Inactivation Of Bacterial Cells Research Articles

Synergistic Strategies of Heat and Peroxyacetic Acid Disinfection Treatments for Salmonella Control.

The food industry has recognized a pressing need for highly effective disinfection protocols to decrease the risk of pathogen emergence and proliferation in food products. The integration of antimicrobial treatments in food production has occurred as a potential strategy to attain food items of superior quality with respect to microbiological safety and sensory attributes. This study aims to investigate the individual and synergistic effects of heat and peroxyacetic acid on the inactivation of bacterial cells, considering various contact times and environmental conditions. Four Salmonella serotypes, isolated from industrial meat production surfaces, were employed as model organisms. By systematically assessing the impacts of individual factors and synergistic outcomes, the effectiveness of bacterial cell inactivation and the efficiency of heat and peroxyacetic acid could be predicted. To better approximate real-world food processing conditions, this study also incorporated a bovine albumin-rich condition as a simulation of the presence of organic loads in processing steps. The findings revealed the essential need for a synergistic interplay of investigated parameters with the following optimized values: 1.5% concentration of peroxyacetic acid, temperature range of 60-65 °C, and contact time of 3 min for the complete effect regardless of the degree of contamination.

Инактивация бактерий в присутствии фотокатализаторов на основе TiO2, модифицированного вольфрамом или железом, при облучении видимым светом

The possibility of photocatalytic inactivation of bacterial cells (Pseudomonas alcaliphila and Pseudomonas fluorescens) in the presence of synthesized photocatalysts based on titanium dioxide modified with inovalent W or Fe cations under irradiation with visible light, is shown.

Construction of a novel double S-scheme structure WO3/g-C3N4/BiOI: Enhanced photocatalytic performance for antibacterial activity

In recent years, the threat to human health from bacteria in wastewater has attracted attention, and photocatalytic technology has emerged as a promising strategy for inactivating bacteria in water. Therefore, it is of great research value to develop a novel high-efficiency photocatalytic system with the visible light response. We successfully designed a double S-scheme heterojunction composite WO3/g-C3N4/BiOI (WCB) in this paper. The preparation of WCB composites was demonstrated by a series of characterizations, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The antibacterial effects of photocatalysts against representative Gram-negative strain Escherichia coli (E. coli) and Gram-positive strain Staphylococcus aureus (S. aureus) were tested under LED light irradiation. The novel photocatalyst presented excellent antibacterial properties, inactivating E. coli in 12 min and S. aureus in 20 min. The bacterial cell inactivation process was studied by scanning electron microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). Active species capture experiments show that the active species present in the WCB composites in the process of inactivating bacteria are h+, e−, OH and O2−. In conclusion, the synthesized double S-scheme WCB photocatalyst exhibits remarkable photocatalytic antibacterial activity under LED light and has broad prospects for practical application in water antibacterial treatment.

Effects of pulsed near infrared light (NIR) on Bacillus subtilis spores.

In this study, we develop a characterization of bacterial spore resistance to NIR pulsed light under modalities traditionally used in multiphoton microscopy. Energy dose and laser power are both key parameters in spore and bacterial cell inactivation. Surprisingly, spores and vegetative cells seem to show a similar sensitivity to pulsed NIR, spores being only 2-fold more resistant than their vegetative counterparts. This work enables us to eliminate certain hypotheses concerning the main driver of spore inactivation processes. Our findings suggest that damage leading to inactivation is mainly caused by photochemical reactions characterized by multiple possible pathways, including DNA damage or oxidation processes.

Electrochemical oxidation of landfill leachate using boron-doped diamond anodes: pollution degradation rate, energy efficiency and toxicity assessment.

