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Graphene oxide (GO) is one of the promising two-dimensional nanomaterials for the development of fluorescent aptasensors. Its limitations are related to the inevitable negative effect of GO on the fluorescence. Here this challenge was explored and solved by ssDNA adsorption on GO and centrifugal separation of GO from the ensembled solution. On this basis, a fluorescent aptasensor was constructed for the detection of staphylococcal enterotoxin A (SEA), in which GO assisted the separation of free aptamers to achieve cDNA-induced structure-switching from SEA/aptamer complex to dsDNA, and GO was added again to separate free cDNA and reduce the background signal. SYBR Green I was inserted into dsDNA as the fluorescent signal to achieve the quantitative analysis. It displayed a wide linear range (1–8000 ng/mL), low detection limit (0.899 ng/mL), and satisfactory application in milk and milk powder. Notably, the method was low-cost, general, and instructive for other two-dimensional nanomaterials. [Display omitted] • A label-free, low-background fluorescent aptasensor for staphylococcal enterotoxin A. • Graphene oxide-assisted ssDNA separation to reduce the background and interference. • The cDNA-induced structure-switching formed dsDNA and amplified the signal. • The method was low-cost, general, and instructive for two-dimensional nanomaterials. [ABSTRACT FROM AUTHOR]

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 6 0.03 and 0.31 6 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 6 0.05 and 0.30 6 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. [ABSTRACT FROM AUTHOR]

The bacterium Staphylococcus aureus is most often recognized as a common cause of food poisoning. S. aureus colonization in humans can cause serious infections, toxinoses and life-threatening diseases. Nisin is a bacteriocin that has been extensively used as a natural preservative in the food industry, but the overall transcriptional response of S. aureus to nisin has not been well characterized. We used whole-genome DNA microarrays of S. aureus to determine the global transcription profile triggered by nisin treatment in S. aureus . In response to nisin treatment, a total of 601 genes were differentially regulated; transcription of 327 genes was up-regulated, and transcription of 274 genes was down-regulated. Various transporter genes showed elevated transcription, including genes involved in capsule polysaccharide (CP) synthesis, cell-wall synthesis, nucleic-acid and nucleotide metabolism as well as genes encoding urease, transport/binding proteins, and lipoproteins. To our knowledge, this transcriptome analysis provides the first insights into the transcriptional response of S. aureus to nisin challenge and enables exploration of the mechanisms of nisin antimicrobial activity toward S. aureus . The findings suggest that nisin regulates multiple desirable targets which could be further explored in the development of new food preservatives to avoid the contamination of S. aureus in food processing and storage. [ABSTRACT FROM AUTHOR]

Biofilm-forming Staphylococcus aureus can easily accumulate on various food contact surfaces which induce cross-contamination and are difficult to eliminate in the food industry. This study aimed to evaluate the anti-biofilm effects of natural product biochanin A against S. aureus. Results showed that biochanin A effectively eradicated established S. aureus biofilms on different food-contact materials. Fluorescence microscopic analyses suggested that biochanin A disintegrated the established biofilms by dissociate extracellular polymeric substance (EPS) in matrix. In addition, biochanin A at the sub-MIC concentration also effectively inhibited the biofilm formation by regulating the expression of biofilm-related genes (icaA, srtA, eno) and suppressing the release of EPS in biofilm matrix. Molecular docking also demonstrated that biochanin A conducted strong interactions with biofilm-related proteins (Ica A, Sortase A, and Enolase). These findings demonstrated that biochanin A has the potential to be developed as a potent agent against S. aureus biofilm in food industries. Key points: • Anti-biofilm effect of biochanin A against S. aureus was revealed for the first time. • Biofilm of S. aureus on various food-contact surfaces were efficiently eradicated. • Biochanin A prevented S. aureus biofilm formation via reducing EPS production. [ABSTRACT FROM AUTHOR]

