Higher Inactivation Rate Research Articles

Plasma-Activated Tap Water with Oxidative Potential Has an Inactivating Effect on Microbiological Contaminants in Aqueous Suspensions.

Plasma-activated water (PAW) generated from tap water has gained attention as a disinfectant when used directly in its pure form. Little is known about the application of PAW for bacterial inactivation in aqueous environments because its use in fluids results in dilutions. We investigated the effect of PAW in aqueous suspensions simulating such dilutions, and we focused on the minimal addition of PAW volumes to bacterial aqueous suspensions still resulting in high inactivation rates. The antimicrobial effect was highly dependent on the activation of PAW. An increase in activation power from 90 to 100 W resulted in a greater microbial reduction with an identical 10 min activation time. The susceptibility to PAW dilutions was analyzed in detail regarding nine Gram-negative species out of Enterobacterales and other waterborne microorganisms as well as four Gram-positive species present in two different matrices, in saline and in tap water, at high concentrations simulating massive contamination situations. For this purpose, the PAW activation setting of 90 W and 30 min was defined in order to be able to differentiate the limitations of inactivation in individual bacterial species. The Gram-negatives in saline demonstrated susceptibility when one volume unit of PAW was added. However, twice the PAW volume was necessary for inactivation when bacteria were present in tap water. Gram-positive microorganisms were more robust, indicated by prolonged contact times before inactivation. Our results indicate that PAW can be used for bacterial decontamination processes in aqueous environments when added in surplus. Optimized activation settings such as electric power to generate PAW and the contact times to the samples increase the effect of the inactivation a wide range of bacteria, regardless of their resistance profiles.

Application of UV LEDs to inactivate antibiotic resistant bacteria: Kinetics, efficiencies, and reactivations

Unregulated antibiotic use has led to the proliferation of antibiotic-resistant bacteria (ARB) in aquatic environments. Ultraviolet light-emitting diodes (UV LEDs) have evolved as an innovative technology for inactivating microorganisms offering several advantages over traditional mercury lamps. This research concentrated on utilizing UV LEDs with three distinct wavelengths (265 nm, 275 nm, and 285 nm) to inactivate E. coli DH10β encoding the ampicillin-resistant blaTEM-1 gene in its plasmid. Non-linear models, such as Geeraerd's and Weibull, provided more accurate characterization of the inactivation profiles than the traditional log-linear model due to the incorporation of both biological mechanisms and a deterministic approach within non-linear models. The inactivation rates of ARB were higher than antibiotic-sensitive bacteria (ASB) when subjected to UV LEDs. The highest inactivation rates were observed when all microorganisms were exposed to 265 nm. Photoreactivation emerged as the primary mechanism responsible for repairing DNA damage induced by UV LEDs. 285 nm showed the highest reactivation efficiencies for ARB under different fluences. At higher fluences, both 265 and 275 nm displayed similar effectiveness in suppressing reactivation, while at lower fluences, 275 nm exhibited better efficacies in controlling the reactivation. Therefore, the inhibition of reactivation was influenced by the extent of damage incurred to both DNA and enzymes. In nutrient-poor media (0.9 % NaCl), ASB did not exhibit any reactivation potential. However, the addition of Luria-Bertani (LB) broth promoted the reactivation of ASB. Lower fluence rate was more beneficial at 265 nm whereas higher fluence rates were more effective for longer wavelengths. The inactivation of ARB was enhanced by dissolved organic carbon (DOC) at low fluences. However, the removal of ARB was reduced due to the presence of DOC at higher fluences. The highest energy demand for ARB inactivation was reported at 285 nm. Environmental implicationThe excessive and unregulated utilization of antibiotics has emerged as a significant issue for public health. This paper presents a comprehensive analysis of the effectiveness of UV LEDs, an emerging technology, in the inactivation of antibiotic-resistant bacteria (ARB). This research paper explores the kinetics of UV LEDs with different wavelengths to inactivate ARB along with the reactivation efficiencies. This research work also explores the impact and relevant mechanisms of the impact of dissolved organic carbon (DOC) on the inactivation of ARB by UV LEDs.

