Decontamination of Minimally-Processed Fresh Lettuce Using Reuterin Produced by Lactobacillus reuteri

High pressure processing plus technologies: Enhancing the inactivation of vegetative microorganisms

High pressure processing (HPP) is a non-thermal technology that can ensure microbial safety without compromising food quality. However, the presence of pressure-resistant sub-populations, the revival of sub-lethally injured (SLI) cells, and the resuscitation of viable but non-culturable (VBNC) cells pose challenges for its further development. The combination of HPP with other methods such as moderate temperatures, low pH, and natural antimicrobials (e.g., bacteriocins, lactate, reuterin, endolysin, lactoferrin, lactoperoxidase system, chitosan, essential oils) or other non-thermal processes (e.g., CO2, UV-TiO2 photocatalysis, ultrasound, pulsed electric fields, ultrafiltration) offers feasible alternatives to enhance microbial inactivation, termed as "HPP plus" technologies. These combinations can effectively eliminate pressure-resistant sub-populations, reduce SLI or VBNC cell populations, and inhibit their revival or resuscitation. This review provides an updated overview of microbial inactivation by "HPP plus" technologies and elucidates possible inactivation mechanisms.

Glycerol and reuterin-producing Limosilactobacillus reuteri enhance butyrate production and inhibit Enterobacteriaceae in broiler chicken cecal microbiota PolyFermS model

BACKGROUND

Administering probiotic strains of Limosilactobacillus reuteri to poultry has been shown to improve poultry performance and health. Some strains of L. reuteri taxa can produce reuterin, a broad-spectrum antimicrobial compound from glycerol conversion, with high inhibitory activity against enterobacteria. However, little is known about the metabolism of glycerol in the complex chicken cecal microbiota nor the effect of glycerol, either alone or combined with L. reuteri on the microbiota. In this study, we investigated the effect of L. reuteri PTA5_F13, a high-reuterin-producing chicken strain and glycerol, alone or combined, on broiler chicken cecal microbiota composition and activity using the continuous PolyFermS model recently developed to mimic chicken cecal fermentation.

METHODS

Three independent PolyFermS chicken cecal microbiota models were inoculated with immobilized cecal microbiota from different animals and operated continuously. The effects of two additional levels of glycerol (50 and 100 mM) with or without daily supplementation of chicken-derived L. reuteri PTA5_F13 (107 CFU/mL final concentration) were tested in parallel second-stage reactors continuously inoculated with the same microbiota. We analyzed the complex chicken gut microbiota structure and dynamics upon treatment using 16S rRNA metabarcoding and qPCR. Microbiota metabolites, short-chain and branched-chain fatty acids, and glycerol and reuterin products were analyzed by HPLC in effluent samples from stabilized reactors.

RESULTS

Supplementation with 100 mM glycerol alone and combined with L. reuteri PTA5_F13 resulted in a reproducible increase in butyrate production in the three modelled microbiota (increases of 18 to 25%). Glycerol alone resulted also in a reduction of Enterobacteriaceae in two of the three microbiota, but no effect was detected for L. reuteri alone. When both treatments were combined, all microbiota quantitatively inhibited Enterobacteriaceae, including in the last model that had very high initial concentrations of Enterobacteriaceae. Furthermore, a significant 1,3-PDO accumulation was measured in the effluent of the combined treatment, confirming the conversion of glycerol via the reuterin pathway. Glycerol supplementation, independent of L. reuteri addition, did not affect the microbial community diversity.

CONCLUSIONS

Glycerol induced a stable and reproducible butyrogenic activity for all tested microbiota and induced an inhibitory effect against Enterobacteriaceae that was strengthened when reuterin-producing L. reuteri was spiked daily. Our in vitro study suggests that co-application of L. reuteri PTA5_F13 and glycerol could be a useful approach to promote chicken gut health by enhancing metabolism and protection against Enterobacteriaceae.

