Common Foodborne Pathogens Research Articles

Cell wall and DNA damage of Staphylococcus aureus by bacteriocin BM1157

Staphylococcus aureus is one of the most common foodborne pathogens, and it can cause food poisoning. As a promising alternative to antibiotic, bacteriocin has been widely used in food as bio-preservative. In this study, the bacteriocin BM1157 had good antibacterial activity against S. aureus according to growth curve. BM1157 treatment reduced positively charged hydrophilic group of cell surface and caused an increase of cell hydrophobicity. SEM and TEM images showed that BM1157 treatment damaged cell wall and caused nonuniform distribution of cytoplasmic materials. Results of propidium iodide (PI) uptake and lactic dehydrogenase (LDH) release indicated that BM1157 treatment damaged cell envelope integrity of S. aureus. Proteome analysis showed that 117 proteins were up-regulated and 408 proteins were down-regulated after BM1157 treatment, among which enzymes involved in peptidoglycan biosynthesis and proteins related to DNA replication and repair were included. Further, real-time quantitative PCR verified the gene down-regulation of proteins of peptidoglycan biosynthesis and DNA replication and repair of S. aureus. Moreover, agarose gel electrophoresis showed that BM1157 could bind to the DNA of S. aureus. This study suggested that BM1157 killed S. aureus by damage of cell wall and DNA.

Ultrasensitive peptide-based multiplexed electrochemical biosensor for the simultaneous detection of Listeria monocytogenes and Staphylococcus aureus.

Anovel electrochemical biosensor is reportedfor simultaneous detection of two of the most common food-borne pathogens: Listeria monocytogenes and Staphylococcus aureus. Thebiosensor is composed of an array of gold nanoparticles-modified screen-printed carbon electrodes on which magnetic nanoparticles coupled to specific peptides were immobilized via streptavidin-biotin interaction. Taking advantage of the proteolytic activities of the protease enzymes produced from the two bacteria on the specific peptides, the detection was achieved in 1min. The detection was realized by measuring the percentage increase of the square wave voltammetric peak current at 0.1V versus aAg/AgCl reference electrode in ferro/ferricyanide redox couple after incubation with the bacteria protease. The integration of the specificity of the bacterial enzymes towards their peptide substrates with the sensitivity of the electrochemical detection on the sensor array allows the rapid, sensitive and selective quantification of the two bacteria. Outstanding sensitivities were achieved using this biosensor array platform with limit of detection of 9CFUmL-1 for Listeria monocytogenes and 3CFUmL-1 for Staphylococcus aureus. The multiplexing capability and selectivity of thearray voltammetric biosensor were demonstrated by analysing samples of Staphylococcus aureus, Listeria monocytogenes or E. coli and also containing a mixture of two or three bacteria. Using this biosensor, the two bacteria were successfully quantified simultaneously in one step without the need for DNA extraction or amplification techniques. This platform offers promise for rapid, simple and cost-effective simultaneous detection of various bacteria. Graphical abstract.

Inhibitory Effects of Combinations of Chemicals on Escherichia coli, Bacillus cereus, and Staphylococcus aureus Biofilms during the Clean-in-Place Process at an Experimental Dairy Plant

In dairy plants, clean-in-place (CIP) equipment cannot be disassembled, making it difficult to clean the inner surface of pipes. In this study, the inhibitory effects of chemical agents on biofilms formed by three foodborne pathogens, Bacillus cereus, Escherichia coli, and Staphylococcus aureus, was evaluated in a dairy CIP system. The experiment was conducted on a laboratory scale. Each of the three bacteria (200 μL) was inoculated onto stainless steel (SS) chips (25 by 25 mm), and the effect of single cleaning agents was evaluated. Individual treatments with NaClO (30, 50, 100, and 200 ppm), NaOH (0.005, 0.01, 0.05, and 0.1%), citric acid (1, 3, 5, and 7%), and nisin (5, 10, 25, 50, 100, and 200 ppm) were used to clean the SS chip for 10 min. The most effective concentration of each solution was selected for further testing in a commercial plant. Simultaneous cleaning with 200 ppm of NaClO (10 min) and 7% citric acid (10 min) reduced the biofilms of B. cereus, E. coli, and S. aureus by 6.9, 7.0, and 8.0 log CFU/cm2, respectively. Both 7% citric acid and 0.1% NaOH were optimal treatments for E. coli. NaClO and citric acid are approved for use as food additives in the Republic of Korea. Our results revealed that a combined treatment with NaClO and citric acid is the most effective approach for reducing biofilms formed by common foodborne pathogens on CIP equipment. These findings can contribute to the production of safe dairy products.