Ethnopharmacological relevance Licochalcone A (LCA) is a characteristic chalcone that is found in licorice, which is a traditional medicinal plant. In traditional medicine, LCA possesses many potential biological activities, including anti-parasitic, anti-inflammatory and antitumor activities. Aim of the study To determine the antioxidant activity of LCA and, on this basis, to investigate the role of its anticancer activity. Materials and methods To validate the antioxidant activity of LCA, the proteins SOD, CAT and GPx1 were analyzed using western blotting and cellular antioxidant activity (CAA) assays. Oxidative free radicals are associated with cancer cells. Therefore, the anticancer activity of LCA was also evaluated. To assess the anticancer activity, cell viability assays were performed and apoptosis was evaluated. In addition, MAPK-related proteins were analyzed using western blotting. Results The experimental data showed that the EC 50 of LCA is 58.79±0.05 μg/mL and 46.29±0.05 μg/mL under the two conditions tested, with or without PBS. In addition, LCA at a concentration of approximately 2–8 μg/mL can induce the expression of SOD, CAT and GPx1 proteins. Further, LCA inhibits the growth of HepG2 cells through cell proliferation arrest and the subsequent induction of apoptosis, and LCA attenuated the p38/JNK/ERK signaling pathway in a dose-dependent manner. Conclusion The results showed that LCA suppresses the oxidation of cells and markedly inhibits the proliferation of cancer cells. These findings confirm the traditional use of LCA in folk medicine. [ABSTRACT FROM AUTHOR]

Nisin is used as a food-safe antimicrobial agent and has been widely applied to daily food products to prevent bacterial growth. However, the practical application of nisin is limited. Although nisin inhibits the growth of Listeria monocytogenes , exposure to this agent is also a risk factor for the development of nisin resistance. p -Anisaldehyde (AS) is used in the pharmaceutical industry to manufacture antimicrobial drugs, but few studies have been reported describing the antibacterial activity of AS in the food field. Combining nisin with AS may enhance antimicrobial activity. The synergy observed in vitro was confirmed by checkerboard microdilution method, with the fractional inhibitory concentration index (FICI) values ranging from 0.125 to 0.281. When AS was combined with nisin, a strong synergistic effect was observed using the time-kill and agar-diffusion assays. SEM and LIVE/DEAD BacLight experiment results also suggest that the bactericidal mechanism of the drug combination involves cell wall lysis and membrane damage. We can use this synergy to achieve a stable antimicrobial effect to overcome antimicrobial drug resistance. [ABSTRACT FROM AUTHOR]

The liquid-chip assay is a new method for detecting bacterial surface antigens. This assay conjugated self-prepared monoclonal antibodies againstEscherichia coliO157:H7,Listeria monocytogenes, Staphylococcus aureus, andSalmonella entericaserovarTyphiwith carboxylated fluorescent microspheres based on the double-antibody sandwich principle. This experiment used dimethylacetamide (DMAC) as the solvent to dissolve 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) andN-hydroxysulfosuccinimide (S-NHS) during conjugation. The modified liquid-chip assay was used to simultaneously detect the four foodborne pathogens. The sensitivity of the assay using the new conjugation method was also evaluated. The limits of detection forE. coliO157:H7,L. monocytogenes, S. aureus, andS. typhiduring multiplex detection using the improved method were 0.25, 0.25, 0.5, and 0.25 cfu/mL, respectively, whereas those using the traditional method were 0.5, 0.5, 1, and 0.5 cfu/mL, respectively. Therefore, the improved method is reliable and effectively improves the detection sensitivity of liquid-chip assays. [ABSTRACT FROM AUTHOR]

To understand the response mechanisms of fungus cells upon exposure to the natural fungicide allicin, we performed commercial oligonucleotide microarrays to determine the overall transcriptional response of allicin-treated Saccharomyces cerevisiae strain L1190. Compared with the transcriptional profiles of untreated cultures, 147 genes were significantly upregulated, and 145 genes were significantly downregulated in the allicin-treated cells. We interpreted the microarray data with the hierarchical clustering tool, T-profiler. Major transcriptional responses were induced by allicin and included the following: first, Rpn4p-mediated responses involved in proteasome gene expression; second, the Rsc1p-mediated response involved in iron ion transporter activity; third, the Gcn4p-mediated response, also known as general amino acid control; finally, the Yap1p-, Msn2/4p-, Crz1p-, and Cin5p-mediated multiple stress response. Interestingly, allicin treatment, similar to mycotoxin patulin and artificial fungicide thiuram treatment, was found to induce genes involved in sulfur amino acid metabolism and the defense system for oxidative stress, especially DNA repair, which suggests a potential mutagenicity for allicin. Quantitative real-time reverse transcription-polymerase chain reaction was performed for selected genes to verify the microarray results. To our knowledge, this is the first report of the global transcriptional profiling of allicin-treated S. cerevisiae by microarray. [ABSTRACT FROM AUTHOR]

