Antibacterial Activity of Thymoquinone Against Shigella flexneri and Its Effect on Biofilm Formation.

Thymoquinone (TQ) has been demonstrated to have anti-cancer, anti-inflammatory, antioxidant, and anti-diabetic activities. Shigella flexneri is the main pathogen causing shigellosis in developing countries. In this study, the antibacterial activity of TQ against S. flexneri and its possible antibacterial mechanism were studied. In addition, the inhibitory effect of TQ on the formation of S. flexneri biofilm was also investigated. The results showed that both the minimum inhibitory concentration and the minimum bactericidal concentration of TQ against S. flexneri ATCC 12022 were 0.2 mg/mL. After treatment with TQ at 0.4 mg/mL in Luria-Bertani broth for 3 h, or treatment with 0.2 mg/mL TQ in phosphate-buffered saline for 60 min, the number of S. flexneri (initial number is 6.5 log colony-forming units/mL) dropped below the detection limit. TQ also displayed good antibacterial activity in contaminated lettuce juice. TQ caused an increase in intracellular reactive oxygen species level, a decrease in intracellular adenosine triphosphate (ATP) concentration, a change in the intracellular protein, damage to cell membrane integrity and changes in cell morphology. In addition, TQ showed the ability to inhibit the formation of S. flexneri biofilm; treatment resulted in a decrease in the amount of biofilm and extracellular polysaccharides, and the destruction of biofilm structure. These findings indicated that TQ had strong antimicrobial and antibiofilm activities and a potential to be applied in the fruit and vegetable processing industry or other food industries to control S. flexneri.

The Role of ptsH in Stress Adaptation and Virulence in Cronobacter sakazakii BAA-894.

Cronobacter sakazakii, an emerging foodborne pathogen that was isolated primarily from powdered infant formula, poses an important issue in food safety due to its high stress tolerance and pathogenicity. The Hpr (encoded by ptsH gene) has been shown to regulate carbon metabolism as well as stress response and virulence. However, the functional properties of ptsH in C. sakzakii have not been investigated. In this study, we clarified the role of ptsH in the C. sakzakii stress response and virulence, and explored its possible regulatory mechanism by RNA-seq. Compared with wild-type, the ΔptsH mutant showed a slower growth rate in the log phase but no difference in the stationary phase. Moreover, the resistance to heat stress (65 °C, 55 °C), simulated gastric fluid (pH = 2.5), biofilm formation and adhesion to HT-29 cells of ΔptsH mutant were significantly decreased, whereas the oxidative resistance (1, 5, 10 mM H2O2), osmotic resistance (10%, 15%, 20% NaCl), and superoxide dismutase activity were enhanced. Finally, RNA-seq analysis revealed the sulfur metabolism pathway is significantly upregulated in the ΔptsH mutant, but the bacterial secretion system pathway is dramatically downregulated. The qRT-PCR assay further demonstrated that the ΔptsH mutant has elevated levels of genes that are related to oxidative and osmotic stress (sodA, rpoS, cpxA/R, osmY). This study provides a great understanding of the role of ptsH in diverse stress responses and virulence in C. sakazakii, and it contributes to our understanding of the genetic determinant of stress resistance and pathogenicity of this important foodborne pathogen.

Effects of cinnamaldehyde against planktonic bacteria and biofilm formation of Shigella flexneri.

Cinnamaldehyde (CA) has demonstrated anti-inflammatory, anti-tumor and anti-cancer activities; Its antimicrobial and antibiofilm actions against Shigella flexneri, on the other hand, have not been investigated. Sh. flexneri is a gram-negative foodborne pathogen that can be widely found in nature and some industrial production environments. In this current research, our aim was to examine the influences of CA on planktonic bacteria and biofilm formation. The minimum inhibitory concentration (MIC) of CA against Sh. flexneri strain was 100 µg/mL, while bacteria treated with CA showed a longer lag phase compared with the untreated control. CA effectively inactivated the Sh. flexneri in LB broth and fresh lettuce juice. CA treatment resulted in cell membrane permeability changes and dysfunction, as proven by cell membrane depolarization, decreased intracellular ATP concentration. In addition, CA was also discovered to increase the level of reactive oxygen species (ROS) in cells, and induce morphological changes in cells. Crystal violet staining showed that the biomass of biofilm was decreased significantly with CA in 24 h. Light microscopy and field emission scanning electron microscopy (FESEM) observations demonstrated decreased biofilm adhesion and destruction of biofilm architecture after treatment with CA. These findings indicated that CA acts as a natural bacteriostatic agent to control Sh. flexneri in food processing and production.

