Bacterial Inactivation Kinetics Research Articles

Poly(Lactic Acid) Composite with Chitosan: Synergistic Effects of Physical Hurdles and Kinetics of Bacterial Inactivation

Poly(Lactic Acid) Composite with Chitosan: Synergistic Effects of Physical Hurdles and Kinetics of Bacterial Inactivation

Water disinfection using hydrogen peroxide with fixed bed hematite catalyst - kinetic and activity studies.

A lab-scale reactor with a fixed-bed hematite catalyst for the effective decomposition of H2O2 and bacteria inactivation was designed. The bactericidal effect is the largest at a low initial bacterial count of 2·103CFU/L, which is typical for natural surface waters. When using a 5mM H2O2 solution and a residence time of 104min, the reduction in the number of E. coli bacteria is about 3.5-log. At a higher initial bacterial count of 1-2·104CFU/L, a 5mM H2O2 solution reduces the bacteria number by about 4-log. The H2O2 decomposition follows the log-linear kinetics of a first-order reaction while the bacterial inactivation does not. The kinetics of bacterial inactivation was described using the Weibull model in the modified form: log10(N0/N) =b · tn. The values of the non-linearity parameter n were found to be lower than 1, indicating that bacterial inactivation slows down over time. With increasing initial H2O2 concentration, the rate parameter b increases while the non-linearity parameter n decreases. With increasing temperature, both parameters increase. The stability of the catalyst has been proved by XRD, FTIR, SEM, and ICP-OES. The concentration of iron leaching into water during disinfection is much lower than the limit declared by WHO for iron in drinking water. The results show that technical-grade hematite is a promising Fenton-like catalyst for water disinfection. The fixed-bed reactor can be the basis of the mobile installations for water purification in emergencies.

Fast Bacterial Inactivation Kinetics on an Inherently Antimicrobial Anionic Block Polymer

Mitigation of the global threat associated with antibiotic-resistant microbes necessitates effective preventative measures. One such strategy relies on self-disinfecting anionic block polymers that undergo a water-activated surface pH drop, which kills over 99.9999% of various microbes in minutes. In this work, we elucidate the time-dependent morphological response of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria to this polymer surface. Since pre-exposure of the polymer to solvent-vapor or hydrothermal annealing alters the tortuosity of pathways responsible for proton diffusion, corresponding changes in bacterial inactivation kinetics are compared and analyzed in the context of a model capable of differentiating between single-stage and more complex inactivation processes.

Bacterial inactivation on sputtered TiOMoN and TiOMoN-Ag thin films under solar simulated light

The bacterial inactivation kinetics of Escherichia coli (E. coli) by innovative sputtered TiMoON and TiMoON-Ag films under simulated solar light irradiation is accounted for in a detailed, comprehensive and systematic form. This study presents the evidence that normal E. coli degrades faster compared to genetically modified porinless E. coli due to Ag+-ions transfer occurring from the beginning of the bacterial inactivation process. The Ag-films were deposited by RF-reactive sputtering and presented a high hydrophobic character, which facilitated their contact/interaction with the bacteria cell wall. To reach homogeneous distribution of Ag in the films, annealing under vacuum at 400 °C was required. The films were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron microscopy (XPS), X-ray fluorescence (XRF) and contact angle (CA) measurements. TiMoON-Ag films led to the formation of highly reactive oxidative radicals (ROS) under solar irradiation. The nature of these species was specifically identified. The formation of TiN and TiO-sites on the film surface was detected by XPS. TiMoON-Ag films with 6.7 and 7.4 at. % Ag led to E. coli inactivation ∼ 90 min under solar simulated light (50 mW/cm2, 320–800 nm). The later films present a practical potential for the disinfection of medical surfaces and devices under solar light due to the narrow film ban-gap of 2.10 eV.

