Evaluation of the metabolic response of Escherichia coli to electrolysed water by 1 H NMR spectroscopy

Recent developments of (bio)-sensors for detection of main microbiological and non-biological pollutants in plastic bottled water samples: A critical review

The importance of water in all biological processes is undeniable. Ensuring access to clean and safe drinking water is crucial for maintaining sustainable water resources. To elaborate, the consumption of water of inadequate quality can have a repercussion on human health. Furthermore, according to the instability of tap water quality, the consumption rate of bottled water is increasing every day at the global level. Although most people believe bottled water is safe, it can also be contaminated by microbiological or chemical pollution, which can increase the risk of disease. Over the last decades, several conventional analytical tools applied to analyze the contamination of bottled water. On the other hand, some limitations restrict their application in this field. Therefore, biosensors, as emerging analytical method, attract tremendous attention for detection both microbial and chemical contamination of bottled water. Biosensors enjoy several facilities including selectivity, affordability, and sensitivity. In this review, the developed biosensors for analyzing contamination of bottled water were highlighted, as along with working strategies, pros and cons of studies. Challenges and prospects were also examined.

Synergistic bactericidal mechanisms of RF energy simultaneously combined with cinnamon essential oil or epsilon-polylysine against Salmonella revealed at cellular and metabolic levels

Radio frequency (RF) heating and antimicrobials are considered to be effective methods for inactivating food pathogens. This study explored the bactericidal effects against Salmonella of RF heating combined with two kinds of natural antimicrobials possessing different hydrophobic properties and their synergistic bactericidal mechanisms. Results showed that RF heating caused sublethal damage to bacterial cells and enhanced the interaction of cells and antimicrobials, leading to synergistic bactericidal effects of the simultaneous combination of RF heating and antimicrobials. The combination of RF heating and ε-polylysine (ε-PL) further promoted cell morphological alteration, raised membrane permeability, intracellular adenosine triphosphate (ATP) leakage and intracellular reactive oxygen species (ROS) accumulation compared to individual treatment. The simultaneous combination of RF heating and cinnamon essential oil nanoemulsion (CEON) also further enhanced membrane permeability and ROS accumulation compared to individual treatment, but impacts were less than those in the combination of RF heating and ε-PL. The major synergistic bactericidal mechanism of RF heating and CEON was significantly inhibiting intracellular ATP synthesis. The untargeted metabolomics analysis revealed that the combined treatments enhanced disturbances to multiple intracellular metabolisms compared to individual treatment, thus leading to synergistic bactericidal effects against Salmonella. These results provide an in-depth understanding of the synergistic bactericidal mechanisms of the combination of RF heating and natural antimicrobials from cellular and metabolic levels.

Metabolomics of natural samples: A tutorial review on the latest technologies

Metabolomics is the study of metabolites present in a living system. It is a rapidly growing field aimed at discovering novel compounds, studying biological processes, diagnosing diseases, and ensuring the quality of food products. Recently, the analysis of natural samples has become important to explore novel bioactive compounds and to study how environment and genetics affect living systems. Various metabolomics techniques, databases, and data analysis tools are available for natural sample metabolomics. However, choosing the right method can be a daunting exercise because natural samples are heterogeneous and require untargeted approaches. This tutorial review aims to compile the latest technologies to guide an early-career scientist on natural sample metabolomics. First, different extraction methods and their pros and cons are reviewed. Second, currently available metabolomics databases and data analysis tools are summarized. Next, recent research on metabolomics of milk, honey, and microbial samples is reviewed. Finally, after reviewing the latest trends in technologies, a checklist is presented to guide an early-career researcher on how to design a metabolomics project. In conclusion, this review is a comprehensive resource for a researcher planning to conduct their first metabolomics analysis. It is also useful for experienced researchers to update themselves on the latest trends in metabolomics.

Bactericidal Efficacy and Mechanisms of Non-Electrolytic Slightly Acidic Hypochlorous Water on Pseudomonas fragi and Pseudomonas fluorescens

