [K4K15]CZS-1 in very low concentrations (0.91 μM) and its thermal stability at high-temperature conditions, is compatible with the food industry. Microscopic and metabolomic analyses suggest cruzioseptin induces anti-Listeria bioactivity through membrane disruption and changes in the intracellular metabolome. We also report that [K4K15]CZS-1 is not resistant to peptidases/proteases emphasizing a key advantage for their use as a food preservative. However, there is a need for further structural and functional optimisations for the potential clinical application as an antibiotic. In conclusion, [K4K15]CZS-1 stand out as membrane-active peptides with the ability to induce shifts in the bacteria metabolome and inspire the development of strategies for the prevention of L. monocytogenes emergence and dissemination.

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.

[Epidemiological study and serotyping by multiple PCR of Listeria monocytogenes isolated from food matrices in Argentina]

Listeria monocytogenes is an opportunistic foodborne pathogen. It can resist stress conditions by adapting through the production of biofilms, which represents a serious problem for the food industry. It is classified into 14 serotypes, although only four (1/2a, 1/2b, 1/2c, and 4b) account for 89.0-98.0% of listeriosis cases worldwide. The objective of this study was to detect and serotype L.monocytogenes isolated from different food matrices from processing plants in Argentina. In the period 2016-2021, 1832 samples (meat, ready-to-eat foods, ice cream, dairy foods, and frozen vegetables) were analyzed, of which 226 (12.34%) isolates compatible with L.monocytogenes were detected. At the same time, environmental and surface samplings were performed in processing plants for ready-to-eat foods, sausages and dairy products, where environmental contamination with L.monocytogenes was detected in numerous critical points of the process, yielding a positivity rate of 22.7%. The molecular analysis of serogroups was performed, where it was observed that serogroup IIb was the most frequent with 66.5% (n=107), and in descending order IIc with 22.3% (n=36), and IIa (n=9) and IVb (n=9) with 5.6%. The serogroup mostly isolated in environmental monitoring was IIb. This work highlights the importance of the detection and serotyping of L.monocytogenes for taking actionable measures and identifying outbreaks, and is the first study in Argentina to describe an extensive study in food matrices.

Influence of microbial cell morphology and composition on radio frequency heating of simple media at different frequencies

The effect of Listeria monocytogenes, Salmonella Typhimurium, and Saccharomyces cerevisiae on RF heating was studied in sterilized Milli-Q water and saline solution during treatments at 27.0 ± 0.6 MHz and 3.0 ± 0.02 MHz for 30 min. The presence of microorganisms caused a significant increase in temperature (maximum to 54.9 °C), with no significant decrease in cell numbers being observed for any conditions. For both media and frequencies, heating rates followed the order S. Typhimurium ≤ L. monocytogenes ≤ S. cerevisiae, except for heating at 3.0 ± 0.02 MHz in saline solution, where heating rates for S. cerevisiae and S. Typhimurium were equal. Generally, heating rates for microorganisms were significantly higher at 27.0 ± 0.6 MHz than at 3.0 ± 0.02 MHz, except for the S. cerevisiae case. Observed phenomena were probably caused by differences in the cell lipid and peptidoglycan content, with interaction effects with salt being present. This study was the first to investigate the influence of the presence of microorganisms on heating behavior of simple media. On the long term, more research on this topic could lead to finding specific RF frequencies more suitable for the heating of specific media and products for various applications.

The Slaughterhouse as Hotspot of CC1 and CC6 Listeria monocytogenes Strains with Hypervirulent Profiles in an Integrated Poultry Chain of Italy

In Europe, very few studies are available regarding the diversity of Listeria monocytogenes (L. monocytogenes) clonal complexes (CCs) and sequence types (ST) in poultry and on the related typing of isolates using whole genome sequencing (WGS). In this study, we used a WGS approach to type 122 L. monocytogenes strains isolated from chicken neck skin samples collected in two different slaughterhouses of an integrated Italian poultry company. The studied strains were classified into five CCs: CC1-ST1 (21.3%), CC6-ST6 (22.9%), CC9-ST9 (44.2%), CC121-ST121 (10.6%) and CC193-ST193 (0.8%). CC1 and CC6 strains presented a virulence gene profile composed of 60 virulence genes and including the Listeria Pathogenicity Island 3, aut_IVb, gltA and gltB. According to cgMLST and SNPs analysis, long-term persistent clusters belonging to CC1 and CC6 were found in one of the two slaughterhouses. The reasons mediating the persistence of these CCs (up to 20 months) remain to be elucidated, and may involve the presence and the expression of stress response and environmental adaptation genes including heavy metals resistance genes (cadAC, arsBC, CsoR-copA-copZ), multidrug efflux pumps (mrpABCEF, EmrB, mepA, bmrA, bmr3, norm), cold-shock tolerance (cspD) and biofilm-formation determinants (lmo0673, lmo2504, luxS, recO). These findings indicated a serious risk of poultry finished products contamination with hypervirulent L. monocytogenes clones and raised concern for the consumer health. In addition to the AMR genes norB, mprF, lin and fosX, ubiquitous in L. monocytogenes strains, we also identified parC for quinolones, msrA for macrolides and tetA for tetracyclines. Although the phenotypical expression of these AMR genes was not tested, none of them is known to confer resistance to the primary antibiotics used to treat listeriosis The obtained results increase the data on the L. monocytogenes clones circulating in Italy and in particular in the poultry chain.