Determining the structure-antibacterial properties relationship and bacterial inactivation kinetics in different morphological-controlled ZnO nanoarchitectures for wastewater applications

This study aimed to systematically evaluate and determine the specific roles of reactive oxygen species (ROS) and Zn2+ ions in governing the antibacterial properties of different ZnO nanoarchitectures. This could differ greatly on model bacteria under different irradiation conditions and affects on the design and scale-up of ZnO-based photocatalytic system for wastewater applications. Various ZnO nanostructures were synthesized, characterised and systematically evaluated for their antibacterial properties on both Gram-positive and Gram-negative bacteria under dark, UV-light, and simulated solar irradiation conditions. Results showed that the 1D-ZnO nanorods possessed the highest photo-deactivation ability with a 3.5-log reduction for B. subtilis and a 4.2-log reduction for E. coli under UV light conditions. This is precisely linked to the 1D rod-like ZnO nanostructures with a higher exposed polar surface that favours the dissolution kinetics of Zn2+ ions. Besides, the surface oxygen vacancies were found to be strongly correlated to the intracellular ROS concentration that imparts bactericidal effect at different extents depending on the ZnO nanostructures used. The photo-deactivation kinetics were found to be best-fitted using the empirical Hom model, as it could represent the non-linear bacterial inactivation kinetics profile with a prolonged tailing characteristic. Finally, the Friedman non-parametric test showed that all experimental datasets for B. subtilis and E. coli surviving cases were significantly different (p-value < 0.05). The post-hoc approach indicated that the Zn2+ ions dissolution was the fundamental factor in dictating the antibacterial properties in different ZnO nanostructures.

Assessing the photodynamic efficacy of different photosensitizer-light treatments against foodborne bacteria based on the number of absorbed photons.

Increasing interests in photodynamic treatment (PDT) for food preservation require a holistic method to evaluate and compare different photosensitizer (PS)-light treatments. In this report, the absorbed photons were used as the basis to assess the antimicrobial photodynamic efficacy of two PSs, chlorophyllin sodium magnesium salt (Chl-Mg) and chlorophyllin sodium copper salt (Chl-Cu), under blue and white light against two typical foodborne pathogens, Gram-negative Escherichia coli, and Gram-positive Staphylococcus aureus. The results showed that the phototoxicity of a PS was predominantly decided by the absorbed photons rather than the characteristics of light sources. Photosensitized Chl-Mg exhibited superior antimicrobial activity as compared to that of ChlCu. The applied treatments were found to be more effective against S. aureus than E. coli. Bacterial inactivation kinetics as a function of the number of absorbed photons could be described by Weibull model with R2 from 0.947-0.962, and kinetics constants D in the range of 0.202×1017 photons/cm2-2.409×1018 photons/cm2. The kinetics models may find promising applications in the design, assessment, and optimization of PDT processes.

Kinetics of Bacterial Inactivation by Peroxynitric Acid in the Presence of Organic Contaminants.

Low-temperature atmospheric-pressure plasma has been studied for disinfection purposes. When plasma is exposed to water, reactive oxygen and nitrogen species are generated and preserved in the water fraction (plasma-treated water [PTW]), which consequently exhibits bactericidal activity. At low temperatures, one of the bactericidal components of PTW is peroxynitric acid (PNA). Importantly, PNA can also be synthesized by chemical reaction, without exposure to plasma. In this study, we evaluated the bactericidal properties of PNA based on reaction kinetics in comparison with other disinfectants. The analysis, based on dose-dependent effects, showed that PNA exhibited about 1 and 10 times the bactericidal activity of hypochlorous acid (HOCl) and peracetic acid, respectively. In addition, we evaluated the influence of organic contaminants on the bactericidal effects of PNA and HOCl. The bactericidal potential of both disinfectants was reduced by bovine serum albumin (BSA); however, PNA showed about 30-times-higher resistance against BSA inhibition than HOCl. Analysis of the dose-dependent effects of PNA revealed that the inhibition of bactericidal effect was caused by its consumption. Further experiments using model substrates containing particular amino acid residues (Met, Cys, Lys, and Leu) suggested that the bacterial inactivation by PNA is less affected by BSA due to the low reactivity and narrow reactivity spectrum of PNA for amino acid residues. Overall, our results suggest that PNA has a great disinfection potential, especially in the presence of organic contaminants (e.g., on the surface of the human body and on medical instruments contaminated with biological fluids).IMPORTANCE A good disinfectant for the human body should have various properties, such as strong bactericidal activity, harmlessness to living tissues, and resistance against biological fluids (or other organic contaminants). Peroxynitric acid (PNA) showed a bactericidal effect that was several tens up to several hundred times higher per unit of molarity than that of sodium hypochlorite and peracetic acid, which are used as general disinfectants for medical equipment. Moreover, the high resistance of PNA to organic load was confirmed, indicating that PNA will inactivate bacteria effectively even on contaminated surfaces, such as used medical devices or the human body surface. Therefore, we propose that PNA can be used as a strong disinfectant for the human body.

