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We investigated the physiological and transcriptomic response of Escherichia coli at the early stationary phase to light-emitting diodes with different wavelengths. The objective of this study was to investigate the effects of 465, 520, and 625 nm illuminated light on the growth and metabolic changes of E. coli O157:H7. 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.

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.

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/cm(2), while illumination alone reduced 1.9 log CFU/mL of L. monocytogenes populations at 57.6 J/cm(2). L. monocytogenes populations on illuminated smoked salmon decreased by 1.0–2.2 log CFU/cm(2) at 1.27–2.76 kJ/cm(2) 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.

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.

AIMS Although a link between agricultural cephalosporin use and resistance in Salmonella has been demonstrated with the drug ceftiofur, the underlying mechanism of the correlation is unclear. This study investigated the impact of ceftiofur exposure in S. Saintpaul on ceftriaxone resistance, the gene expression and the conjugative transfer of the blaCTX-M-65 gene. METHODS AND RESULTS Prior ceftiofur exposure caused a twofold increase in MIC from 1024 to 2048 µg ml-1 towards ceftriaxone and increased the enzymatic activity of BlaCTX-M-65 2·2 folds from 3·46 to 7·67 nmol nitrocefin hydrolysed min-1 . A threefold upregulation in gene expression of the blaCTX-M-65 gene was also observed. Donors exposed to ceftiofur subsequently demonstrated a 2·5-fold decrease in transfer efficiency. CONCLUSIONS Prior exposure of S. Saintpaul to ceftiofur led to increased phenotypic resistance towards ceftriaxone while its ability to spread the cephalosporin resistance through conjugation, conversely, was impaired. SIGNIFICANCE AND IMPACT OF THE STUDY Findings from this study shed light on one possible mechanism in which agricultural cephalosporin exposure in Salmonella may subsequently impact clinical treatment. The finding that cephalosporin exposure in donors may hinder the subsequent spread of resistance instead of aiding it up was counter-intuitive.

Foodborne disease caused by pathogenic bacteria is one of main concerns in food industry. To supply safe food products, chemical and thermal intervention technologies have been widely applied in food industry, however these treatments have their own limitations. The concept of biopreservation has recently received increased attention in response to industrial and consumer demands. The biopreservation technologies mainly include bacteriocin, bacteriophage, bacteriophage-encoded enzymes, and endolysins. Among them, bacteriocins have been widely recognized as a main biopreservative and have also been most studied. Bacteriocins, mainly consisting of antibacterial peptides, may have bactericidal or bacteriostatic effect which could prolong the shelf-life as well as maintain safety of foods. This review article offers a brief research trend about bacteriocins, focusing on microbial food safety. The antimicrobial mechanism of bacteriocins has been discussed and some efforts to inactivate foodborne pathogens have been analyzed in this review article. The challenges facing the application of bacteriocins have also been evaluated. Thus, this review will provide insights for researchers working in bacteriocin as well as industry personnel looking for a new method for fighting foodborne pathogens.

Salmonella is a major cause of foodborne illness throughout the world and has resulted in a serious of public health issues over the past decades. The conventional culture methods for Salmonella detection are laborious and time-consuming; thus a variety of new methods have been developed to enable rapid detection. Among them, immuno- and nucleic acid-based methods are fast developing because the advancing of molecular science provides more target antibodies and genes for Salmonella detection. These new targets might enable a lower detection limit and higher sensitivity/specificity and, therefore shorten the detection period while ensuring the detection accuracy. This review emphasizes the effect of current immuno- and nucleic acid-based techniques for Salmonella detection. The target antibodies and target genes identified and applied during the latest research are also listed out as a reference. Besides, the main features of various immune- and nucleic acid-based techniques used for Salmonella detection in food are also summarized and compared. This review would provide the in-time and comprehensive guidance to achieve rapid and accurate detection of foodborne Salmonella.

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.

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.

