Combined antibacterial effect of 460 nm light-emitting diode illumination and chitosan against Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes on fresh-cut melon, and the impact of combined treatment on fruit quality.

This study evaluated the combined antibacterial effect of 460 nm LED illumination and chitosan on Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes on fresh-cut melon surface and its impact on the quality of melon at a total dose of 2.4 kJ/cm2 at 4 and 10 °C. Results showed that the antibacterial effect of LED illumination in combination with chitosan (0.5 and 1.0%) was much better than that of LED illumination alone, showing their synergistic effect. Among the pathogens, L. monocytogenes was the most susceptible pathogen to LED illumination. Although the color of melons became paler after LED illumination, there was little to no change in ascorbic acid content, total flavonoid content, or antioxidant capacity of the illuminated fruits compared with non-illuminated fruits. Thus, these results suggest that chitosan-mediated 460 nm LED illumination could be applied to inactivate foodborne pathogens on fresh-cut melons during storage at food establishments.

Biofilm formation in food processing plants and novel control strategies to combat resistant biofilms: the case of Salmonella spp.

Salmonella is one of the pathogens that cause many foodborne outbreaks throughout the world, representing an important global public health problem. Salmonella strains with biofilm-forming abilities have been frequently isolated from different food processing plants, especially in poultry industry. Biofilm formation of Salmonella on various surfaces can increase their viability, contributing to their persistence in food processing environments and cross-contamination of food products. In recent years, increasing concerns arise about the antimicrobial resistant and disinfectant tolerant Salmonella, while adaptation of Salmonella in biofilms to disinfectants exacerbate this problem. Facing difficulties to inhibit or remove Salmonella biofilms in food industry, eco-friendly and effective strategies based on chemical, biotechnological and physical methods are in urgent need. This review discusses biofilm formation of Salmonella in food industries, with emphasis on the current available knowledge related to antimicrobial resistance, together with an overview of promising antibiofilm strategies for controlling Salmonella in food production environments.

Antioxidative and Anti-Inflammatory Activities of Rosebud Extracts of Newly Crossbred Roses.

Oxidative stress and inflammation are basic pathogenic factors involved in tissue injury and pain, as well as acute and chronic diseases. Since long-term uses of synthetic steroids and non-steroidal anti-inflammatory drugs (NSAIDs) cause severe adverse effects, novel effective materials with minimal side effects are required. In this study, polyphenol content and antioxidative activity of rosebud extracts from 24 newly crossbred Korean roses were analyzed. Among them, Pretty Velvet rosebud extract (PVRE) was found to contain high polyphenols and to show in vitro antioxidative and anti-inflammatory activities. In RAW 264.7 cells stimulated with lipopolysaccharide (LPS), PVRE down-regulated mRNA expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), and thereby decreased nitric oxide (NO) and prostaglandin E2 (PGE2) production. In a subcutaneous air-pouch inflammation model, treatment with PVRE decreased λ-carrageenan-induced tissue exudation, infiltration of inflammatory cells, and inflammatory cytokines such as tumor necrosis factor-α and interleukin-1ß concentrations, as achieved with dexamethasone (a representative steroid). Notably, PVRE also inhibited PGE2, similar to dexamethasone and indomethacin (a representative NSAID). The anti-inflammatory effects of PVRE were confirmed by microscopic findings, attenuating tissue erythema, edema, and inflammatory cell infiltration. These results indicate that PVRE exhibits dual (steroid- and NSAID-like) anti-inflammatory activities by blocking both the iNOS-NO and COX-2-PG pathways, and that PVRE could be a potential candidate as an anti-inflammatory material for diverse tissue injuries.

Genome-wide transcriptional response of Escherichia coli O157:H7 to light-emitting diodes with various wavelengths.