Chilled pork is frequently contaminated with Pseudomonas fragi and Pseudomonas fluorescens. In this study, the bactericidal efficacy and mechanisms of non-electrolytic slightly acidic hypochlorous water (NE-SAHW) against two strains of these two species were evaluated. The results showed that the antibacterial efficacy of NE-SAHW was positively correlated with the concentration level of NE-SAHW and negatively correlated with the initial populations of the strains. The strains of small populations were completely inhibited when provided with each level of NE-SAHW. The killed cells of P. fragi were 0.94, 1.39, 4.02, and 5.60 log10 CFU/mL, respectively, and of P. fluorescens they were 1.21, 1.52, 4.14, and 5.74 log10 CFU/mL, respectively, when the initial populations of the strains were at high levels (about 7 log10 CFU/mL). Both strains were completely killed within 12 s with the available chlorine concentration (ACC) of 50 mg/L of NE-SAHW. Morphological changes in both cells were observed by using a Scanning Electron Microscope (SEM) and it was discovered that the cell membranes were damaged, which led to the leakage of the intracellular substances, including K+, nucleic acid, and protein. In terms of the Fourier Transform Infrared Spectroscopy (FTIR) results, NE-SAHW destroyed the structures of membrane proteins and cell structure proteins, and influenced the composition of polysaccharides. The bacteria were definitely dead after treatment by NE-SAHW compared to the control according to the results of flow cytometry. These results demonstrated the potential bactericidal property of NE-SAHW when applied to the meat and other food sterilization industries.

Pathogen inhibition and indication by gelatin nonwoven mats with incorporation of polyphenol derivatives

There is a need for non-pharmaceutical intervention methods that can prevent and indicate the risk of airborne disease spread. In this study, we developed a nonwoven mat based on the polyphenol gallic acid, which can inhibit pathogens growth and also indicate pathogen levels in the surrounding environment. Using nuclear magnetic resonance, Fourier-transform infrared spectroscopy, and high-performance liquid chromatography, we characterized this novel gelatin-based nonwoven mat and investigated the mechanism governing its ability to indicate pathogen levels. We demonstrated that the incorporation of gallic acid serves a vital role in indicating the presence of bacteria, causing the nonwoven mat to change in color from white to brown. We have proposed a plausible mechanism for this color change behavior based on a reaction of gallic acid with components excreted by bacteria, including glutamate, valine, and leucine. The concentrations of these components reflect the bacterial counts, enabling a real-time indication of pathogen levels in the surrounding air. In summary, the nonwoven mat presented herein can serve as an excellent antibacterial agent and as an indicator of nearby bacteria for fabricating personal protection equipment like filtration mask.

Metabolomics investigation of global responses of Cronobacter sakazakii against common sanitizing in infant formula processing environments

Cronobacter sakazakii, an opportunistic bacterium, has raised a serious outbreak in powdered infant formula recent years. In this work, four sanitizing strategies used during infant formula processing, including chlorine, quaternary ammonium chloride (QAC), 60 °C heating, and malic acid (MA), were utilized against C. sakazakii among planktonic, air-dried (A), and air-dried & washed (AW) state, followed by an exploration of the metabolic responses induced by these treatments via a dual-platform metabolomics analysis with the ultra-high performance liquid chromatography-mass spectrometry and nuclear magnetic resonance. In the planktonic state, MA was the most effective in inhibiting bacterial growth, followed by chlorine, QAC, and 60 °C heating. Under A state, the efficacy of heating improved considerably, compared to that in the planktonic state, and remained unaltered under AW state. Chlorine and QAC were ineffective to control bacterial growth under A state, but their efficacy rose under AW state. Furthermore, the metabolomic analysis revealed chlorine induces amino acids catabolism, membrane lysis, and depression in carbohydrate and nucleotide metabolism in both planktonic and AW states, while the initiation of antioxidation mechanism was only found under AW state. Although the metabolic change caused by QAC in the planktonic state was similar to chlorine, the accumulation of osmoprotectant and membrane phospholipids within the AW cells reflected the effort to restore intracellular homeostasis upon QAC. Heating was characterized by considerable amino acid anabolism, along with mildly perturbed carbohydrate and nucleotide metabolism for heat shock protein preparation in both states. Lastly, MA promoted amino acid-dependent acid resistance under the planktonic state, and the regulation of antioxidation and osmoprotection under AW state. The metabolomics study elucidated the intracellular perturbation induced by common sanitizing, as well as the bacterial response, which provides insights for novel sanitization development.

Effect of low temperature on the resistance of Listeria monocytogenes and Escherichia coli O157:H7 to acid electrolyzed water