본 연구에서는 460 nm 파장의 청색 가시광선을 압출 떡의 표면에 조사하기 위하여 장치의 최적 디자인을 시뮬레이션을 통하여 확인하고 청색광이 압출 떡의 표면에서 식품 위해균인 B. cereus group에 미치는 영향을 확인하였다. LED 장치에서 광원모듈의 세 가지 배열(centered, cross, evenly spaced) 및 광원과 샘플 표면 사이의 거리(22, 32, 42 mm)에 따른 조사 면적에서 빛의 세기 패턴을 시뮬레이션을 통하여 계산하고, Petri factor를 통하여 균일도를 확인하였다. LED 배열의 균일도는 evenly spaced 배열에서 가장 균일한 패턴을 보였으며, 광원과의 거리가 32 및 42 mm일 경우 Petri factor가 0.9 이상으로 높은 균일도를 나타내었다. 떡볶이 떡에 LED 청색광을 조사한 경우 24 h 후 균 수가 초기 균 수에 비하여 감소하였으며, LED를 조사하지 않은 대조군에서는 초기 균 수가 증가하여 1.21 log CFU/g의 차이를 보였다. LED 조사 시 광원과 샘플의 거리가 증가할수록 Petri factor는 증가하나 감균 효과가 낮아지는 결과를 나타내었다. 따라서 Petri factor가 0.9 이상임을 만족하는 evenly spaced 배열의 32 mm 거리가 떡의 유통기한 연장을 위한 LED 장치의 디자인에 적합함을 확인하였다.

Black raspberry (Rubus occidentalis), which is known as Bokbunja in Korea, has traditionally known to possess various physiological functions such as anticarcinogenic and antioxidant effects. Although these functions have been well studied previously, little work has been done on its antimicrobial effect against foodborne pathogens. Thus, the objective of this study was to evaluate the antimicrobial activity of ethanolic and aqueous Bokbunja extracts against Escherichia coli, E. coli O157:H7 and Staphylococcus aureus cultures. The antimicrobial activity was assessed by determining the minimum inhibitory concentration (MIC) of each extract with each bacterial strain. The 10, 20 and 30% (w/v) EtOH extracts of the fruit pomace and an aqueous extract of the ripened fruit had lower MIC values (4-6 mg/100 μL) for both E. coli and S. aureus than the other extracts (8-12 mg/100 μL). Based on these results, these four extracts were further compared for their antimicrobial activities using time kill assay. Among the four extracts, the DW extract of ripened fruit decreased the populations of E. coli O157:H7 and S. aureus by 1.5 and 2.4 log CFU/mL for 24 h at 37℃, respectively, which were higher log reductions than those of the other three extracts. Thus, these results suggest that the DW extract of ripened Bokbunja fruit could be used as a natural preservative for the food products.

L. monocytogenes is able to form biofilms as survival strategy in food processing environments. This study aimed to evaluate biofilm formation and sanitizer resistance of L. monocytogenes under a simulated salmon processing environment, involving low temperature, presence of organic matter and cultivable indigenous microorganisms (CIMs) in fresh salmon. Biofilms of L. monocytogenes in single- and mixed-species with CIMs were formed on stainless steel coupons by incubating in diluted trypticase soy broth (dTSB, 1:20) or salmon broth at 4 and 15 °C for 14 days. Biofilm cell counts before and after exposure to Whisper™ V (quaternary ammonium compounds, 200 ppm) were determined on day 1, 4, 7, and 14. Results showed that L. monocytogenes single-species biofilms developed at 15 °C had higher populations compared with those formed at 4 °C from day 1 to day 7. The cell populations of the 4 °C-grown biofilms increased by 1–2 log CFU/cm2 after 14 days, whereas the cell density of 15 °C-grown biofilms on day 14 was not significantly (P > 0.05) different from that on day 1. The presence of CIMs led to lower L. monocytogenes populations in mixed-species biofilms on day 7 and day 14, whereas it did not significantly (P > 0.05) influence the sanitizer sensitivity of L. monocytogenes. By PCA analysis, culture medium was identified a dominant factor influencing biofilm formation and QAC resistance compared with other factors. Specifically, salmon broth promoted L. monocytogenes biofilm formation and diminished the efficacy of sanitizer compared with dTSB. Confocal images showed thick matrix of biofilms cultured in salmon broth, and a visible coating layer can be observed on the surface. This conditioning layer might explain for the lower sanitizer susceptibility of L. monocytogenes in salmon broth. Thus, these results could advance our understanding towards persistence of L. monocytogenes in salmon processing environments, with emphasize on food-related broth in increasing its biofilm formation and sanitizer resistance. Our study suggests that food-related broth should be applied in biofilm study instead of chemical culture medium, which might lead to underestimation of L. monocytogenes survival at food premises.