In-situ magnetic alginate coated chitosan core@shell beads with excellent performance in simulated and real wastewater treatment: Behavior, mechanisms, and new perspectives

Herein, a new hybrid magnetic core@shell biocomposite was prepared based on an alginate-bentonite core and a chitosan shell layer (mAB@Cs) where magnetic Fe3O4 NPs (50.7 nm) were in-situ generated on the surface via a simple non-thermal co-precipitation approach. The biocomposite has a high ability to magnetically separate and remove organic (ciprofloxacin (CPX)) and seven toxic inorganic (Cu2+, Cd2+, Co2+, Ni2+, Pb2+, Zn2+, and Hg2+) contaminants from simulated wastewater. Experimental results showed a CPX monolayer chemisorption with a Langmuir maximum adsorption capacity of 264.7 mg/g, maintained effectiveness up to the fifth cycle, and high removal rates of heavy metals ranging from 74.89 % to 99.86 % corresponding to adsorption capacities ranging from 12 to 20 mg/g. For a more accurate evaluation, the biocomposite was tested on a real urban wastewater sample (RWW) and it has manifested a noteworthy efficiency in removing a mixture of inorganic pollutants in terms of potassium K+ and orthophosphate phosphorous P-PO43−, and organic matter in terms of biological oxygen demand (BOD) and chemical oxygen demand (COD) with 46 %, 90 %, 84 %, and 64 % removal efficiencies, respectively. On top of this, a high inactivation rate of E. coli of the order of 96 % was recorded, making the prepared magnetic biocomposite adept for the simultaneous removal of emergent wastewater pollutants, from organic, inorganic, to pathogen microorganisms.

Caspase‐2 Inhibition for Treatment of Alzheimer’s Disease

AbstractBackgroundThe enzyme caspase‐2 plays a central role in cellular apoptosis and is involved in the early stages of β‐amyloid 42 and tau deposition, making it a promising therapeutic target for Alzheimer’s Disease (AD). Caspase‐2 is highly expressed in the brains of patients with AD (1, 4) and those with mild cognitive impairment, which often precedes AD. This indicates the upregulation of caspase‐2 early in disease progression, which is not observed in healthy adult brains (1‐3).MethodNew irreversible small peptidomimetics (LJ2a and LJ3a) inhibit human caspase‐2 with a remarkably high inactivation rate. (5) In primary hippocampal neurons treated with β‐amyloid oligomers, submicromolar concentrations of LJ2a and LJ3a prevent synapse loss. Using a tamoxifen‐inducible Cre system for the global removal of caspase‐2, a series of experiments were performed on mice stereotaxically injected with β‐amyloid 42. This model was used to validate caspase‐2 blockade by assessing the cellular specificity of caspase‐2 activation, the induction of downstream targets, and cell death marker expression via immunohistochemistry and western blot.ResultReplication of these experiments remains underway.ConclusionPresentation of current data can inform the rationality for using caspase‐2 inhibitors as a therapeutic treatment.

High-efficiency and low-carbon inactivation of UV resistant bacteria in reclaimed water by flow-through electrode system (FES)

With the increasingly serious shortage of water resources globally, it has been paid more attention on how to secure the biosafety of reclaimed water and other non-traditional water sources. However, the 3 most applied disinfection technics, which are chlorine, ultraviolet (UV), and ozone disinfection, all have their disadvantages of selecting undesired bacteria and low energy utilization efficiency. Electrode disinfection is a promising solution, but the current electrode disinfection process still needs to be optimized in terms of the use conditions of the configuration reactivation. In this paper, we built a flow electrode system (FES). To evaluate the disinfection techniques more precisely, we isolated ultraviolet-resistant bacteria (URB) bacteria from the water of the full-scale water plant and tested the disinfection performance of FES and UV. The inactivation rate, reactivation potential, and energy consumption were analyzed. FES could inactivate 99.99 % of the URB and cause irreversible damage to the residual bacteria. FES could make all bacteria strains apoptosis in the subsequent 24 h of storage after alternating pulse current (APC) treatment, 3 V, within 27.7 s. Besides, the energy consumption of FES is about 2 orders lower than that of UV disinfection under the same inactivation rate. In summary, APC-FES is an efficient and low-carbon alternative for future water disinfection, which could achieve the ideal disinfection effect of a high inactivation rate, no reactivation, and low energy consumption.