We investigated the physiological and transcriptomic response of Escherichia coli at the early stationary phase to light-emitting diodes with different wavelengths. The growth and metabolic changes of E. coli O157:H7 were examined under the influence of 465, 520, and 625 nm illuminated light. Under 465 nm illumination, the growth of E. coli O157:H7 was significantly retarded compared to 520 nm and 625 nm illumination and non-illuminated control. Metabolic changes were examined under these illumination and non-illuminated conditions based on transcriptomic reads. Transcriptomic response under 520 nm and 625 nm remained almost similar to control except few up-and down-regulated genes. Carbohydrates metabolic transcriptomic reads were greatly down-regulated under 465 nm illumination compared to 520 nm and 625 nm illumination and non-illuminated control showing depletion of glucose as a sole energy source during the exponential phase. Fatty acid degradation such as fad regulon-related genes was up-regulated in cells under 465 nm illumination revealing the shifting of cells to use fatty acid as a new carbon energy source during the early stationary phase. Exposure of E. coli O157:H7 cells to 465 nm illuminated light down-regulated virulence factor genes such as hlyA, hlyB, hlyC, stx1A, stx2B, paa, and bdm. Under the stress of 465 nm illumination, expression of stress and flagellar motility-related genes were up-regulated causing consumption of energy and reduction in cell growth. Also, oxidative phosphorylated transcriptomic reads were up-regulated under 465 nm illumination probably due to the production of ROS that might involve in the reduction of cell growth during the early stationary phase. These results indicate that pathogenic E. coli O157:H7 respond differentially to a different wavelength of the light-emitting diodes used in this study.

Chitosan enhances antibacterial efficacy of 405 nm light-emitting diode illumination against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. on fresh-cut melon.

This study aimed to evaluate the influence of chitosan on the antibacterial efficacy of 405 nm LED illumination against Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes on fresh-cut melons. The antibacterial efficacy of LED illumination (a total dose of 1.3 kJ/cm2) with or without chitosan (0.5 and 1.0 %) against these three pathogens was determined at 4 and 10 °C, respectively. Non-illuminated and chitosan-treated fruits were stored in the dark for 36 h under the same temperature. Color changes, ascorbic acid content, and total flavonoid content of illuminated and non-illuminated fruits were also analyzed. The results showed that the populations of all three pathogens on the non-illuminated and chitosan-treated fruits remained unchanged during storage. Regardless of bacterial species and chitosan concentrations, LED illumination in combination with chitosan greatly reduced the bacterial populations by 1.5 - 3.5 log/cm2, which was greater than LED illumination alone. Among the three pathogens, L. monocytogenes was the most susceptible to chitosan-mediated LED illumination. However, the whiteness index of illuminated fruits significantly increased by 1.3-fold compared to that of non-illuminated fruits, regardless of the presence of chitosan. Unlike color, no significant difference was observed in ascorbic acid and total flavonoid contents between illuminated and non-illuminated fruits. Although the fruit color was changed by LED illumination, these results indicate that adding chitosan could enhance the antibacterial efficacy of 405 nm LED illumination against major foodborne pathogens on fresh-cut melons without changing nutritional quality.

A review on recent advances in LED-based non-thermal technique for food safety: current applications and future trends.

Light-emitting diodes (LEDs) is an eco-friendly light source with broad-spectrum antimicrobial activity. Recent studies have extensively been conducted to evaluate its efficacy in microbiological safety and the potential as a preservation method to extend the shelf-life of foods. This review aims to present the latest update of recent studies on the basics (physical, biochemical and mechanical basics) and antimicrobial activity of LEDs, as well as its application in the food industry. The highlight will be focused on the effects of LEDs on different types (bacteria, yeast/molds, viruses) and forms (planktonic cells, biofilms, endospores, fungal toxin) of microorganisms. The antimicrobial activity of LEDs on various food matrices was also evaluated, together with further analysis on the food-related factors that lead to the differences in LEDs efficiency. Besides, the applications of LEDs on the food-related conditions, packaged food, and equipment that could enhance LEDs efficiency were discussed to explore the future trends of LEDs technology in the food industry. Overall, the present review provides important insights for future research and the application of LEDs in the food industry.

