Listeria Monocytogenes Strains Research Articles

Draft genome sequences of Listeria monocytogenes strains from human listeriosis in Sweden harboring premature stop codons in the virulence determinant inlA.

Premature stop codons in the internalin virulence determinant inlA are common in serotype 1/2a Listeria monocytogenes from food/food processing environments but rare among human clinical isolates. Here, we report the genome sequences of serotype 1/2a (STs 121 and 3258) human listeriosis isolates from Sweden harboring such mutations in inlA.

Listeriosis: Characteristics, Occurrence in Domestic Animals, Public Health Significance, Surveillance and Control.

Listeriosis is a dangerous zoonosis caused by bacteria of the genus Listeria, with Listeria monocytogenes (LM) being the most pathogenic species. Listeria monocytogenes has been detected in various animal species and in humans, and its ability to evolve from an environmental saprophyte to a powerful intracellular pathogen is driven by the invasion mechanisms and virulence factors that enable cell invasion, replication and cell-to-cell spread. Key regulatory systems, including positive regulatory factor A (PrfA) and the stress-responsive sigma factor σB, control the expression of virulence genes and facilitate invasion of host cells. Listeriosis poses a significant threat to cattle, sheep and goat herds, leading to abortions, septicemia and meningoencephalitis, and ruminants are important reservoirs for Listeria, facilitating transmission to humans. Other Listeria species such as Listeria ivanovii and Listeria innocua can also cause disease in ruminants. Resilience of LM in food processing environments makes it an important foodborne pathogen that is frequently transmitted through contaminated meat and dairy products, with contamination often occurring along the food production chain. In humans, listeriosis primarily affects immunocompromised individuals, pregnant women and the elderly and leads to severe conditions, such as meningitis, septicemia and spontaneous abortion. Possible treatment requires antibiotics that penetrate the blood-brain barrier. Despite the relatively low antimicrobial resistance, multidrug-resistant LM strains have been detected in animals, food and the environment. Controlling and monitoring the disease at the herd level, along with adopting a One Health approach, are crucial to protect human and animal health and to minimize the potential negative impacts on the environment.

Exploring the modulation of extracellular metabolites in different Listeria monocytogenes strains under cold-stress

Exploring the modulation of extracellular metabolites in different Listeria monocytogenes strains under cold-stress

Deciphering transcript architectural complexity in bacteria and archaea.

RNA transcripts are potential therapeutic targets, yet bacterial transcripts have uncharacterized biodiversity. We developed an algorithm for transcript prediction called tp.py using it to predict transcripts (mRNA and other RNAs) in Escherichia coli K12 and E2348/69 strains (Bacteria:gamma-Proteobacteria), Listeria monocytogenes strains Scott A and RO15 (Bacteria:Firmicute), Pseudomonas aeruginosa strains SG17M and NN2 strains (Bacteria:gamma-Proteobacteria), and Haloferax volcanii (Archaea:Halobacteria). From >5 million E. coli K12 and >3 million E. coli E2348/69 newly generated Oxford Nanopore Technologies direct RNA sequencing reads, 2,487 K12 mRNAs and 1,844 E2348/69 mRNAs were predicted, with the K12 mRNAs containing more than half of the predicted E. coli K12 proteins. While the number of predicted transcripts varied by strain based on the amount of sequence data used, across all strains examined, the predicted average size of the mRNAs was 1.6-1.7 kbp, while the median size of the 5'- and 3'-untranslated regions (UTRs) were 30-90 bp. Given the lack of bacterial and archaeal transcript annotation, most predictions were of novel transcripts, but we also predicted many previously characterized mRNAs and ncRNAs, including post-transcriptionally generated transcripts and small RNAs associated with pathogenesis in the E. coli E2348/69 LEE pathogenicity islands. We predicted small transcripts in the 100-200 bp range as well as >10 kbp transcripts for all strains, with the longest transcript for two of the seven strains being the nuo operon transcript, and for another two strains it was a phage/prophage transcript. This quick, easy, and reproducible method will facilitate the presentation of transcripts, and UTR predictions alongside coding sequences and protein predictions in bacterial genome annotation as important resources for the research community.IMPORTANCEOur understanding of bacterial and archaeal genes and genomes is largely focused on proteins since there have only been limited efforts to describe bacterial/archaeal RNA diversity. This contrasts with studies on the human genome, where transcripts were sequenced prior to the release of the human genome over two decades ago. We developed software for the quick, easy, and reproducible prediction of bacterial and archaeal transcripts from Oxford Nanopore Technologies direct RNA sequencing data. These predictions are urgently needed for more accurate studies examining bacterial/archaeal gene regulation, including regulation of virulence factors, and for the development of novel RNA-based therapeutics and diagnostics to combat bacterial pathogens, like those with extreme antimicrobial resistance.

