Antibacterial activity of acidified sodium benzoate against Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in tryptic soy broth and on cherry tomatoes

Improved Anti-Oxidant and Anti-Bacterial Capacities of Skim Milk Fermented by Lactobacillus plantarum

Milk, on account of its abundant protein content, is recognized as a vital source of bioactive substances. In this study, the bioactive ingredients in milk were obtained by a combination of protease hydrolysis and fermentation with Lactobacillus plantarum. The compositions of protease hydrolysate (PM) and fermentation supernatant (FM) were determined, and their anti-oxidant and anti-bacterial activities were evaluated. Using LC-MS/MS, the molecular weights and sequences of the peptides were characterized, among which a total of 25 bioactive peptides were identified. The DPPH radical scavenging results demonstrated that FM exhibited an enhanced anti-oxidant capacity compared to PM. The bacterial survival rate results revealed that FM had a remarkable anti-bacterial ability compared to PM. Additionally, the anti-bacterial component and potential anti-bacterial mechanisms were determined. The results of cytoplasmic membrane depolarization, cell membrane permeability, and morphological observation indicated that FM could interact with bacterial membranes to achieve its anti-bacterial effect. These findings suggested that FM, as a bioactive substance of natural origin, holds potential applications in the functional food, pharmaceutical, and cosmetic industries.

Impact of food-relevant conditions and food matrix on the efficacy of prenylated isoflavonoids glabridin and 6,8-diprenylgenistein as potential natural preservatives against Listeria monocytogenes

Prenylated isoflavonoids can be extracted from plants of the Leguminosae/Fabaceae family and have shown remarkable antimicrobial activity against Gram-positive food-borne pathogens, such as Listeria monocytogenes. Promising candidates from this class of compounds are glabridin and 6,8-diprenylgenistein. This research aimed to investigate the potential of glabridin and 6,8-diprenylgenistein as food preservatives against L. monocytogenes. Their antimicrobial activity was tested in vitro at various conditions relevant for food application, such as different temperatures (from 10 °C to 37 °C), pH (5 and 7.2), and in the presence or absence of oxygen. The minimum inhibitory concentrations of glabridin and 6,8-diprenylgenistein in vitro were between 0.8 and 12.5 μg/mL in all tested conditions. Growth inhibitory activities were similar at 10 °C compared to higher temperatures, although bactericidal activities decreased when the temperature decreased. Notably, lower pH (pH 5) increased the growth inhibitory and bactericidal activity of the compounds, especially for 6,8-diprenylgenistein. Furthermore, similar antimicrobial efficacies were shown anaerobically compared to aerobically at the tested conditions. Glabridin showed a more stable inhibitory and bactericidal activity when the temperature decreased compared to 6,8-diprenylgenistein. Therefore, we further determined the antimicrobial efficacy of glabridin against L. monocytogenes growth on fresh-cut cantaloupe at 10 °C. In these conditions, concentrations of glabridin of 50, 100 and 250 μg/g significantly reduced the growth of L. monocytogenes compared to the control, resulting on average in >1 Log CFU/g difference after 4 days compared to the control. Our results further underscored the importance of considering the food matrix when assessing the activity of novel antimicrobials. Overall, this study highlights the potential of prenylated isoflavonoids as naturally derived food preservatives.

A Meta-Analysis and Systematic Review of Listeria monocytogenes Response to Sanitizer Treatments

Listeria monocytogenes is a ubiquitous organism that can be found in food-related environments, and sanitizers commonly prevent and control it. The aim of this study is to perform a meta-analysis of L. monocytogenes response to sanitizer treatments. According to the principle of systematic review, we extracted 896 records on the mean log-reduction of L. monocytogenes from 84 publications as the dataset for this study. We applied a mixed-effects model to describe L. monocytogenes response to sanitizer treatment by considering sanitizer type, matrix type, biofilm status, sanitizer concentration, treatment time, and temperature. Based on the established model, we compared the response of L. monocytogenes under different hypothetical conditions using forest plots. The results showed that environmental factors (i.e., sanitizer concentration, temperature, and treatment time) affected the average log-reduction of L. monocytogenes (p < 0.05). L. monocytogenes generally exhibited strong resistance to citric acid and sodium hypochlorite but had low resistance to electrolyzed water. The planktonic cells of L. monocytogenes were less resistant to peracetic acid and sodium hypochlorite than the adherent and biofilm cells. Additionally, the physical and chemical properties of the contaminated or inoculated matrix or surface also influenced the sanitizer effectiveness. This review may contribute to increasing our knowledge of L. monocytogenes resistance to sanitizers and raising awareness of appropriate safety precautions.