Dose-Response Behavior of Pathogens and Surrogate Microorganisms across the Ultraviolet-C Spectrum: Inactivation Efficiencies, Action Spectra, and Mechanisms.

The dose-response behavior of pathogens and inactivation mechanisms by UV-LEDs and excimer lamps remains unclear. This study used low-pressure (LP) UV lamps, UV-LEDs with different peak wavelengths, and a 222 nm krypton chlorine (KrCl) excimer lamp to inactivate six microorganisms and to investigate their UV sensitivities and electrical energy efficiencies. The 265 nm UV-LED had the highest inactivation rates (0.47-0.61 cm2/mJ) for all tested bacteria. The bacterial sensitivity strongly fitted the absorption curve of nucleic acids at wavelengths of 200-300 nm; however, indirect damage induced by reactive oxygen species (ROS) was the leading cause of bacterial inactivation under 222 nm UV irradiation. In addition, the guanine and cytosine (GC) content and cell wall constituents of bacteria affect inactivation efficiency. The inactivation rate constant of Phi6 (0.13 ± 0.002 cm2/mJ) at 222 nm due to lipid envelope damage was significantly higher than other UVC (0.006-0.035 cm2/mJ). To achieve 2log reduction, the LP UV lamp had the best electrical energy efficiency (required less energy, average 0.02 kWh/m3) followed by 222 nm KrCl excimer lamp (0.14 kWh/m3) and 285 nm UV-LED (0.49 kWh/m3).

Evaluation of altered environmental conditions as a decontamination approach for SARS-CoV-2 when applied to aircraft related materials.

The purpose of this study was to evaluate the effects of altered environmental conditions, specifically elevated temperature at various levels of expected relative humidity (RH), on the inactivation of SARS-CoV-2 when applied to U.S. Air Force aircraft materials. SARS CoV-2 (USA-WA1/2020) was spiked (∼1×105 TCID50) in either synthetic saliva or lung fluid, dried onto porous (e.g. Nylon strap) and nonporous materials (e.g. bare aluminum, silicone, and ABS plastic), placed in a test chamber and exposed to environmental conditions ranging from 40 to 51.7 °C and RH ranging from 0% to 50%. The amount of infectious SARS-CoV-2 was then assessed at various timepoints from 0 to 2 days. Warmer test temperatures, higher RH, and longer exposure duration resulted in higher inactivation rates per material type. Synthetic saliva inoculation vehicle was more readily decontaminated compared to materials inoculated with synthetic lung fluid. SARS-CoV-2 was readily inactivated below limit of quantitation (LOQ) for all materials inoculated using synthetic saliva vehicle within 6 hours when exposed to environmental conditions of 51.7 °C and RH≥25%. Synthetic lung fluid vehicle did not follow the general trend of an increase in RH resulting in increased efficacy. The lung fluid performed best at the 20%-25% RH range to achieve complete inactivation below LOQ.

Evaluation of steam heat as a decontamination approach for SARS-CoV-2 when applied to common transit-related materials.

The purpose of this study was to evaluate the efficacy of steam heat for inactivation of SARS-CoV-2 when applied to materials common in mass transit installations. SARS CoV-2 (USA-WA1/2020) was resuspended in either cell culture media or synthetic saliva, inoculated (∼1×106 TCID50) onto porous and nonporous materials and subjected to steam inactivation efficacy tests as either wet or dried droplets. The inoculated test materials were exposed to steam heat ranging from 70°C to 90°C. The amount of infectious SARS-CoV-2 remaining after various exposure durations ranging from 1 to 60 s was assessed. Higher steam heat application resulted in higher inactivation rates at short contact times. Steam applied at 1-inch distance (∼90°C at the surface) resulted in complete inactivation for dry inoculum within 2 s of exposure (excluding two outliers of 19 test samples at the 5-s duration) and within 2-30 s of exposure for wet droplets. Increasing the distance to 2 inches (∼70°C) also increased the exposure time required to achieve complete inactivation to 15 or 30 s for materials inoculated with saliva or cell culture media, respectively. Steam heat can provide high levels of decontamination (>3 log reduction) for transit-related materials contaminated with SARS-CoV-2 using a commercially available steam generator with a manageable exposure time of 2-5 s.