Genetic Diversity, Virulence Factors and Antibiotic Resistance of Listeria monocytogenes from Food and Clinical Samples in Southern Poland.

Listeriosis is one of the most serious foodborne diseases under surveillance, with an overall mortality rate in the EU currently being high at 18.1%. Therefore, this study aims to investigate Listeria monocytogenes strains isolated from clinical and food samples for susceptibility to antimicrobials, presence of virulence factors, and genetic diversity. Species were identified using the MALDI-TOF, resistance to 11 antibiotics was determined according to EUCAST guidelines, and multiplex PCR was used for serotyping and detecting virulence genes. Strains were genotyped using the PFGE method. Clinical strains showed full sensitivity to all tested antibiotics. In total, 33.3% of strains from food products were found to be resistant to ciprofloxacin and 4.2% to tetracycline. Most of the tested isolates (79.2%) belonged to serotype 1/2a-3a, and the rest (20.8%) belonged to serotype 4ab-4b,4d-4e. Five virulence genes (prfA, hlyA, plcB, inlA, and lmo2672) were detected in all strains studied. The llsX gene was the least common, in 37.5% of clinical strains and 18.75% of strains isolated from food products. Among the analyzed strains, 13 strains displayed unique PFGE profiles. The other 11 strains belong to 3 clusters of pulsotypes: cluster 1 (2 strains), cluster 2 (6 strains), and cluster 3 (2 strains). The percentage of hospitalizations and deaths of Polish patients with listeriosis indicates the seriousness of this disease, especially in an aging society, while the molecular testing of clinical strains has been rarely performed, which makes it difficult to determine the source of infection.

Determination of strain variability and kinetics of food-associated microorganisms following ultrasound treatment

Ultrasound is a promising emerging technology known for its antimicrobial efficacy. However, existing studies have not fully addressed the impact of strain variability and inactivation kinetics on US efficacy. Ten strains of Listeria monocytogenes, Lactiplantibacillus plantarum, Saccharomyces cerevisiae and Escherichia coli were exposed to US treatment (26 kHz, 200 mL, 100 % amplitude, 200 W, 65–71 W/cm2) under dynamic conditions to investigate their resistance profile. Furthermore, the inactivation kinetics of selected resistant/sensitive strains were assessed. The result showed significant intra-species variability in resistance (p < 0.05) for the four target microorganisms evaluated in this study. L6 and NCTC 10357 were the most resistant and sensitive L. monocytogenes strains respectively, having a reduction difference of ∼3.4 log CFU/mL. Regarding L. plantarum, FBR04 emerged as the most resistant strain (4.4 log reduction), while E. coli FAM21845, FAM21805 and FAM21843 (∼2 log reduction) emerged as the most resistant strains. On the other hand, the most resistant strains of S. cerevisiae were CBS 1544, AD 1890 and 077.0001 (<1 log reduction) while S. cerevisiae AD 2913, 028.0404 and 028.0315 were the most sensitive (>5 log reduction). The survival curves of most of the strains exhibited an initial phase of insignificant microbial inactivation followed by a relatively fast log-linear inactivation period. The estimated D-value showed that L. monocytogenes strains exhibited higher resistance to US treatment than any other species, while other species displayed comparable resistance. The findings on strain variability resistance and inactivation kinetics following US treatment are essential for food safety and will pave the way for further research on microbial response to US stress, risk assessment and optimisation studies.