Electrochemical oxidation (EO), due to high efficiency and small carbon footprint, is regarded as an attractive option for on-site treatment of highly contaminated wastewater. This work shows the effectiveness of EO using three boron-doped diamond electrodes (BDDs) in sustainable management of landfill leachate (LL). The effect of the applied current density (25-100mAcm-2) and boron doping concentration (B/C ratio: 500ppm, 10,000ppm and 15,000ppm) on the performance of EO was investigated. It was found that, of the electrodes used, the one most effective at COD, BOD20 and ammonia removal (97.1%, 98.8% and 62%, respectively) was the electrode with the lowest boron doping. Then, to better elucidate the ecological role of LLs, before and after EO, cultivation of faecal bacteria and microscopic analysis of total (prokaryotic) cell number, together with ecotoxicity assay (Daphnia magna, Thamnocephalus platyurus and Artemia salina) were combined for the two better-performing electrodes. The EO process was very effective at bacterial cell inactivation using each of the two anodes, even within 2h of contact time. In a complex matrix of LLs, this is probably a combined effect of electrogenerated oxidants (hydroxyl radicals, active chlorine and sulphate radicals), which may penetrate into the bacterial cells and/or react with cellular components. The toxicity of EO-treated LLs proved to be lower than that of raw ones. Since toxicity drops with increased boron doping, it is believed that appropriate electrolysis parameters can diminish the toxicity effect without compromising the nutrient-removal and disinfection capability, although salinity of LLs and related multistep-oxidation pathways needs to be further elucidated.

Red Phosphorus Nanodot-Decorated Polymeric Carbon Nitride Nanotubes for Visible-Light-Driven Photocatalytic Bacterial Inactivation

Pathogenic microorganisms related to infectious diseases severely threaten human health, and visible-light-driven (VLD) photocatalysis is a promising strategy for mitigating microbial-induced health crises. In this work, a superior and effective VLD photocatalyst comprising a red phosphorus nanodot-modified one-dimensional carbon nitride nanotube (RP-CN) heterostructure was synthesized with a simple chemical vapor deposition method and used for bacterial inactivation. The optimized RP (40)-CN rapidly and completely destroyed Escherichia coli and Staphylococcus aureus (107 CFU mL–1) within 25 and 30 min under irradiation with a white LED, respectively. The efficient photocatalytic activity was attributed to the fact that the matching work function in the CN-RP heterojunction promotes the charge migration/separation that occurs at the CN and RP interface and the broad absorption spectra by RP loading. Additional unpaired photoelectrons reacted with water to generate •O2– radicals and H2O2 for efficient bacterial cell inactivation. The present study highlights the design of nanostructured photocatalysts with wide spectral responses for efficient energy conversion and wide antibacterial scope.

Component release after exposure of Staphylococcus aureus cells to pulsed electric fields

The objective of this work was to get further insights on the mechanism of inactivation of bacterial cells by pulsed electric fields (PEF) through the study of the release of intracellular components after exposing Staphylococcus aureus cells in McIvlaine buffer (pH 7.0, 2 mS/cm) to PEF treatments of different intensity (18 and 25 kV/cm) and treatment times (from 20 to 400 μs). Release of most compounds, except proteins, was almost immediate after the treatment, but the relative amount released depended on the molecule studied. A good correlation between the release of the smallest components studied (particularly ions) and membrane permeabilization (as measured by NaCl sensitization and PI entry) was observed. On the other hand, results obtained suggested that S. aureus inactivation by PEF would be related to the exit of cytoplasmic proteins of a molecular weight higher than 6 kDa. Results obtained in this work indicated that increasing PEF treatment time would reduce the capability of S. aureus cells to repair the electropores formed and suggested that this might be due to the formation of pores of a larger size, which S. aureus cells would be unable to reseal in a situation of homeostasis loss. Industrial relevanceResults reported here can help to design more effective treatments for microbial inactivation using PEF on food, and therefore facilitate its industrial implementation.