Antimicrobial Compounds in Food Packaging

This review presents current knowledge on antimicrobial agents that are already used in the food packaging industry. At the beginning, innovative ways of food packaging were discussed, including how smart packaging differs from active packaging, and what functions they perform. Next, the focus was on one of the groups of bioactive components that are used in these packaging, namely antimicrobial agents. Among the antimicrobial agents, we selected those that have already been used in packaging and that promise to be used elsewhere, e.g., in the production of antimicrobial biomaterials. Main groups of antimicrobial agents (i.e., metals and metal oxides, organic acids, antimicrobial peptides and bacteriocins, antimicrobial agents of plant origin, enzymes, lactoferrin, chitosan, allyl isothiocyanate, the reuterin system and bacteriophages) that are incorporated or combined with various types of packaging materials to extend the shelf life of food are described. The further development of perspectives and setting of new research directions were also presented.

Effectiveness of a Phage Cocktail as a Potential Biocontrol Agent against Saprophytic Bacteria in Ready-To-Eat Plant-Based Food

This study aimed to evaluate the effectiveness of the phage cocktail to improve the microbiological quality of five different mixed-leaf salads: rucola, mixed-leaf salad with carrot, mixed-leaf salad with beetroot, washed and unwashed spinach, during storage in refrigerated conditions. Enterobacterales rods constituted a significant group of bacteria in the tested products. Selected bacteria were tested for antibiotic resistance profiles and then used to search for specific bacteriophages. Forty-three phages targeting bacteria dominant in mixed-leaf salads were isolated from sewage. Their titer was determined, and lytic activity was assessed using the Bioscreen C Pro automated growth analyzer. Two methods of phage cocktail application including spraying, and an absorption pad were effective for rucola, mixed leaf salad with carrot, and mixed leaf salad with beetroot. The maximum reduction level after 48 h of incubation reached 99.9% compared to the control sample. In washed and unwashed spinach, attempts to reduce the number of microorganisms did not bring the desired effect. The decrease in bacteria count in the lettuce mixes depended on the composition of the autochthonous saprophytic bacteria species. Both phage cocktail application methods effectively improved the microbiological quality of minimally processed products. Whole-spectral phage cocktail application may constitute an alternative food microbiological quality improvement method without affecting food properties.

Application of the Reuterin System as Food Preservative or Health-Promoting Agent: A Critical Review

The reuterin system is a complex multi-component antimicrobial system produced by Limosilactobacillus reuteri by metabolizing glycerol. The system mainly includes 3-hydroxypropionaldehyde (3-HPA, reuterin), 3-HPA dimer, 3-HPA hydrate, acrolein and 3-hydroxypropionic acid, and has great potential to be applied in the food and medical industries due to its functional versatility. It has been reported that the reuterin system possesses regulation of intestinal flora and anti-infection, anti-inflammatory and anti-cancer activities. Typically, the reuterin system exerts strong broad-spectrum antimicrobial properties. However, the antimicrobial mechanism of the reuterin system remains unclear, and its toxicity is still controversial. This paper presents an updated review on the biosynthesis, composition, biological production, antimicrobial mechanisms, stability, toxicity and potential applications of the reuterin system. Challenges and opportunities of the use of the reuterin system as a food preservative or health-promoting agent are also discussed. The present work will allow researchers to accelerate their studies toward solving critical challenges obstructing industrial applications of the reuterin system.