One-step immunoassay based on filtration for detection of food poisoning-related bacteria

A one-step immunoassay based on filtration was presented, which used microbeads for target analyte detection and filters with appropriate pore sizes to distinguish the complexity of target analyte and microbeads. For effective bacterial detection, the microbead size and the filter's pore size must be optimized. The optimal concentrations of the enzyme (urease) and antibody were determined at the maximum absorbance change, that is, the maximum pH change. The pH change was measured using a field-effect transistor (FET). The correlation between pH change and threshold voltage was estimated to be 21.7 mV/pH, and the correlation between pH change and the source-drain current was estimated to be -379 nA/pH. For the one-step immunoassay, antibodies against target bacteria were isolated from horse serum by filtration, and these antibodies were estimated to have a sufficiently high specificity to overcome cross-reactivity among five types of food poisoning-related bacteria: Escherichia coli O157, Salmonella typhimurium, Listeria monocytogenes, Bacillus cereus, and Staphylococcus aureus. Finally, the FET-based one-step immunoassay was demonstrated for five types of food poisoning-related bacteria in human serum.

Structure-Based Design of Dual Bactericidal and Bacteria-Releasing Nanosurfaces

Here, we report synergistic nanostructured surfaces combining bactericidal and bacteria-releasing properties. A polystyrene-block-poly(methyl methacrylate) (PS-block-PMMA) diblock copolymer is used to fabricate vertically oriented cylindrical PS structures ("PS nanopillars") on silicon substrates. The results demonstrate that the PS nanopillars (with a height of about 10 nm, size of about 50 nm, and spacing of about 70 nm) exhibit highly effective bactericidal and bacteria-releasing properties ("dual properties") against Escherichia coli for at least 36 h of immersion in an E. coli solution. Interestingly, the PS nanopillars coated with a thin layer (≈3 nm thick) of titanium oxide (TiO₂) ("TiO₂ nanopillars") show much improved dual properties against E. coli (a Gram-negative bacterium) compared to the PS nanopillars. Moreover, the dual properties emerge against Listeria monocytogenes (a Gram-positive bacterium). To understand the mechanisms underlying the multifaceted property of the nanopillars, coarse-grained molecular dynamics (MD) simulations of a lipid bilayer (as a simplified model for E. coli) in contact with a substrate containing hexagonally packed hydrophilic nanopillars were performed. The MD results demonstrate that when the bacterium-substrate interaction is strong, the lipid heads adsorb onto the nanopillar surfaces, conforming the shape of a lipid bilayer to the structure/curvature of nanopillars and generating high stress concentrations within the membrane (i.e., the driving force for rupture) at the edge of the nanopillars. Membrane rupture begins with the formation of pores between nanopillars (i.e., bactericidal activity) and ultimately leads to the membrane withdrawal from the nanopillar surface (i.e., bacteria-releasing activity). In the case of Gram-positive bacteria, the adhesion area to the pillar surface is limited due to the inherent stiffness of the bacteria, creating higher stress concentrations within a bacterial cell wall. The present study provides insight into the mechanism underlying the "adhesion-mediated" multifaceted property of nanosurfaces, which is crucial for the development of next-generation antibacterial surface coatings for relevant medical applications.