Assessment of phytochemical, antioxidant and antibacterial properties of &lt;em&gt;ziziphus lotus&lt;/em&gt; leaves extracts

Herbal medicines are used to treat a variety of chronic and acute diseases with little to no harmful side effects. They have played a significant part in health systems throughout the world. The phytochemical profile, antioxidant activity, and antibacterial activity of different extracts of Ziziphus lotus leaves (ZLL) were the subject of this study. According to the analysis of the extraction yield, the aqueous extract had the highest yield, followed by methanol, ethanol, and last, hexane (p&lt;0.05). Phytochemical analysis of ZLL extracts revealed the presence of several bioactive molecules such as phenolic compounds and alkaloids. Water, methanol 50%, methanol 80%, methanol, ethanol, and hexane are the 6 different solvents which were used in order to evaluate the phytochemical profile as well as the biological activities of ZLL, and whose aqueous extract showed the best results. The aqueous extract showed the highest total contents of phenols, flavonoids, and tannins (120,53± 0. 37 mg GAE/g DM, 60.15 ± 0.06 mg QE/g DM, and 09.41 ± 0.36 mg CE/g DM, respectively), while the hexane extract revealed the lowest contents (20.42 ± 0.50 mg GAE/g DM, 14.45± 0.36 mg QE/g DM, and 04.20 ± 0.17 mg CE/g DM, respectively). By using the DPPH, ABTS, and FRAP methods, ZLL extracts demonstrated considerable antioxidant capacities, with the values IC50=31.20 ±0.69, IC50=61.35±0.30 and IC0.5=23.89±0.80, respectively, and this for the aqueous extract. All of the ZLL extracts, showed antibacterial efficacy against the bacterial strains of Listeria monocytogenes, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa.

Reducing the degree of crosslinking of peptidoglycan in Listeria monocytogenes promoted the secretion of membrane vesicles.

Listeria monocytogenes (LM) is a Gram-positive (G+) bacterium that secretes nanoscale membrane vesicles (MVs). LM MVs comprise various bacterial components and may have potential as an antigen or drug-delivery vehicle; however, the low yield of the LM MVs limits related research. G+-bacterial MVs germinate from the bacterial plasma membrane and must pass through a thick crosslinked peptidoglycan layer for release. Herein, we aimed to increase the release of MVs by reducing the degree of crosslinking of peptidoglycan. We knocked out two genes related to the longitudinal crosslinking of peptidoglycan, dal and dat, and supplemented the knocked-out dal gene through plasmid expression to obtain a stably inherited recombinant strain LMΔdd::pCW633. The structure, particle size, and main protein components of MVs secreted by this recombinant strain were consistent with those secreted from the wild strain, but the yield of MVs was considerably increased (p < 0.05). Furthermore, Listeria ivanovii (LI) was found to secrete MVs that differed in the composition of the main proteins compared with those of LM MVs. The abovementioned method was also feasible for promoting the secretion of MVs from the attenuated LM strain and LI wild-type and attenuated strains. Our study provides a new method to increase the secretion of MVs derived from Listeria that could be extended to other G+ bacteria.

The Relationship between Biofilm Phenotypes and Biofilm-Associated Genes in Food-Related Listeria monocytogenes Strains.