Wastewater disinfection: long-term laboratory and full-scale studies on performic acid in comparison with peracetic acid and chlorine

Chemical disinfection of municipal wastewater to preserve the microbiological quality of discharges has traditionally relied on chlorine, and more recently on peracetic acid (PAA). A more recent option is performic acid (PFA). This work uses laboratory and full-scale studies over a span of 15 years and five wastewater treatment plants (WWTPs) in Italy, to compare the efficacy of these three disinfectants and identify the differences among peracids in a context where both can be an alternative to chlorine. The investigations focused on treatment effectiveness and bacterial inactivation kinetics using E. coli and the more resistant enterococci, as well as on PFA and PAA decomposition as the residuals may affect the downstream microenvironment. Furthermore, the potential for the two peracids to oxidize organic substances and create troublesome byproducts was also studied. Chlorine, applied as hypochlorite (“HYP”) and here essentially functioning as chloramines, was used as a baseline comparison for the two peracids. Appropriate statistical tests were applied to the data from different WWTPs to account for potential interferences and compounding effects of the different matrices. Average doses of 0.8, 2.9 and 1.4 mg/L and contact times of 18, 21 and 31 min, respectively for PFA, chlorine and PAA guaranteed with a high level of assurance the 5000 CFU/100 mL E. coli limit; the order of effectiveness was PFA > HYP > PAA, refined as PFA > HYP ≈ PAA against E. coli and PFA ≈ HYP > PAA with enterococci. Similar bacterial reductions for the peracids were found at higher disinfectant doses used for the kinetic tests. PFA decayed more quickly than PAA. The first-order decay constants were 0.031 and 0.007 min−1, respectively, suggesting that disinfection residuals when PFA is used may be less of a concern than with PAA. This faster decomposition did not affect the PFA oxidation power on estrone, which was as weak as that of PAA.

Insights into the Photocatalytic Bacterial Inactivation by Flower-Like Bi2WO6 under Solar or Visible Light, Through in Situ Monitoring and Determination of Reactive Oxygen Species (ROS)

This study addresses the visible light-induced bacterial inactivation kinetics over a Bi2WO6 synthesized catalyst. The systematic investigation was undertaken with Bi2WO6 prepared by the complexation of Bi with acetic acid (carboxylate) leading to a flower-like morphology. The characterization of the as-prepared Bi2WO6 was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area (SSA), and photoluminescence (PL). Under low intensity solar light (&lt;48 mW/cm2), complete bacterial inactivation was achieved within two hours in the presence of the flower-like Bi2WO6, while under visible light, the synthesized catalyst performed better than commercial TiO2. The in situ interfacial charge transfer and local pH changes between Bi2WO6 and bacteria were monitored during the bacterial inactivation. Furthermore, the reactive oxygen species (ROS) were identified during Escherichia coli inactivation mediated by appropriate scavengers. The ROS tests alongside the morphological characteristics allowed the proposition of the mechanism for bacterial inactivation. Finally, recycling of the catalyst confirmed the stable nature of the catalyst presented in this study.