Isolation of Listeria monocytogenes from poultry red mite (Dermanyssus gallinae) infesting a backyard chicken farm in Greece

The poultry red mite (PRM), Dermanyssus gallinae, is arguably the most harmful, ubiquitous haematophagous ectoparasite infesting egg-laying hens. PRM is a vector of various microorganisms, with some being important for food microbiology and public health. The present study aimed to investigate the presence of specific pathogens, including Escherichia coli, Salmonella spp. and Listeria spp., carried by PRM infesting a chicken farm in Greece. Mites were caught using cardboard traps (Avivet), and 100 unwashed PRM were homogenized and used for microbiological cultures. Microbiological cultures were carried out on general and selective substrates to detect the above-mentioned bacteria. Specifically for Listeria spp., DNA was extracted from bacteria grown in Tryptone Soya Yeast Extract Agar using a commercial kit. The hly gene encoding the Listeriolysin O protein was amplified by PCR. Mites were identified as D. gallinae using morphological keys as well as by COI DNA barcoding. Microbiological cultures and PCR assays were positive for Listeria monocytogenes. No other bacteria were detected. The current study constitutes the first molecular isolation of L. monocytogenes from D. gallinae, confirming that PRM can carry this food-borne pathogen. PRM control measures and hygiene practices should be applied to minimize any possible contamination risk of poultry products with L. monocytogenes and safeguard public health.

Quantification of Total and Viable Cells and Determination of Serogroups and Antibiotic Resistance Patterns of Listeria monocytogenes in Chicken Meat from the North-Western Iberian Peninsula

Twenty samples of minced chicken meat procured from butcher’s shops in León (Spain; 10 samples) and Vila Real (Portugal; 10 samples) were analyzed. Microbial concentrations (log10 cfu/g) of 7.53 ± 1.02 (viable aerobic microbiota), 7.13 ± 1.07 (psychrotrophic microorganisms), and 4.23 ± 0.88 (enterobacteria) were found. The detection method described in the UNE-EN ISO 11290-1 standard (based on isolation from the chromogenic medium OCLA) with confirmation by the polymerase chain reaction (PCR; lmo1030) (OCLA−PCR), revealed Listeria monocytogenes in 14 samples (70.0% of the total), nine of Spanish origin and five of Portuguese (p > 0.05). The levels of viable and inactivated L. monocytogenes in the samples were determined with a q-PCR using propidium monoazide (PMAxx) as a viability marker. Seven samples tested positive both with the OCLA−PCR and with the q-PCR, with estimated concentrations of viable cells varying between 2.15 log10 cfu/g (detection limit) and 2.94 log10 cfu/g. Three samples tested negative both with the OCLA−PCR and with the q-PCR. Seven samples were positive with the OCLA−PCR, but negative with the q-PCR, and three samples tested negative with the OCLA−PCR and positive with the q-PCR. The percentage of viable cells relative to the total ranged between 2.4% and 86.0%. Seventy isolates of L. monocytogenes (five from each positive sample) were classified in PCR serogroups with a multiplex PCR assay. L. monocytogenes isolates belonged to serogroups IIa (52 isolates; 74.3%), IIc (7; 10.0%), IVa (2; 2.9%), and IVb (9; 12.9%). The susceptibility of the 70 isolates to 15 antibiotics of clinical interest was tested. The strains presented resistance to between three and eight antibiotics. The average number of resistances was greater (p < 0.001) among strains isolated from Spanish samples (6.20 ± 1.08), than in those from Portugal (5.00 ± 1.08). In both groups of strains, a prevalence of resistance higher than 95% was observed for oxacillin, cefoxitin, cefotaxime, and cefepime. The need to handle minced chicken meat correctly, taking care to cook it sufficiently and to avoid cross-contamination, so as to reduce the danger of listeriosis, is emphasized. A combination of culture-dependent and culture-independent methods offers complementary routes for the detection in food of the cells of L. monocytogenes in various different physiological states.

Bacterial Surface Disturbances Affecting Cell Function during Exposure to Three-Compound Nanocomposites Based on Graphene Materials

Combating pathogenic microorganisms in an era of ever-increasing drug resistance is crucial. The aim of the study was to evaluate the antibacterial mechanism of three-compound nanocomposites that were based on graphene materials. To determine the nanomaterials' physicochemical properties, an analysis of the mean hydrodynamic diameter and zeta potential, transmission electron microscope (TEM) visualization and an FT-IR analysis were performed. The nanocomposites' activity toward bacteria species was defined by viability, colony forming units, conductivity and surface charge, cell wall integrity, ATP concentration, and intracellular pH. To ensure the safe usage of nanocomposites, the presence of cytokines was also analyzed. Both the graphene and graphene oxide (GO) nanocomposites exhibited a high antibacterial effect toward all bacteria species (Enterobacter cloacae, Listeria monocytogenes, Salmonella enterica, and Staphylococcus aureus), as well as exceeded values obtained from exposure to single nanoparticles. Nanocomposites caused the biggest membrane damage, along with ATP depletion. Nanocomposites that were based on GO resulted in lower toxicity to the cell line. In view of the many aspects that must be considered when investigating such complex structures as are three-component nanocomposites, studies of their mechanism of action are crucial to their potential antibacterial use.