Genuine selective caspase-2 inhibition with new irreversible small peptidomimetics

Caspase-2 (Casp2) is a promising therapeutic target in several human diseases, including nonalcoholic steatohepatitis (NASH) and Alzheimer’s disease (AD). However, the design of an active-site-directed inhibitor selective to individual caspase family members is challenging because caspases have extremely similar active sites. Here we present new peptidomimetics derived from the VDVAD pentapeptide structure, harboring non-natural modifications at the P2 position and an irreversible warhead. Enzyme kinetics show that these new compounds, such as LJ2 or its specific isomers LJ2a, and LJ3a, strongly and irreversibly inhibit Casp2 with genuine selectivity. In agreement with the established role of Casp2 in cellular stress responses, LJ2 inhibits cell death induced by microtubule destabilization or hydroxamic acid-based deacetylase inhibition. The most potent peptidomimetic, LJ2a, inhibits human Casp2 with a remarkably high inactivation rate (k3/Ki ~5,500,000 M−1 s−1), and the most selective inhibitor, LJ3a, has close to a 1000 times higher inactivation rate on Casp2 as compared to Casp3. Structural analysis of LJ3a shows that the spatial configuration of Cα at the P2 position determines inhibitor efficacy. In transfected human cell lines overexpressing site-1 protease (S1P), sterol regulatory element-binding protein 2 (SREBP2) and Casp2, LJ2a and LJ3a fully inhibit Casp2-mediated S1P cleavage and thus SREBP2 activation, suggesting a potential to prevent NASH development. Furthermore, in primary hippocampal neurons treated with β-amyloid oligomers, submicromolar concentrations of LJ2a and of LJ3a prevent synapse loss, indicating a potential for further investigations in AD treatment.

Pulsed Light (PL) Treatments on Almond Kernels: Salmonella enteritidis Inactivation Kinetics and Infrared Thermography Insights

Extending the shelf-life and ensuring microbiological safety of food products while preserving the nutritional properties are key aspects that must be addressed. Heat processing of food matrices has been the golden standard during the last decades, while certain non-thermal processing options have recently gained ground. In the present study, experimental pulsed light (PL) surface inactivation treatments of Salmonella enteritidis on almonds kernels are performed. The PL system is set to test different operative conditions, namely power (1000, 1250, and 1500 W) and frequency (1.8, 3.0, and 100.0 Hz) at different treatment times (from 5 to 250 s), which result in applied fluence doses in the 0–100 J·cm−2 range. Additionally, temperature measurements are collected at each operative condition on the almond surface (using infrared (IR) thermography) and at the superficial layer of the almond (1-mm depth using a thermocouple). The observed PL inactivation kinetics are then modelled using four different models. The best goodness-of-fit is found for the two-parameter Weibull model (R2 > 0.98 and RMSE < 0.33 for all cases). The maximum achieved log-CFU reductions are 6.02 for the 1.8-Hz system, 4.69 for the 3.0-Hz system, and 3.66 for 100.0-Hz system. The offset between the collected temperature readings by the two sensors is contrasted against the inactivation rate (following the two-parameter Weibull model). It was found that the highest inactivation rate corresponds approximately to the point where the infrared camera detects a slowdown in the surface heating.Graphical

Efficacy optimization of plasma-activated water for food sanitization through two reactor design configurations