Pathogenic and Commensal Gut Bacteria Harboring Glycerol/Diol Dehydratase Metabolize Glycerol and Produce DNA-Reactive Acrolein

Bacteria harboring glycerol/diol dehydratase (GDH) encoded by the genes pduCDE metabolize glycerol and release acrolein during growth. Acrolein has antimicrobial activity, and exposure of human cells to acrolein gives rise to toxic and mutagenic responses. These biological responses are related to acrolein's high reactivity as a chemical electrophile that can covalently bind to cellular nucleophiles including DNA and proteins. Various food microbes and gut commensals transform glycerol to acrolein, but there is no direct evidence available for bacterial glycerol metabolism giving rise to DNA adducts. Moreover, it is unknown whether pathogens, such as Salmonella Typhymurium, catalyze this transformation. We assessed, therefore, acrolein formation by four GDH-competent strains of S. Typhymurium grown under either aerobic or anaerobic conditions in the presence of 50 mM glycerol. On the basis of analytical derivatization with a heterocyclic amine, all wild-type strains were observed to produce acrolein, but to different extents, and acrolein production was not detected in fermentations of a pduC-deficient mutant strain. Furthermore, we found that, in the presence of calf thymus DNA, acrolein-DNA adducts were formed as a result of bacterial glycerol metabolism by two strains of Limosilactobacillus reuteri, but not a pduCDE mutant strain. The quantification of the resulting adducts with increasing levels of glycerol up to 600 mM led to the production of up to 1.5 mM acrolein and 3600 acrolein-DNA adducts per 108 nucleosides in a model system. These results suggest that GDH-competent food microbes, gut commensals, and pathogens alike have the capacity to produce acrolein from glycerol. Further, the acrolein production can lead to DNA adduct formation, but requires high glycerol concentrations that are not available in the human gut.

Impact of microcin J25 on the porcine microbiome in a continuous culture model

The increased prevalence of Salmonella spp. resistance in swine spurs the search for alternatives to antibiotics. Microcin J25 (MccJ25), a bacteriocin produced by Escherichia coli, is a potent inhibitor of several pathogenic bacteria including Salmonella enterica. In this study, we aimed to evaluate in vitro the impact of MccJ25 on the composition and the metabolic activity of the swine colonic microbiota. The PolyFermS in vitro continuous fermentation model was used here with modified Macfarlane medium to simulate the porcine proximal colon. During 35 days of fermentation, a first-stage reactor containing immobilized swine fecal microbiota fed two second-stage control and test reactors operated in parallel and used to test the effects of MccJ25 on the composition and the metabolic activity of the microbiota. Reuterin, a broad-spectrum antimicrobial compound produced by Limosilactobacillus reuteri, a lactic acid bacterium naturally present in the gastro-intestinal tract of human and animals, and the antibiotic rifampicin were tested for comparison. Sequencing of 16S rRNA was performed using the Illumina MiSeq technology to evaluate microbial diversity, and liquid chromatography coupled to mass spectrometry (LC-MS) followed by multivariate analysis was used to assess the bacteriocin/antibiotic degradation products and to monitor changes in the swine colonic microbiota metabolome. The results show that MccJ25 or reuterin treatments only induce subtle changes of both the microbial diversity and the metabolome of the swine colon microbiota, while rifampicin induces significant modification in amino acid levels. Although these findings need being validated in vivo, this study affords a first proof of concept for considering MccJ25 as a possible alternative to antibiotics for veterinary and farming applications, taking into account its pathogen-selective and potent inhibitory activity.

Fecal miR-142a-3p from dextran sulfate sodium-challenge recovered mice prevents colitis by promoting the growth of Lactobacillus reuteri

Feces are enriched with microRNAs (miRNAs) that shape the gut microbiota. These miRNAs are differentially expressed in the feces of healthy and diseased subjects. However, whether fecal miRNAs in subjects with inflammatory bowel diseases are involved in regulating microbiota composition and whether they have any beneficial effects remains unknown. Here, we studied the fecal microbiome composition and miRNA abundance in mice with dextran sulfate sodium (DSS)-induced colitis and mice at the recovery phase to explore different miRNAs expressed, their relations with microbial abundance, and their effects on colitis. We found that miR-142a-3p expression was significantly increased in the feces of mice recovered from colitis and that it could alleviate disease symptoms in mice treated with DSS in a microbiome-dependent manner. Specifically, miR-142a-3p promoted the growth of Lactobacillus reuteri, which had a high abundance in the feces of mice recovered from colitis, by regulating transcripts of polA and locus tag LREU_RS03575. Moreover, L. reuteri, as well as its metabolite reuterin, could alleviate DSS-induced disease symptoms. These results highlight the role of fecal miR-142a-3p in the prevention of colitis. We propose that the feces of subjects who have recovered from diseases might be enriched with miRNAs with preventive effects against those diseases.