Frozen Vegetable Processing Plants Can Harbour Diverse Listeria monocytogenes Populations: Identification of Critical Operations by WGS

Frozen vegetables have emerged as a concern due to their association with foodborne outbreaks such as the multi-country outbreak of Listeria monocytogenes serogroup IVb linked to frozen corn. The capacity of L. monocytogenes to colonize food-processing environments is well-known, making the bacteria a real problem for consumers. However, the significance of the processing environment in the contamination of frozen foods is not well established. This study aimed to identify potential contamination niches of L. monocytogenes in a frozen processing plant and characterize the recovered isolates. A frozen vegetable processing plant was monitored before cleaning activities. A total of 78 points were sampled, including frozen vegetables. Environmental samples belonged to food-contact surfaces (FCS); and non-food-contact surfaces (n-FCS). Positive L. monocytogenes samples were found in FCS (n = 4), n-FCS (n = 9), and the final product (n = 1). A whole-genome sequencing (WGS) analysis revealed two clusters belonging to serotypes 1/2a-3a and 1/2b-3b). The genetic characterization revealed the presence of four different sequence types previously detected in the food industry. The isolate obtained from the final product was the same as one isolate found in n-FCS. A multi-virulence-locus sequence typing (MVLST) analysis showed four different virulence types (VT). The results obtained highlight the relevant role that n-FCS such as floors and drains can play in spreading L. monocytogenes contamination to the final product.

Expansion of Intestinal Secretory Cell Population Induced by Listeria monocytogenes Infection: Accompanied With the Inhibition of NOTCH Pathway

Listeria monocytogenes, as a model organism, is a causative agent of enteric pathogen that causes systemic infection. However, the interaction of L. monocytogenes and small intestinal epithelium has not been fully elucidated yet. In this study, mice and intestinal organoids were chosen as the models to investigate the influence of L. monocytogenes infection on the intestinal secretory cells and its differentiation-related pathways. Results confirmed the phenomenon of intestinal damage that L. monocytogenes infection could lead to villi damage in mice, which was accompanied by the increase of TNF-α production in jejunum as well as lipopolysaccharide (LPS) secretion in serum. Moreover, it was demonstrated that L. monocytogenes infection increased the number of goblet and Paneth cells in mice and intestinal organoids and upregulated the expression of Muc2 and Lyz. Furthermore, L. monocytogenes decreased the relative expression of Notch pathway-related genes (Jag1, Dll4, Notch1, and Hes1) while upregulating the relative expression of Math1 gene in mice and intestinal organoids. This indicated that L. monocytogenes infection caused the inhibition of Notch pathway, which may be the reason for the increased number of goblet and Paneth cells in the intestine. Collectively, these results are expected to provide more information on the mechanism of L. monocytogenes infection in the intestine.

Promising strategies to control persistent enemies: Some new technologies to combat biofilm in the food industry-A review

Biofilm is an advanced form of protection that allows bacterial cells to withstand adverse environmental conditions. The complex structure of biofilm results from genetic-related mechanisms besides other factors such as bacterial morphology or substratum properties. Inhibition of biofilm formation of harmful bacteria (spoilage and pathogenic bacteria) is a critical task in the food industry because of the enhanced resistance of biofilm bacteria to stress, such as cleaning and disinfection methods traditionally used in food processing plants, and the increased food safety risks threatening consumer health caused by recurrent contamination and rapid deterioration of food by biofilm cells. Therefore, it is urgent to find methods and strategies for effectively combating bacterial biofilm formation and eradicating mature biofilms. Innovative and promising approaches to control bacteria and their biofilms are emerging. These new approaches range from methods based on natural ingredients to the use of nanoparticles. This literature review aims to describe the efficacy of these strategies and provide an overview of recent promising biofilm control technologies in the food processing sector.