Listeria monocytogenes is an important pathogen responsible for listeriosis, a serious foodborne illness associated with high mortality rates. Therefore, L. monocytogenes is considered a challenge for the food industry due to the ability of some strains to persist in food-associated environments. Biofilm production is presumed to contribute to increased L. monocytogenes resistance and persistence. The aims of this study were to (1) assess the biofilm formation of L. monocytogenes isolates from a meat processing facility and sheep farm previously characterized and subjected to whole-genome sequencing and (2) perform a comparative genomic analysis to compare the biofilm formation and the presence of a known set of biofilm-associated genes and related resistance or persistence markers. Among the 37 L. monocytogenes isolates of 15 sequence types and four serogroups involved in this study, 14%, 62%, and 24% resulted in the formation of weak, moderate, and strong biofilm, respectively. Increased biofilm-forming ability was associated with the presence of the stress survival islet 1 (SSI-1), inlL, and the truncated inlA genes. Combining the phenotypic and genotypic data may contribute to understanding the relationships between biofilm-associated genes and L. monocytogenes biofilm-forming ability, enabling improvement in the control of this foodborne pathogen.

Comparative genomics analysis to explore the biodiversity and mining novel target genes of Listeria monocytogenes strains from different regions.

As a common foodborne pathogen, infection with L. monocytogenes poses a significant threat to human life and health. The objective of this study was to employ comparative genomics to unveil the biodiversity and evolutionary characteristics of L. monocytogenes strains from different regions, screening for potential target genes and mining novel target genes, thus providing significant reference value for the specific molecular detection and therapeutic targets of L. monocytogenes strains. Pan-genomic analysis revealed that L. monocytogenes from different regions have open genomes, providing a solid genetic basis for adaptation to different environments. These strains contain numerous virulence genes that contribute to their high pathogenicity. They also exhibit relatively high resistance to phosphonic acid, glycopeptide, lincosamide, and peptide antibiotics. The results of mobile genetic elements indicate that, despite being located in different geographical locations, there is a certain degree of similarity in bacterial genome evolution and adaptation to specific environmental pressures. The potential target genes identified through pan-genomics are primarily associated with the fundamental life activities and infection invasion of L. monocytogenes, including known targets such as inlB, which can be utilized for molecular detection and therapeutic purposes. After screening a large number of potential target genes, we further screened them using hub gene selection methods to mining novel target genes. The present study employed eight different hub gene screening methods, ultimately identifying ten highly connected hub genes (bglF_1, davD, menE_1, tilS, dapX, iolC, gshAB, cysG, trpA, and hisC), which play crucial roles in the pathogenesis of L. monocytogenes. The results of pan-genomic analysis showed that L. monocytogenes from different regions exhibit high similarity in bacterial genome evolution. The PCR results demonstrated the excellent specificity of the bglF_1 and davD genes for L. monocytogenes. Therefore, the bglF_1 and davD genes hold promise as specific molecular detection and therapeutic targets for L. monocytogenes strains from different regions.

Complete genome of the Listeria monocytogenes strain AUF, used as a live listeriosis veterinary vaccine

Listeria monocytogenes (Lm) is a highly pathogenic bacterium that can cause listeriosis, a relatively rare food-borne infectious disease that affects farm, domestic, wild animals and humans as well. The infected livestock is the frequent sources of Lm. Vaccination is one of the methods of controlling listeriosis in target farm animals to prevent Lm-associated food contamination. Here we report the complete sequence of the Lm strain AUF attenuated from a fully-virulent Lm strain by ultraviolet irradiation, successfully used since the 1960s as a live whole-cell veterinary vaccine. The de novo assembled genome consists of a circular chromosome of 2,942,932 bp length, including more than 2,800 CDSs, 17 pseudogenes, 5 antibiotic resistance genes, and 56/92 virulence genes. Two wild Lm strains, the EGD and the 10403S that is also used in cancer Immunotherapy, were the closest homologs for the Lm strain AUF. Although all three strains belonged to different sequence types (ST), namely ST12, ST85, and ST1538, they were placed in the same genetic lineage II, CC7.