Combating biofilms of foodborne pathogens with bacteriocins by lactic acid bacteria in the food industry.

Most foodborne pathogens have biofilm-forming capacity and prefer to grow in the form of biofilms. Presence of biofilms on food contact surfaces can lead to persistence of pathogens and the recurrent cross-contamination of food products, resulting in serious problems associated with food safety and economic losses. Resistance of biofilm cells to conventional sanitizers urges the development of natural alternatives to effectively inhibit biofilm formation and eradicate preformed biofilms. Lactic acid bacteria (LAB) produce bacteriocins which are ribosomally synthesized antimicrobial peptides, providing a great source of nature antimicrobials with the advantages of green and safe properties. Studies on biofilm control by newly identified bacteriocins are increasing, targeting primarily onListeria monocytogenes, Staphylococcus aureus, Salmonella, and Escherichia coli. This review systematically complies and assesses the antibiofilm property of LAB bacteriocins in controlling foodborne bacterial-biofilms on food contact surfaces. The bacteriocin-producing LAB genera/species, test method (inhibition and eradication), activity spectrum and surfaces are discussed, and the antibiofilm mechanisms are also argued. The findings indicate that bacteriocins can effectively inhibit biofilm formation in a dose-dependent manner, but are difficult to disrupt preformed biofilms. Synergistic combination with other antimicrobials, incorporation in nanoconjugates and implementation of bioengineering can help to strengthen their antibiofilm activity. This review provides an overview of the potential and application of LAB bacteriocins in combating bacterial biofilms in food processing environments, assisting in the development and widespread use of bacteriocin as a promising antibiofilm-agent in food industries.

Developing an LED preservation technology to minimize strawberry quality deterioration during distribution.

This study investigated the effect of LED illumination on the inactivation of Rhizopus stolonifer and Botrytis cinerea on strawberries and physicochemical properties of the strawberries. Twelve days of illumination resulted in an antifungal effect of 3.4 and 1.9 log CFU/g on R. stolonifer and B. cinerea respectively. The illumination caused no significant effect (P ≥ 0.05) on the mass, color and texture of strawberries. Furthermore, total phenolic content, trolox equivalent antioxidant capacity and anthocyanin content of the illuminated strawberries significantly increased (P < 0.05). Vitamin C content of illuminated strawberries was only significantly different (P < 0.05) from the control starting from Day 9. These results show that 405 nm LED illumination can potentially complement temperature and humidity control in preventing mold spoilage and preserving physicochemical quality of strawberries during refrigerated storage.

Recent advances in understanding the effect of acid-adaptation on the cross-protection to food-related stress of common foodborne pathogens.

Acid stress is one of the most common stresses that foodborne pathogens encounter. It could occur naturally in foods as a by-product of anaerobic respiration (fermentation), or with the addition of acids. However, foodborne pathogens have managed to survive to acid conditions and consequently develop cross-protection to subsequent stresses, challenging the efficacy of hurdle technologies. Here, we cover the studies describing the cross-protection response following acid-adaptation, and the possible molecular mechanisms for cross-protection. The current and future prospective of this research topic with the knowledge gaps in the literature are also discussed. Exposure to acid conditions (pH 3.5 - 5.5) could induce cross-protection for foodborne pathogens against subsequent stress or multiple stresses such as heat, cold, osmosis, antibiotic, disinfectant, and non-thermal technology. So far, the known molecular mechanisms that might be involved in cross-protection include sigma factors, glutamate decarboxylase (GAD) system, protection or repair of molecules, and alteration of cell membrane. Cross-protection could pose a serious threat to food safety, as many hurdle technologies are believed to be effective in controlling foodborne pathogens. Thus, the exact mechanisms underlying cross-protection in a diversity of bacterial species, stress conditions, and food matrixes should be further studied to reduce potential food safety risks.HighlightsFoodborne pathogens have managed to survive to acid stress, which may provide protection to subsequent stresses, known as cross-protection.Acid-stress may induce cross-protection to many stresses such as heat, cold, osmotic, antibiotic, disinfectant, and non-thermal technology stress.At the molecular level, foodborne pathogens use different cross-protection mechanisms, which may correlate with each other.