Prevalence and characteristics of Listeria species from selected African countries

Listeriosis, caused by Listeria spp., presents varying clinical manifestations among individuals, from moderate fecal infections such as diarrhea to severe infections such as septicemia, meningitis and abortion or newborn listeriosis in perinatal patients. In Africa, listeriosis is attributed to poor sanitation and cross-contamination in food processing environments, particularly ready to eat (RTE) foods including dairy products, leafy vegetables, fish and meat. Despite the global increase in reported cases and research on listeriosis, data from Africa remains scarce and this could lead to possible underestimation of the importance of listeriosis on the continent. This paper therefore presents a comprehensive overview of currently available reports on Listeria spp. in Africa with emphasis on molecular characteristics, antimicrobial susceptibility, and prevalence in food, animal and environmental samples. The majority of studies on Listeria spp. in Africa have so far focused on the prevalence and antibiotic susceptibility of L. monocytogenes isolated from RTE foods and raw meat but rarely from humans, animals, and the environment. The overall calculated average prevalence values from the available reports are 23.7 and 22.2% for Listeria spp. and L. monocytogenes, respectively. Listeria spp. isolated from different parts of Africa are generally sensitive to ciprofloxacin, but resistant to penicillin. The majority of these studies employed conventional culture and biochemical tests to characterize Listeria spp. However, the use of modern molecular techniques such as PCR and whole-genome sequencing is on the rise. Most of the studies employing molecular tools were carried out in South Africa and Nigeria, with the predominant strain reported in South Africa being ST6. In order to provide a better understanding of the importance of listeria in Africa, there is the need for extensive and coordinated studies using modern molecular-based techniques to characterize the various Listeria species, and to assess the disease epidemiology using the one health concept.

LincRNA-Cox2 regulates IL6/JAK3/STAT3 and NF-κB P65 pathway activation in Listeria monocytogenes-infected RAW264.7 cells

Listeria monocytogenes (Lm) can lead to high mortality rates relative to other foodborne pathogens. Lm-induced inflammation is partly characterized by macrophage activation. Long non-coding RNAs (lncRNAs) have important roles in various biological processes. However, it is unknown how lncRNAs regulate the host response to Lm infection. To identify the role of lncRNA in Lm infection, we used in vitro and in vivo models. We found that lincRNA-Cox2 was highly expressed in Lm-infected RAW264.7 cells. LincRNA-Cox2 knockdown resulted in reduced proinflammatory cytokines, apoptosis, migration ability and enhanced phagocytosis of Lm. LincRNA-Cox2 knockdown also reduced the phosphorylation of Janus kinase 3 (JAK3) and signal transducer and activator of transcription (STAT3) and the nuclear translocation of nuclear factor (NF)-κB P65, which are known to be involved in inflammatory responses. Experimentally inhibiting the protein and phosphorylation levels of STAT3 resulted in reduced proinflammatory cytokines and enhanced phagocytosis of Lm by the RAW264.7 cells. Our research suggests that lincRNA-Cox2 plays important roles in inflammation, the phagocytic function and cell migration ability of RAW264.7 cells by activating interleukin (IL)-6/JAK3/STAT3 signaling, and lincRNA-Cox2 also regulates NF-κB P65 nuclear translocation. Our research provides new insights into the regulatory role of lincRNA-Cox2 in Lm infection.

Contamination of chicken carcasses and the abattoir environment with Listeria monocytogenes in Taiwan

1. The following study provides the first data on the detection and types of Listeria monocytogenes isolated from broiler chickens during processing and from six Taiwanese abattoir environments.2. Listeria monocytogenes was not detected in any cloacal (n = 120) or environmental (n = 256) samples collected before and during processing, indicating that faecal material and the environment of abattoirs were not important sources of L. monocytogenes for poultry carcases. However, 28 of 246 (11.4%; 95% CI: 7.7-16.0) rinse samples collected from carcases post-evisceration from three abattoirs were positive for L. monocytogenes.3. The only serotypes detected were 1/2a (82.1%; 95% CI: 63.1-93.9) and 1/2b (14.3%; 95% CI: 4.0-32.7), with 3.6% (95% CI: 0.1-18.3) non-typable isolates.4. Characterisation by Pulsed Field Gel Electrophoresis (PFGE) identified five PFGE types, confirming cross-contamination with L. monocytogenes during evisceration, chilling and post-chilling.5. These findings highlight the potential for cross-contamination to occur through direct contact between carcases, especially whilst in chilling tanks.