The chemistry, antimicrobial efficacy and energy consumption of plasma-activated water (PAW) was optimized by altering the discharge frequency, ground-electrode configuration, gas flow rate and initial water conductivity for two reactor configurations, i.e., air pin-to-liquid discharge and air plasma-bubble discharge in water. The ratio of NO2− and NO3− formation was altered to optimise the antimicrobial effects of PAW, tested against two Gram-negative bacteria. An initial solution conductivity of 0.2 S·m−1 and 2000-Hz discharge frequency with the ground electrode positioned inside the pin reactor showed the highest antimicrobial effect resulting in a 3.99 ± 0.13-log10 reduction within 300 s against Escherichia coli and 5.90 ± 0.24-log10 reduction within 240 s for Salmonella Typhimurium. An excellent energy efficiency of reactive oxygen and nitrogen species (RONS) generation of 10.1 ± 0.1 g·kW−1·h−1 was achieved. Industrial relevancePlasma-activated water (PAW) is deemed as an eco-friendly alternative to chemical disinfection because its bactericidal activity is temporary. Optimizing the design and operation of PAW reactors to achieve high inactivation rates of more than 5-log10 reductions, as demonstrated in this work, will support the industrial application of this technology and the scaleup at industrial level.

The role of nanoparticles (titanium dioxide, graphene oxide) on the inactivation of co-existing bacteria in the presence and absence of quartz sand.

The increased mass production and application of engineered nanomaterials (ENMs) have resulted in the release of nanoparticles (NPs) in the environment, raising uncertainties regarding their environmental impacts. This study examines the effect of graphene oxide (GO) and titanium dioxide (TiO2) NPs on the inactivation of the three model bacteria originated by mammalians including humans: Escherichia (E.) coli, Enterococcus (E.) faecalis, and Staphylococcus (S.) aureus. A series of dynamic batch experiments were conducted at constant room temperature (22°C) in order to examine the inactivation of co-existing bacteria by NPs, in the presence and absence of quartz sand. The inactivation experimental data were satisfactorily fitted with a pseudo-first order expression with a time dependent rate coefficient. The inactivation of E. coli and S. aureus was shown to increase in the co-presence of GO or TiO2 NPs and quartz sand comparing with the presence of GO or TiO2 NPs alone. For E. faecalis, no clear trend was observed. Moreover, quartz sand was shown to affect inactivation of bacteria by GO and TiO2 NPs. Among the bacteria examined, the highest inactivation rates were observed for S. aureus.

Inactivation of Coronaviruses and Phage Phi6 from Irradiation across UVC Wavelengths.

Ultraviolet (UV) devices emitting UVC irradiation (200–280 nm) have proven to be effective for virus disinfection, especially on surfaces and in air, due to their rapid effectiveness and limited to no material corrosion. Numerous studies of UV-induced inactivation focused on nonenveloped viruses. Little is known about UVC action on enveloped viruses across UVC wavelengths. In this study, we determined inactivation efficiencies of two coronaviruses (ssRNA) and an enveloped dsRNA bacteriophage surrogate in buffered aqueous solution (pH 7.4) using five commonly available UVC devices that uniquely emit light at different wavelengths spanning 222 nm emitting krypton chloride (KrCl*) excimers to 282 nm emitting UVC LEDs. Our results show that enveloped viruses can be effectively inactivated using UVC devices, among which the KrCl* excimer had the best disinfection performance (i.e., highest inactivation rate) for all three enveloped viruses. The coronaviruses exhibited similar sensitivities to UV irradiation across the UVC range, whereas the bacteriophage surrogate was much more resistant and exhibited significantly higher sensitivity to the Far UVC (<230 nm) irradiation. This study provides necessary information and guidance for using UVC devices for enveloped virus disinfection, which may help control virus transmission in public spaces during the ongoing COVID-19 pandemic and beyond.

Analytical study of the intensification of the mass transfer process during inactivation of soybean grain in an ultrasonic installation

The article is devoted to improving the effectiveness of technological impact on soy in order to remove anti – nutritional substances from it-trypsin inhibitors and urease enzymes. This is achieved by intensifying the mass transfer during extraction by ultrasonic pulsating micro-flows and cavitation with the formation of the oxidizer hydrogen peroxide H2O2. The developed technical means provide high inactivation rates and increase the productivity of the process.