Elucidating sulfate radical-mediated disinfection profiles and mechanisms of Escherichia coli and Enterococcus faecalis in municipal wastewater

Practical applications of disinfection technologies for engineered waters require an in‒depth understanding of disinfection profiles and mechanisms of pathogenic bacteria in a complex matrix. This study investigated the inactivation of E. coli and E. faecalis by SO4•−, an emerging advanced disinfectant, in ultrapure water (UPW) and wastewater effluent (WE). Based on the bacterial inactivation kinetics in UPW in a zerovalent iron/peroxydisulfate system, the second order rate constants (k) for SO4•− reacting with E. coli and E. faecalis were measured to be (1.39 ± 0.1) × 109 M−1 s−1 and (6.71 ± 0.1) × 109 M−1 s−1, respectively. The morphological images of both bacteria by the scanning electron microscope indicated that SO4•− initiates oxidative reactions on the wall/membranes, causing their irreversible damage, ultimately affecting membrane permeability and physiological functions. To profile the inactivation kinetics of two strains of bacteria in WE matrix, a mechanistic process‒based model with the obtained k values was developed. Sensitivity and uncertainty analyses indicated that the key parameters for the model predictions were the concentrations of halide ions (i.e., Br− and Cl−) in WE and their k values reacting with SO4•− accounting for >80% of uncertainty or variance expected in predicted bacterial inactivation. This model allows precise estimation of required disinfectant dose even in complex water matrices, shedding lights on the extension of application of SO4•−‒based technology in wastewater treatments.

Ohmic heating of blended citrus juice: Numerical modeling of process and bacterial inactivation kinetics

Abstract A comprehensive 3D, transient-free convection, and multiphase model was developed to determine the performance of ohmic heating (150, 200 and 250 V; 120 s; 99.4 °C) and conventional heating (90 °C; 15 min) for the inactivation of Escherichia coli, Staphylococcus aureus, Salmonella enterica subsp. enterica serovar Paratyphi A, Salmonella Typhi, Shigella dysenteriae, and Shigella flexneri in blended citrus juice (sweet lemon and orange). Results indicated the computed temperatures were in good agreement with the experimentally measured data (below 5% deviation). The examination of velocity and temperature patterns throughout the computational domain explained the reasons for significant differences between the conventional and ohmic heating process. The homogeneously distributed vortices in ohmic heating lead to a more uniform and rapid temperature rise in temperature (from 26 to 99.4 °C) while compared with the conventional method with a stratified flow pattern. Based on the evaluation of temperature rise, increasing in the applied voltage from 150 to 250 V was deducted to reduce the inactivation time about 20–30% for the investigated pathogens. The inactivation rate of pathogens during ohmic heating process was maximum for S. aureus, followed by E. coli, S. enterica subsp. enterica serovar Paratyphi A, S. Typhi, S. dysenteriae and S. flexneri. In conclusion, the developed numerical modeling can be conveniently applied to simulate and predict the ohmic heating for the inactivation of pathogenic bacteria. Industrial relevance Several thermophysical phenomena affect the optimization and design of ohmic heating systems such as heat and mass transport as well as electrical field distribution. The implementation of the computational fluid dynamics (CFD) method is an efficient and economical technique that can provide valuable data for researchers. Moreover, the determination of off-design thermal spots, heat-loss magnitude and apparatus efficiency can be determined via numerical calculations.