Evaluation of non-thermal effect of microwave radiation and its mode of action in bacterial cell inactivation

A growing body of literature has recognized the non-thermal effect of pulsed microwave radiation (PMR) on bacterial systems. However, its mode of action in deactivating bacteria has not yet been extensively investigated. Nevertheless, it is highly important to advance the applications of PMR from simple to complex biological systems. In this study, we first optimized the conditions of the PMR device and we assessed the results by simulations, using ANSYS HFSS (High Frequency Structure Simulator) and a 3D particle-in-cell code for the electron behavior, to provide a better overview of the bacterial cell exposure to microwave radiation. To determine the sensitivity of PMR, Escherichia coli and Staphylococcus aureus cultures were exposed to PMR (pulse duration: 60 ns, peak frequency: 3.5 GHz) with power density of 17 kW/cm2 at the free space of sample position, which would induce electric field of 8.0 kV/cm inside the PBS solution of falcon tube in this experiment at 25 °C. At various discharges (D) of microwaves, the colony forming unit curves were analyzed. The highest ratios of viable count reductions were observed when the doses were increased from 20D to 80D, which resulted in an approximate 6 log reduction in E. coli and 4 log reduction in S. aureus. Moreover, scanning electron microscopy also revealed surface damage in both bacterial strains after PMR exposure. The bacterial inactivation was attributed to the deactivation of oxidation-regulating genes and DNA damage.

New Functionalized Macroparticles for Environmentally Sustainable Biofilm Control in Water Systems.

Reverse osmosis (RO) depends on biocidal agents to control the operating costs associated to biofouling, although this implies the discharge of undesired chemicals into the aquatic environment. Therefore, a system providing pre-treated water free of biocides arises as an interesting solution to minimize the discharge of chemicals while enhancing RO filtration performance by inactivating bacteria that could form biofilms on the membrane system. This work proposes a pretreatment approach based on the immobilization of an industrially used antimicrobial agent (benzalkonium chloride—BAC) into millimetric aluminum oxide particles with prior surface activation with DA—dopamine. The antimicrobial efficacy of the functionalized particles was assessed against Escherichia coli planktonic cells through culturability and cell membrane integrity analysis. The results showed total inactivation of bacterial cells within five min for the highest particle concentration and 100% of cell membrane damage after 15 min for all concentrations. When reusing the same particles, a higher contact time was needed to reach the total inactivation, possibly due to partial blocking of immobilized biocide by dead bacteria adhering to the particles and to the residual leaching of biocide. The overall results support the use of Al2O3-DA-BAC particles as antimicrobial agents for sustainable biocidal applications in continuous water treatment systems.

The Thermal Death Time Concept and Its Implications Revisited

Apart from actual incubation and/or testing, the mandated way to determine the microbial safety of thermally preserved foods is still anchored in the premise that the isothermal inactivation of bacterial cells and spore survival follows first-order kinetics. This is despite growing evidence to the contrary, and that the D value’s temperature-dependence too need not follow the log-linear model. Also, for technical reasons, the experimental detection level of survival ratios is usually four to six orders of magnitudes higher than that expected to assure a safe product. The theoretical implications of such a gap combined with non-linear inactivation kinetics are explored through simulations with especially constructed mathematical survival models. One of these models produces apparently log-linear or Weibullian survival patterns above the detection despite having a definite thermal death time, while the other has a substantial asymptotic residual survival level albeit below the detection level. The simulations highlight the notion that there is not enough information in an experimental survival curve’s shape to allow its continuation to below the detection level. Thus any thermal death time determined by extrapolation has no logical basis and can lead to either underestimation or overestimation of the thermal process’s lethality depending on the model chosen to describe it. The analysis lends support to the notion that safety factors and efficacy criteria in thermal processes should be based on observable survival ratios and not on log-linear kinetics.

Bacterial Cell Inactivation Using a Single-Frequency Batch-Type Ultrasound Device

Ultrasound technology employs cavitation to generate high-pressure soundwaves to disrupt bacterial cells. This study reveals the effectiveness of a single frequency ultrasound device for bacterial cell inactivation. A low-cost ultrasound device having a single frequency, i.e. 22 kHz for lab-scale application, was developed first, and the prototype was mechanically designed and analyzed using the finite-element method to assure the targeted natural frequency could be achieved. The prototype was then tested inactivating bacterial cells, Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis), in a simple medium and a food system, and the results were then compared to a commercial system. A treatment time of up to 15 minutes was able to reduce E. coli and B. subtilis cells by 3.3 log and 2.8 log, respectively, and these results were similar to those of the commercial system. The effectiveness of bacterial cell inactivation using the developed single-frequency ultrasound device is then discussed. The findings are useful for designing low-cost ultrasound devices for application in the food industry.