Low temperature can affect the resistance of pathogenic bacteria to other external stress. The present study was envisaged to assess the tolerance of L. monocytogenes and E. coli O157:H7 to acidic electrolyzed water (AEW) under low temperature stress. AEW treatment caused a damage to cell membrane of the pathogenic bacteria, which led to protein leakage and DNA damage. Compared with the pathogenic bacteria cultured at 37 °C (pure culture), the L. monocytogenes and E. coli O157:H7 cells cultivated at low temperature presented a less damage and had a higher survival rate when exposed to AEW. Therefore, 4 °C or 10 °C grown bacteria were less susceptible to AEW than those cultured at 37 °C. And this phenomenon was verified when AEW was used to treat the pathogenic bacteria inoculated in salmon. In addition, transcriptomic sequencing technology (RNA-seq) was used to reveal the mechanism of AEW tolerance of L. monocytogenes under low temperature stress. Transcriptomic analysis showed the expression of the cold shock protein, regulation of DNA-templated transcription, ribosome pathway, phosphotransferase system (PTS), bacteria chemotaxis, SOS response and DNA repair were involved in the resistance of L. monocytogenes to AEW. We speculated that the direct modulation of the expression of cold shock protein CspD, the indirect effect on the expression of cspD by inhibiting the expression of Crp/Fnr family transcriptional regulator or enhancing the level of cAMP by regulating PTS could reduce the resistance of L. monocytogenes cultivated at 4 °C to AEW. Our study contributes to solving the problem of the reduced bacteriostatic effect in cold storage environment.

Production of glycerate from glucose using engineered Escherichiacoli

In this study, glycerate was produced from glucose using engineered Escherichia coli BW25113. Plasmid pSR3 carrying gpd1 and gpp2 encoding two isoforms of glycerol-3-phosphate dehydrogenase from Saccharomyces cerevisiae and plasmid pLB2 carrying aldO encoding alditol oxidase from Streptomyces violaceoruber were introduced into E. coli to enable the production of glycerate from glucose via glycerol. Disruptions of garK and glxK genes in the E. coli genome were performed to minimize the consumption of glycerate produced. As a result, E. coli carrying these plasmids could produce nearly three times higher concentration of glycerate (0.50 ± 0.01 g/L) from 10 g/L glucose compared to E. coli EG_2 (0.14 ± 0.02 g/L). In M9 medium, disruption of garK and glxK resulted in an impaired growth rate with low production of glycerate, while supplementation of 0.5 g/L casamino acids and 0.5 g/L manganese sulfate to the medium replenished the growth rate and elevated the glycerate titer. Further disruption of glpF, encoding a glycerol transporter, increased the glycerate production to 0.80 ± 0.00 g/L. MR2 medium improved the glycerate production titers and specific productivities of E. coli EG_4, EG_5, and EG_6. Upscale production of glycerate was carried out in a jar fermentor with MR2 medium using E. coli EG_6, resulting in an improvement in glycerate production up to 2.37 ± 0.46 g/L with specific productivity at 0.34 ± 0.11 g-glycerate/g-cells. These results indicate that E. coli is an appropriate host for glycerate production from glucose.

Toxic reactive oxygen species stresses for reconfiguring central carbon metabolic fluxes in foodborne bacteria: Sources, mechanisms and pathways

The toxic reactive oxygen species (toxROS) is the reactive oxygen species (ROS) beyond the normal concentration of cells, which has inactivation and disinfection effects on foodborne bacteria. However, foodborne bacteria can adapt and survive by physicochemical regulation of antioxidant systems, especially through central carbon metabolism (CCM), which is a significant concern for food safety. It is thus necessary to study the antioxidant regulation mechanisms of CCM in foodborne bacteria under toxROS stresses. Therefore, the purpose of this review is to provide an update and comprehensive overview of the reconfiguration of CCM fluxes in foodborne bacteria that respond to different toxROS stresses. In this review, two key types of toxROS including exogenous toxROS (exo-toxROS) and endogenous toxROS (endo-toxROS) are introduced. Exo-toxROS are produced by disinfectants, such as H₂O₂ and HOCl, or during food non-thermal processing such as ultraviolet (UV/UVA), cold plasma (CP), ozone (O₃), electrolyzed water (EW), pulsed electric field (PEF), pulsed light (PL), and electron beam (EB) processing. Endo-toxROS are generated by bioreagents such as antibiotics (aminoglycosides, quinolones, and β-lactams). Three main pathways for CCM in foodborne bacteria under the toxROS stress are also highlighted, which are glycolysis (EMP), pentose phosphate pathway (PPP), and tricarboxylic acid cycle (TCA). In addition, energy metabolisms throughout these pathways are discussed. Finally, challenges and future work in this area are suggested. It is hoped that this review should be beneficial in providing insights for future research on bacterial antioxidant CCM defence under both exo-toxROS stresses and endo-toxROS stresses.

Advances in Microbial NMR Metabolomics

Confidently, nuclear magnetic resonance (NMR) is the most informative technique in analytical chemistry and its use as an analytical platform in metabolomics is well proven. This chapter aims to present NMR as a viable tool for microbial metabolomics discussing its fundamental aspects and applications in metabolomics using some chosen examples.