Antimicrobial Resistance of Listeria monocytogenes Strains Isolated in Food and Food-Processing Environments in Italy

Listeria monocytogenes, along with various other pathogenic bacteria, may show resistance against a broad spectrum of antibiotics. Evaluating the extent of resistance in harmful microorganisms like Listeria monocytogenes holds significant importance in crafting novel therapeutic strategies to mitigate or combat the rise of infections stemming from antibiotic-resistant bacteria. The present work aims to investigate the occurrence of antimicrobial resistance among Listeria monocytogenes strains in meat products (n = 173), seafood (n = 54), dairy products (n = 19), sauces (n = 2), confectionary products (n = 1), ready-to-eat rice dishes (n = 1), and food-processing environments (n = 19). A total of 269 Listeria monocytogenes strains belonging to eight different serovars were tested against 10 antimicrobials. In the classes of antibiotics, most of the strains were resistant antibiotics belonging to the family of β-lactams (92.94%). High proportions of L. monocytogenes isolates were resistant to oxacillin (88.48%), followed by fosfomycin (85.87%) and flumenique (78.44%). The lowest level of resistance was observed against gentamycin (1.49%). A total of 235 strains (n = 87.36%) showed a profile of multidrug resistance. In conclusion, a high occurrence of resistant and multidrug-resistant strains of Listeria monocytogenes was observed among the examined serotypes isolated from different food sources. This understanding enables the adoption of suitable measures to avert contamination and the spread of resistant bacteria via food.

Amoxicillin and Ceftriaxone: A Synergistic Association Against Listeria monocytogenes.

Among 15 strains of Listeria monocytogenes tested, a synergy between amoxicillin and ceftriaxone was observed in 14 (93%) according to minimal inhibitory concentration strips and 12 (80%) per the checkerboard methods, as well as for 2 of the 3 strains tested by the time-killing curve. This association may be an alternative treatment for listeriosis in the future.

An Innovative Approach to Various Industrial Applications: The Fingered Citron

The fingered citron (Citrus medica L. var. sarcodactylis), which originates from India, has spread to different parts of the world over time. In opposition to the increasing resistance to traditional antimicrobial agents, the application of alternative treatments developed using herbs has recently gained interest. The aim of this study is to investigate alternative applications of the fingered citron in the cosmetics and pharmaceutical industries. For this purpose, the antimicrobial activity of fingered citron leaf water extract (FCLWE) against test microorganisms was evaluated using a disk diffusion assay. Minimum inhibitory concentration (MIC) and minimum cidal concentrations (bactericidal - MBC or fungicidal - MFC) of the extract were also determined. For FCLWE, among the pathogenic test microorganisms, Listeria monocytogenes strain ATCC 7644 and Staphylococcus aureus strain ATCC 25923 showed the smallest and the largest inhibition zone diameters, with values of 7.06 and 11.57 mm, respectively. MIC and MBC or MFC values of FCLWE varied from 10 to 40 µg/µl. In addition, the sun protection factors (SPF) of FCLWE and a mixture of FCLWE and commercial sun creams at different concentrations were determined. The SPF value of FCLWE was found to be 25. The mixture of FCLWE and commercial sun cream at an amount of 10 ml yielded an SPF value of 12.26. Next, the biological activity of the cream formulation obtained with commercial cream, FCLWE and Limosilactobacillus fermentum MA-7 (cream-leaf water extract-probiotic - CWP) was investigated against test microorganisms using the well diffusion method. CWP exhibited inhibitory activity against L. monocytogenes ATCC 7644 (2.56 mm), Candida glabrata RSKK 04019 (2.81 mm), C. albicans ATCC 10231 (4.54 mm) and S. aureus ATCC 25923 (5.00 mm). It was observed that the cream formulation of CWP increased the diameters of the inhibition zone by creating a synergistic effect against all pathogenic test microorganisms. FCLWE may potentially be used as an alternative natural additive to chemical preservatives in the cosmetics and pharmaceutical industries.