The Antibacterial Efficacy and Mechanism of Plasma-Activated Water Against Salmonella Enteritidis (ATCC 13076) on Shell Eggs.

Eggs are one of the most commonly consumed food items. Currently, chlorine washing is the most common method used to sanitize shell eggs. However, chlorine could react with organic matters to form a potential carcinogen, trihalomethanes, which can have a negative impact on human health. Plasma-activated water (PAW) has been demonstrated to inactivate microorganisms effectively without compromising the sensory qualities of shell eggs. For this study, various amounts (250, 500, 750, or 1000 mL) of PAW were generated by using one or two plasma jet(s) at 60 watts for 20 min with an air flow rate at 6 or 10 standard liters per minute (slm). After being inoculated with 7.0 log CFU Salmonella Enteritidis, one shell egg was placed into PAW for 30, 60, or 90 s with 1 or 2 acting plasma jet(s). When 2 plasma jets were used in a large amount of water (1000 mL), populations of S. Enteritidis were reduced from 7.92 log CFU/egg to 2.84 CFU/egg after 60 s of treatment. In addition, concentrations of ozone, hydrogen peroxide, nitrate, and nitrite in the PAW were correlated with the levels of antibacterial efficacy. The highest concentrations of ozone (1.22 ppm) and nitrate (55.5 ppm) were obtained with a larger water amount and lower air flow rate. High oxidation reduction potential (ORP) and low pH values were obtained with longer activation time, more plasma jet, and a lower air flow rate. Electron paramagnetic resonance (EPR) analyses demonstrated that reactive oxygen species (ROS) were generated in the PAW. The observation under the scanning electron microscope (SEM) revealed that bacterial cells were swollen, or even erupted after treatment with PAW. These results indicate that the bacterial cells lost control of cell permeability after the PAW treatment. This study shows that PAW is effective against S. Enteritidis on shell eggs in a large amount of water. Ozone, nitrate, and ROS could be the main causes for the inactivation of bacterial cells.

Influence of metallic species for efficient photocatalytic water disinfection: bactericidal mechanism of in vitro results using docking simulation.

TiO2-based heterogeneous photocatalysis systems have been reported with remarkable efficiency to decontaminate and mineralize a range of pollutants present in air and water medium. In the present study, a series of visible light active metal oxide TiO2 nanoparticle were synthesized and evaluated for their photodegradation efficiency against emerging textile pollutant (Reactive Yellow 145) and antibacterial applications. In the first phase, nanomaterial synthesis was carried out following various synthesis parameters like addition of metallic impurities (different types and concentration) and calcination temperature. In the second phase, synthesized nanomaterials were screened for their performance in terms of photocatalytic degradation of RY145 and the best one (Fe-1-T-3 with 100% RY145 removal within 80min of irradiation) was further optimized against various reaction parameters. To get knowledge about the insights of nanomaterial performance for degradation of different environmental pollutants, the most important is to understand their physicochemical properties utilizing different characterization techniques. The physical morphology and elemental dispersion of metal-doped TiO2 nanomaterials were analyzed and results indicated that added metallic impurities were well dispersed onto the substrate surface. The efficient nanomaterials selected from initial screening were further assessed for photocatalytic disinfection efficiency against human pathogenic bacterial strains. Antimicrobial activities of the metal oxide nanomaterial were tested against gram-positive and gram-negative pathogenic bacterial strains. Possible mode of interaction of nanomaterial with bacterial DNA for bacterial cell inactivation was predicted using molecular docking simulation. The research project has the potential to contribute to multiple disciplines like material synthesis, water disinfection, and as green solutions for the textile industry replacing traditional technologies.