Biological effects of Thymol loaded chitosan nanoparticles (TCNPs) on bacterial plant pathogen Xanthomonas campestris pv. campestris

Engineered nanomaterials can provide eco-friendly alternatives for crop disease management. Chitosan based nanoparticles has shown beneficial applications in sustainable agricultural practices and effective healthcare. Previously we demonstrated that Thymol loaded chitosan nanoparticles (TCNPs) showed bactericidal activity against Xanthomonas campestris pv campestris (Xcc), a bacterium that causes black rot disease in brassica crops. Despite the progress in assessing the antibacterial action of TCNPs, the knowledge about the molecular response of Xcc when exposed to TCNPs is yet to be explored. In the present study, we combined physiological, spectroscopic and untargeted metabolomics studies to investigate the response mechanisms in Xcc induced by TCNPs. Cell proliferation and membrane potential assays of Xcc cells exposed to sub-lethal concentration of TCNPs showed that TCNPs affects the cell proliferation rate and damages the cell membrane altering the membrane potential. FTIR spectroscopy in conjunction with untargeted metabolite profiling using mass spectrometry of TCNPs treated Xcc cells revealed alterations in amino acids, lipids, nucleotides, fatty acids and antioxidant metabolites. Mass spectroscopy analysis revealed a 10-25% increase in nucleic acid, fatty acids and antioxidant metabolites and a 20% increase in lipid metabolites while a decrease of 10-20% in amino acids and carbohydrates was seen in in TCNP treated Xcc cells. Overall, our results demonstrate that the major metabolic perturbations induced by TCNPs in Xcc are associated with membrane damage and oxidative stress, thus providing information on the mechanism of TCNPs mediated cytotoxicity. This will aid towards the development of nano- based agrochemicals as an alternative to chemical pesticides in future.

Overexpression of bacteriophage T4 and T7 endolysins differentially regulate the metabolic fingerprint of host Escherichia coli

Bioactive proteins are often overexpressed in different host systems for biotechnological/biomedical applications. Endolysins are natural bactericidal proteins that cleave the bacterial peptidoglycan membrane, and have the potential to be the next-generation enzybiotics. Therefore, the present study aims to elucidate the impact of two endolysins (T4L, T7L) overexpression on metabolic fingerprint of E. coli using NMR spectroscopy. The ¹H NMR-based metabolomics analysis revealed global metabolite profiles of E. coli in response to endolysins. The study has identified nearly 75 metabolites, including organic acids, amino acids, sugars and nucleic acids. RNA Polymerase (RNAP) has been considered as reference protein for marking the specific alterations in metabolic pathways. The data suggested downregulation of central carbon metabolic pathway in both endolysins overexpression, but to a different extent. Also, the endolysin overexpression have highlighted the enhanced metabolic load and stress generation in the host cells, thus leading to the activation of osmoregulatory pathways. The overall changes in metabolic fingerprint of E. coli highlights the enhanced perturbations during the overexpression of T4L as compared to T7L. These untargeted metabolic studies shed light on the regulation of molecular pathways during the heterologous overexpression of these lytic enzymes that are lethal to the host.

Integrated metabolomics of "big six" Escherichia coli on pea sprouts to organic acid treatments

Naturally occurring organic acids (OAs) have demonstrated satisfactory effects in inhibiting common pathogens on fresh produce; however, their effectiveness on "big six" Escherichia coli serotypes, comprised of E. coli O26:H11, O45:H2, O103:H11, O111, O121:H19 and O145, remained unaddressed. Regarding this, using nuclear magnetic resonance (NMR) spectroscopy and ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS), the sanitising efficacy and the underlying antimicrobial mechanisms of 10-min treatments with 0.2 mol/L ascorbic acid (AA), citric acid (CA) and malic acid (MA) against the "big six" strains on pea sprouts were thoroughly investigated in this study. Despite the varying antimicrobial efficacy (AA: 0.12-0.99, CA: 0.36-1.72, MA: 0.75-3.28 log CFU/g reductions), the three OAs induced consistent metabolic changes in the E. coli strains, particularly in the metabolism of membrane lipids, nucleotide derivatives and amino acids. Comparing all strains, the most OA-resistant strain, O26 (0.36-1.12 log CFU/g reductions), had the largest total amino acids accumulated to resist osmotic stress; its ulteriorly suppressed cell activity further strengthened its endurance. In contrast, the lowest OA-resistance of O121 (0.99-3.28 log CFU/g reductions) might be explained by the depletion of putrescine, an oxidative stress regulator. Overall, the study sheds light on the effectiveness of a dual-platform metabolomics investigation in elucidating the metabolic responses of "big six" E. coli to OAs. The manifested antimicrobial effects of OAs, especially MA, together with the underlying metabolic perturbations detected in the "big six" strains, provided scientific basis for applying OA treatments to future fresh produce sanitisation.