Efficacy of photoactivated curcumin to decontaminate food surfaces under blue light emitting diode

AbstractThe efficacy of photoactivated curcumin in decontaminating food surfaces using a 465 nm light emitting diode (LED) light source was investigated. Under studied conditions, LED illumination alone had negligible antibacterial effects while photoactivated curcumin exhibited strong bactericidal activities against Escherichia coli. Minimum inhibitory concentration of photosensitized curcumin against E. coli on nutrient agar surface at a concentration of 1.5 × 105 cfu/cm2 was estimated to be 1.60 × 10−3 M, combined with irradiation of 27.2 J/cm2 at 465 nm. Bacterial inactivation kinetics could be described by a Weibull model (R2 = 0.979–0.999, RMSE = 0.019–0.229). When the treatment was applied on grape surface, the efficiency was lower as compared to that on the agar surface. Photoactivation enhanced quality retention of the samples during storage with significant preservation of vitamin C, color, texture, and reduction of weight losses.Practical applicationsThe study provides an alternative method for food surface decontamination. Inactivation of pathogens and spoilage microorganism by combined visible LED light source and natural photosensitizers minimizes the adverse processing effects on organoleptic and physicochemical quality of the treated foods. The approach could be further optimized, scaled up, and applied in food industries.

Mechanisms of the Antibacterial Effects of TiO2–FeOx under Solar or Visible Light: Schottky Barriers versus Surface Plasmon Resonance

This study reports the significant mechanistic difference between binary-oxide antibacterial films with the same composition but different microstructures. Binary TiO2-FeOx films were found to present a faster bacterial inactivation kinetics under visible light irradiation than each single oxide acting independently. The interaction between the film active surface species and the bacteria within the disinfection period was followed by X-ray photoelectron spectroscopy (XPS) and provided the evidence for a redox catalysis taking place during the bacterial inactivation time. The optical and surface properties of the films were evaluated by appropriate surface analytical methods. A differential mechanism is suggested for each specific microstructure inducing bacterial inactivation. The surface FeOx plasmon resonance transferred electrons into the conduction band of TiO2 because of the Schottky barrier after Fermi level equilibration of the two components. An electric field at the interface between TiO2 and FeOx, favors the separation of the photo-generated charges leading to a faster bacterial inactivation by TiO2–FeOx compared to the bacterial inactivation kinetics by each of the single oxides.

Monitoring the energy of the metal ion-content plasma-assisted deposition and its implication for bacterial inactivation

Cu-polyester (Cu-PES) was sputtered by high power impulse magnetron sputtering (HIPIMS) and by low energy direct current magnetron sputtering (DCMS). The total amount and distribution of the Ar+, Cu+ and Cu2+ ions were determined as well as the bacterial inactivation kinetics mediated by DCMS and HIPIMS samples. The separation of extracellular and intracellular processes leading to bacterial inactivation was assessed on normal and genetically modified E. coli.

Effect of suspended solids on peracetic acid decay and bacterial inactivation kinetics: Experimental assessment and definition of predictive models

The work addresses the effect of total suspended solids (TSS) on disinfection by peracetic acid (PAA) concerning both PAA decay and bacterial inactivation kinetics. The effect of TSS on PAA decay was evaluated at five TSS concentrations (5, 40, 80, 120 and 160 mg/L), obtained from stock TSS solutions prepared from activated sludge samples. The influence of the soluble matter associated to the suspended solids on PAA decay was evaluated separately, using the same stock TSS solution after the removal of solids by filtration. The contributions of suspended and soluble fractions were found to be independent, and a predictive model formed by two additive sub-models was proposed to describe the overall PAA decay kinetics. Moreover, an uncertainty analysis was performed by a series of Monte Carlo simulations to propagate the uncertainties associated to the coefficients of the model. Then, the disinfectant dose (mg/L min) was highlighted as the main parameter determining disinfection efficiency on a pure culture of E. coli and an inactivation kinetic model was developed based on the response of E. coli to various PAA doses. Finally, the effect of TSS (40 and 160 mg/L) on the inactivation of free-swimming E. coli was investigated at two PAA doses (5 and 20 mg/L min). TSS reduced inactivation extent an average of 0.4 logs at 5 mg/L min and 1.5 logs at 20 mg/L min. It was hypothesized that this might be due to the formation of bacteria aggregates as defense mechanism against disinfection, enhanced by the presence of solids.