Development of a multiplex PCR method for the detection of six common foodborne pathogens

This study developed a multiplex PCR method for the screening and detection of six common foodborne pathogens in Macao. The m-PCR procedure, which uses six pairs of primers, produced specific amplicons of the expected sizes from mixed populations of reference bacterial strains in food samples and from pure cultures. The verocytotoxin (stx) gene of Escherichia coli O157:H7, the hemolysin (hly) gene of Listeria monocytogenes, the invasion (invA) gene of Salmonella spp., the cholera toxin (ctx) gene of Vibrio cholerae, the thermolabile hemolysin (tlh) gene of V. parahaemolyticus, and the thermostable nuclease (nuc) gene of Staphylococcus aureus were used as target genes for m-PCR detection. The detection limit of the assay for the bacterial targets was 1-100 cfu per mL. The m-PCR analysis was designed for three main food clusters; meat and meat products testing for Salmonella spp., L. monocytogenes, and E. coli O157: H7, seafood and seafood products testing for V. cholerae and V. parahaemolyticus and ready-to-eat foods testing for S. aureus. Overall, results of the present study indicate that the m-PCR is a potential technique for the rapid detection of foodborne bacteria for routine monitoring and risk assessment of food.

Characterization of Bacillus cereus in Dairy Products in China.

Bacillus cereus is a common and ubiquitous foodborne pathogen with an increasing prevalence rate in dairy products in China. High and unmet demands for such products, particularly milk, raise the risk of B. cereus associated contamination. The presence of B. cereus and its virulence factors in dairy products may cause food poisoning and other illnesses. Thus, this review first summarizes the epidemiological characteristics and analytical assays of B. cereus from dairy products in China, providing insights into the implementation of intervention strategies. In addition, the recent achievements on the cytotoxicity and mechanisms of B. cereus are also presented to shed light on the therapeutic options for B. cereus associated infections.

Antimicrobial Activity of Five Apitoxins from Apis mellifera on Two Common Foodborne Pathogens.

Antimicrobial resistance is one of today’s major public health challenges. Infections caused by multidrug-resistant bacteria have been responsible for an increasing number of deaths in recent decades. These resistant bacteria are also a concern in the food chain, as bacteria can resist common biocides used in the food industry and reach consumers. As a consequence, the search for alternatives to common antimicrobials by the scientific community has intensified. Substances obtained from nature have shown great potential as new sources of antimicrobial activity. The aim of this study was to evaluate the antimicrobial activity of five bee venoms, also called apitoxins, against two common foodborne pathogens. A total of 50 strains of the Gram-negative pathogen Salmonella enterica and 8 strains of the Gram-positive pathogen Listeria monocytogenes were tested. The results show that the minimum inhibitory concentration (MIC) values were highly influenced by the bacterial genus. The MIC values ranged from 256 to 1024 µg/mL in S. enterica and from 16 to 32 µg/mL in L. monocytogenes. The results of this study demonstrate that apitoxin is a potential alternative agent against common foodborne pathogens, and it can be included in the development of new models to inhibit the growth of pathogenic bacteria in the food chain.

Review on Major Food-Borne Zoonotic Bacterial Pathogens.