Susceptibility to Nisin, Bactofencin, Pediocin and Reuterin of Multidrug Resistant Staphylococcus aureus, Streptococcus dysgalactiae and Streptococcus uberis Causing Bovine Mastitis

Antibiotics are the most effective strategy to prevent and treat intramammary infections. However, their misuse has led to the dissemination of multidrug resistant bacteria (MDR) for both animals and humans. Efforts to develop new alternative strategies to control bacterial infections related to MDR are continuously on the rise. The objective of this study was to evaluate the antimicrobial activity of different bacteriocins and reuterin against MDR Staphylococcus and Streptococcus clinical isolates involved in bovine mastitis. A bacterial collection including S. aureus (n = 19), S. dysgalactiae (n = 17) and S. uberis (n = 19) was assembled for this study. Antibiotic resistance profiles were determined by the disk diffusion method. In addition, sensitivity to bacteriocins and reuterin was evaluated by determining minimum inhibitory concentrations (MIC). A total of 21 strains (37.5%) were MDR. MICs ranged from ≤1.0 μg/mL to ≥100 μg/mL for nisin and 2.0 to ≥250 μg/mL for bactofencin. Reuterin was active against all tested bacteria, and MICs vary between 70 and 560 μg/mL. Interestingly, 20 MDR strains were inhibited by bactofencin at a concentration of ≤250 μg/mL, while 14 were inhibited by nisin at an MIC of ≤100 μg/mL. Pediocin did not show an inhibitory effect.

Production, Storage Stability, and Susceptibility Testing of Reuterin and Its Impact on the Murine Fecal Microbiome and Volatile Organic Compound Profile

Background: Probiotics are generally considered as safe, but infections may rarely occur in vulnerable patients. Alternatives to live microorganisms to manage dysbiosis may be of interest in these patients. Reuterin is a complex component system exhibiting broad spectrum antimicrobial activity and a possible candidate substance in these cases.

Methods: Reuterin supernatant was cultured from Lentilactobacillus diolivorans in a bioreactor in a two-step process. Storage stability at −20°C and effect of repeated freeze-thaw cycles were assessed by high performance liquid chromatography (HPLC). Antimicrobial activity was tested against Clostridium difficile, Listeria monocytogenes, Escherichia coli, Enterococcus faecium, Staphylococcus (S.) aureus, Staphylococcus epidermidis, Streptococcus (S.) agalactiae, Propionibacterium acnes, and Pseudomonas aeruginosae. Male BALBc mice were gavage fed with reuterin supernatant (n = 10) or culture medium (n = 10). Fecal volatile organic compounds (VOC) were assessed by gas chromatography mass spectroscopy; the microbiome was examined by 16S rRNA gene sequencing.

Results: The supernatant contained 13.4 g/L reuterin (3-hydroxypropionaldehyde; 3-HPA). 3-HPA content remained stable at −20°C for 35 days followed by a slow decrease of its concentration. Repeated freezing/thawing caused a slow 3-HPA decrease. Antimicrobial activity was encountered against S. aureus, S. epidermidis, and S. agalactiae. Microbiome analysis showed no differences in alpha and beta diversity markers. Linear discriminant effect size (LEfSe) analysis identified Lachnospiraceae_bacterium_COE1 and Ruminoclostridium_5_uncultured_Clostridiales_ bacterium (in the reuterin medium group) and Desulfovibrio_uncultured_ bacterium, Candidatus Arthromitus, Ruminococcae_NK4A214_group, and Eubacterium_xylanophilum_group (in the reuterin group) as markers for group differentiation. VOC analysis showed a significant decrease of heptane and increase of 3-methylbutanal in the reuterin group.