Electrospun Zein/Polyoxyethylene Core-Sheath Ultrathin Fibers and Their Antibacterial Food Packaging Applications

The purpose of this work is to develop a novel ultrathin fibrous membrane with a core-sheath structure as antibacterial food packaging film. Coaxial electrospinning was exploited to create the core-sheath structure, by which the delivery regulation of the active substance was achieved. Resveratrol (RE) and silver nanoparticles (AgNPs) were loaded into electrospun zein/polyethylene oxide ultrathin fibers to ensure a synergistic antibacterial performance. Under the assessments of a scanning electron microscope and transmission electron microscope, the ultrathin fiber was demonstrated to have a fine linear morphology, smooth surface and obvious core-sheath structure. X-ray diffraction and Fourier transform infrared analyses showed that RE and AgNPs coexisted in the ultrathin fibers and had good compatibility with the polymeric matrices. The water contact angle experiments were conducted to evaluate the hydrophilicity and hygroscopicity of the fibers. In vitro dissolution tests revealed that RE was released in a sustained manner. In the antibacterial experiments against Staphylococcus aureus and Escherichia coli, the diameters of the inhibition zone of the fiber were 8.89 ± 0.09 mm and 7.26 ± 0.10 mm, respectively. Finally, cherry tomatoes were selected as the packaging object and packed with fiber films. In a practical application, the fiber films effectively reduced the bacteria and decreased the quality loss of cherry tomatoes, thereby prolonging the fresh-keeping period of cherry tomatoes to 12 days. Following the protocols reported here, many new food packaging films can be similarly developed in the future.

Light Regulates Acinetobacter baumannii Chromosomal and pAB3 Plasmid Genes at 37°C

The opportunistic pathogen A. baumannii has a remarkable capacity to persist in the hospital environment and cause devastating human infections. This capacity can be attributed partly to the sensing and regulatory systems that enable this pathogen to modify its physiology based on environmental cues. One of the signals that A. baumannii senses and responds to is light through the sensing and regulatory roles of the BlsA photoreceptor protein in cells cultured at temperatures below 30°C. This report presents evidence that a light stimulon is operational at 37°C, a condition at which the BlsA production and activity are drastically impaired. Global transcriptional analysis showed that the 37°C light stimulon includes the differential expression of chromosomal genes encoding a wide range of functions that are known to be involved in the adaptation to different metabolic conditions, as well as virulence and persistence in the host and the medical environment. Unexpectedly, the 37°C light stimulon also includes the differential expression of conjugation functions encoded by pAB3 plasmid genes. Our work further demonstrates that the TetR1 and H-NS regulators encoded by this conjugative plasmid control the expression of H2O2 resistance and surface motility, respectively. Furthermore, our data showed that pAB3 has an overall negative effect on the expression of these phenotypes and plays no significant virulence role. Although the nature of the bacterial factors and the mechanisms by which the regulation is attained at 37°C remain unknown, taken together, our work expands the current knowledge about light sensing and gene regulation in A. baumannii. IMPORTANCE As a facultative pathogen, Acinetobacter baumannii persists in various environments by sensing different environmental cues, including light. This report provides evidence of light-dependent regulation at 37°C of the expression of genes coding for a wide range of functions, including those involved in the conjugation of the pAB3 plasmid. Although this plasmid affects the expression of virulence traits when tested under laboratory conditions, it does not have a significant impact when tested using ex vivo and in vivo experimental models. These findings provide a better understanding of the interplay between light regulation and plasmid persistence in the pathobiology of A. baumannii.