Food-borne microorganisms are major pathogens affecting food safety and cause human illness worldwide as a result of consumption of foodstuff, mainly animal products contaminated with vegetative pathogens or their toxins. Most of these microbes have zoonotic importance resulting in significant impact on both public health and economic sectors. Bacteria are the causative agents of two-thirds of human food-borne diseases worldwide with high burden in developing countries. Hence, the objectives of this review paper are to highlight the background of food-borne bacterial pathogens and to review common major food-borne zoonotic bacterial pathogens. Food animals are the major reservoirs of many food-borne zoonotic bacterial pathogens, and food products of animal origin are the main vehicles of transmission. Meat, dairy products, and eggs are the main ways by which people are exposed to zoonotic bacteria. S. aureus, Salmonella species, Campylobacter species, L. monocytogenes, and E. coli are the major zoonotic bacterial pathogens which are the causative agents of food-borne illness and death in the world associated with consumption of contaminated animal products. Production of toxins and structural virulent factors are responsible for the pathogenesis of these bacteria. These major zoonotic bacteria cause human infections which are characterized mainly by gastrointestinal symptoms including nausea, vomiting, diarrhea, abdominal cramps, and other agent-specific symptoms. Some bacteria may cause severe complications. Conventional (culturing), serological, and molecular techniques are important for detection of these common zoonotic bacteria and their toxins in food. Good hygiene, GMP, sanitation in operating procedures, and implementation of standardized HACCP and pasteurization procedures are effective methods for the control and prevention. Currently, the emergence of multidrug-resistant zoonotic bacteria associated with consumption of contaminated animal products is a great concern for the public health, and there should be coordinated surveillance and monitoring system for food-borne zoonotic bacterial pathogens particularly in developing countries including Ethiopia.

Multiplexed Stn and Plca based specific genetic marker for early detection of Salmonella enterica and Listeria monocytogenes in milk samples

In this study conventional PCR and multiplex PCR based method was developed for the detection of two common foodborne pathogens Salmonella enterica and Listeria monocytogenes in 20 raw milk samples. The PCR was undertaken to detect two genes namely, Salmonella enterotoxin (stn) gene and phosphatidylinositol-specific phospholipase C gene (plcA) from both the organisms. The DNA templates (for both organisms) were amplified using specific set of primers. The resulting amplicons were found to be 265 bp and 147 bp respectively. Validation studies were further performed in artificial spiked milk samples and raw milk samples using multiplex PCR. The available detection methods are bacterial culturing, biochemical tests, serological tests, antibiotic sensitivity, ELISA and PCR. All these methods are either expensive or non-confirmatory and have some limitations. The reported multiplexed PCR based genetic marker completes overall analysis in 80 min which is the minimum time reported so far for the confirmation of these foodborne pathogens. Sensitivity and specificity of developed method was calculated and compared with different conventional methods. The detection limit of the assay for the S. enterica was 6.6 x100 CFU/mL and for L. monocytogenes was 4.5x100 CFU/mL.

Formation and Control of the Viable but Non-culturable State of Foodborne Pathogen Escherichia coli O157:H7.

As a common foodborne pathogen, Escherichia coli O157:H7 produces toxins causing serious diseases. However, traditional methods failed in detecting E. coli O157:H7 cells in the viable but non-culturable (VBNC) state, which poses a threat to food safety. This study aimed at investigating the formation, control, and detection of the VBNC state of E. coli O157:H7. Three factors including medium, salt, and acid concentrations were selected as a single variation. Orthogonal experiments were designed with three factors and four levels, and 16 experimental schemes were used. The formation of the VBNC state was examined by agar plate counting and LIVE/DEAD® BacLightTM bacterial viability kit with fluorescence microscopy. According to the effects of environmental conditions on the formation of the VBNC state of E. coli O157:H7, the inhibition on VBNC state formation was investigated. In addition, E. coli in the VBNC state in food samples (crystal cake) was detected by propidium monoazide–polymerase chain reaction (PMA-PCR) assays. Acetic acid concentration showed the most impact on VBNC formation of E. coli O157:H7, followed by medium and salt concentration. The addition of 1.0% acetic acid could directly kill E. coli O157:H7 and eliminate its VBNC formation. In crystal cake, 25, 50, or 100% medium with 1.0% acetic acid could inhibit VBNC state formation and kill E. coli O157:H7 within 3 days. The VBNC cell number was reduced by adding 1.0% acetic acid. PMA-PCR assay could be used to detect E. coli VBNC cells in crystal cake with detection limit at 104 CFU/ml. The understanding on the inducing and inhibitory conditions for the VBNC state of E. coli O157:H7 in a typical food system, as well as the development of an efficient VBNC cell detection method might aid in the control of VBNC E. coli O157:H7 cells in the food industry.