NMR-Based Metabolomic Approach for Evaluation of the Harvesting Time and Cooking Characteristics of Different Cassava Genotypes

Cassava is an important staple food for low-income countries. However, its cooking characteristics are especially affected by genotype. In this study, two groups of genotypes, namely hard to cook (HTC) and easy to cook (ETC), were harvested at different times (9 and 15 months), and evaluated by NMR coupled to chemometrics. Additionally, lignin of these materials was studied by ¹H-¹³C HSQC NMR. The carbohydrates were the most important class of compounds to differentiate the cassava genotypes. The correlation of NMR with cooking time and starch content showed that the higher content of primary metabolites, mostly glucose, can be associated with longer cooking times and reduction of starch, corroborating the metabolic pathways analysis. Furthermore, it was observed that the lignin from cell walls did not differentiate the cooking performance of the genotypes.

Metabolic Responses of "Big Six" Escherichia coli in Wheat Flour to Thermal Treatment Revealed by Nuclear Magnetic Resonance Spectroscopy

Escherichia coli outbreaks linked to wheat flour consumption have kept emerging in recent years, which necessitated an antimicrobial step being incorporated into the flour production process. The objectives of this in vivo study were to holistically evaluate the sanitizing efficacy of thermal treatment at 60 and 70°C against the "big six" E. coli strains (O26:H11, O45:H2, O103:H11, O111, O121:H19, and O145) in wheat flour and to assess the strain-specific metabolic responses using nuclear magnetic resonance (NMR) spectroscopy. The 70°C treatment temperature indiscriminatingly inactivated all strains by over 4.3-log CFU/g within 20 min, suggesting the high sanitization effectiveness of this treatment temperature, whereas the treatment at 60°C inactivated the strains to various degrees during the 1-h process. The most resistant strains at 60°C, O26 and O45, were characterized by amino acid and sugar depletion, and their high resistance was attributed to the dual effects of activated heat shock protein (HSP) synthesis and promoted glycolysis. O121 also demonstrated these metabolic changes, yet its thermal resistance was largely impaired by the weakened membrane structure and diminished osmotic protection due to phosphorylcholine exhaustion. In contrast, O111, O145, and O103 presented a substantial elevation of metabolites after stress at 60°C; their moderate thermal resistance was mainly explained by the accumulation of amino acids as osmolytes. Overall, the study enhanced our understanding of the metabolic responses of big six E. coli to heat stress and provided a model for conducting NMR-based metabolomic studies in powdered food matrices. IMPORTANCE "Big six" Escherichia coli strains have caused several outbreaks linked to wheat flour consumption in the last decade, revealing the vital importance of adopting an antimicrobial treatment during the flour production process. Therefore, the present study was carried out to evaluate the efficacy of a typical sanitizing approach, thermal treatment, against the big six strains in wheat flour along with the underlying antimicrobial mechanisms. Findings showed that thermal treatment at 60 and 70°C could markedly mitigate the loads of all strains in wheat flour. Moreover, activated heat shock protein synthesis combined with expedited glycolysis and enhanced osmotic protection were identified as two major metabolic alteration patterns in the E. coli strains to cope with the heat stress. With the responses of big six in wheat flour to thermal treatment elucidated, scientific basis for incorporating a thermal inactivation step in wheat flour production was provided.

Molecular Methods for Pathogenic Bacteria Detection and Recent Advances in Wastewater Analysis

With increasing concerns about public health and the development of molecular techniques, new detection tools and the combination of existing approaches have increased the abilities of pathogenic bacteria monitoring by exploring new biomarkers, increasing the sensitivity and accuracy of detection, quantification, and analyzing various genes such as functional genes and antimicrobial resistance genes (ARG). Molecular methods are gradually emerging as the most popular detection approach for pathogens, in addition to the conventional culture-based plate enumeration methods. The analysis of pathogens in wastewater and the back-estimation of infections in the community, also known as wastewater-based epidemiology (WBE), is an emerging methodology and has a great potential to supplement current surveillance systems for the monitoring of infectious diseases and the early warning of outbreaks. However, as a complex matrix, wastewater largely challenges the analytical performance of molecular methods. This review synthesized the literature of typical pathogenic bacteria in wastewater, types of biomarkers, molecular methods for bacterial analysis, and their recent advances in wastewater analysis. The advantages and limitation of these molecular methods were evaluated, and their prospects in WBE were discussed to provide insight for future development.