Didecyldimethylammonium bromide: Application to control biofilms of Staphylococcus aureus and Pseudomonas aeruginosa alone and in combination with slightly acidic electrolyzed water.

This project explored the antibacterial mechanism of didecyldimethylammonium bromide (DDAB) toward Staphylococcus aureus and Pseudomonas aeruginosa, and its removal effect on biofilms. Furthermore, we explored the effect of treatment by DDAB combined with slightly acidic electrolyzed water (SAEW) on biofilms of S. aureus or P. aeruginosa. First, DDAB has bacteriostatic and biofilm removal effects. Second, The effect of DDAB combined with SAEW on biofilm is more obvious than that of the two alone. DDAB at a concentration of 16 MIC combined with SAEW (ACC 30 mg/L, ORP 875 mV, pH 6.30) completely cleared the biofilm. In addition, the results of Confocal laser scanning microscopy (CLSM), Field emission scanning electron microscopy (FESEM) and Attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR) showed that DDAB combined with SAEW could disrupt the structure of biofilms, reduce polysaccharides, proteins and phospholipids in biofilms. This method has the potential to be used in food production chains to control S. aureus and P. aeruginosa and their biofilms, and it can be used in other industries.

A Flexible Dual-Analyte Electrochemical Biosensor for Salivary Glucose and Lactate Detection.

Electrochemical biosensors have been widely applied in the development of metabolite detection systems for disease management. However, conventional intravenous and fingertip blood tests are invasive and cannot track dynamic trends of multiple metabolites. Among various body fluids, saliva can be easily accessed and is regarded as a promising candidate for non-invasive metabolite detection. Recent works on the development of electrochemical biosensors for monitoring salivary metabolites have demonstrated high sensitivity and wide linear range. However, most of this research has been focused on salivary detection of a single metabolite. Here, we present a dual-channel electrochemical biosensor for simultaneous detection of lactate and glucose in saliva based on a flexible screen-printed electrode with two working electrodes. The sensitivities of glucose and lactate channels were 18.7 µA/(mM·cm2) and 21.8 µA/(mM·cm2), respectively. The dual-channel biosensor exhibited wide linear ranges of 0-1500 µM for the glucose channel and 0-2000 µM for the lactate channel and the cross-talk between the two detection channels was negligible, which made it adequately suitable for sensing low-level salivary metabolites. Such attractive characteristics demonstrate the potential of this dual-analyte biosensor in the development of wearable devices for monitoring disease progression and fitness.

Triple-synergistic MOF-nanozyme for efficient antibacterial treatment.

The abuse of antibiotics makes bacterial infection an increasingly serious global health threat. Reactive oxygen species (ROS) are the ideal alternative antibacterial approach for quick and effective sterilization. Although various antibacterial strategies based on ROS have been developed, many of them are still limited by insufficient antibacterial efficiency. Here, we have developed an acid-enhanced dual-modal antibacterial strategy based on zeolitic imidazolate frameworks-8 (ZIF8) -derived nanozyme. ZIF8, which can release Zn2+, is chosen as the carrier to integrate glucose oxidase (GOx) and gold nanoparticles (Au NPs) which can produce ROS via a cascade catalytic reaction. Thus, the bactericidal capability of ROS and Zn2+ have been integrated. More importantly, gluconic acid, a "by-product" of the catalytic reaction, can generate an acidic environment to promote both the ROS-producing and Zn2+-releasing, enhancing the overall antibacterial performance further. This triple-synergistic strategy exhibits extraordinary bactericidal ability at a low dosage of 4 µg/mL (for S. aureus) and 8 µg/mL (for E. coli), which shows a great potential of MOF-derived nanozyme for efficient bacterial eradication and diverse biomedical applications.

Efficacy of 405-nm LED illumination and citral used alone and in combination for the inactivation of Cronobacter sakazakii in reconstituted powdered infant formula.

Cronobacter sakazakii, a foodborne opportunistic pathogen, mainly affects neonates and infants, with mortality rates of 26.9%. Most outbreaks arise from powdered infant formula (PIF). The aim of this study was to investigate the efficacy and mechanism of 405-nm light-emitting diode (LED) and citral treatment used in combination against C. sakazakii in reconstituted PIF. LED-illumination combined with citral showed better antimicrobial effects than either treatment alone. In reconstituted PIF, the abundance of C. sakazakii cells was reduced by 6.5 log 10 CFU/mL following combined LED and 9 µL/mL citral treatment for 90 min compared with untreated controls, respectively. Combined LED and 6 µL/mL citral treatment destroyed C. sakazakii cellular morphology and membrane integrity, prolonged the recovery time of sublethally-injured cells, and induced lipid peroxidation. Besides, LED treatment decreased the amount of lipid peroxidation caused by citral treatment alone. Neither LED illumination nor citral treatment resulted in breakdown of C. sakazakii genomic DNA. Because of its safe, environmentally-friendly, economical, and high-performance characteristics, the combination of LED-illumination and citral treatment has the potential to be developed into a strategy to control C. sakazakii contamination in stored and reconstituted PIF.