Conclusion: The supernatant produced in this study contained acceptable amounts of 3-HPA remaining stable for 35 days at −20°C and exhibiting an antimicrobial effect against S. aureus, S. agalactiae, and S. epidermidis. Under in vivo conditions, the reuterin supernatant caused alterations of the fecal microbiome. In the fecal, VOC analysis decreased heptane and increased 3-methylbutanal were encountered. These findings suggest the high potential of the reuterin system to influence the intestinal microbiome in health and disease, which needs to be examined in detail in future projects.

In vitro investigation of gastrointestinal stability and toxicity of 3-hyrdoxypropionaldehyde (reuterin) produced by Lactobacillus reuteri

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Reuterin (3-hyrdoxypropionaldehyde (3-HPA)) is a highly potent metabolite of Lactobacillus reuteri.

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Reuterin is highly stable in gastrointestinal condition.

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Human colorectal adenocarcinoma cells’ viability and membrane integrity remained unaltered by reuterin.

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No significant hemolytic activity was detected.

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Reuterin is a promising therapeutic and/or food preservative.

Reuterin (3-hyrdoxypropionaldehyde (3-HPA)) is a highly potent metabolite of L. reuteri, which has applications in food, health, and veterinary sectors. Similar to other natural antimicrobial compounds, the approval of reuterin as a bio-preservative or therapeutic agent by regulatory agencies relies on sufficient data on its cytotoxicity and behavior in the gastrointestinal environment. Although the antimicrobial activity of reuterin has been broadly studied, its safety and toxicity are yet to be explored in detail. In this study, the stability and activity of reuterin were investigated in the gastrointestinal tract using in vitro models simulating gastrointestinal conditions. In addition, hemolytic activity and in vitro cytotoxicity of reuterin were evaluated by neutral red assay and lactate dehydrogenase (LDH) colorimetric assay using the same cell line. Activity of reuterin was observed to be stable during gastrointestinal transit. Viability and membrane integrity of cells remained unaltered by reuterin up to 1080 mM concentration. Furthermore, no hemolysis was observed in blood cells exposed to 270 mM reuterin. This study provides unique and highly relevant in vitro data regarding gastrointestinal behavior and toxicity of reuterin. In conclusion, the current study indicates that within a certain concentration range, reuterin can be safely used in bio-preservation and therapeutics applications. However, further in vivo studies are required to confirm these findings.

High pressure processing combined with selected hurdles: Enhancement in the inactivation of vegetative microorganisms

High pressure processing (HPP) as a nonthermal processing (NTP) technology can ensure microbial safety to some extent without compromising food quality. However, for vegetative microorganisms, the existence of pressure-resistant subpopulations, the revival of sublethal injury (SLI) state cells, and the resuscitation of viable but nonculturable (VBNC) state cells may constitute potential food safety risks and pose challenges for the further development of HPP application. HPP combined with selected hurdles, such as moderately elevated or low temperature, low pH, natural antimicrobials (bacteriocin, lactate, reuterin, endolysin, lactoferrin, lactoperoxidase system, chitosan, essential oils), or other NTP (CO₂ , UV-TiO₂ photocatalysis, ultrasound, pulsed electric field, ultrafiltration), have been highlighted as feasible alternatives to enhance microbial inactivation (synergistic or additive effect). These combinations can effectively eliminate the pressure-resistant subpopulation, reduce the population of SLI or VBNC state cells and inhibit their revival or resuscitation. This review provides an updated overview of the microbial inactivation by the combination of HPP and selected hurdles and restructures the possible inactivation mechanisms.