This study evaluated the antimicrobial activities of combined use of essential oil (EO) compounds against E. coli O157:H7, using the Fractional Inhibitory Concentration (FIC) index and time-kill assay. The mechanisms of enhanced antimicrobial efficacies in EO combinations were evaluated using flow cytometry, and their application potentials as decontamination rinse were assessed using fresh-cut lettuce. Thymol (Thy), carvacrol (Car), trans-cinnamaldehyde (TC), eugenol (Eug) and vanillin (Van) displayed minimum inhibitory concentrations (MICs) in a range of 0.63–2.5 mg/mL, whereas citral (Cit) and linalool (Lin) were ineffective (MIC > 10 mg/mL). FIC indices (1.00–2.00) suggested additive interactions of all EO combinations, and time kill assay showed enhanced bactericidal activities in Thy/Eug, Car/Eug and TC/Eug combinations. The stronger antimicrobial efficacy in EO combination was attributed to increased membrane damages. Application of Thy/Eug and Car/Eug on fresh-cut lettuce as decontamination rinse caused a significant (P

Photodynamic inactivation is a phenomenon that has the potential to cause microbial inactivation using visible light. It works on the principle that photosensitizers within the microbial cell can be activated using specific wavelengths to trigger a series of cytotoxic reactions. In the last few years, efforts to apply this intervention technology for food safety have been on the rise. This review article offers a detailed commentary on this research. The mechanism of photodynamic inactivation has been discussed as have the factors that influence its efficacy in food. Efforts to inactivate bacteria, fungi, and viruses have been analyzed in dedicated sections and so has the application of this technology to specific product classes such as fresh produce, dry fruits, seafood, and poultry. The challenges and opportunities facing the application of this technology to food systems have been evaluated and future research directions proposed. Thus, this review will provide insights for researchers and industry personnel looking for a novel solution to combat microbial contamination and resistance.

This study evaluated the potential of blue light-emitting diodes (LED) of wavelength 405 and 460 nm in combination with sodium chlorophyllin to inactivate Listeria monocytogenes and Salmonella spp. on cantaloupe rind. A cocktail culture of L. monocytogenes or Salmonella spp. strains was surface inoculated onto cantaloupe rinds to reach a final concentration of 4 log CFU/cm2 and dip-treated in a 100 μM sodium copper chlorophyllin solution. The cantaloupe samples were then exposed to 405 or 460 nm LEDs at a total dose of 1210 J/cm2 and 5356 J/cm2, respectively, at 4 and 20 °C. Results showed that the antibacterial efficacy against both pathogens on cantaloupe rinds between LED alone and LED with the chlorophyllin were statistically similar with bacterial inactivation ranging from 1.1 to 3 log CFU/cm2 in most of the cases or the difference was only minimal. A similar inactivation of 3 log CFU/cm2 was obtained in the case of L. monocytogenes and Salmonella spp. when illuminated by 405 nm LEDs while the inactivation of L. monocytogenes was higher than Salmonella spp. when illuminated by 460 nm LED. The δ value, a modified Weibull model parameter defined as the time (h) taken to reduce the bacterial population by 90%, was computed to compare the inactivation rates of the conditions. It was inferred that illumination with 405 nm LED required a lower δ value than 460 nm LED illumination (P

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.

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.

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.

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.

Salmonellosis, caused by multidrug-resistant Salmonella species, in particular, is one of the leading notifiable foodborne diseases in Singapore and an emerging public health concern worldwide. The objectives of this study were to determine the prevalence, antibiotic resistance and the presence of gyrA and parC mutations in Salmonella isolated from retail fresh chicken meat in Singapore. A significantly higher prevalence of Salmonella was found in chicken meat from the wet markets (25%, 30/120), as compared to supermarkets (12.7%, 19/150). The top four serovars isolated in this study were S. Saintpaul (32.7%, 17/52), followed by S. Brancaster (21.2%, 11/52), S. Albany (11.5%, 6/52), and S. Stanley (9.6%, 5/52). More than 80% of Salmonella isolates exhibited resistance to at least one of eleven antibiotics tested. The most common phenotypic resistances exhibited were towards ampicillin (78.8%, 41/52), tetracycline and chloramphenicol (61.5%, 32/52), sulfamethoxazole-trimethoprim (55.8%, 29/52) and nalidixic acid (30.8%, 16/52). Of the 52 Salmonella isolates, 59.6% (31/52) were multi-drug resistant strains, resistant to 3 or more antibiotic classes. No mutation in parC gene was found in any of the isolates that expressed phenotypic resistance or reduced susceptibility towards quinolone and/or fluoroquinolone. Mutations at two different sites of gyrA gene were found in 7 isolates, which further discriminates the quinolone resistance genotype in Salmonella isolates from fresh chicken meat. Our findings provide opportunities for risk assessment and management of salmonellosis and antibiotic-resistant Salmonella species in the country and the region.