Ageing and rejuvenation models reveal changes in key microbial communities associated with healthy ageing

BACKGROUND

The gut microbiota is associated with diverse age-related disorders. Several rejuvenation methods, such as probiotic administration and faecal microbiota transplantation, have been applied to alter the gut microbiome and promote healthy ageing. Nevertheless, prolongation of the health span of aged mice by remodelling the gut microbiome remains challenging.

RESULTS

Here, we report the changes in gut microbial communities and their functions in mouse models during ageing and three rejuvenation procedures including co-housing, serum-injection and parabiosis. Our results showed that the compositional structure and gene abundance of the intestinal microbiota changed dynamically during the ageing process. Through the three rejuvenation procedures, we observed that the microbial community and intestinal immunity of aged mice were comparable to those of young mice. The results of metagenomic data analysis underscore the importance of the high abundance of Akkermansia and the butyrate biosynthesis pathway in the rejuvenated mouse group. Furthermore, oral administration of Akkermansia sufficiently ameliorated the senescence-related phenotype in the intestinal systems in aged mice and extended the health span, as evidenced by the frailty index and restoration of muscle atrophy.

CONCLUSIONS

In conclusion, the changes in key microbial communities and their functions during ageing and three rejuvenation procedures, and the increase in the healthy lifespan of aged mice by oral administration of Akkermansia. Our results provide a rationale for developing therapeutic strategies to achieve healthy active ageing. Video abstract.

Research Trends on the Application of Electrolyzed Water in Food Preservation and Sanitation

Electrolyzed water (EW) has been proposed as a novel promising sanitizer and cleaner in recent years. It is an effective antimicrobial and antibiofilm agent that has several advantages of being on the spot, environmentally friendly, cheap, and safe for human beings. Therefore, EW has been applied widely in various fields, including agriculture, food sanitation, livestock management, medical disinfection, clinical, and other fields using antibacterial technology. Currently, EW has potential significance for high-risk settings in hospitals and other clinical facilities. The research focus has been shifted toward the application of slightly acidic EW as more effective with some supplemental chemical and physical treatment methods such as ultraviolet radiations and ultrasound. This review article summarizes the possible mechanism of action and highlights the latest research studies in antimicrobial applications.

Synergistic inactivation of Escherichia coli O157:H7 and Staphylococcus aureus by gallic acid and thymol and its potential application on fresh-cut tomatoes

Antibacterial activity against Escherichia coli O157:H7 and Staphylococcus aureus of five typical plant-derived compounds [gallic acid (G.A), citral (Cit), thymol (Thy), salicylic acid (S.A), lauric acid (L.A)] were investigated by determining the minimum inhibitory concentration (MIC) and the fractional inhibitory concentration index (FICI). The results showed that only a combination of Thy and G.A (TGA), with a concentration of 0.1 and 1.25 mg/mL, respectively, had a synergistic effect (FICI = 0.5) on both E. coli O157:H7 and S. aureus. The amount of Thy and G.A in mixture were four-fold lower than the MICs of the individuals shown to cause the equivalent antimicrobial activity in trypticase soy broth (TSB). The microbial reduction obtained in TSB with addition of TGA were significantly higher (P < 0.05) than the reduction shown for the broth supplemented with the separated phenolics. TGA caused the changes of morphology and membrane integrity of bacteria. Additionally, the application of TGA on fresh-cut tomatoes are investigated. Fresh-cut tomatoes inoculated with E. coli O157:H7and S. aureus were washed for 2min, 5min, 10min at 4 °C, 25 °C, 40 °C in 0.3% NaOCl, or water containing TGA at various concentrations. Overall, the reduction of TGA achieved against S. aureus is higher than E. coli O157:H7. Same concentrations of combined antimicrobials at a temperature of 40 °C further increased the degree of microbial inactivation, with an additional 0.89-1.51 log CFU/g reduction compared to that at 25 °C. Moreover, 1/2MIC_Thy+1/2MIC_G.A at 25 °C for 10min or 40 °C for 5min were generally acceptable with sensorial scores higher than 7. Our results showed that TGA could work synergistically on the inactivation of the tested bacteria and may be used as an alternative disinfectant of fresh produce.