A lateral flow strip combined with Cas9 nickase-triggered amplification reaction for dual food-borne pathogen detection

Nucleic acid-based detection methods are accurate and rapid, which are widely-used in food-borne pathogen detection. However, traditional nucleic acid-based detection methods usually rely on special instruments, weakening their practicality for on-site tests in resource-limited locations. In this work, we developed a convenient and affordable method for food-borne pathogen detection based on a lateral flow strip combined with Cas9 nickase-triggered isothermal DNA amplification, which allows instrument-free and dual target detection. The genomic DNAs of two most common foodborne pathogens, Salmonella typhimurium and Escherichia coli, were simultaneously amplified in a one-pot reaction using specific sgRNAs and primers. The amplicons of genomic DNAs were double-labelled by digoxin/biotin and FITC/biotin tags, respectively, and directly visualized on a simple lateral flow strip. Our method exhibited a high specificity and sensitivity with a detection limit of 100 copies for genomic DNAs and 100 CFU/mL for bacteria. We believe that this method has potential to provide a convenient and low-cost point-of-care test for pathogen detection in the food quality surveillance.

Rapid detection of antibiotic resistance in Salmonella with screen printed carbon electrodes

Salmonella, one of the most common foodborne pathogens, poses a serious threat to human health. In recent years, the antibiotic resistance of Salmonella has become serious as well, which has strengthened the harm of Salmonella to human health. In this paper, a simple and effective electrochemical approach was developed to obtain profile of the antimicrobial susceptibility. Screen-printed carbon electrodes (SPCEs) were used to detect various concentrations of target bacteria at the same time, which have good stability, low cost, and easy mass production. The electroactive redox, resazurin, was used to monitor levels of metabolically active bacteria. As a demonstration, the antibacterial effect of ofloxacin and penicillin on Salmonella gallinarum (S. gallinarum) isolates was evaluated, and the minimum inhibitory concentration (MIC) was measured as well. In the real sample measurement, the MIC obtained was similar to that obtained by conventional antimicrobial susceptibility testing (AST). In this assay, bacterial activity was quantified sensitively and accurately, and the detection time was greatly reduced compared with conventional AST (16–20 h), which means that metabolic capacity of live bacteria could be observed after 1 h of incubation. We were able to clearly detect bacteria above 102 CFU/m. This method aims to nonspecific and can be widely applied to the detection of a variety of drug-resistant bacteria, providing an experimental basis for the rational use of antibiotics and bacterial resistance mechanisms.

Antibacterial Effect of Caprylic Acid and Potassium Sorbate in Combination against Listeria monocytogenes ATCC 7644

Listeria monocytogenes is a common foodborne pathogen that cause life-threatening infection with high mortality rates. Biofilm development of L. monocytogenes decreases its sensitivity to antibiotics, which has long attracted attention globally. Caprylic acid (CA) and potassium sorbate (PS) are both widely used food preservatives, but their synergistic effect against L. monocytogenes has not been described. This study explored the antibacterial activities of the CA-PS combination against L. monocytogenes ATCC 7644 grown in planktonic or biofilm cultures. The fractional inhibitory concentration index values, determined by the checkerboard microdilution method, were 0.37 ± 0.03 and 0.31 ± 0.04, showing their synergistic antimicrobial effects against L. monocytogenes ATCC 7644 in planktonic and biofilm cultures, respectively. CA-PS effectively eradicated the biofilm biomass to 10.8% by crystal violet assay and to 8.63% by fluorescence microscopic analysis compared with the control. The apoptosis rates of microbial cells embedded within biofilm significantly increased to 51.4%. Subsequent analysis revealed that the combination inhibited biofilm formation by affecting extracellular DNA release and polysaccharide intercellular adhesion expression, which was decreased from 8.93 to 1.04 ng of extracellular DNA per relative biomass and to 54.7% of the control, respectively. In addition, the combination inhibited the growth of L. monocytogenes ATCC 7644 by up to 0.67 ± 0.05 and 0.30 ± 0.03 log CFU/cm2 in planktonic and biofilm modes on a carrot surface, respectively. The synergistic antibacterial effects of CA-PS against L. monocytogenes ATCC 7644 were statistically significant, and the combination is an excellent candidate to be a novel food preservative.