Microwave-assisted synthesis of defective tungsten trioxide for photocatalytic bacterial inactivation: Role of the oxygen vacancy

Surface defect modulation has emerged as a potential strategy for promoting the photocatalytic activity of photocatalysts for various applications, while the impact of the oxygen vacancy on bacterial inactivation is still debated. In this study, oxygen vacancies were introduced to tungsten trioxide nanosheets (WO3–x) via a microwave-assisted route. The as-prepared WO3–x nanosheets exhibited excellent visible-light-driven photocatalytic activity toward E. coli K-12 inactivation, and 6 log orders of the bacterial cells could be completely inactivated within 150 min. The obtained bacterial inactivation rate constant was 15.2 times higher than that of pristine WO3 without oxygen vacancies, suggesting that the surface oxygen vacancy could significantly promote the bacterial inactivation efficiency. The mechanism study indicated that the inactivation of bacterial cells occurs via a direct h+ oxidation pathway. In addition, the role of the oxygen vacancy was studied in detail; the oxygen vacancy was found to not only promote interfacial charge separation but also tune the band structure of WO3, thereby leading to increased h+ oxidation power. Finally, a possible oxygen vacancy-dominated photocatalytic bacterial inactivation mechanism is proposed. This work is expected to offer new insights into the microwave-assisted synthesis of defective photocatalysts and the use of the oxygen vacancy for promoting photocatalytic antibacterial activities.

Platinum disc electrode for in-situ electrochemical inactivation of bacterial growth in culture media

We report electrochemical response of non-adherent E. coli cells on a platinum disc electrode and in-situ inactivation through electro-stimulation to reduce their growth. Anodic peak current in cyclic voltammetry (CV) was gradually enhanced with an increased cell density due to increase in redox protein riboflavin secreted by the viable bacterial cells. The presence of the bacterial cells showed capacitive nature of the electric double layer capacitance and reduced interfacial charge transfer resistance in impedance of Nyquist plot. Formation of bacterial layer on the electrode surface was also evident from the rise in both anodic peak current and potential with scan rate at fixed cell concentration. The electrochemical inactivation of bacterial cells showed significant reduction in colony formation and growth. The observed inhibitory response with electro-stimulation was in comparison with the inactivation of bacterial cells treated with UV irradiation and sonication. Negative bias potential as compare to positive or periodic bias potential has been more effective for inactivation of the viable bacterial cells in suspension.

Decoration of Fe3O4 base material with Ag/AgCl nanoparticle as recyclable visible-light driven photocatalysts for highly-efficient photocatalytic disinfection of Escherichia coli

Effective and environmental water disinfectants are of great importance to address increasing health concerns in drinking water. Hence, in present paper, a highly efficient, recyclable and magnetically separable nanoparticles Ag/AgCl/Fe3O4 was prepared, comprehensively characterized (SEM, TEM, XRD, XPS, UV–vis and PL) and investigated as photocatalytic disinfectants for Escherichia coli K-12 (E. coli K-12). And the Ag/AgCl/Fe3O4 nanocomposites exhibited excellent disinfection performance for eliminating E. coli K-12 under visible light irradiation, with a maximum inactivation rate of 9.1-log at 0.2 g L−1 in 60 min. Consistent disinfection performance was verified with five successive stability tests and reused five times without significant decrease in photocatalytic disinfection. The synergistic effects of Ag/AgCl andFe3O4 in the hybrid could also contribute to the improved photo stability and the reusability towards bacteria inactivation. The potential disinfection mechanism was investigated on the fluorescence assays, Cell morphology (SEM), TOC level and K+ leakage, and the results shown that the bacterial cell inactivation begins with the cell wall destruction with the leakage of the cellular components in the present photocatalytic system. Further photochemical investigation indicated that H+, OH and H2O2 were the crucial active species. These results demonstrated effectiveness and potential applications for the developed Ag/AgCl/Fe3O4 nanocomposites in waste water disinfection.