Antagonistic effects of Lactobacillus reuteri against Escherichia coli O157:H7 in white-brined cheese under different storage conditions

This study aimed to investigate the survival of the foodborne pathogen Escherichia coli O157:H7 in white-brined cheeses as influenced by the presence of Lactobacillus reuteri. The white cheeses were made from pasteurized bovine milk inoculated with E. coli O157:H7 (cocktail of 3 strains) to achieve ∼5 log₁₀ cfu/g with absence or presence of Lb. reuteri (∼6 log₁₀ cfu/g). Cheese samples were brined in 10% or 15% NaCl solution and stored at 10°C and 25°C for 28 d. The white-brined cheeses were assessed for salt content, pH, water activity (A_w), and numbers of E. coli O157:H7, Lb. reuteri, nonstarter lactic acid bacteria (NSLAB), yeasts, and molds. Results showed that E. coli O157:H7 survived in cheese stored in both brine solutions at 10°C and 25°C regardless of the presence of Lb. reuteri. A substantial reduction was observed in cheese stored in 10% NaCl brine at 25°C, followed by cheese stored in 15% NaCl brine at 10°C by 2.64 and 2.16 log₁₀ cfu/g, respectively, in the presence of Lb. reuteri and by 1.02 and 1.87 log₁₀ cfu/g, respectively, in the absence of Lb. reuteri under the same conditions. The pathogen in brine solutions survived but at a lower rate. Furthermore, the growth of Lb. reuteri and NSLAB were enhanced or slightly decreased in cheese and brine by 28 d, respectively. The salt concentrations of cheese ranged from 4 to 6% and 5 to 7% (wt/wt), during 28-d ripening in 10 and 15% brine, respectively. Values of pH and A_w slightly increased at d 1 after exposure to brine and reached 4.69 to 6.08 and 0.91 to 0.95, respectively, in all treatments. Therefore, the addition of Lb. reuteri can be used as a biopreservation method to inhibit the survival of E. coli O157:H7 in white-brined cheese when combined with the appropriate temperature, NaCl level, and storage time.

Occurrence, diversity and temperature-dependent growth kinetics of Aeromonas spp. in lettuce

Bagged, pre-cut and prewashed lettuce products are marketed as ready to eat. This concept poses a food safety concern, due to lack of efficient hurdles to eliminate possible microbial contaminants from the fresh produce and/or the processing itself. Aeromonas spp. are potential foodborne pathogens that are frequently isolated from lettuce. High counts of, e.g., A. hydrophila have been found in retail ready-to-eat (RTE) vegetable salads. The aim of this study was to assess the general microbiological quality, the occurrence and diversity of potential human pathogenic mesophilic Aeromonas spp. of retail RTE lettuce products. Additionally, temperature-dependent growth kinetic parameters of Aerobic Plate Counts (APC) and Aeromonas spp. in one selected RTE lettuce product, rocket lettuce, were quantified by performing storage experiments at 4 °C, 8 °C and 12 °C. The Aeromonas isolates were further characterized regarding pathogenic traits and phylogenetic relationship. The overall hygienic quality of the lettuce products was unsatisfactory, as 60% of the products had an APC level higher than 7.0 log CFU/g. Presumptive Aeromonas spp. were detected in 52% of the samples, levels ranging from approximately 2.0-6.0 log CFU/g. Significantly lower counts of APC and Aeromonas spp. were found in uncut and unwashed products. Presumptive Aeromonas spp. were able to proliferate in rocket lettuce stored at 4 °C (μmax = 0.39 ± 0.06/d and μmax = 0.43 ± 0.05/d for lettuce from producers A and B, respectively), and μmax was approximately 2× higher at 8 °C and 3× higher at 12 °C. Eighty-four percent of the collected isolates were identified as A. media, based on partial gyrB sequencing. Additionally A. salmonicida and A. bestiarum were detected. The pathogenic potential in this material was high, most of the isolates harbored at least one of the toxin genes, act, ast, alt.