Antimicrobial and antioxidant competence of sustainable grumixama leaves extracts in nanoemulsion system

The spontaneous emulsification method was used to produce nanoemulsions loaded with grumixama leaves extracts (GLE) to protect and improve its functionality as a natural additive in food. Nanoemulsions were characterized for physicochemical stability, morphology, thermal analyses, antioxidant capacity, and antimicrobial activity. The formulations showed encapsulation efficiency (EE%) >89%, sizes between 182 and 290 nm, low polydispersity, and zeta potential near −30 mV. The formulations were kinetically stable since these parameters remained constant for up to 180 days at 4°C. The nanoemulsion with 125 mg GLE exhibited better droplet structure, which favored greater phenolic compounds protection and thermal resistance. The antioxidant capacity of all formulations remained stable over 30 days. The nanoemulsions acted as a bactericidal agent (MBC/MIC ratio ≤ 4) against Staphylococcus aureus, Bacillus cereus, and Listeria monocytogenes strains. However, GLE-loaded nanoemulsions offer a sustainable and functional alternative for use as a natural additive to meet trends such as a clean label.

Profile of pathogenic bacteria isolated from cow's milk in N'Djamena: associated risk factors and antibiotic resistance

Raw milk and its derivatives are foodstuffs vulnerable to contamination by microorganisms including pathogenic bacteria and failure to comply with hygiene rules. The objective of this study was to determine the profile of pathogenic bacteria isolated from cow's milk and to evaluate the effectiveness of antibiotics commonly used in veterinary and human medicine against these bacteria in Chad. This was a prospective and analytical study based on bacteriological examination including 180 milk samples collected in 10 districts of N'Djamena. The isolation, identification and testing of sensitivity of isolated bacteria to antibiotics were carried out under standard food bacteriology conditions. Among 180 milk samples which were screened by bacteriological examination, 71 (34.44%) cases were positive. The bacterial strains isolated were: Staphylococcus aureus (38.03%), Streptococcus agalactiae (18.31%), Staphylococcus hyicus (11.27%), Streptococcus uberis (7.04%), Escherichia coliO157H7 (7.04%), Streptococcus pyogenes (5.63%), Aeromonas hydrophila (5.63%), Listeria monocytogenes (4.22%) and Mycobacterium tuberculosis (2.81%). The risk factors most frequently associated with milk contamination were hand milking (100%) followed by unsanitary environment (65%), 35% of milks were sold in reused bottles and 58% of vendors and producers were uneducated. The antibiogram of the 69 isolated bacterial agents showed reduced sensitivities to beta-lactams and aminoglycosides, and varied resistance to cyclins and fluoroquinolones. Streptomycin remains an aminoglycoside most sensitive to all strains of pathogenic bacteria with an average level of 95.7%. Staphylococci (Staphylococcus aureus and Staphylococcus hyicus) developed an average resistance of 80.15% to methycillin, 80.1% to vancomycin and all bacteria showed an average resistance of 85% to metronidazole. Streptococci strains (Streptococcus agalactiae, Streptococcus uberis and Streptococcus pyogenes) were very sensitive (76.3%) to vancomycin. The isolated Listeria monocytogenes strains were 100%sensitive to aminoglycosides and beta-lactams. The two-strains of Mycobacterium tuberculosis detected by GeneXpert had a profile of 50%sensitivity and 50%resistance to rifampicin. This study not only made it possible to know the high rate and frequency of pathogenic bacteria in cow's milk as well as the associated risk factors, but also showed a reduction in sensitivity of bacteria to aminopenicillins and aminoglycosides, a strong resistance of Staphylococcus aureus to methicillin and vancomycin and a high sensitivity of streptococci to vancomycin.