Antibacterial Cascade Catalytic Glutathione-Depleting MOF Nanoreactors.

Nanozymes with peroxidase-like activity have great application potential in combating pathogenic bacterial infections and are expected to become an alternative to antibiotics. However, the near-neutral pH and high glutathione (GSH) levels in the bacterial infection microenvironment severely limit their applications in antibacterial therapy. In this work, a metal-organic framework (MOF)-based cascade catalytic glutathione-depleting system named MnFe2O4@MIL/Au&GOx (MMAG) was constructed. The MMAG cascade-catalyzed glucose to provide H+ and produces a large amount of toxic reactive oxygen species. In addition, MMAG consumed GSH, which can result in bacterial death more easily. Systematic antibacterial experiments illustrated that MMAG has superior antibacterial effects on both Gram-positive bacteria and Gram-negative bacteria.

Antibacterial Activity and Mechanism of Coenzyme Q0 Against Escherichia coli.

Coenzyme Q0 (CoQ0) is a natural compound found in Antrodia cinnamomea, which has a variety of biological activities. Here, the antibacterial activity and possible antibacterial mechanism of CoQ0 against Escherichia coli were investigated. The antibacterial effect was evaluated by determining minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values, and by assessing bacterial survival and the effect on the growth of E. coli after CoQ0 treatment in Luria-Bertani (LB) broth. To reveal the antibacterial mechanism of CoQ0, changes in intracellular adenosine triphosphate (ATP) concentration, membrane potential, and bacterial protein content, as well as effects on cell morphology and membrane integrity, were investigated. Both the MICs and MBCs of CoQ0 against E. coli were 0.1 mg/mL. After treatment of E. coli (6.5 log colony-forming units/mL) with 0.1 mg/mL of CoQ0 in LB broth for 3 h, the number of viable cells dropped below the detection limit. In addition, CoQ0 treatment resulted in the reduction in intracellular ATP concentration, cell membrane hyperpolarization, decreased bacterial protein concentrations, and damage to cell membrane integrity and cellular morphology. These results indicated that CoQ0 has effective antibacterial activity against E. coli, suggesting potential applications in food industry safety.

Dual-Modal Therapeutic Role of the Lactate Oxidase-Embedded Hierarchical Porous Zeolitic Imidazolate Framework as a Nanocatalyst for Effective Tumor Suppression.

The increasing evidence supports the fact that lactate in the tumor microenvironment (TME) plays a vital role in tumor proliferation, metastasis, and recurrence, which in turn is emerging as one of the most interesting molecular targets for tumor treatment. Here, hierarchical porous zeolitic imidazolate framework-8 (ZIF-8) as the nanocarrier is fabricated to simultaneously load lactate oxidase (LOD) and Fe3O4 nanoparticles (NPs), called LOD & Fe3O4@ZIF-8 NPs (LFZ NPs), for tumor therapy. On one hand, the sharp consumption of lactate in the TME by LOD will change the essential "soil" where tumor cells live so as to suppress tumor rapid growth. On the other hand, hydrogen peroxide (H2O2) is produced in the TME from the oxidation of lactate catalyzed by LOD and subsequently converted to highly toxic hydroxyl radicals (•OH) catalyzed by Fe3O4 NPs via Fenton-like reactions to kill tumor cells. Based on the endogenous catalysis, this dual-modal strategy of tumor therapy based on lactate is simple, safe, and effective, which deserves to be well concerned.

Inactivation of Pseudomonas aeruginosa Biofilms by 405-Nanometer-Light-Emitting Diode Illumination.