Responses of Escherichia coli and Listeria monocytogenes to ozone treatment on non-host tomato: Efficacy of intervention and evidence of induced acclimation

Because of the continuous rise of foodborne illnesses caused by the consumption of raw fruits and vegetables, effective post-harvest anti-microbial strategies are necessary. The aim of this study was to evaluate the anti-microbial efficacy of ozone (O₃) against two common causes of fresh produce contamination, the Gram-negative Escherichia coli O157:H7 and Gram-positive Listeria monocytogenes, and to relate its effects to potential mechanisms of xenobiosis by transcriptional network modeling. The study on non-host tomato environment correlated the dose × time aspects of xenobiosis by examining the correlation between bacterial survival in terms of log-reduction and defense responses at the level of gene expression. In E. coli, low (1 μg O₃/g of fruit) and moderate (2 μg O₃/g of fruit) doses caused insignificant reduction in survival, while high dose (3 μg/g of fruit) caused significant reduction in survival in a time-dependent manner. In L. monocytogenes, moderate dose caused significant reduction even with short-duration exposure. Distinct responses to O₃ xenobiosis between E. coli and L. monocytogenes are likely related to differences in membrane and cytoplasmic structure and components. Transcriptome profiling by RNA-Seq showed that primary defenses in E. coli were attenuated after exposure to a low dose, while the responses at moderate dose were characterized by massive upregulation of pathogenesis and stress-related genes, which implied the activation of defense responses. More genes were downregulated during the first hour at high dose, with a large number of such genes getting significantly upregulated after 2 hr and 3 hr. This trend suggests that prolonged exposure led to potential adaptation. In contrast, massive downregulation of genes was observed in L. monocytogenes regardless of dose and exposure duration, implying a mechanism of defense distinct from that of E. coli. The nature of bacterial responses revealed by this study should guide the selection of xenobiotic agents for eliminating bacterial contamination on fresh produce without overlooking the potential risks of adaptation.

Impact of Phytochemicals on Viability and Cereulide Toxin Synthesis in Bacillus cereus Revealed by a Novel High-Throughput Method, Coupling an AlamarBlue-Based Assay with UPLC-MS/MS

Due to its food-poisoning potential, Bacillus cereus has attracted the attention of the food industry. The cereulide-toxin-producing subgroup is of particular concern, as cereulide toxin is implicated in broadscale food-borne outbreaks and occasionally causes fatalities. The health risks associated with long-term cereulide exposure at low doses remain largely unexplored. Natural substances, such as plant-based secondary metabolites, are widely known for their effective antibacterial potential, which makes them promising as ingredients in food and also as a surrogate for antibiotics. In this work, we tested a range of structurally related phytochemicals, including benzene derivatives, monoterpenes, hydroxycinnamic acid derivatives and vitamins, for their inhibitory effects on the growth of B. cereus and the production of cereulide toxin. For this purpose, we developed a high-throughput, small-scale method which allowed us to analyze B. cereus survival and cereulide production simultaneously in one workflow by coupling an AlamarBlue-based viability assay with ultraperformance liquid chromatography–mass spectrometry (UPLC-MS/MS). This combinatory method allowed us to identify not only phytochemicals with high antibacterial potential, but also ones specifically eradicating cereulide biosynthesis already at very low concentrations, such as gingerol and curcumin.