A Diffusion Model to Quantify Membrane Repair Process in Listeria monocytogenes Exposed to High Pressure Processing Based on Fluorescence Microscopy Data

The effects of environmental stresses on microorganisms have been well-studied, and cellular responses to stresses such as heat, cold, acids, and salts have been extensively discussed. Although high pressure processing (HPP) is becoming more popular as a preservation method in the food industry, the characteristics of the cellular damage caused by high pressure are unclear, and the microbial response to this stress has not yet been well-explored. We exposed the pathogen Listeria monocytogenes to HPP (400 MPa, 8 min, 8°C) and found that the high pressure created plasma membrane pores. Using a common staining technique involving propidium iodide (PI) combined with high-frequency fluorescence microscopy, we monitored the rate of diffusion of PI molecules into hundreds of bacterial cells through these pores on days 0, 1, 2, 3, and 4 after pressurization. We also developed a mathematical dynamic model based on mass transfer and passive diffusion laws, calibrated using our microscopy experiments, to evaluate the response of bacteria to HPP. We found that the rate of diffusion of PI into the cells decreased over the 4 consecutive days after exposure to HPP, indicating repair of the pressure-created membrane pores. The model suggested a temporal change in the size of pores until closure. To the best of our knowledge, this is the first time that pressure-created membrane pores have been quantitatively described and shown to diminish with time. In addition, we found that the membrane repair rate in response to HPP was linear, and growth was temporarily arrested at the population level during the repair period. These results support the existence of a progressive repair process in some of the cells that take up PI, which can therefore be considered as being sub-lethally injured rather than dead. Hence, we showed that a subgroup of bacteria survived HPP and actively repaired their membrane pores.

Antilisterial Potential of Lactic Acid Bacteria in Eliminating Listeria monocytogenes in Host and Ready-to-Eat Food Application

Listeriosis is a severe food borne disease with a mortality rate of up to 30% caused by pathogenic Listeria monocytogenes via the production of several virulence factors including listeriolysin O (LLO), transcriptional activator (PrfA), actin (Act), internalin (Int), etc. It is a foodborne disease predominantly causing infections through consumption of contaminated food and is often associated with ready-to-eat food (RTE) and dairy products. Common medication for listeriosis such as antibiotics might cause an eagle effect and antibiotic resistance if it is overused. Therefore, exploration of the use of lactic acid bacteria (LAB) with probiotic characteristics and multiple antimicrobial properties is increasingly getting attention for their capability to treat listeriosis, vaccine development, and hurdle technologies. The antilisterial gene, a gene coding to produce antimicrobial peptide (AMP), one of the inhibitory substances found in LAB, is one of the potential key factors in listeriosis treatment, coupled with the vast array of functions and strategies; this review summarizes the various strategies by LAB against L. monocytogenes and the prospect in development of a ‘generally regarded as safe’ LAB for treatment of listeriosis.

Growth of Listeria monocytogenes in Partially Cooked Battered Chicken Nuggets as a Function of Storage Temperature

Battered poultry products may be wrongly regarded and treated by consumers as ready-to-eat and, as such, be implicated in foodborne disease outbreaks. This study aimed at the quantitative description of the growth behavior of Listeria monocytogenes in fresh, partially cooked (non-ready-to-eat) battered chicken nuggets as function of temperature. Commercially prepared chicken breast nuggets were inoculated with L. monocytogenes and stored at different isothermal conditions (4, 8, 12, and 16 °C). The pathogen’s growth behavior was characterized via a two-step predictive modelling approach: estimation of growth kinetic parameters using a primary model, and description of the effect of temperature on the estimated maximum specific growth rate (μ_max) using a secondary model. Model evaluation was undertaken using independent growth data under both constant and dynamic temperature conditions. According to the findings of this study, L. monocytogenes may proliferate in battered chicken nuggets in the course of their shelf life to levels potentially hazardous for susceptible population groups, even under well-controlled refrigerated storage conditions. Model evaluation demonstrated a satisfactory performance, where the estimated bias factor (B_f) was 0.92 and 1.08 under constant and dynamic temperature conditions, respectively, while the accuracy factor (A_f) value was 1.08, in both cases. The collected data should be useful in model development and quantitative microbiological risk assessment in battered poultry products.

Inhibition of Listeria monocytogenes growth in turkey fillets by alginate edible coating with Trachyspermum ammi essential oil nano-emulsion

The objective of this study was to determine the chemical composition and antibacterial activity of Trachyspermum ammi essential oil (TAEO). Moreover, the present study comparatively investigated TAEO in the forms of emulsion and Nano-emulsion in alginate-based edible coatings against inoculated Listeria monocytogenes in turkey fillets during 12 days in cold storage (at a temperature of 4 ± 1 °C). Alginate solutions with two levels of TAEO (in emulsion and Nano-emulsion forms) were prepared in this study. The bacterial count was performed on days 0, 1, 2, 4, 8, and 12. Based on the obtained results of the current study, a comparison of different treatments with the blank samples (without any coating) showed that the highest considerable result was observed in the samples with Nano-emulsion coating (P < 0.05). Nano-emulsion loaded alginate coating prevented the growth of listeria in turkey fillets even after 12 days of cold storage. According to the findings of this study, the application of alginate edible coatings containing TAEO, especially in Nano-form, can be very effective in controlling the growth of L. monocytogenes, as a foodborne pathogen, during storage; therefore, it is a good choice to be applied in the meat industry.