Recent advances on sputtered films with Cu in ppm concentrations leading to an acceleration of the bacterial inactivation

Abstract This review focuses on the acceleration of the bactericidal and fungicidal effects by uniform, adhesive Cu-based nanocomposites on textile and thin polymer surfaces. The acceleration of the bacterial inactivation kinetics mediated by Cu, TiO2/Cu and ZrO2-TiO2-Cu films in aerobic and anaerobic media is discussed for Gram negative, Gram positive bacteria and fungi. The Cu induced bacterial inactivation kinetics in the dark was observed to occur within the minute range for diverse bacteria. The characterization of the innovative Cu-films microstructure by several surface science techniques is described. This allows the correlation of the surface-reactivity features of the Cu-composite films mediating bacterial inactivation. The redox reactions on the Cu-films during the bacterial inactivation are documented by X-ray-photoelectron spectroscopy (XPS). Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy was used to monitor the changes in the functional groups leading to bacterial inactivation as a function of the bacterial inactivation time. The dependence of the inactivation kinetics on the Cu-loaded surface roughness is accounted for in qualitative way by atomic force microscopy (AFM). A mechanism for the bacterial inactivation induced by the Cu-nanoparticles by way of reactive oxygen species (ROS) in aerobic and anaerobic processes is discussed. The interfacial charge transfer (IFCT) mechanism under light irradiation between Cu and TiO2 or for the Cu with the binary oxide ZrO2-TiO2 is suggested. The relative potential band-position in the Cu-sputtered semiconductors responsible for the charge transfer is discussed. Evidence was found for the presence in anaerobic media of highly oxidative valence band holes (h+)vb at −0.4 eV generated by Cu2O. The variation in the interface surface potential (Eigenvalues) of the Cu-films during the bacterial inactivation was monitored and allowed to suggest the bacterial mineralization mechanism. Details for the reactions of the Cu-surfaces with Escherichia coli (E. coli) and Methicillin Resistant Staphylococcus Aureus (MRSA) inactivation are described. Evidence for the synergism between Cu and the TiO2 accelerating the bacterial inactivation kinetics is presented in this review.

Bacterial adhesion and inactivation on Ag decorated TiO2-nanotubes under visible light: Effect of the nanotubes geometry on the photocatalytic activity.

This study investigates the effect of the diameter of TiO2 nanotubes and silver decorated nanotubes on optical properties and photocatalytic inactivation of Escherichia coli under visible light. The TiO2 nanotubes (TiO2-NTs) were prepared using the electrochemical method varying the anodization potential starting from 20 V until 70 V. The Ag nanoparticles were carried out using the photoreduction process under the same experimental conditions. The diameter size was determined using the scanning electronic microscopy (SEM). TiO2-NTs diameter reached ∼100 nm at 70 V. Transmission electronic microscopy (TEM) imaging confirmed the TiO2-NTs surface decoration by silver nanoparticles. The Ag-NPs average size was found to be equal to 8 nm. The X-Ray diffraction (XRD) analysis confirm that all TiO2-NTs crystallize in the anatase phases regardless the used anodization potential. The decrease of the photoluminescence (PL) intensity of Ag NPs decorated TiO2-NTs indicates the decrease of the specific area when the nanotubes diameter increases. The UV-vis absorbance show that the absorption edges was bleu shifted with the increasing of nanotubes diameter, which can be explained by the increase of the crystallites average size. The bacterial adhesion and inactivation tests were carried in the dark and under light. Bacteria were seen to adhere on TiO2-NTs in the dark; however, under light the bacteria were killed before they establish a strong contact with the TiO2-NTs and Ag/TiO2-NTs surfaces. Bacterial inactivation kinetics were faster when the anodizing potential of the NTs-preparation increases. A total bacterial inactivation was obtained on ∼100 nm nanotubes diameter within 90 min. This result was attributed to the enhancement of the TNTs crystallinity leading to reduced surface defects. Redox catalysis was seen to occur under light on the TiO2-NTs and Ag/TiO2-NTs. the photo-induced antibacterial activity on the AgO/Ag2O decorated TiO2-NTs was attributed to the interfacial charge transfer mechanism (IFCT).