The aim of this study was to evaluate the antibacterial effect of 405 nm light-emitting diode (LED) against Listeria monocytogenes and Salmonella spp. on the surface of ready-to-eat (RTE) fresh salmon, and to determine the susceptibility of LED-illuminated bacterial cells to simulated gastric fluid (SGF). A cocktail culture of L. monocytogenes or Salmonella spp. was inoculated onto the freshly cut salmon surface and then illuminated by 405 nm LED (16 ± 2 mW/cm2) for 8 h at 4 and 12 °C. Illuminated cells were subsequently exposed to SGF at 37 °C. Results showed that the populations of LED-illuminated L. monocytogenes and Salmonella cells were significantly (P

Salmonella Enteritidis may be encountered in poultry processing plants in the form of biofilms on food contact surfaces. Little is known about the fate of Salmonella in mixed-species biofilms with other bacteria commonly found in food processing environment. Thus, the objectives of this study were to determine biofilm formation and sanitizer resistance of two S. Enteritidis strains (rdar and bdar, cellulose expression positive and negative, respectively), in the absence and presence of Pseudomonas aeruginosa, under conditions encountered in poultry processing plants. S. Enteritidis in single-species and dual-species biofilms with P. aeruginosa at two mixed ratios (Salmonella: Pseudomonas cells at 1:1 and 0.01:1, respectively) were formed on stainless steel coupons in chicken juice for 6 days at 25 °C. On days 1 and 6 of the incubation period, biofilm cell populations were determined before and after chlorine treatment (50 ppm, 1 min). Results showed that population of S. Enteritidis in dual-species biofilms was significantly lower (P

This study investigated the antibacterial effect of a 460 nm light emitting diode (LED) in combination with riboflavin on the inactivation of Listeria monocytogenes on smoked salmon. The influence of irradiance and temperature on this inactivation was examined. Smoked salmon fillets, surface-inoculated with a 4-strain cocktail of L. monocytogenes and topically administered with 25, 50 and 100 μM riboflavin, were illuminated by 460 nm LEDs at three different irradiances (15, 31 and 58 mW/cm2) and two temperatures (4 and 12 °C). Three conceptually different mathematical models - log-linear, modified Weibull and reduced Baranyi were used to fit the inactivation curves. The color of smoked salmon was also monitored during the illumination. A dosage of 2.4 kJ/cm2 LED illumination in combination with riboflavin caused 0.7–1.2 log CFU//cm2 reductions of L. monocytogenes at all irradiances and temperatures. Three-way ANOVA showed that all the three variables significantly influenced the inactivation of L. monocytogenes (P

The objective of this study was to evaluate the anti-biofilm effect of 405-nm light-emitting diodes (LEDs) against Listeria monocytogenes in salmon exudate at 4, 15, and 25 °C, and to compare the susceptibility of LED-illuminated and non-illuminated pre-formed biofilm cells to sanitizer treatment. For the biofilm-forming scenario, stainless-steel (SS) or acrylic (AC) coupons in sterilized salmon exudate were inoculated with L. monocytogenes and then illuminated with 405-nm LEDs (26 ± 2 mW/cm 2 ) at each temperature for 8 h. For the pre-formed biofilm scenario, L. monocytogenes biofilms were pre-formed onto each coupon at 25 °C for 24 h and subsequently illuminated at each temperature, followed by treatment with 200 ppm quaternary ammonium compound (QAC) for 10 s to compare the sensitivity of LED-illuminated biofilm cells to the sanitizer treatment. Regardless of illumination temperature, the results showed that 405-nm LED illumination significantly ( P P ≥ 0.05) changes in the planktonic and biofilm cell populations, for the pre-formed biofilm scenario, in response to LED illumination at 4 and 15 °C. However, significant biofilm cell reductions were observed on SS and AC coupons in response to LED illumination at 25 °C for 8 h. Regardless of coupon type, LED-illuminated biofilm cells were found to be more sensitive to QAC treatment under the pre-formed biofilm scenario than non-illuminated cells. These results indicate that 405-nm LED illumination may be effective in controlling L. monocytogenes during the biofilm formation process, and at inducing sensitivity to sanitizer treatment in pre-formed biofilm cells. Thus, this study suggests the potential of LED technology in controlling L. monocytogenes biofilms during the processing and storage of ready-to-eat salmon, minimizing the chance of cross-contamination from contaminated surfaces.