A Cross-Protective Vaccine Against 4b and 1/2b Listeria monocytogenes

Listeria monocytogenes (Lm) is a foodborne zoonotic pathogen that causes listeriosis with a mortality rate of 20-30%. Serovar 4b and 1/2b isolates account for most of listeriosis outbreaks, however, no listeriosis vaccine is available for either prophylactic or therapeutic use. Here, we developed a triple-virulence-genes deletion vaccine strain, and evaluated its safety, immunogenicity, and cross-protective efficiency. The virulence of NTSNΔactA/plcB/orfX was reduced 794-folds compared with the parental strain. Additionally, it was completely eliminated in mice at day 7 post infection and no obvious pathological changes were observed in the organs of mice after prime-boost immunization for 23 days. These results proved that the safety of the Lm vaccine strain remarkably increased. More importantly, the NTSNΔactA/plcB/orfX strain stimulated higher anti-Listeriolysin O (LLO) antibodies, induced significantly higher expression of IFN-γ, TNF-α, IL-17, and IL-6 than the control group, and afforded 100% protection against serovar 4b and 1/2b challenges. Taken together, our research demonstrates that the triple-genes-deletion vaccine has high safety, can elicit strong Th1 type immune response, and affords efficient cross-protection against two serovar Lm strains. It is a promising vaccine for prevention of listeriosis.

PlcA-based nanofabricated electrochemical DNA biosensor for the detection of Listeria monocytogenes in raw milk samples

The electrochemical DNA biosensor has been developed for the detection of Listeria monocytogenes in raw milk samples. The electrochemical studies of the developed biosensor was recorded by cyclic voltammetry (CV) and electrochemical impedance (EI) using methylene blue (MB) and potassium ferricyanide K₃Fe(CN)^- ₆ as redox indicators. The selectivity of the developed biosensor was demonstrated using complementary and mismatch oligonucleotide sequences. The sensitivity (S) of the developed sensor was recorded as 3461 (μA/cm²)/ng and limit of detection (LOD) was found to be 82 fg/6 µl with the regression coefficient (R ²) 0.941 using CV. The sensor was characterized by field emission scanning electron microscopy (FE-SEM). The electrode was found to be stable for six months, with only 10% loss in the initial CV current.

Listeria monocytogenes in poultry: Detection and strain characterization along an integrated production chain in Italy

In this study, thirteen batches of broiler chicken from an integrated Italian poultry company were investigated for the detection of Listeria monocytogenes. The prevalence was evaluated in faeces samples at farm level and after transport, caecal contents and carcass neck skin from 2 slaughterhouses (M1 and M2), for a total of 2080 samples, throughout a 27-month period. No positive results were recorded in faeces, while the overall prevalence of contamination in carcass neck skin was 26.7%. Then, 123 isolates out of 139 positive skin samples, with the prevalent serotypes 4b (76%) and 1/2b (94%) from slaughterhouses M1 and M2 respectively, were PFGE characterized, showing the presence of 18 different pulsotypes and 8 genetic clusters. The same pulsotypes were found in carcasses from different farms, but slaughtered in the same abattoir, highlighting the environmental origin of contamination. The persistence of the pathogen over long time seemed to be very likely, considering that undistinguishable pulsotypes were found in carcasses slaughtered in the same slaughterhouse after periods up to 18 months long. The implementation of cleaning and sanitation at slaughterhouse level could represent the main factor for the control of such pathogen in the poultry meat processing line.