Biofilm formation by Pseudomonas aeruginosa contributes to its survival on surfaces and represents a major clinical threat because of the increased tolerance of biofilms to disinfecting agents. This study aimed to investigate the efficacy of 405-nm light-emitting diode (LED) illumination in eliminating P. aeruginosa biofilms formed on stainless steel coupons under different temperatures. Time-dependent killing assays using planktonic and biofilm cells were used to determine the antimicrobial and antibiofilm activities of LED illumination. We also evaluated the effects of LED illumination on the disinfectant susceptibility, biofilm structure, extracellular polymeric substance (EPS) structure and composition, and biofilm-related gene expression of P. aeruginosa biofilm cells. Results showed that the abundance of planktonic P. aeruginosa cells was reduced by 0.88, 0.53, and 0.85 log CFU/ml following LED treatment for 2 h compared with untreated controls at 4, 10, and 25°C, respectively. For cells in biofilms, significant reductions (1.73, 1.59, and 1.68 log CFU/cm2) were observed following LED illumination for 2 h at 4, 10, and 25°C, respectively. Moreover, illuminated P. aeruginosa biofilm cells were more sensitive to benzalkonium chloride or chlorhexidine than untreated cells. Scanning electron microscopy and confocal laser scanning microscopic observation indicated that both the biofilm structure and EPS structure were disrupted by LED illumination. Further, reverse transcription-quantitative PCR revealed that LED illumination downregulated the transcription of several genes associated with biofilm formation. These findings suggest that LED illumination has the potential to be developed as an alternative method for prevention and control of P. aeruginosa biofilm contamination.IMPORTANCEPseudomonas aeruginosa can form biofilms on medical implants, industrial equipment, and domestic surfaces, contributing to high morbidity and mortality rates. This study examined the antibiofilm activity of 405-nm light-emitting diode (LED) illumination against mature biofilms formed on stainless steel coupons. We found that the disinfectant susceptibility, biofilm structure, and extracellular polymeric substance structure and composition were disrupted by LED illumination. We then investigated the transcription of several critical P. aeruginosa biofilm-related genes and analyzed the effect of illumination temperature on the above characteristics. Our results confirmed that LED illumination could be developed into an effective and safe method to counter P. aeruginosa biofilm contamination. Further research will be focused on the efficacy and application of LED illumination for elimination of complicated biofilms in the environment.

Photon Momentum Transfer in Single-Photon Double Ionization of Helium.

We theoretically and experimentally investigate the photon momentum transfer in single-photon double ionization of helium at various large photon energies. We find that the forward shifts of the momenta along the light propagation of the two photoelectrons are roughly proportional to their fraction of the excess energy. The mean value of the forward momentum is about 8/5 of the electron energy divided by the speed of light. This holds for fast and slow electrons despite the fact that the energy sharing is highly asymmetric and the slow electron is known to be ejected by secondary processes of shake off and knockout rather than directly taking its energy from the photon. The biggest deviations from this rule are found for the region of equal energy sharing where the quasifree mechanism dominates double ionization.

Rational design of MnO nanoparticles assemblies for sensitive magnetic relaxation detection of melamine.

A versatile protocol has been developed for highly sensitive magnetic relaxation detection of the analyte based on the fabrication of MnO nanoparticles (NPs) assemblies. Based on the strategy that positively charged analyte could induce the assembly of negatively charged MnO NPs through electrostatic interaction, which will generate the change of magnetic relaxation rate of MnO NPs, we achieved highly sensitive and convenient detection of the analytes. By applying the detection of melamine as an example, we found that the detection limit can be as low as 0.733 ppb. Furthermore, this strategy has been applied for the initially detection of commercially available milk spiked with melamine as proof of its potential applicability of detection in complicated food samples.

Proposal for Measuring Electron Displacement Induced by a Short Laser Pulse.

In laser-matter interaction, most previous studies have focused on the change of the electron momentum induced by the external fields. Here, we theoretically investigate the electron displacement induced by an ultrashort pulse, whose precise waveform is hard to determine experimentally. We propose and numerically demonstrate a scheme to accurately measure the electron displacement using a ruler formed by the interfering spirals in the photoelectron momentum distribution generated by two oppositely circularly polarized pulses. The scheme is robust against the focusing volume effects and the jitter of the carrier envelope phase of the two circular pulses. The ability to measure the electron displacement by an arbitrary pulse may pave the way to quantitative control of the charge migration in matter on the scale of Ångström.

Efficient time-sampling method in Coulomb-corrected strong-field approximation.

One of the main goals of strong-field physics is to understand the complex structures formed in the momentum plane of the photoelectron. For this purpose, different semiclassical methods have been developed to seek an intuitive picture of the underlying mechanism. The most popular ones are the quantum trajectory Monte Carlo (QTMC) method and the Coulomb-corrected strong-field approximation (CCSFA), both of which take the classical action into consideration and can describe the interference effect. The CCSFA is more widely applicable in a large range of laser parameters due to its nonadiabatic nature in treating the initial tunneling dynamics. However, the CCSFA is much more time consuming than the QTMC method because of the numerical solution to the saddle-point equations. In the present work, we present a time-sampling method to overcome this disadvantage. Our method is as efficient as the fast QTMC method and as accurate as the original treatment in CCSFA. The performance of our method is verified by comparing the results of these methods with that of the exact solution to the time-dependent Schrödinger equation.