Abstract Staphylococcus aureus (S. aureus) is a Gram-positive bacterium that causes a wide range of diseases, including food poisoning. Tea tree oil (TTO), an essential oil distilled from Melaleuca alternifolia , is well-known for its antibacterial activities. TTO effectively inhibited all 19 tested strains of S. aureus biofilm and planktonic cells. Phenotype analyses of S. aureus biofilm cells exposed to TTO were performed by biofilm adhesion assays, eDNA detection and PIA release. RNA sequencing (RNA-seq) was used in our study to elucidate the mechanism of TTO as a potential antibacterial agent to evaluate differentially expressed genes (DEGs) and the functional network in S. aureus ATCC 29213 biofilms. TTO significantly changed (greater than a 2- or less than a 2-fold change) the expression of 304 genes in S. aureus contained in biofilms. The levels of genes related to the glycine, serine and threonine metabolism pathway, purine metabolism pathway, pyrimidine metabolism pathway and amino acid biosynthesis pathway were dramatically changed in the biofilm exposed to TTO. Furthermore, the expression changes identified by RNA-seq analysis were verified by real-time RT-PCR. To the best of our knowledge, this research is the first study to report the phenotype and expression profiles of S. aureus in biofilms exposed to TTO. Highlights • The inhibitory effect of TTO on S. aureus biofilms was determined. • 304 genes were differentially expressed treated with TTO versus the control biofilm. • GO enrichment and KEGG pathway analysis were provided by RNA-seq. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus ( S. aureus ) infections resistant to a variety of drugs have been increasingly documented in recent years. Drug resistance has appeared largely due to extensive use of antibiotics. Nisin has been widely used in food industry to prevent bacterial growth. However, nisin resistance has been found in several foodborne pathogenic bacteria. p -Anisaldehyde (AS), an extract from Pimpinella anisum seeds, is a very common digestive herb of north India. In this study, synergistic interactions of nisin combined with AS against S. aureus were observed. The synergy was confirmed by checkerboard microdilution method, with the fractional inhibitory concentration index values ranging from 0.25 to 0.375. The positive interactions were verified by the challenge tests in pasteurized milk and agar diffusion assays. In addition, when treatment with nisin or AS alone or in combination, an obvious loss of 260 nm absorbing materials was observed. And flow cytometry assay showed that nisin or AS alone or in combination caused bacterial membrane permeabilization. The LIVE/DEAD Bac Light experiment, scanning electron microscope and transmission electron microscopy observation further confirmed that the compounds could kill bacteria via disrupting membranes. All results above verified that the combination of nisin and AS which showed antibacterial activity by a membrane damage mechanism could not only reduce drug resistance but also be used as a new promising naturally sourced food preservative. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus ( S . aureus ) is the leading cause of a broad range of human infections and associated with food poisoning worldwide. Nisin can be considered as a natural preservative and is widely used by the food industry. However, resistance of nisin has been reported in several species of bacteria. Identification of antibacterial agents that are synergistic with nisin is a method of minimising resistance to nisin. Cinnamaldehyde (CA), a well-studied essential oil isolated from cinnamon bark, has been reported to exhibit a broad spectrum of antimicrobial activity across a wide range of microorganisms. Previous studies have demonstrated that CA could be used in the food industry due to its active antibacterial activity and its safety. In this study, the synergistic antibacterial activity in vitro of nisin and CA against 13 food-borne isolates of S. aureus and S. aureus ATCC 29213 were evaluated by a checkerboard assay. The FICI values of nisin combined with CA ranged from 0.1875 to 0.375, which demonstrated a synergistic effect. The positive interactions were verified using the challenge tests in pasteurized milk and agar diffusion assays. The LIVE/DEAD BacLight experiment and scanning electron microscope (SEM) assay were also performed to distinguish the intact and damaged both of cell walls and membranes with the compounds, the combination group displayed stronger damage both of cell wall and cell membrane than when nisin or CA was used alone. These findings indicated that the combination of nisin and CA could not only be used as a promising naturally sourced food preservative but also to reduce the problem of bacterial resistance. [ABSTRACT FROM AUTHOR]