Plasma-Functionalized Water: from Bench to Prototype for Fresh-Cut Lettuce

Fresh-cut produce like lettuce may contain a very high microbial load, including human pathogens. Therefore, the need for antimicrobial agents at post-harvest stages to mitigate microbial cross-contamination and growth is evident. Sanitation based on non-thermal plasma (NTP) reveals innovative food processing possibilities by application at different points along the food chain, for production, modification, and preservation, as well as in packaging of plant- and animal-based food. The aim of the present study was to evaluate the applicability of plasma-treated water (PTW) as antimicrobial process water additives for washing in fresh-cut lettuce processing. Antibacterial activities of PTW the natural occurring microflora of lettuce were examined. Different process variants of PTW application inside the washing process were investigated. Fresh-cut lettuce were investigated regarding microbiological safety and food quality. Samples were analyzed for antimicrobial and metabolic activity as well as metabolic vitality to prove food safety. The investigations for food quality included color and texture analyses and nitrate concentration detection in fresh tissue as well as microscopic measurements by scanning electron microscopy (SEM) and atomic force microscopy (AFM) for tissue surface structure and transmission electron microscopy (TEM) for cell organelle investigations. The application of PTW allowed up to 5 log10 cycle reduction, depending on the process variant and scale (lab and pilot scale). The increase of antimicrobial activity was accompanied by a reduction of metabolic activity, but not consequently by a decrease in metabolic vitality. Food quality was not affected by the use of PTW in the washing process of the fresh-cut lettuce. The promising results in color and texture were supported by the results of the microscopic assays. These promising results may lead to an industrial application of PTW as process water additive in fresh-cut produce processing to reduce the microbial load on the food surface and in addition in the process water or on food processing surfaces.

Lactic Acid Bacteria as Antibacterial Agents to Extend the Shelf Life of Fresh and Minimally Processed Fruits and Vegetables: Quality and Safety Aspects

Eating fresh fruits and vegetables is, undoubtedly, a healthy habit that should be adopted by everyone (particularly due to the nutrients and functional properties of fruits and vegetables). However, at the same time, due to their production in the external environment, there is an increased risk of their being infected with various pathogenic microorganisms, some of which cause serious foodborne illnesses. In order to preserve and distribute safe, raw, and minimally processed fruits and vegetables, many strategies have been proposed, including bioprotection. The use of lactic acid bacteria in raw and minimally processed fruits and vegetables helps to better maintain their quality by extending their shelf life, causing a significant reduction and inhibition of the action of important foodborne pathogens. The antibacterial effect of lactic acid bacteria is attributed to its ability to produce antimicrobial compounds, including bacteriocins, with strong competitive action against many microorganisms. The use of bacteriocins, both separately and in combination with edible coatings, is considered a very promising approach for microbiological quality, and safety for postharvest storage of raw and minimally processed fruits and vegetables. Therefore, the purpose of the review is to discuss the biopreservation of fresh fruits and vegetables through the use of lactic acid bacteria as a green and safe technique.

Isolation and Comparative Genomic Analysis of Reuterin-Producing Lactobacillus reuteri From the Chicken Gastrointestinal Tract