The aim of this study was to elucidate the antibacterial mechanism of riboflavin-mediated 460 nm light emitting diode (LED) illumination against Listeria monocytogenes in phosphate buffered saline (PBS) solution and on the surface of smoked salmon by determining reactive oxygen species (ROS) production, bacterial membrane permeability, and DNA damage in PBS as well as bacterial metabolic inhibition on smoked salmon. Its antibacterial efficacy against L. monocytogenes in PBS and on the surface of smoke salmon was also evaluated. The results showed that LED illumination alone reduced 0.6 log CFU/ml of L. monocytogenes at dose of 0.2 kJ/cm2, while illumination with riboflavin (100 μM) inactivated 5.6 log CFU/ml in PBS at 20 °C. On the surface of smoked salmon, LED illumination with/without riboflavin reduced less than 1.0 log CFU/cm2 of L. monocytogenes populations at 4 °C at 12.8 kJ/cm2. At 10 °C, bacterial populations on non-illuminated and illuminated samples increased to 5.9 and 4.4 log CFU/cm2, respectively, whereas riboflavin-mediated LED illumination inactivated 1.0 log CFU/cm2. The amount of ROS observed in illuminated cells with riboflavin was higher than those of non-illuminated and illuminated cells. LED illumination alone induced cellular damage to metabolism of RNA and protein, while riboflavin-mediated illumination caused additional metabolic inhibition to DNA. Therefore, these results suggest that the antibacterial mechanism of riboflavin-mediated 460 nm LED illumination might be due to membrane and DNA damages by ROS generated from photo-reaction of riboflavin as well as metabolic inhibition. This study could provide novel insight in the application of riboflavin-mediated 460 nm LED technology to preserve smoked salmon at refrigeration temperatures, minimizing the risk of listeriosis.

Extracts from medicinal plants have been reported to possess good antimicrobial properties, but a majority of them remain unexplored. This study aimed at identifying a novel plant extract with antimicrobial activity, to validate its efficacy in food model, and to elucidate its composition and antimicrobial mechanism. A total of 125 plant extracts were screened, and Cinnamomum javanicum leaf and stem extract showed potential antimicrobial activity against Listeria monocytogenes (MIC=0.13mg/mL). Total phenolic content of the extract was 78.3mg GAE/g extract and its antioxidant activity was 57.2-326.5mg TE/g extract. When applied on cold smoked salmon, strong strain-dependent antimicrobial effectiveness was observed, with L. monocytogenes LM2 (serotype 4b) and LM8 (serotype 3a) being more resistant compared to SSA81 (serotype 1/2a). High extract concentration (16mg/mL) was needed to inhibit or reduce the growth of L. monocytogenes on smoked salmon, which resulted in surface color change. GC-MS revealed that eucalyptol (25.54 area%) was the most abundant compound in the crude extract. Both crude extract and eucalyptol induced significant membrane damages in treated L. monocytogenes. These results suggest anti-L. monocytogenes activity of C. javanicum plant extract, identified its major volatile components, and elucidated its membrane-damaging antimicrobial mechanisms.