Influence of temperature and relative humidity on the antifungal effect of 405 nm LEDs against Botrytis cinerea and Rhizopus stolonifer and their inactivation on strawberries and tomatoes.

In recent years, photodynamic inactivation (PDI) has emerged as a promising preservation method to complement refrigeration in the fresh produce supply chain. However, due to infrastructural limitations in the supply chain, fresh produce is often exposed to environmental conditions rather than recommended storage conditions. Hence, this study aimed to investigate the influence of two important environmental variables in the fresh produce supply chain - temperature and relative humidity (RH), on the PDI of fruit spoilage molds. It also aimed to demonstrate proof-of-concept of their inactivation on fruit surfaces. In the in vitro stage, Botrytis cinerea and Rhizopus stolonifer, the two molds selected for this study, were illuminated with 405 nm LEDs on Dichloran Rose-Bengal Chloramphenicol (DRBC) agar at three levels of temperature (7, 16 and 25 °C) and relative humidity (40, 60 and 80%). Illumination under these conditions caused reductions greater than 94% in the mold populations, at all temperatures and relative humidities. Even so, a temperature of 25 °C was observed to be marginally better for the inactivation as compared to 7 and 16 °C, as it necessitated the lowest dose (6-7 kJ) for the first log reduction of both the molds. Similarly, an RH of 40% worked slightly better for the inactivation of B. cinerea, as it induced inactivation without any lag phase and required the lowest dose (8.03 kJ) for the first log reduction. When the antifungal effect was investigated on fruit surfaces, it was discovered that the illumination reduced the populations of B. cinerea and R. stolonifer on strawberries by 67% and 19%, whereas on tomatoes, the respective inactivations were 79% and 70% respectively. These results demonstrate further promise of PDI as a postharvest technology for reducing the risk of fruit spoilage. This study is also the first to demonstrate the potential of PDI to add value to supply chains where compliance to ideal storage conditions is not feasible.

Antimicrobial activity of 405 nm light-emitting diode (LED) in the presence of riboflavin against Listeria monocytogenes on the surface of smoked salmon.

This study investigated the antimicrobial activity of 405 nm light-emitting diode (LED) with and without riboflavin against Listeria monocytogenes in phosphate buffered saline (PBS) and on smoked salmon at different storage temperatures and evaluated its impact on food quality. The results show that riboflavin-mediated LED illumination in PBS 25 °C significantly inactivated L. monocytogenes cells by 6.2 log CFU/mL at 19.2 J/cm2, while illumination alone reduced 1.9 log CFU/mL of L. monocytogenes populations at 57.6 J/cm2. L. monocytogenes populations on illuminated smoked salmon decreased by 1.0-2.2 log CFU/cm2 at 1.27-2.76 kJ/cm2 at 4, 12, and 25 °C, regardless of the presence of riboflavin. Although illumination with and without riboflavin caused the lipid peroxidation and color change in smoked salmon, this study demonstrates the potential of a 405 nm LED to preserve the smoked salmon products, reducing the risk of listeriosis.

Gut Microbiome Prolongs an Inhibitory Effect of Korean Red Ginseng on High-Fat-Diet-Induced Mouse Obesity.