Oleuropein (OL), a natural phenolic compound, comprises the major constituent of Olea europea leaves and unprocessed olives, and OL is considered to be the principal components that confer the characteristic taste and stability of olive oil. Oxidative damage induced by H 2 O 2 treatment can irreversibly damage the L-02 cells, resulting in cell death and apoptosis. Whether the effects of oxidative stress could be attenuated in cultured human L-02 cells by incubation with OL is still unknown. In this research, the function of OL in protecting human L-02 cells against H 2 O 2 induced cell death and cell apoptosis was investigated, and the mechanism by which OL underlies the effect was also examed. L-02 cells were exposed to 100 μM H 2 O 2 with or without OL pretreatment at different concentrations. Cell viabilities were monitored by WST-1 assay. ALT, AST and LDH production in culture medium were also determined. ROS levels were detected by L-012 chemiluminescence, and OL increased SOD1, CAT and GPx1 expression in a concentration-dependent manner. Further studies showed that OL also inhibited H 2 O 2 -induced P38 and JNK phosphorylation but enhanced ERK1/2 phosphorylation in a dose-dependent manner. These findings suggested that OL as a potent antioxidant agent and a natural compound found in several plants, may be exploited as a potentially useful method for hepatopathy prevention. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus ( S. aureus ), a major food-borne pathogen, causes disease in mammalian hosts by producing a wide variety of exoproteins, such as α-hemolysin and staphylococcal enterotoxins. Tea tree oil (TTO), an essential oil, has broad-spectrum antimicrobial activity. The objectives of this study were to evaluate the inhibitory effects of TTO on S. aureus growth and on α-hemolysin, enterotoxins A and B production. In this study, the effect of TTO on S. aureus growth in laboratory medium and pasteurized milk was determined by time-kill assays. Treatment with half of minimal inhibitory concentration (MIC) of TTO demonstrated very little or no reduction in numbers of viable ATCC 29213 cells; however, 1 × MIC of TTO reduced the viable cell count more noticeably, and 2 × MIC of TTO demonstrated an even greater reduction in the viable cell count, both in TSB and milk. The influence of TTO on enterotoxins was determined by real-time reverse transcriptase-PCR (real-time RT-PCR), a hemolysis assay, Western blot and a tumor necrosis factor alpha (TNF-α) assay. The real-time RT-PCR results revealed that the transcription of genes encoding α-hemolysin, staphylococcal enterotoxin A (SEA) and staphylococcal enterotoxin B (SEB) were down regulated after S. aureus was exposed to TTO (0.0625 mg/mL-0.5 mg/mL). The hemolytic assay showed that S. aureus hemolytic activity was inhibited by subinhibitory concentrations of TTO (0.0625 mg/mL-0.5 mg/mL). The Western blot assay identified that the production of the three virulence factors was inhibited by TTO (0.0625 mg/mL-0.5 mg/mL). Moreover, the enzyme linked immunosorbent assay (ELISA) demonstrated that TNF-α production was suppressed by TTO treatment in RAW264.7 cells stimulated by S. aureus supernatant containing staphylococcal enterotoxins (SEs). [ABSTRACT FROM AUTHOR]