Impact of surface reflection on microbial inactivation in a UV LED treatment duct

Modeling of a UV-C LED air treatment duct showed that use of highly reflective duct surfaces significantly increased microbial inactivation and minimized the impact of LED positions on inactivation levels. This result was independent of the number of LEDs used. Four wall reflection resulted in higher inactivation rates than solely side-side or top–bottom surface reflection, but beyond three reflections of intensity the number of LEDs controlled the maximum inactivation. The model consisted of a radiation routine which calculated fluence rate from LED intensities and specular surface reflection, integrated with a fluid flow routine which determined air residence time and an inactivation routine which combined microbe inactivation rate constants with fluence levels. Model predictions compared well with data from a 2-cm square test treatment system that achieved 99.9% inactivation of Staphylococcus aureus at low flow rates. These results can guide treatment system designs and expand modeling capabilities for such systems.

Inactivation effect and mechanisms of combined ultraviolet and metal-doped nano-TiO2 on treating Escherichia coli and Enterococci in ballast water.

The discharge of ship ballast water (containing large amounts of alien organisms) has caused severe ecological hazards to marine environments. In this study, three metal elements (Ag, Fe, and Gd) were doped to nano-TiO2 material respectively (content: 0.4%, 0.7%, and 1.0%) to improve inactivation effect of Escherichia coli and Enterococci in ballast water. Experimental results indicate that compared with the sole ultraviolet (UV) and the UV and original nano-TiO2, the UV and metal-doped nano-TiO2 increased the bacterial inactivation rate to different extents. For each metal element, high external metal content (1.0%) corresponded to high inactivation effort. The doping of Ag resulted in optimal inactivation effort, and the addition of Fe and Gd caused unobvious effort. At the end of the inactivation process (20 s), the UV and 1% Ag-doped nano-TiO2 reached the highest logarithmic sterilization rates (0.915 for Escherichia coli and 0.805 for Enterococcus). The doping of Ag, Fe, and Gd did not change the anatase phase TiO2 crystal form, and 1% Ag-doped nano-TiO2 had the smallest particle diameter and the evenest distribution of nanoparticles. Compared with the sole UV, the UV and Ag-doped nano-TiO2 treatment resulted in higher malondialdehyde contents (0.0646 μmol/L for Escherichia coli and 0.0529 μmol/L for Enterococci) and lower superoxide dismutase activities (0.672 U/mL for Escherichia coli and 0.792 U/mL for Enterococci), which were in accordance with high inactivation rates in these cases.

A comparison of photolytic, photochemical and photocatalytic processes for disinfection of recirculation aquaculture systems (RAS) streams

The development of technologically advanced recirculation aquaculture systems (RAS) implies the reuse of water in a high recirculation rate (>90%). One of the most important phases for water management in RAS involves water disinfection in order to avoid proliferation of potential pathogens and related fish diseases. Accordingly, different approaches have been assessed in this study by performing a comparison of photolytic (UV-LEDs) at different wavelengths (λ = 262, 268 and 262 + 268 nm), photochemical (UV-LEDs/H2O2, UV-LEDs/HSO5− and UV-LEDs/S2O82−) and photocatalytic (TiO2/SiO2/UV-LEDs and ZnO/SiO2/UV-LEDs) processes for the disinfection of water in RAS streams. Different laboratory tests were performed in batch scale with real RAS stream water and naturally occurring bacteria (Aeromonas hydrophyla and Citrobacter gillenii) as target microorganisms. Regarding photolytic processes, higher inactivation rates were obtained by combining λ262+268 in front of single wavelengths. Photochemical processes showed higher efficiencies by comparison with a single UV-C process, especially at 10 mg L−1 of initial oxidant dose. The inactivation kinetic rate constant was improved in the range of 15–38%, with major efficiency for UV/H2O2 ∼ UV/HSO5− > UV/S2O82−. According to photocatalytic tests, higher efficiencies were obtained by improving the inactivation kinetic rate constant up to 55% in comparison with a single UV-C process. Preliminary cost estimation was conducted for all tested disinfection methods. Those results suggest the potential application of UV-LEDs as promoter of different photochemical and photocatalytic processes, which are able to enhance disinfection in particular cases, such as the aquaculture industry.