Integrated gold superparticles into lateral flow immunoassays for the rapid and sensitive detection of Escherichia coli O157:H7 in milk

Escherichia coli O157:H7 is a common harmful foodborne pathogen that can cause severe diseases at low infectious doses. Traditional lateral flow immunoassay (LFIA) for the rapid screening of E. coli O157:H7 in food suffers from low sensitivity due to its dependence on 20- to 40-nm gold nanoparticles (AuNP) with insufficient brightness as labels. To address this issue, we reported for the first time the successful synthesis of gold superparticles (GSP) by encapsulating numerous small AuNP into a polymer nanobead using an evaporation-induced self-assembly method. Results indicated that the resultant GSP exhibited remarkably enhanced absorbance compared with the most widely used 40 nm AuNP in LFIA. In addition, the absorbance of GSP could be easily tuned by varying GSP sizes. Under optimized conditions, we achieved a rapid and sensitive determination of E. coli O157:H7 in milk with a detection limit of 5.95 × 102 cfu/mL when using the GSP with a size of 342 nm as LFIA signal reporters, exhibiting improvement of approximately 32-fold relative to the conventional 40 nm AuNP-LFIA method. We further demonstrated the selectivity, accuracy, reliability, and practicality of the proposed GSP-LFIA strip. In summary, this work offers a new strategy for improving LFIA sensitivity using assembled GSP as markers and demonstrates huge potential in rapidly and sensitively detecting foodborne pathogens.

Diverse dendritic cell subsets promote infection and induction of CD8 T cell responses after foodborne Listeria monocytogenes infection

Abstract Listeria monocytogenes (Lm) is a common foodborne pathogen which causes mild gastrointestinal distress in healthy hosts, and systemic listeriosis in immunocompromised individuals. While immune responses have been rigorously examined after intravenous Lm infection, less is understood about Lm dissemination from the intestines or the induction of adaptive immune responses after physiologic infection through the consumption of contaminated food. Consequently, this study focused on the cells involved in early immune responses in the intestinal mucosa using foodborne Lm infection in mice. After foodborne infection, Lm trafficked intracellularly from the intestines to the mesenteric lymph nodes (MLN) and were associated with Batf3-independent dendritic cells (DC) in the lymphatics. Consistent with this observation, dissemination of Lm from the gut to the MLN occurred normally in Batf3−/− mice. Activated migratory DC accumulated in the MLN by 3 days post-infection (dpi) where they surrounded Lm foci. At this time, Lm burden in the MLN was reduced in Batf3−/− mice implicating Batf3-DC in the maximal accumulation of Lm. While both conventional type 1 DC (cDC1) and type 2 DC in the MLN contained Lm by 3 dpi, Batf3−/− mice exhibited a profound defect in the induction and gut homing of Lm-specific CD8 T cells. Surprisingly, restoration of pathogen burden was unable to restore CD8 T cell responses in Batf3−/− mice. Thus, cDC1 play a critical role in the generation of potent anti-Lm immunity following foodborne infection. Collectively, these data demonstrate that DC play diverse and dynamic roles in the early events that follow foodborne Lm infection, and in the establishment of protective, anti-Lm intestinal immunity.