Metabolomic analyses on microbial primary and secondary oxidative stress responses

Food safety is veryimportant in our daily life. In food processing or disinfection, microorganisms are commonly exposed to oxidative stress perturbations. However, microorganisms can adapt and respond to physicochemical interventions, leading to difficulty and complexity for food safety assurance. Therefore, understanding the response mechanisms of microbes and providing an overview of the responses under oxidative stress conditions are beneficial for ensuring food safety for the industry. The current review takes the metabolomics approach to reveal small metabolite signatures and key pathway alterations during oxidative stress at the molecular and technical levels. These alterations are involved in primary oxidative stress responses due to inactivation treatments such as using hypochlorite (HOCl), hydrogen peroxide (H₂ O₂ ), electrolyzed water (EW), irradiation, pulsed light (PL), electron beam (EB), and secondary oxidative stress responses due to exposures to excessive conditions such as heat, pressure, acid, and alkaline. Details on the putative origin of exogenous or endogenous reactive oxygen species (ROS) are discussed, with particular attention paid to their effects on lipid, amino acid, nucleotide, and carbohydrate metabolism. In addition, mechanisms on counteracting oxidative stresses, stabilization of cell osmolality as well as energy provision for microbes to survive are also discussed.

Metabolomic approaches for the determination of metabolites from pathogenic microorganisms: A review

Metabolomics is a high precision analytical approach to obtaining detailed information of varieties of metabolites produced in biological systems, including foods. This study reviews the use of metabolomic approaches such as liquid chromatography mass spectrometry (LCMS), gas chromatography mass spectrometry (GC-MS), matrix assisted laser desorption /ionization tandem time of flight mass spectrometry (MALDI-TOF-MS) and nuclear magnetic resonance (NMR) for investigating the presence of foodborne pathogens and their metabolites. Pathogenic fungi and their notable metabolites (mycotoxins) have been studied more extensively using metabolomics as compared to bacteria, necessitating further studies in this regard. Nevertheless, such identified fungal and bacteria metabolites could be used as biomarkers for a more rapid detection of these pathogens in food. Other important compounds detected through metabolomics could also be correlated to functionality of these pathogenic strains, determined by the composition of the foods in which they exist, thereby providing insights into their metabolism. Considering the prevalence of these food pathogens, metabolomics still has potentials in the determination of food-borne pathogenic microorganisms especially for the determination of pathogenic bacteria toxins and is expected to generate research interests for further studies and applications.

Top-Down Characterization of an Antimicrobial Sanitizer, Leading From Quenchers of Efficacy to Mode of Action

We developed a top-down strategy to characterize an antimicrobial, oxidizing sanitizer, which has diverse proposed applications including surface-sanitization of fresh foods, and with benefits for water resilience. The strategy involved finding quenchers of antimicrobial activity then antimicrobial mode of action, by identifying key chemical reaction partners starting from complex matrices, narrowing down reactivity to specific organic molecules within cells. The sanitizer electrolyzed-water (EW) retained partial fungicidal activity against the food-spoilage fungus Aspergillus niger at high levels of added soils (30–750 mg mL^–1), commonly associated with harvested produce. Soil with high organic load (98 mg g^–1) gave stronger EW inactivation. Marked inactivation by a complex organics mix (YEPD medium) was linked to its protein-rich components. Addition of pure proteins or amino acids (≤1 mg mL^–1) fully suppressed EW activity. Mechanism was interrogated further with the yeast model, corroborating marked suppression of EW action by the amino acid methionine. Pre-culture with methionine increased resistance to EW, sodium hypochlorite, or chlorine-free ozonated water. Overexpression of methionine sulfoxide reductases (which reduce oxidized methionine) protected against EW. Fluoroprobe-based analyses indicated that methionine and cysteine inactivate free chlorine species in EW. Intracellular methionine oxidation can disturb cellular FeS-clusters and we showed that EW treatment impairs FeS-enzyme activity. The study establishes the value of a top-down approach for multi-level characterization of sanitizer efficacy and action. The results reveal proteins and amino acids as key quenchers of EW activity and, among the amino acids, the importance of methionine oxidation and FeS-cluster damage for antimicrobial mode-of-action.