Tubular Cellulose from Orange Juice By-Products as Carrier of Chemical Preservatives; Delivery Kinetics and Microbial Stability of Orange Juice

The quality and safety of juices are assured mainly through heat treatments and chemical preservatives. However, there is a growing trend in the food industry for lowering energy and water demands, and the chemicals and additives that may have negative effects οn human health. Following that trend, in the present study, the reduced use of chemical preservatives in orange juice is proposed by using encapsulated sodium benzoate (SB) in tubular cellulose (TC), derived from orange pulp. The effects of SB concentration and contact time on SB encapsulation were evaluated. The use of the wet impregnation method, 12% w/v SB solution and 2 h of contact proved to be ideal for application in the juice industry. The use of starch gel resulted in a more stable composite (TC/SB-SG) with a slower SB delivery, showing its potential for future controlled delivery applications. Furthermore, similar delivery rates of SB in juice were noted at 25 and 2 °C. The TC/SB-SG proved capable of inhibiting the growth and reducing the numbers of spoilage microorganisms (yeasts and lactic acid bacteria). The results of the present study are promising for potential applications; however, more research is needed in order to evaluate the controlled delivery of SB in juice.

The gut-microbiome as a target for the treatment of schizophrenia: A systematic review and meta-analysis of randomised controlled trials of add-on strategies

The gut-microbiome has been hypothesised as a novel potential target for intervention for schizophrenia. We tested this hypothesis with a systematic review and meta-analysis of studies investigating the efficacy and acceptability of add-on strategies known to affect the gut-microbiome for the treatment of schizophrenia. Following PRISMA guidelines, we searched from inception to August 2019 all the randomised double-blind controlled trials of add-on antibiotics, antimicrobials, pre/probiotics, and faecal transplant in schizophrenia. Primary outcomes were severity of negative symptoms and acceptability of treatment. Data were independently extracted by multiple observers and a random-mixed model was used for the analysis. Heterogeneity was assessed with the I² index. We identified 28 eligible trials: 21 investigated antibiotics, 4 antimicrobials (Artemisinin, Artemether, and Sodium Benzoate), 3 pre/probiotics, none faecal transplant. Results showed no effect of D-Cycloserine (10 studies; SMD, -0.16; 95% CI -0.40, 0.08; P = .20; I²: 28.2%), Minocycline (7 studies; SMD: -0.35; 95% CI -0.70, 0.00; P = .05, I²:77.7%), other antibiotics (2 studies), probiotics alone (1 study), and Artemisinin (1 study) on negative symptoms of schizophrenia when compared to placebo. Limited evidence suggests efficacy on negative symptoms for Sodium benzoate (2 studies; SMD, -0.63; 95%CI -1.03, -0.23; P < .001; I²:0%), Artemether (1 study), and probiotics combined with Vitamin D (1 study) when compared to placebo. Acceptability of intervention was similar to placebo. Negative findings were mainly led by antibiotics trials, with paucity of evidence available on pre/probiotics. There is a need of expanding our knowledge on the clinical relevance of gut-microbiome-host interaction in psychosis before engaging in further trials.

Mapping of the benzoate metabolism by human gut microbiome indicates food-derived metagenome evolution

Sodium benzoate is one of the widely used food preservatives and its metabolism in the human body has been studied only with the host perspective. Despite the human gut microbiome being considered as a virtual human organ, its role in benzoate metabolism is yet to be elucidated. The current study uses a multi-omic approach to rationalize the role of human gut microbes in benzoate metabolism. Microbial diversity analysis with multiple features synchronously indicates the dominance of Bacteroidetes followed by Firmicutes, Actinobacteria, and Proteobacteria. Metagenomic exploration highlights the presence of benzoate catabolic protein features. These features were mapped on to the aerobic and anaerobic pathways of benzoate catabolism. Benzoate catabolism assays identified statistically significant metabolites (P < 0.05) associated with the protocatechuate branch of the beta-ketoadipate pathway of the benzoate metabolism. Analysis of the 201 human gut metagenomic datasets across diverse populations indicates the omnipresence of these features. Enrichment of the benzoate catabolic protein features in human gut microbes rationalizes their role in benzoate catabolism, as well as indicates food-derived microbiome evolution.

GC-MS-Based Metabolomics Analysis of Prawn Shell Waste Co-Fermentation by Lactobacillus plantarum and Bacillus subtilis

GC-MS-based metabolomics were used to investigate metabolic changes in prawn shell waste during fermentation. Microbial strains Lactobacillus plantarum and Bacillus subtilis were co-fermented in a shake flask comprising of 5% (w/v) prawn shell waste and 20% (w/v) glucose as a carbon source. Analysis of the prawn shell waste fermentation showed a total of 376 metabolites detected in the culture supernatant, including 14 amino acids, 106 organic acids, and 90 antimicrobial molecules. Results show that the liquid fraction of the co-fermentation is promising for harvesting valuable metabolites for probiotics application.