Black phosphorus/graphitic carbon nitride: A metal-free photocatalyst for “green” photocatalytic bacterial inactivation under visible light

In the drive toward the ever-increasing standards for high-quality drinking water, exploring stable and efficient photocatalysts with excellent visible light (VL) harvesting ability for the photocatalytic water disinfection is still a challenging problem. However, most photocatalysts are solely metal-based or contain at least one metal-containing cocatalyst with detrimental environmental impacts. Here, we show that a novel metal-free 2D heterostructure (BP-CN) composed of black phosphorus (BP) and graphitic carbon nitride (CN) can be used as a VL-driven photocatalyst to achieve highly efficient water disinfection. The activity of BP-CN photocatalyst was about 7 times better compared with that of pure CN for the disinfection of indicator bacteria, with the complete inactivation of bacterial cells (107 cfu·mL−1) within 60 min. The bacterial inactivation mechanism was thoroughly investigated, and hydroxyl radical (OH) and H2O2 were determined to be the major reactive oxygen species (ROSs) for water disinfection. The BP-CN photocatalyst is composed of low-cost and earth-abundant materials and holds great promise in “green” photocatalytic disinfection applications.

Implications of Chemical Reduction Using Hydriodic Acid on the Antimicrobial Properties of Graphene Oxide and Reduced Graphene Oxide Membranes.

The antimicrobial properties of graphene-based membranes such as single-layer graphene oxide (GO) and modified graphene oxide (rGO) on top of cellulose ester membrane are reported in this study. rGO membranes are made from GO by hydriodic acid (HI) vapor treatment. The antibacterial properties are tested after 3 h contact time with selected model bacteria. Complete bacterial cell inactivation is found only after contact with rGO membranes, while no significant bacterial inactivation is found for the control i) GO membrane, ii) the mixed cellulose ester support, and the iii) rGO membrane after additional washing that removes the remaining HI. This indicates that the antimicrobial effect is neither caused by the graphene nor the membrane support. The antimicrobial effect is found to be conclusively linked to the HI eliminating microbial growth, at concentrations from 0.005%. These findings emphasize the importance of caution in the reporting of antimicrobial properties of graphene-based surfaces.

Prussian blue-encapsulated Fe3O4 nanoparticles for reusable photothermal sterilization of water

Waterborne health issues continue to grow despite the large number of available solutions. Current sterilization techniques to fight with waterborne diseases struggle to meet the demands on cost, efficiency and reach. Effective alternatives are pressingly required. Here we introduce Prussian blue coated ferroferric oxide (Fe3O4@PB) composites for water sterilization. The composites exhibit superior photothermal inactivation of bacteria under solar-light irradiation, with nearly complete inactivation of bacterial cells in only 15 min. Even for the mixed bacteria in authentic water matrices, the composites show excellent bacterial inactivation performance. Moreover, the highly magnetized iron core of the Fe3O4@PB enables magnetic separation and recycling. Multiple cycle runs reveal that Fe3O4@PB composites have exceptional stability and reusability. This work demonstrates a scalable, low-cost, high-efficiency and reusable sterilization method to improve water quality and safety.

Quaternized polysulfones-based blends: Surface properties and performance in life quality and environmental applications

Development of new quaternized polysulfones-based blends, which possess multifunctionality, antibacterial, and sustainability fundamental characteristics, was performed as a result of membrane technology requirements. Therefore, solutions of ionic polysulfones (PSFQ) with a tunable content of cellulose acetate phthalate (CAP) have been processed to obtain new membrane materials explored for wastewater treatment. The cumulative effects generated by the CAP versatile nature along with molecular functionalization of polysulfone were responsible for improving the workability, surface properties, and membranes performance, minimizing the adhesion of organic foulants/bacteria and maximizing the inactivation of bacterial cells. Additionally, the specific microarchitecture, determined using atomic force microscopy, represents excellent scaffolds as porous membranes. By evaluation of bacterial adhesion to surface, the practical applicability of membranes was tested, in order to clarify their suitability for life quality and environmental applications. The performed experiments represent the basis to future applications of these blends as membranes and confirm their performance in industrial field.