Lactobacillus reuteri is a natural inhabitant of selected animal and human gastrointestinal tract (GIT). Certain strains have the capacity to transform glycerol to 3-hydroxypropionaldehyde (3-HPA), further excreted to form reuterin, a potent antimicrobial system. Reuterin-producing strains may be applied as a natural antimicrobial in feed to prevent pathogen colonization of animals, such as in chicken, and replace added antimicrobials. To date, only seven L. reuteri strains isolated from chicken have been characterized which limits phylogenetic studies and host-microbes interactions characterization. This study aimed to isolate L. reuteri strains from chicken GIT and to characterize their reuterin production and antimicrobial resistance (AMR) profiles using phenotypic and genetic methods. Seventy strains were isolated from faces, crops and ceca of six chicken from poultry farms and samples from slaughterhouse. Twenty-five strains were selected for further characterization. Draft genomes were generated for the new 25 isolates and integrated into a phylogenetic tree of 40 strains from different hosts. Phylogenetic analysis based on gene content as well as on core genomes showed grouping of the selected 25 L. reuteri chicken isolates within the poultry/human lineage VI. Strains harboring pdu-cob-cbi-hem genes (23/25) produced between 156 mM ± 11 and 330 mM ± 14 3-HPA, from 600 mM of glycerol, in the conditions of the test. All 25 chicken strains were sensitive to cefotaxime (MIC between 0.016 and 1 μg/mL) and penicillin (MIC between 0.02 and 4 μg/mL). Akin to the reference strains DSM20016 and SD2112, the novel isolates were resistant to penicillin, possibly associated with identified point mutations in ponA, pbpX, pbpF and pbpB. All strains resistant to erythromycin (4/27) carried the ermB gene, and it was only present in chicken strains. All strains resistant to tetracycline (5/27) harbored tetW gene. This study confirms the evolutionary history of poultry/human lineage VI and identifies pdu-cob-cbi-hem as a frequent trait but not always present in this lineage. L. reuteri chicken strains producing high 3-HPA yield may have potential to prevent enteropathogen colonization of chicken.

Reuterin Demonstrates Potent Antimicrobial Activity Against a Broad Panel of Human and Poultry Meat Campylobacter spp. Isolates

Reuterin is a broad-spectrum antimicrobial system produced by specific strains of Lactobacillus reuteri during anaerobic metabolism of glycerol. Acrolein is the main component responsible for its antimicrobial activity. Here, the sensitivity of Campylobacter jejuni (n = 51) and Campylobacter coli (n = 20) isolates from chicken meat and human stool samples to reuterin was investigated. The minimum inhibitory concentration (MIC) of C. jejuni and C. coli strains was measured between 1.5 and 3.0 µM of acrolein, below the MIC of the sensitive indicator strain Escherichia coli K12 (16.5 µM acrolein). The interaction of C. jejuni N16-1419 and the reuterin-producing L. reuteri PTA5_F13 was studied during 24 h co-cultures with or without glycerol. A high C. jejuni growth was observed in cultures without glycerol. In contrast, C. jejuni growth decreased from 7.3 ± 0.1 log CFU/mL to below detection limit (1 log CFU/mL) during co-cultures added with 28 mM glycerol. This bactericidal effect could be attributed to in situ reuterin production. The low MIC observed and the high sensitivity towards in situ produced reuterin suggests L. reuteri combined with glycerol, as a possible intervention option to reduce Campylobacter in the food chain.

The Transformative Possibilities of the Microbiota and Mycobiota for Health, Disease, Aging, and Technological Innovation

The gut microbiota is extremely important for the health of the host across its lifespan.Recent studies have elucidated connections between the gut microbiota and neurological diseaseand disorders such as depression, anxiety, Alzheimer's disease (AD), autism, and a host of otherbrain illnesses. Dysbiosis of the normal gut flora can have negative consequences for humans,especially throughout key periods during our lifespan as the gut microbes change with age in bothphenotype and number of bacterial species. Neurologic diseases, mental disorders, and euthymicstates are influenced by alterations in the metabolites produced by gut microbial milieu. Weintroduce a new concept, namely, the mycobiota and microbiota-gut-brain neuroendocrine axis anddiscuss co-metabolism with emphasis on means to influence or correct disruptions to normal gutflora throughout the lifespan from early development to old age. These changes involveinflammation and involve the permeability of barriers, such as the intestine blood barrier, the blood⁻brain barrier, and others. The mycobiota and microbiota⁻gut⁻brain axis offer new research horizonsand represents a great potential target for new therapeutics, including approaches based aroundinflammatory disruptive process, genetically engineered drug delivery systems, diseased cellculling "kill switches", phage-like therapies, medicinal chemistry, or microbial parabiosis to namea few.