Modeling of the bacterial inactivation kinetics of dialdehyde cellulose in aqueous suspension

The purpose of this study was to estimate the antibacterial properties of aqueous suspensions of dialdehyde microcrystalline cellulose (DAMC), and a model of the observed antibacterial kinetics was proposed and validated. The DAMC was prepared from microcrystalline cellulose by periodate oxidation. The bacterial inactivation kinetics of aqueous suspensions of DAMC was investigated by measuring the bactericidal effect after different contact times. The results indicated that with a DAMC aldehyde content of 6.34 mmol/g, the MICs for S. aureus, E. coli, B. subtilis and S. typhimurium were 15, 15, 15 and 30 mg/mL, respectively. This research thus establishes an antibacterial kinetics model of DAMC with 6.34 mmol/g of aldehyde content. At 37 °C and atmospheric pressure, the bacterial inactivation kinetic conformed to the equation: Log reduction of bacteria = − k [DAMC] t.

Innovative Ti1- xNb xN-Ag Films Inducing Bacterial Disinfection by Visible Light/Thermal Treatment.

This study presents innovative Ti1- xNb xN-Ag films obtained by a suitable combination of low-energy and high-energy sputtering leading to bacterial inactivation. The bacterial inactivation kinetics by the TiNbN layers was drastically enhanced by the addition of 6-7% Ag and proceeded to completion within 3 h after the film autoclaving. By X-ray photoelectron spectroscopy (XPS), the samples after autoclaving presented in their upper layers TiO2, Nb2O5 and Ag2O with a surface composition of Ti0.81Nb0.19N0.99Ag0.068. Surface potential/pH changes in the Ti1- xNb xN-Ag films were monitored during bacterial inactivation. Surface redox processes during the bacterial inactivation were detected by XPS. The diffusion of Ag in the Ti1- xNb xN-Ag films was followed at 50 and 70 °C pointing. The beneficial thermal treatment points out to the bifunctional bacterial inactivation properties of these films and their potential application in healthcare facilities. Interfacial charge transfer (IFCT) under light irradiation between Ag2O, Nb2O5 and TiO2 is suggested consistent with the data found during the course of this study. The TiO2/Nb2O5 lattice mechanism is discussed in the framework of the Verwey's controlled valence model. The surface properties of the Ti1- xNb xN-Ag films were investigated by X-ray diffraction, atomic force microscopy, and scanning electron microscopy.

Inactivation of Planktonic Escherichia coli by Focused 2-MHz Ultrasound

This study was motivated by the desire to develop a non-invasive means to treat abscesses, and represents the first steps toward that goal. Non-thermal, high-intensity focused ultrasound (HIFU) was used to inactivate Escherichia coli (∼1 × 109 cells/mL) in suspension. Cells were treated in 96-well culture plate wells using 1.95-MHz ultrasound and incident focal acoustic pressures as high as 16 MPa peak positive and 9.9 MPa peak negative (free field measurements). The surviving fraction was assessed by coliform culture and the alamarBlue assay. No biologically significant heating was associated with ultrasound exposure. Bacterial inactivation kinetics were well described by a half-life model, with a half-time of 1.2 min. At the highest exposure levels, a 2log inactivation was typically achieved within 10 min. The free field-equivalent peak negative acoustic pressure threshold for inactivation was ∼7 MPa. At the highest acoustic pressures used, inactivation efficacy was insensitive to reciprocal changes in pulse length and pulse repetition frequency at constant duty factor. Although treated volumes were very small, proof of principle was provided by these experiments.