Prolonging the Shelf Life of Cherry Tomatoes by Pullulan Coating with Ethanol Extract of Propolis During Refrigerated Storage

Cherry tomatoes are one of the most popular tomato varieties known for their bioactive compounds and sensory properties. One way to reduce the contamination of tomato is to coat them with natural or antimicrobial substances. In this study, an ethanolic extract of propolis (EEP) was obtained, and its chemical composition was analyzed using high-performance liquid chromatography with diode array detector (HPLC-DAD), and minimum inhibitory concentration (MIC) and the minimum bactericidal/fungicidal concentration (MBC/MFC) were determined using the serial microdilution method. The antimicrobial activity of 5 and 10% EEP and pullulan films containing EEP (5 and 10%) against Listeria monocytogenes, Salmonella Typhimurium, Escherichia coli O157, Penicillium chrysogenum, Fusarium solani, and Botrytis cinerea were compared. The influence of a pullulan coating containing EEP (5 and 10%) on reducing the number of bacteria and molds, physicochemical properties (weight loss (WL), total soluble solids (TSS), titratable acidity (TA), maturity index, pH, and color), and sensory properties (color and brightness of skin, aroma, flavor, overall quality, and general preference) of cherry tomatoes during refrigerated storage was evaluated. Pullulan films with EEP inhibited the growth of microorganisms on cherry tomatoes. These coatings did not affect the TSS and pH values of tomatoes, but a slight decrease in TA and WL was observed. Cherry tomatoes coated with pullulan coatings containing EEP did not show any adverse changes in their sensory properties. It was found that the addition of EEP to the pullulan coatings enriched them with antimicrobial properties and enhanced their action while reducing the WL and maturation time of cherry tomatoes.

Xenobiotic Effects of Chlorine Dioxide to Escherichia coli O157:H7 on Non-host Tomato Environment Revealed by Transcriptional Network Modeling: Implications to Adaptation and Selection

Escherichia coli serotype O157:H7 is one of the major agents of pathogen outbreaks associated with fresh fruits and vegetables. Gaseous chlorine dioxide (ClO2) has been reported to be an effective intervention to eliminate bacterial contamination on fresh produce. Although remarkable positive effects of low doses of ClO2 have been reported, the genetic regulatory machinery coordinating the mechanisms of xenobiotic effects and the potential bacterial adaptation remained unclear. This study examined the temporal transcriptome profiles of E. coli O157:H7 during exposure to different doses of ClO2 in order to elucidate the genetic mechanisms underlying bacterial survival under such harsh conditions. Dosages of 1 μg, 5 μg, and 10 μg ClO2 per gram of tomato fruits cause different effects with dose-by-time dynamics. The first hour of exposure to 1 μg and 5 μg ClO2 caused only partial killing with significant growth reduction starting at the second hour, and without further significant reduction at the third hour. However, 10 μg ClO2 exposure led to massive bacterial cell death at 1 h with further increase in cell death at 2 and 3 h. The first hour exposure to 1 μg ClO2 caused activation of primary defense and survival mechanisms. However, the defense response was attenuated during the second and third hours. Upon treatment with 5 μg ClO2, the transcriptional networks showed massive downregulation of pathogenesis and stress response genes at the first hour of exposure, with decreasing number of differentially expressed genes at the second and third hours. In contrast, more genes were further downregulated with exposure to 10 μg ClO2 at the first hour, with the number of both upregulated and downregulated genes significantly decreasing at the second hour. A total of 810 genes were uniquely upregulated at the third hour at 10 μg ClO2, suggesting that the potency of xenobiotic effects had led to potential adaptation. This study provides important knowledge on the possible selection of target molecules for eliminating bacterial contamination on fresh produce without overlooking potential risks of adaptation.