Although the anti-obesity effect of Korean red ginseng (Panax ginseng Meyer) has been revealed, its underlying mechanisms are not clearly understood. Here, we demonstrate an involvement of gut microbiome in the inhibitory effect of Korean red ginseng on high-fat-diet (HFD)-induced mouse obesity, and further provides information on the effects of saponin-containing red ginseng extract (SGE) and saponin-depleted red ginseng extract (GE). Mice were fed with either SGE or GE every third day for one month, and their food intakes, fat weights, plasma glucose, and insulin and leptin levels were measured. Immunofluorescence assays were conducted to measure pancreatic islet size. Stools from the mice were subjected to metagenomic analysis. Both SGE and GE attenuated HFD-induced gain of body weight, reducing HFD-induced increase of food intakes and fat weights. They also reduced HFD-increased plasma glucose, insulin, and leptin levels, decreased both fasting and postprandial glucose concentrations, and improved both insulin resistance and glucose intolerance. Immunofluorescence assays revealed that they blocked HFD-induced increase of pancreatic islet size. Our pyrosequencing of the 16S rRNA gene V3 region from stools revealed that both SGE and GE modulated HFD-altered composition of gut microbiota. Therefore, we conclude that Korean red ginseng inhibits HFD-induced obesity and diabetes by altering gut microbiome.

Evaluation of standard enrichment broths for recovery of healthy and chlorine-injured Escherichia coli O157:H7 cells in kimchi.

This study aimed to evaluate three standard enrichment broth preparations for the recovery of healthy and chlorine-injured E. coli O157:H7 cells in kimchi. The growth of healthy and chlorine-injured cells in kimchi was observed in three different broths for 24 h. Results showed that the three broths were equally effective for the growth of healthy cells, although the broth described by the International Organization for Standardization (ISO) showed better performance in terms of maximum growth rate when compared to the other two broths described by the Korea Food Code (KFC) and the Food and Drug Administration (FDA). In the case of chlorine-injured cells, similar growth patterns were observed in KFC and ISO broths, whereas inhibition or no growth was found in FDA broth. Thus, this study suggests that KFC and ISO broths were more suitable than FDA broth for the enrichment of E. coli O157:H7 cells in kimchi.

Whole genome sequencing (WGS) fails to detect antimicrobial resistance (AMR) from heteroresistant subpopulation of Salmonella enterica.

Due to rapidly falling costs, whole genome sequencing (WGS) is becoming an essential tool in the surveillance of antimicrobial resistance (AMR) in Salmonella enterica. Although there have been many recent works evaluating the accuracy of WGS in predicting AMR from a large number of Salmonella isolates, little attention has been devoted to deciphering the underlying causes of disagreement between the WGS genotype and experimentally determined AMR phenotype. This study analyzed the genomes of six S. enterica isolates previously obtained from raw chicken which exhibited disagreements between WGS genotype and AMR phenotype. A total of five WGS false negative predictions toward ampicillin, amoxicillin/clavulanate, colistin, and fosfomycin resistance were presented in conjunction with their corresponding empirical phenotypic and/or genetic evidence of heteroresistance. A further case study highlighting the inherent limitations of WGS to detect the underlying genetic mechanisms of colistin heteroresistance was presented. These findings implicate heteroresistance as an underlying cause for false negative WGS-based AMR predictions in S. enterica and suggest that widespread use of WGS in the surveillance of AMR in food isolates might severely underestimate true resistance rates.

Stress response and survival of Salmonella Enteritidis in single and dual species biofilms with Pseudomonas fluorescens following repeated exposure to quaternary ammonium compounds.