Three-dimensional epicuticular wax on plant surface reduces attachment and survival rate of Salmonella during storage

Abstract Salmonella is the second most common foodborne pathogen for leafy vegetables, therefore understanding how to reduce Salmonella attachment onto produce surface is crucial to combat salmonellosis. Epicuticular wax is the outermost layer on the leaf surface that directly interact with food pathogen attachment. The hydrophobic nature of epicuticular wax was found to increase pathogen resistance, however, there is limited study on if three-dimensional epicuticular wax on the leaf can reduce Salmonella attachment. This study aims to test whether the presence of three-dimensional epicuticular wax crystals decreases the attachment of Salmonella on leafy green surfaces. Using gum arabic paste, three-dimensional epicuticular wax was removed from three waxy plants (USVL188-NG, USVL115-NG, and ‘Top Bunch’ collard). Leafy surfaces in disks were dip-inoculated with a mixture of Salmonella Typhimurium and Tennessee at day 0, followed by aerobic storage at 4.0 ± 0.2 °C for 14 d. After 30-minute inoculation, significantly lower (P

Green Synthesis of Silver Nanoparticles with Antimicrobial Properties Using Phyla dulcis Plant Extract.

Foodborne illnesses caused by the consumption of food contaminated with foodborne pathogens at infectious doses are becoming a common health issue throughout the world. Metal nanoparticles with potential antimicrobial properties are an area that can be explored to discover novel antimicrobial agents. The traditional synthesis methods of metal nanoparticles involve the use of toxic chemicals and the generation of harmful byproducts. In this study, a greener method to synthesize silver nanoparticles (AgNPs) with potential antimicrobial properties was investigated. The aqueous extract of the medicinal plant Phyla dulcis Trev. (verbenaceae) was used as the reducing and stabilizing agent to synthesize AgNPs using microwave irradiation. The formation of AgNPs was confirmed using ultraviolet-visible spectroscopy by the appearance of characteristic surface plasmon resonance peaks in the 430-440 nm wavelength range. The size and stability of the AgNPs were studied using Zetasizer nano-series for 5 weeks after synthesis. The average particle size remained between 63 and 76 nm during the first 4 weeks and increased to 114 nm in the fifth week showing possible aggregation after the fourth week. The zeta potential remained between -20 and -24 mV throughout the 5 weeks showing relatively good stability. Scanning electron microscopy/energy dispersive X-ray spectroscopy showed the association of phytoconstituents with the AgNPs. X-ray photoelectron spectroscopy analysis confirmed the formation of metallic nanoparticles starting from silver nitrate. Finally, the AgNPs were tested to be effective against Escherichia coli O157:H7 (ATCC 43888), Salmonella Typhimurium (novobiocin and nalidixic acid resistant strain), Listeria monocytogenes (4b; ATCC 19115), and Staphylococcus aureus (ATCC 6538) strains, which are known to be common foodborne pathogens.

Rapid Classification of Single Bacterium Based on Backscattering Microscopic Spectrum—A Pilot Study

Rapid detection of foodborne pathogens is one of the most effective ways to solve food safety problems. To achieve rapid and noninvasive detection and classification of foodborne pathogens, we modified a fiber confocal backscattering micro-spectral system to suit an extremely small biological sample, that is, a bacterium. This system offers single-bacterium level, label-free, convenient, and environmentally friendly characterization. Three categories of common foodborne pathogens (Salmonella typhimurium, Escherichia coli, and Staphylococcus aureus) were measured. The scattering spectrum ranging from 450 to 900 nm was selected, and by the model of principal component analysis (PCA) and error back propagation algorithm of back propagation neural network (BPNN), the backscattering microscopic spectra of three categories of pathogens were dimensionality reduced, identified and classified. The results showed that the identification accuracy of three categories of pathogens was above 90%, under neutral, acidic and alkaline culturing conditions，respectively. The preliminary results demonstrated the feasibility of using confocal backscattering microscopic spectra combined with PCA and BPNN algorithm to identify and classify single bacterium in a rapid, noninvasive, and label-free manner.