This paper reports a novel aptamer-based fluorescent detection method for small molecules represented by acetamiprid based on the specific binding of aptamers with acetamiprid, and the inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (CdTe QDs). When CdTe QDs were mixed with AuNPs, the fluorescence of CdTe QDs was significantly quenched via IFE. The IFE efficiency could be readily modulated by the absorption and the aggregation state of AuNPs. The presence of salt could easily induce the aggregation of AuNPs, resulting in the fluorescence recovery of the quenched QDs. Acetamiprid-binding aptamer (ABA) could adsorb on the negatively charged AuNPs through the coordination interaction to protect AuNPs from salt-induced aggregation, so the fluorescence of CdTe QDs would be quenched by the IFE of AuNPs. However, the specific binding of ABA with acetamiprid could release the ABA from the surfaces of AuNPs and decrease the salt tolerance of AuNPs, so the IFE-decreased fluorescence of CdTe QDs was regained with the presence of acetamiprid, and the fluorescence enhancement efficiency was driven by the concentration of acetamiprid. Based on this principle, the aptamer-based fluorescent method for acetamiprid has been established and optimized. The assay exhibited excellent selectivity towards acetamiprid over its analogues and other pesticides which may coexist with acetamiprid. Under the optimum experiment conditions, the established method could be applied for the determination of acetamiprid with a wide linear range from 0.05 to 1.0 μM, and a low detection limit of 7.29 nM (3σ). Furthermore, this IFE-based method has been successfully utilized to detect acetamiprid in six types of vegetables, and the results were in full agreement with those from HPLC and LC-MS. The proposed method displays remarkable advantages of high sensitivity, rapid analysis, excellent selectivity, and would be suitable for the practical application of target screening in real samples. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Background: Food safety is an important worldwide public health concern, and microbial contamination in foods not only leads to food deterioration and shelf life reduction but also results in economic losses and disease. Objective: The main aim of the present study was to evaluate the effect of epsilon-poly-L-lysine (s-PL) and citral combination against Escherichia coli O157:H7 (E. coli O157:H7) strains. The preliminary antioxidant and antitumor activities were also studied. Design: Synergism is a positive interaction created when two compounds combine and exert an inhibitory effect that is greater than the sum of their individual effects. The synergistic antimicrobial effect of s-PL and citral was studied using the checkerboard method against E. coli O157:H7. The minimal inhibitory concentration, time-kill, and scanning electron microscope assays were used to determine the antimicrobial activity of s-PL and citral alone or in combination; 2,2-diphenyl-1-picrylhydrazyl-scavenging assay and western blotting were used in antioxidant activity assays; cell viability assay was carried out to finish preliminary antitumor test. Results: Minimal inhibitory concentrations of s-PL and citral resisted to the five E. coli O157:H7 strains were 2-4 µg/mL and 0.5-1 µg/mL, and the fractional inhibitory concentration indices were 0.25-0.375. The results of time-kill assay revealed that a stronger bactericidal effect in a laboratory medium might be exerted in the combination against E. coli O157:H7 than that in a food model. The compounds alone or in combination exhibited a potential 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activity, and the expression of superoxide dismutase 1 and glutathione peroxidase 1 protein increased. The preliminary antitumor activity effect of the combination was better than s-PL or citral alone. Conclusions: These findings indicated that the combination of s-PL and citral could not only be used as a promising naturally sourced food preservative but also be used in the pharmaceutical industry. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus ( S. aureus) causes a wide variety of infections, which are of major concern worldwide. S. aureus produces multiple virulence factors, resulting in food infection and poisoning. These virulence factors include hyaluronidases, proteases, coagulases, lipases, deoxyribonucleases and enterotoxins. Among the extracellular proteins produced by S. aureus that contribute to pathogenicity, the exotoxins α-hemolysin, staphylococcal enterotoxin A (SEA) and staphylococcal enterotoxin B (SEB) are thought to be of major significance. Totarol, a plant extract, has been revealed to inhibit the proliferation of several pathogens effectively. However, there are no reports on the effects of totarol on the production of α-hemolysin, SEA or SEB secreted by S. aureus. The aim of this study was to evaluate the effects of totarol on these three exotoxins. Hemolysis assay, western blotting and real-time reverse transcriptase-PCR assay were performed to identify the influence of graded subinhibitory concentrations of totarol on the production of α-hemolysin and the two major enterotoxins, SEA and SEB, by S. aureus in a dose-dependent manner. Moreover, an enzyme linked immunosorbent assay showed that the TNF-α production of RAW264.7 cells stimulated by S. aureus supernatants was inhibited by subinhibitory concentrations of totarol. Form the data, we propose that totarol could potentially be used as a promising natural compound in the food and pharmaceutical industries. [ABSTRACT FROM AUTHOR]

Nisin has been widely used as a natural preservative in foods including dairy products, but the emergence of the nisin-resistant strains could compromise its use to control food-borne pathogens. It has been reported that coenzyme Q (CoQ) is a powerful antioxidant, but a small number of studies have described the antibacterial activity of CoQ. One of the most abundant forms of CoQ is CoQ10. CoQ0 is chosen for this study, which is the water-soluble homolog of CoQ10. In the present study, the in vitro interaction of nisin and CoQ0 against 15 food-borne isolates of Staphylococcus aureus was assessed using a checkerboard microdilution method. Synergism was observed in strains tested, the FICI values ranging from 0.25 to 0.375. No antagonistic interaction between nisin and CoQ0 occurred. The positive interactions were verified confirmed using the time-killing test and agar diffusion assay. Our discovery of efficacy of combining nisin with CoQ0 might pave the way for a novel solution for spoilage problem in food industry and provide an alternative approach to overcome antimicrobial drug resistance. [ABSTRACT FROM AUTHOR]

A novel virulent phage named JL1 against Escherichia coli O157:H7 was isolated from raw sewage. It was found that JL1 has an icosahedral head and a long flexible non-contractile tail. The complete genome of JL1 is composed of a linear double-stranded DNA of 43,457 base pairs in length, with 54.77 % G+C content and 60 putative open reading frames. Morphology and bioinformatics analysis revealed that phage JL1 is a member of the family Siphoviridae of the order Caudovirales. It is different from previously reported phages of E. coli O157:H7 but is homologous to Sodalis phage SO-1, Shigella phage EP23, Escherichia phage HK578 and Escherichia phage SSL-2009a. [ABSTRACT FROM AUTHOR]