Electrochemical disinfection of secondary effluent from a wastewater treatment plant: Removal efficiency of ARGs and variation of antibiotic resistance in surviving bacteria

Abstract Laboratory-scale electrochemical (EC) disinfection experiments were carried out to investigate its removal efficiency for 23 antibiotic resistance genes (ARGs) that confer against 8 classes of antibiotics and its effects on the antibiotic resistance of surviving bacteria. EC treatments were conducted at different current densities (D treatment) and with different reaction times (T treatment). Prolonged electrolysis resulted in a higher inactivation rate than an increased current density, while the former was less efficient in the removal of ARGs. For example, the inactivation ratios for the T20 and D80 treatments were both >99%, while the decrease in the relative abundance of ARGs with D80 (from 0.54 to 4.1) was greater than that with T20 (from 5.4 to 5.2). The detection frequency of bacteria resistant to the tested antibiotics decreased by 9–100% after EC treatment. This was mainly attributed to a change in bacterial composition. The proportion of bacteria with high antibiotic resistance frequencies decreased (such as Escherichia), while that with low resistance frequencies (like Acinetobacter and Pseudomonas) increased. In addition, fewer multi-antibiotic-resistant bacteria survived EC disinfection, which also contributed to the significant decrease in the frequency of antibiotic resistant bacteria as well as in the multi-antibiotic-resistance indices of wastewater samples (from 0.47 to 0.35) after EC treatment (P

Photodynamic inactivation of S. aureus with a water-soluble curcumin salt and an application to cheese decontamination.

In this study, the optimal parameters for the photodynamic inactivation (PDI) of Staphylococcus aureus in bacterial suspensions and in cheese were assessed using a water-soluble curcumin salt as the photosensitizer (PS). The in vitro study aimed at finding the optimal concentration and light dose to promote S. aureus photokilling. Four main groups were proposed: CONTROL (L-C-), LIGHT (L+C-), CUR (L-C+) and PDI (L+C+). A fixed light dose (LED, 450 ± 10 nm, 10 J cm-2) was applied using four different PS concentrations (0.75, 1.0, 1.5 and 3.0 mg mL-1). The dose also varied from 10-100 J cm-2 for a fixed concentration. High inactivation rates were observed for all light doses, with a maximum reduction of 7.58 log10 at 100 J cm-2 (p ≪ 0.05). Saturation of the PDI effect was observed after a 10 minute illumination time, as well as a slight decrease in the S. aureus population for increasing illumination times in the L+C- group. As an application, the concentration showing the best decontamination performance in vitro (0.75 mg mL-1) was applied to decontaminate cheese in loco. PDI in two types of coalho cheese, a rennet-coagulated cheese commonly consumed in Brazil, was investigated. The results showed no significant inactivation in unpasteurized cheese, but a 4.34 log10 reduction for t > 5 min in pasteurized specimens. In conclusion, the present PDI-catalyzed curcumin photosensitizer inactivated S. aureus at statistically significant levels in vitro, in pasteurized cheese, but not in unpasteurized specimens.

Rapid Aerobic Inactivation and Facile Removal of Escherichia coli with Amorphous Zero-Valent Iron Microspheres: Indispensable Roles of Reactive Oxygen Species and Iron Corrosion Products.

Zero valent iron (ZVI) is recently regarded as a promising alternative for water disinfection, but still suffers from low efficiency. Herein we demonstrate that amorphous zerovalent iron microspheres (A-mZVI) exhibit both higher inactivation rate and physical removal efficiency for the disinfection of Escherichia coli than conventional crystalline nanoscale ZVI (C-nZVI) under aerobic condition. The enhanced E. coli inactivation performance of A-mZVI was mainly attributed to more reactive oxygen species (ROSs), especially free •OH, generated by the accelerated iron dissolution and molecular oxygen activation in bulk solution. In contrast, C-nZVI preferred to produce surface bound •OH, and its bactericidal ability was thus hampered by the limited physical contact between C-nZVI and E. coli. More importantly, hydrolysis of dissolved iron released from A-mZVI produced plenty of loose FeOOH to wrap E. coli, increasing the dysfunction of E. coli membrane. Meanwhile, this hydrolysis process lowered the stability of E. coli colloid and caused its rapid coagulation and sedimentation, favoring its physical removal. These findings clarify the indispensable roles of ROSs and iron corrosion products during the ZVI disinfection, and also provide a promising disinfection material for water treatment.