Preliminary study on the antibacterial activity of liquid smoke from cacao pod shells (Theobroma cacao L)

Cacao pod shells (Theobroma cacao L) form biomass waste that can be used as raw material for liquid smoke because this biomass contains lignin, cellulose, and hemicellulose. This research studied the antimicrobial activity of liquid smoke from cacao pod shells on several common food-borne pathogens, such as Salmonella choleraesuis, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis. The liquid smoke used was obtained from cacao pod shells that were pyrolyzed at 300 °C (T1), 340 °C (T2), and 380 °C (T3). Liquid smoke concentration varied from 1% to 5%. The antbacterial activity test was conducted using the Kirby–Bauer method. The results showed that liquid smoke produced from T1 and T2 (and at liquid smoke concentrations of 4% and 5%) could inhibit the growth of all the tested bacteria. At T3 and 1–5% of liquid smoke, only E. coli was consistently inhibited (inhibition zone = 6–7.05 mm), while the growth of S. choleraesuis and S. aureus was inhibited at 3–5% liquid smoke with the inhibition zone ranging from 6 mm to 7.2 mm. B. subtilis was inhibited by a 2–5% liquid smoke concentration. All the tested bacteria showed sensitivity to liquid smoke, but E. coli was the stronger resistant compared to others. The results of this study show that liquid smoke from cacao pod shells could be used as a preservative agent to inhibit microorganisms in food.

Light-driven antimicrobial activities of vitamin K3 against Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella Enteritidis

Due to the lack of thermal inactivation steps, the fresh produce industry is actively looking for new, environmentally friendly and effective non-thermal control strategies to eliminate foodborne pathogens on produce surfaces and to prevent cross-contamination. Photodynamic inactivation of bacteria has emerged as a novel alternative approach to inactivate microorganisms on fresh produce. In this study, the photo-sensitizing efficacy of vitamin K3 (VK3) under UV-A and simulated sunlight and their antimicrobial efficacy against common foodborne pathogens in broth and on lemon surfaces were investigated. The minimal bactericidal concentration (MBC) of VK3 against Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella Enteritidis PT30 in darkness was 625.0, 156.3, and 625.0 μg/ml, respectively. When treatments were carried out under light, the MBC values of VK3 (VK3 + light) were reduced in strain, light source, and exposure time dependent manners. The enhanced antimicrobial effect can be attributed to the production of reactive oxygen species of VK3, including hydroxyl radical and singlet oxygen under light exposure. Based on scanning electron microscope examination, VK3 + light treatment damaged the cell integrity of L. monocytogenes and Salmonella; and altered the cell morphology of E. coli O157:H7 including filament formation and fewer fimbriae/flagella. When applied on artificially inoculated lemon surfaces, VK3 + light treatments at MBC levels immediately reduced the levels of L. monocytogenes and E. coli O157:H7 by more than 5.0 Log10 CFU/disk and S. Enteritidis PT30 by ~4.0 Log10 CFU/disk. Bacterial populations of all tested strains were reduced to below the limit of detection (1.0 Log10 CFU/disk) after one day of storage at 4 °C; the numbers of positive samples after enrichment further decreased as the storage time increased, demonstrating the continuous antimicrobial effects the VK3 generated on lemon surfaces. In summary, the results of this study demonstrated the promising antimicrobial effects of VK3 + light treatments and their great application potential for fresh produce industry.

Salmonella Virulence and Immune Escape.

Salmonella genus represents the most common foodborne pathogens causing morbidity, mortality, and burden of disease in all regions of the world. The introduction of antimicrobial agents and Salmonella-specific phages has been considered as an effective intervention strategy to reduce Salmonella contamination. However, data from the United States, European countries, and low- and middle-income countries indicate that Salmonella cases are still a commonly encountered cause of bacterial foodborne diseases globally. The control programs have not been successful and even led to the emergence of some multidrug-resistant Salmonella strains. It is known that the host immune system is able to effectively prevent microbial invasion and eliminate microorganisms. However, Salmonella has evolved mechanisms of resisting host physical barriers and inhibiting subsequent activation of immune response through their virulence factors. There has been a high interest in understanding how Salmonella interacts with the host. Therefore, in the present review, we characterize the functions of Salmonella virulence genes and particularly focus on the mechanisms of immune escape in light of evidence from the emerging mainstream literature.