Biofilms formed on food contact surfaces are frequently exposed to disinfectants at different concentrations. This study was designed to evaluate how S. Enteritidis in single species and dual species biofilms with P. fluorescens respond to quaternary ammonium compounds (QAC) residues on food contact surfaces. The 48 h-biofilms of S. Enteritidis and P. fluorescens in single/dual species were continuously exposed to 20 ppm QAC for 5 days, followed by QAC challenge at 200 ppm and 100 ppm for attached and detached cells, respectively. Biofilm structures were observed by confocal laser scanning microscopy (CLSM) and extracellular polymeric substances (EPS)-related gene expression was also evaluated. Results showed that QAC stress led to one log lower cell counts of S. Enteritidis and P. fluorescens single species biofilms. More cellulose observed by CLSM images and increased transcript levels of cellulose-related genes (csgD, bcsA and ardA) of S. Enteritidis were induced by QAC stress. Nevertheless, high percentage of membrane damaged cells in QAC pre-exposed biofilms might contribute to the increased sensitivity of S. Enteritidis in both attached and detached cells. Previous QAC exposure did not influence S. Enteritidis viable cell counts in dual specie biofilms, in which S. Enteritidis showed strong resistance to QAC with <2 log CFU/cm2 reductions. Decreased transcript levels of cellulose-related genes were observed of S. Enteritidis in dual species biofilms, but EPS-related gene expression of P. fluorescens was not affected by single/duals species. The dual species biofilm matrix which has big microcolonies extruding from bottom layers with great amounts of polysaccharides mainly produced by P. fluorescens could possibly protect S. Enteritidis against disinfection. Enhanced survival of S. Enteritidis in dual species biofilms was also found when they were detached from the coupons. Overall, our findings highlight that although repeated exposures to low dose of QAC sensitized S. Enteritidis, the presence of P. fluorescens in dual species biofilms could enhance QAC resistance of S. Enteritidis, probably contributing to survival of S. Enteritidis in food processing plants.

Mealworm larvae (Tenebrio molitor L.) exuviae as a novel prebiotic material for BALB/c mouse gut microbiota.

The objective of this study was to evaluate the effect of yellow mealworm (Tenebrio molitor L.) exuviae (ME) given as a prebiotic in 20% of the diet fed to BALB/c mice. Analysis of the ME revealed that it was mostly composed of crude protein (52.94%), crude fiber (10.70%), and moisture (10.54%). When ME was fed to mice for 8 weeks, the number of intestinal lactic acid bacteria increased, reaching similar numbers (4.50 ± 0.80 CFU/mL) to those (4.70 ± 0.80 CFU/mL) of the control group not fed ME. Microbiome analysis showed that 8 weeks feeding of ME promoted the growth of Bifidobacteriaceae and Lactobacillaceae compared to the POS group, indicating the positive effects of feeding 20% ME on the intestinal microbiota of mice. These results suggest that ME can be considered as a dietary prebiotics to improve human gut microbial population, but further application study to human is necessary.

Development of an Effective Two-Step Enrichment Process to Enhance Bax System Detection of Healthy and Injured Salmonella Enteritidis in Liquid Whole Egg and Egg Yolk.

ABSTRACT: The BAX system for pathogen detection has been highly accurate in a variety of food products. However, false-negative results have been reported for the detection of pathogens in liquid egg products because of failed pathogen resuscitation and the existence of inhibitory components. In this study, a short-time enrichment step was used to simultaneously resuscitate the target cells to the detection level and to dilute the inhibitory components to reduce detection interference. The MP medium (BAX system) enabled faster multiplication of healthy Salmonella cells than did buffered peptone water (BPW) in tested liquid whole egg and egg yolk. However, MP failed to resuscitate heat-injured cells even after 24 h of incubation. Therefore, MP was replaced with BPW as the enrichment broth for the BAX system. However, the use of BPW for a one-step enrichment was not effective for removal of PCR inhibitors in egg yolk, and unstable detection results were obtained. To improve detection accuracy, a second step of enrichment with brain heart infusion was added. This two-step enrichment process shortened the enrichment time to 14 h and greatly increased the number of samples in which the pathogen was detected during the same enrichment time, especially in the liquid egg yolk samples. The validation study revealed 100% diagnostic accuracy of the two-step enrichment process plus the BAX system. These results indicate that a two-step enrichment process added to the BAX system can improve the detection of pathogenic Salmonella in liquid egg products.

Effects of Sublethal Thymol, Carvacrol, and trans-Cinnamaldehyde Adaptation on Virulence Properties of Escherichia coli O157:H7.