Antibiofilm activities of the cinnamon extract against Vibrio parahaemolyticus and Escherichia coli

Vibrio parahaemolyticus and Escherichia coli are two major foodborne pathogens. In this paper, the antibiofilm activities of the ethanol extract of cinnamon against these two bacteria were studied in detail. The antibacterial activity and the MIC of the extract were determined, and the inhibition and removing effects of the extract on the biofilms of V. parahaemolyticus and E. coli were investigated. The biofilms stained with fluorescein isothiocyanate (FITC) and concanavalin A (Con A) were also observed by confocal laser scanning microscope (CLSM). The results indicated that the extract exhibited high antibacterial activity, with the MIC against V. parahaemolyticus and E. coli was 6.25 mg/mL. The effects on V. parahaemolyticus biofilm were significant with the inhibition rate of 75.46% at MIC, and the eradication rate of 93.26% at 32MIC, respectively. As to E. coli, the inhibition rate was 48.18% at MIC, and the eradication rate was 46.16% at 8MIC. Meanwhile, the extract could notably reduce the metabolic activities and the secretion of EPS in biofilm, it inhibited 78.57% EPS formation in V. parahaemolyticus biofilm at MIC, and eliminated 61.28% EPS in mature biofilm at 4MIC. CLSM images showed that the EPS of the treated biofilm became thinner and biofilm structure was looser, when compared with the untreated control. This study elucidated that the cinnamon extract was effective to prevent biofilm formation and eradicate mature biofilms of V. parahaemolyticus and E. coli.

Recent advances in the application of metabolomics for food safety control and food quality analyses

As one of the omics fields, metabolomics has unique advantages in facilitating the understanding of physiological and pathological activities in biology, physiology, pathology, and food science. In this review, based on developments in analytical chemistry tools, cheminformatics, and bioinformatics methods, we highlight the current applications of metabolomics in food safety, food authenticity and quality, and food traceability. Additionally, the combined use of metabolomics with other omics techniques for "foodomics" is comprehensively described. Finally, the latest developments and advances, practical challenges and limitations, and requirements related to the application of metabolomics are critically discussed, providing new insight into the application of metabolomics in food analysis.

Applications of Electrolyzed Water as a Sanitizer in the Food and Animal-By Products Industry

Food demand is increasing every year and, usually animal-derived products are generated far from consumer-places. New technologies are being developed to preserve quality characteristics during processing and transportation. One of them is electrolyzed water (EW) that helps to avoid or decrease the development of foodborne pathogens, or losses by related bacteria. Initially, EW was used in ready-to-eat foods such as spinach, lettuce, strawberries, among others; however, its application in other products is under study. Every product has unique characteristics that require an optimized application of EW. Different sanitizers have been developed; unfortunately, they could have undesirable effects like deterioration of quality or alterations in sensory properties. Therefore, EW is gaining popularity in the food industry due to its characteristics: easy application and storage, no corrosion of work surfaces, absence of mucosal membrane irritation in workers handling food, and it is considered environmentally friendly. This review highlights the advantages of using EW in animal products like chicken, pork, beef, eggs and fish to preserve their safety and quality.

Acid Tolerance Response of Listeria monocytogenes in Various External pHs with Different Concentrations of Lactic Acid

This study evaluated the acid tolerance response (ATR) of two strains of Listeria monocytogenes (serotype 1/2a and 4b) and one strain of Listeria innocua under different mildly acid conditions. Cells were incubated in combinations of three concentrations of lactic acid medium (3, 4.75, and 15 mM) and three external pH's (pHex 5.0, 6.0, and 6.5), plus, a HCl control, and a blank control (pH 7.4). Results showed that lactic acid induced lower log reduction of all three strains when challenged in severe acid conditions (pH 3.0) after being habituated at a pHex of 5.5 or 6.0 until the log phase, compared with a pHex of 6.5 or the two controls. This indicates that when the pHex was either 5.5 or 6.0 this induced a higher ATR of the strains, which may be caused by the ability of the strains to retain intracellular pH (pHi) homeostasis with pHi maintained in the range of 7.4-7.9. It was also found that a pHex of 5.5 resulted in the highest pHi of the strains across all incubated conditions, which indicates that the pHi may play an important role in the induction of ATR when Listeria cells are habituated in lactic acid, and if the higher pHi can be maintained, the ATR would be stronger. The concentration of lactic acid per se has no significant effect on ATR, which it is proposed was due to the pHi homeostasis maintained within the cells. However, the difference in ATR among three strains was also significant, which cannot be explained by the stable pHi of all tested strains. Therefore, other underlying mechanisms to mediate ATR under different conditions need to be explored in further studies.