BACKGROUND Singapore’s status as a first world island city-state which relies chiefly on food imports to meet the demand for consumption presents unique challenges in terms of microbial food safety and quality. Despite the efforts of the Ministry of Health in Singapore, in conjunction with the Agri-Food & Veterinary Authority of Singapore and the National Environment Agency actively collaborate together to promote safety in Singapore, foodborne diseases are still a major public health issue. OBJECTIVE The aim of the review was to summarize the various foodborne diseases reported in Singapore in the past few years as well as to give an account of all the currently available microbiological findings indicating safety and quality of poultry, vegetables, fruits, and seafood sold in Singapore.

The objective of this study was to investigate the effect of 460 nm light-emitting diode (LED) on the inactivation of foodborne bacteria. Additionally, the change in the endogenous metabolic profile of LED illuminated cells was analyzed to understand the bacterial response to the LED illumination. Six different species of bacteria (Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O157:H7, Pseudomonas aeruginosa and Salmonella Typhimurium) were illuminated with 460 nm LED to a maximum dose of 4080 J/cm2 at 4, 10 and 25 °C. Inactivation curves were modeled using Hom model. Metabolic profiling of the non-illuminated and illuminated cells was performed using a Liquid chromatography–mass spectrometry system. Results indicate that the 460 nm LED significantly (p < 0.05) reduced the populations of all six bacterial species. For example, the population of S. aureus reached below detection limit within 7 h. B. cereus was most resistant to photo-inactivation and exhibited about 3-log reduction in 9 h. Metabolic profiling of the illuminated cells indicated that several metabolites e.g. 11-deoxycortisol, actinonin, coformycin, tyramine, chitobiose etc. were regulated during LED illumination. These results elucidate the effectiveness of 460 nm LED against foodborne bacteria and hence, its suitability as a novel antimicrobial control method to ensure food safety.

The objective of this study was to investigate the effectiveness of various decontamination treatments of raw salmon fillets, namely acidic electrolyzed water (AEW), ultraviolet light (UV), ultrasound (US), and their combinations against Listeria monocytogenes and natural microbiota including total viable count (TVC), total coliforms, Escherichia coli, and yeasts and molds. The changes in quality and sensory parameters of treated salmon samples were also evaluated. The combined treatments: UV + US and UV + US + AEW showed significantly (P ≤ 0.05) higher reduction in L. monocytogenes of 0.79 and 0.75 log CFU/g, respectively, compared to control (0.17 log CFU/g) washed with sterile distilled water (dH2O). TVC was reduced by 0.59 and 0.64 log CFU/g after UV + US and UV + US + AEW treatments, respectively. The color and odor of salmon were significantly affected after combined treatments, but the texture and firmness of tissue were not significantly (P > 0.05) changed. These results indicate that UV + US and UV + US + AEW were the most effective at reducing the populations of L. monocytogenes and natural microbiota on raw salmon fillets. The AEW treatment by itself was found to be ineffective for raw salmon sanitation. However, these combined treatments should be improved by optimizing other factors such as treatment temperature, time and the distance between UV and food sample to enhance their anti-listerial or antimicrobial effects.

This study investigated the biofilm formation by three S. Enteritidis strains in a simulated liquid egg processing environment using 0.1% peptone water (PW) (control), 10% whole eggs (WE), 10% egg yolks (EY) and 10% egg whites (EW) as growth media, and evaluated the effectiveness of chlorine (200 ppm, 5 min) and hot water (71 °C, 30 s) treatments against S. Enteritidis biofilms. The results showed that S. Enteritidis formed significantly (P

Blue light emitting diodes (LEDs) have emerged as an intervention against Salmonella, which colonizes and grows on fresh-cut fruits. This study evaluated their efficacy on fresh-cut pineapples. Pineapple slices were surface-inoculated with a Salmonella cocktail and illuminated with 460 nm LEDs at different irradiances (92, 147.7 and 254.7 mW/cm2) and temperatures (7, 16 and 25 °C). The resulting differences in the populations of control and illuminated samples were modeled to determine the antibacterial effect. The color of the slices was also measured. Bactericidal action was observed at 7 and 16 °C and growth inhibition at 25 °C. An adapted Weibull model best described the inactivation, with the D values ranging from 15 to 27 kJ/cm2. Temperature influenced the antibacterial effect but the irradiance had no significant effect (P ≥ 0.05). Though the illuminated pineapple slices tended to be bleached, this study demonstrated the potential of 460 nm LEDs against Salmonella on fresh-cut pineapple slices.

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

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. HIGHLIGHTS

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.

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.