The combined effect of chitosan and High Hydrostatic Pressure on Listeria monocytogenes and Escherichia coli

This study explores the combined effect of different High Hydrostatic Pressures (HHP; 200–300 MPa) with various chitosan concentrations (up to 0.2%) on five Listeria monocytogenes strains and one of Escherichia coli, at temperatures 20 & 35 °C. Cells were resuspended in ACES buffer 1 h prior to HHP. A synergistic effect of chitosan and HHP was reported for first time in the above bacterial species tested. Synergistic effect up to 1 log reduction was observed at 300 MPa and chitosan at 20 °C against L.monocytogenes LO28 with FBR13 being the most sensitive strain at 250 MPa and 0.1% chitosan. Higher combined effect was found at 35 °C compared to 20 °C at 200 MPa highlighting for first time the significant role of temperature in the above synergistic action. Pressure and temperature had a greater impact on inactivation and synergism than chitosan concentrations. Synergistic effect (1 log reduction) was also observed in E. coli K12 at 0.1% chitosan and 200 MPa. Industrial relevanceThis study presents the significance of combining HHP with natural antimicrobials to control L. monocytogenes and E. coli. Even though the technology is used for 3 decades in the food industry, its cost is still relatively high. Therefore, it is important to investigate novel ways to reduce the pressure intensity resulting in reduced costs, lower energy consumption and a broader product portfolio. This research demonstrates for first time the synergistic action of chitosan and HHP on L. monocytogenes and E. coli and the significant role of temperature that could contribute in the enhancement of the antimicrobial effect and optimization of the processing conditions. This aligns also with the growing demand for more sustainable and natural systems regarding the food production.

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.

Phenotypic microarray characterization of hemolytic and non-hemolytic strains of Listeria monocytogenes

Limited information is available on the phenotypic characteristics of Listeriamonocytogenes that may affect its virulence of L.monocytogenes. The study focused on comparing the differences between two strains of L. monocytogenes, one hemolytic (LLO+) and one non-hemolytic (tLLO). Using Phenotype Microarray (PM) technology, carbon, nitrogen, and phosphorus-sulfur source utilization by the strains was performed and the KEGG pathway involvement in substrate utilization was analyzed. Of the 285 substrates screened, the results suggested that d-gluconic acid and l-serine may play a role in L. monocytogenes hemolytic activity towards LLO production by generating pyruvate as an intermediate and amino acid biosynthesis, which may play an important role in virulence protein translation. d-gluconic acid and l-serine showed no effect on the tLLO strain in PM analysis and validation tests. Notably, the scope of this study was limited to these two strains of L. monocytogenes. While these findings provide valuable insights into the metabolic differences between hemolytic and non-hemolytic strains, further research is necessary to expand this understanding to a broader range of strains and explore additional factors that may influence LLO functionality.

Differential mechanism between Listeria monocytogenes strains with different virulence contaminating ready-to-eat sausages during the simulated gastrointestinal tract

Listeria monocytogenes exhibits varying levels of pathogenicity when entering the host through contaminated food. However, little is known regarding the stress response and environmental tolerance mechanism of different virulence strains to host gastrointestinal (GI) stimuli. This study analyzed the differences in the survival and genes of stress responses among two strains of L. monocytogenes 10403S (serotype 1/2a, highly virulent strain) and M7 (serotype 4a, low-virulence strain) during simulated gastrointestinal digestion. The results indicated that L. monocytogenes 10403S showed greater acid and bile salt tolerance than L. monocytogenes M7, with higher survival rates and less cell deformation and cell membrane permeability during the in vitro digestion. KEGG analysis of the transcriptomes indicated that L. monocytogenes 10403S displayed significant activity in amino acid metabolism, such as glutamate and arginine, associated with acid tolerance. Additionally, L. monocytogenes 10403S demonstrated a higher efficacy in promoting activities that preserve bacterial cell membrane integrity and facilitate flagellar protein synthesis. These findings will contribute valuable practical insights into the tolerance distinctions among different virulence strains of L. monocytogenes in the GI environment.