Resistance Profiles of Salmonella Isolates Exposed to Stresses and the Expression of Small Non-coding RNAs

Salmonella can resist various stresses and survive during food processing, storage, and distribution, resulting in potential health risks to consumers. Therefore, evaluation of bacterial survival profiles under various environmental stresses is necessary. In this study, the resistance profiles of five Salmonella isolates [serotypes with Agona, Infantis, Typhimurium, Enteritidis, and a standard strain (ATCC 13076, Enteritidis serotype)] to acidic, hyperosmotic, and oxidative stresses were examined, and the relative expressions of non-coding small RNAs were also evaluated, including CyaR, MicC, MicA, InvR, RybB, and DsrA, induced by specific stresses. The results indicated that although all tested strains displayed a certain resistance to stresses, there was great diversity in stress resistance among the strains. According to the reduction numbers of cells exposed to stress for 3 h, S. Enteritidis showed the highest resistance to acidic and hyperosmotic stresses, whereas ATCC 13076 showed the greatest resistance to oxidative stress, with less than 0.1 Log CFU/ml of cell reduction. Greater resistance of cells to acidic, hyperosmotic, and oxidative stresses was observed within 1 h, after 2 h, and from 1 to 2 h, respectively. The relative expression of sRNAs depended on the isolate for each stress; acidic exposure for the tested isolates induced high expression levels of DsrA, MicC, InvR, RybB, MicA, and CyaR. The sRNA RybB, associated with sigma E and outer membrane protein in bacteria, showed a fold change of greater than 7 in S. Enteritidis exposed to the tested stresses. CyaR and InvR involved in general stress responses and stress adaptation were also induced to show high expression levels of Salmonella exposed to hyperosmotic stress. Overall, these findings demonstrated that the behaviors of Salmonella under specific stresses varied according to strain and were likely not related to other profiles. The finding also provided insights into the survival of Salmonella subjected to short-term stresses and for controlling Salmonella in the food industry.

Elucidating antimicrobial mechanism of nisin and grape seed extract against Listeria monocytogenes in broth and on shrimp through NMR-based metabolomics approach

Nisin and grape seed extract (GSE) have been widely used as food preservatives; however, the mechanism against pathogens at molecular level has not been well elucidated. This work aimed to investigate their antimicrobial effect against Listeria monocytogenes and to elucidate the mechanism by NMR-based metabolomics. Nisin exhibited enhanced in vitro antilisterial effect when combined with GSE (4.49 log CFU/mL reduction). Marked change in cell membrane permeability was observed in the combination group using confocal laser scanning microscopy; this was verified by increased leakage of protein and nucleic acid. The underlying antimicrobial mechanism was revealed by NMR coupled with multivariate analysis. Significant decreases in threonine, cysteine, ATP, NADP, adenine were observed, whereas a few of metabolites such as lactic acid and γ-aminobutyric acid (GABA) increased after nisin-GSE treatment (P < 0.05). Pathway analysis further manifested that the nisin-GSE inhibited the survival of L. monocytogenes by blocking the TCA cycle, amino acid biosynthesis and energy-producing pathway. Lastly, nisin and GSE were applied to shrimp and binary combination showed remarkably antilisterial activity (1.79 log CFU/g reduction). GABA shunt and protein degradation from shrimp compensated the unbalanced glycolysis and amino acid metabolism by providing energy and carbon source for L. monocytogenes inoculated on shrimp. Thus, they were more tolerant to nisin and GSE stresses as compared to the broth-grown culture.

Metabolic characterisation of eight Escherichia coli strains including "Big Six" and acidic responses of selected strains revealed by NMR spectroscopy

The metabolic diversity of Escherichia coli strains (non-pathogenic E. coli ATCC 25922, and pathogenic E. coli O157:H7, O26:H11, O45:H2, O103:H11, O111, O121:H19, and O145) was tested using nuclear magnetic resonance. Based on two representative two-dimensional ¹H-¹³C spectra, 38 metabolites were identified in E. coli intracellular samples. Principal component analysis indicated that metabolites including lysine, arginine, α-ketoglutaric acid, adenosine, and fumaric acid were responsible for the separation of E. coli ATCC 25922. Relatively large metabolic differences between ATCC 25922 and the pathogenic strains were recoded. The most varied pairwise group (ATCC 25922 vs. O26:H11) was further analysed. The screened metabolites and enrichment pathway tests revealed different amino acid metabolism and higher requirement for energy production in the pathogenic strains. The acidic responses of the selected strains were further tested. The in vitro and in vivo inactivation kinetics, morphological changes, and protein leakage showed higher acid tolerance of E. coli O26:H11. Metabolic analysis of the two strains under acidic stress revealed alternative metabolites and pathways in the two groups. Pathogenic O26:H11 was characterised by higher energy production and amino acid metabolism (lysine and glutamic acid). Real-time PCR tests confirmed that glutamic acid dependent decarboxylase/antiporter system was the major acid resistance mechanism.