Persistent Listeria monocytogenes Isolates from a Poultry-Processing Facility Form more Biofilm but Do Not Have a Greater Resistance to Disinfectants Than Sporadic Strains

Some strains of Listeria monocytogenes can persist in food-processing environments, increasing the likelihood of the contamination of foodstuffs. To identify traits that contribute to bacterial persistence, a selection of persistent and sporadic L. monocytogenes isolates from a poultry-processing facility was investigated for biofilm-forming ability (crystal violet assay). The susceptibility of sessile cells to treatments (five minutes) with sodium hypochlorite having 10% active chlorine (SHY: 10,000 ppm, 25,000 ppm, and 50,000 ppm) and benzalkonium chloride (BZK: 2500 ppm, 10,000 ppm, and 25,000 ppm) was also studied. All isolates exhibited biofilm formation on polystyrene. Persistent strains showed larger (p < 0.001) biofilm formation (OD580 = 0.301 ± 0.097) than sporadic strains (OD580 = 0.188 ± 0.082). A greater susceptibility to disinfectants was observed for biofilms of persistent strains than for those of sporadic strains. The application of SHY reduced biofilms only for persistent strains. BZK increased OD580 in persistent strains (2500 ppm) and in sporadic strains (all concentrations). These results indicate that the use of BZK at the concentrations tested could represent a public health risk. Findings in this work suggest a link between persistence and biofilm formation, but do not support a relationship between persistence and the resistance of sessile cells to disinfectants.

Prevalence, Molecular Typing, and Determination of the Biofilm-Forming Ability of Listeria monocytogenes Serotypes from Poultry Meat and Poultry Preparations in Spain

A study was undertaken of the presence of Listeria monocytogenes in 260 samples of poultry meat obtained from retail outlets in northwestern Spain. L. monocytogenes was detected in 20 samples (7.7%). Twenty strains (one strain per positive sample) were characterized. The strains belonged to 10 serotypes: 1/2a (2 strains), 1/2b (2), 1/2c (2), 3a (1), 3b (2), 3c (2), 4a (2), 4b (4), 4c (1), and 4d (2). Cluster analysis (ribotyping; EcoRI) showed a strong genetic relationship between strains isolated from samples coming from different outlets. Ribotyping permitted some isolates of the same serotype to be differentiated, which points to the possible usefulness of this technique in the epidemiological surveillance of L. monocytogenes. All strains formed biofilm on polystyrene, as shown by confocal laser scanning microscopy. The biovolume (between 621.7 ± 36.0 µm3 and 62,984.0 ± 14,888.2 µm3 in the observational field of 14,161 μm2), percentage of surface coverage (from 2.17 ± 0.84% to 94.43 ± 3.97%), roughness (between 0.399 ± 0.052 and 0.830 ± 0.022), and maximum thickness (between 9.00 ± 0.00 µm and 24.00 ± 14.93 µm) of biofilms varied between strains (p < 0.05). These results expand knowledge of the characteristics of L. monocytogenes isolates from poultry.

Characterization of Listeria Monocytogenes Originating from the Spanish Meat-Processing Chain

Using agglutination techniques, 118 Listeria monocytogenes isolates from red meat and poultry were serotyped. Strains were ascribed to the serotypes 4b/4e (44.1% of the strains), 1/2 (a, b or c; 28.0%), 4c (6.8%), 4d/4e (5.9%) and 3 (a, b or c; 2.5%). Among these are the serotypes most frequently involved in cases of human listeriosis. The susceptibility of 72 strains to 26 antibiotics of clinical importance was determined by disc diffusion (Clinical and Laboratory Standards Institute; CLSI). High levels of resistance were observed to cefoxitin (77.8% of the strains showed resistance), cefotaxime (62.5%), cefepime (73.6%), and nalidixic acid (97.2%), nitrofurantoin (51.4%) and oxacillin (93.1%). Less than 3% of the strains showed resistance to the antibiotic classes used in human listeriosis therapy (i.e., ampicillin, gentamicin, rifampicin, chloramphenicol, enrofloxacin, vancomycin, trimethoprim-sulfamethoxazole, erythromycin, and tetracycline). The influence of species and serotype on the growth kinetics (modified Gompertz equation) and on the adhesion ability (crystal violet staining) of nine isolates of L. monocytogenes (serotypes 1/2a, 1/2b, 1/2c, 3a, 3b, 3c, 4a, 4b, and 4d), and one strain of Listeria ivanovii were investigated. The maximum growth rate (ΔOD420-580/h) varied between 0.073 ± 0.018 (L. monocytogenes 1/2a) and 0.396 ± 0.026 (L. monocytogenes 4b). The isolates of L. monocytogenes belonging to serotypes 3a and 4a, as well as L. ivanovii, showed a greater (p < 0.05) biofilm-forming ability than did the remaining strains, including those that belong to the serotypes commonly implied in human listeriosis (1/2a, 1/2b, 1/2c and 4b). The need for training in good hygiene practices during the handling of meat and poultry is highlighted to reduce the risk of human listeriosis.