Essential oils (EOs) have demonstrated wide-spectrum antimicrobial activities and have been actively studied for their application in foods as alternative natural preservatives. However, information regarding microbial adaptive responses and changes in virulence properties following sublethal EO exposure is still scarce. The present study investigated the effect of sublethal thymol (Thy), carvacrol (Car), or trans-cinnamaldehyde (TC) adaptation on virulence gene expression and virulence properties of Escherichia coli O157:H7. The results demonstrated that E. coli O157:H7 grown to the early stationary phase in the presence of sublethal EO showed significantly (P < 0.05) reduced motility (reversible after stress removal), biofilm-forming ability, and efflux pump activity, with no induction of antibiotic resistance and no significant changes to its adhesion and invasion ability on a human colon adenocarcinoma (Caco-2) cell line. Reverse transcription-quantitative PCR revealed reduced expression of relevant virulence genes, including those encoding flagellar biosynthesis and function, biofilm formation regulators, multidrug efflux pumps, and type III secretion system components. This study demonstrated that Thy, Car, and TC at sublethal concentrations did not potentiate virulence in adapted E. coli O157:H7, which could benefit to their application in the food industry.IMPORTANCE The present study was conducted to evaluate changes in virulence properties in Escherichia coli O157:H7 adapted to sublethal essential oils (EOs). The results demonstrated reduced motility, biofilm-forming ability, and efflux pump activities in EO-adapted E. coli O157:H7, with no induction of antibiotic resistance or infection (adhesion and invasion) on Caco-2 cells. Reverse transcription-quantitative PCR results revealed changes in the expression of related virulence genes. Thus, the present study provides new insights into microbial virulence behavior following EO adaptation and suggests that Thy, Car, and TC sublethal exposure did not constitute a significant risk in inducing microbial virulence.

Survival of an emerging foodborne pathogen: Group B Streptococcus (GBS) serotype III sequence type (ST) 283-under simulated partial cooking and gastric fluid conditions.

Group B Streptococcus (GBS) was previously not known to be transmitted through food, but an outbreak investigation in Singapore in 2015 documented for the first time an association between GBS Type III Sequence Type 283 infection and consumption of raw fish dishes. As very little is known about the survival of GBS during heat treatment and the stomach transit, its survival under simulated conditions was studied, in comparison with that of Escherichia coli O157:H7 and Listeria monocytogenes. The mean D-values of four GBS strains ranging from 0.72 to 0.88 min in neutral pH tryptone soy broth at 56.4 °C and 0.44-1.43 min at pH 2.35 at 37 °C in simulated gastric fluid, were significantly lower (p < 0.05) than those of E. coli O157:H7 and L. monocytogenes. This study suggests possible factors other than acid or heat resistance of GBS to be instrumental to its pathogenicity.

Effects of the colonization sequence of Listeria monocytogenes and Pseudomonas fluorescens on survival of biofilm cells under food-related stresses and transfer to salmon.

This study evaluated how the colonization sequence of Listeria monocytogenes and Pseudomonas fluorescens affects biofilm formation and biofilm cell response to food-related stress (desiccation or disinfection) as well as the transferability of L. monocytogenes to salmon products. The results showed that the colonization sequence did not affect the population of dual species biofilms. Furthermore, survival number of L. monocytogenes was 0.8 log CFU/cm2 higher when P. fluorescens was the first colonizer during desiccation or disinfectant treatment in comparison with dual-species biofilms with other colonization sequences. A lower transfer rate of L. monocytogenes biofilm cells from dual-species biofilms was observed as compared to single species biofilms. In particular, L. monocytogenes cells detached at a slower rate during transfer to 10 slices of salmon from dual-species biofilms first established by P. fluorescens. Confocal images revealed more exopolysaccharide production in dual-speciesbiofilms first established by P. fluorescens than in biofilms generated via other sequences. These results indicate that preexisting P. fluorescens biofilms on stainless steel can enhance resistance of L. monocytogenes to desiccation and disinfection, although this setup decreased the transfer rate of L. monocytogenes to salmon slices. Thus, this study highlights the risk of L. monocytogenes contamination in pre-formed Pseudomonas biofilms at salmon processing facilities.