Increase In Rate Of Inactivation Research Articles

Experimental study on enhancing single-pass air disinfection efficacy for portable disinfection systems with different Far-UVC sources

Two single-pass air disinfection systems utilizing different form factors of Far-UVC sources were designed to achieve indoor air disinfection. The first system, namely the external-module-equipped (EME) system, featured a rectangular UV source module attached to the envelope of the disinfection box chamber. The second system, known as the internal-tube-equipped (ITE) system, incorporated a centrally positioned UV tube within the chamber. To assess their air disinfection efficacy, two bacteria, Salmonella enterica and Staphylococcus epidermidis, and one bacteriophage, MS2 were selected as challenges for the systems operating at a flow rate over 100 m3/h. The baseline EME system inactivated the microbes with the efficacies of 81.4 %, 16.9 %, and 25.1 % for S. enterica, S. epidermidis, and MS2, respectively. In comparison, the baseline ITE system demonstrated higher inactivation efficacies due to a wider irradiated area, with respective efficacies of 94.4 %, 25.8 %, and 37.8 % for the tested microorganisms. Two enhancement measures were implemented by redirecting airflow to the areas with high UV irradiance and enhancing UV reflectance, increasing the inactivation efficacy of the systems by up to 207.0 %. When tested against Staphylococcus epidermidis, compared with an upper-room Far-UVC, the modified EME and ITE systems presented an increase in inactivation rate by 23.0 % and 29.2 % respectively. These results demonstrated the potential of the systems to efficiently and sustainably inactivate a broad spectrum of microbes in future practical applications.

Removal of virus aerosols by the combination of filtration and UV-C irradiation.

The COVID-19 pandemic remains ever prevalent and afflicting—partially because one of its transmission pathways is aerosol. With the widely used central air conditioning systems worldwide, indoor virus aerosols can rapidly migrate, thus resulting in rapid infection transmission. It is therefore important to install microbial aerosol treatment units in the air conditioning systems, and we herein investigated the possibility of combining such filtration with UV irradiation to address virus aerosols. Results showed that the removal efficiency of filtration towards f2 and MS2 phages depended on the type of commercial filter material and the filtration speed, with an optimal velocity of 5 cm/s for virus removal. Additionally, it was found that UV irradiation had a significant effect on inactivating viruses enriched on the surfaces of filter materials; MS2 phages had greater resistance to UV-C irradiation than f2 phages. The optimal inactivation time for UV-C irradiation was 30 min, with higher irradiation times presenting no substantial increase in inactivation rate. Moreover, excessive virus enrichment on the filters decreased the inactivation effect. Timely inactivation is therefore recommended. In general, the combined system involving filtration with UV-C irradiation demonstrated a significant removal effect on virus aerosols. Moreover, the system is simple and economical, making it convenient for widespread implementation in air-conditioning systems.

Proteomics-based mechanistic study of sub-lethally injured Saccharomyces cerevisiae by pulsed electric fields

The pulsed electric fields (PEF) technology has been widely applied to inactivate spoilage and pathogenic microorganisms in food products because of its conspicuous advantages. However, the inevitable production of sub-lethally injured microorganisms limited its further application and development. In the present study, we investigated the mechanisms underlying the PEF-induced inactivation and sublethal damage of microorganisms to enhance the bactericidal effect of PEF treatments. In our work, Saccharomyces cerevisiae was used as a model organism, and the lethal and sublethal injury of microorganisms induced by PEF was estimated using non-selective and selective media. We found that PEF treatment with 20 kV/cm intensity for 200 or 400 μs, or with 15 kV/cm intensity for 400 μs, caused more sub-lethally injured cells. The PEF with 55 °C treatment produced the highest inactivation rate and the lowest sublethal injury rate. Then two-dimensional electrophoresis with mass spectrometry analysis was conducted to analyze the protein differences of S. cerevisiae under different PEF treatments. Compared with the PEF treatment (20 kV/cm, 200 μs) alone, many proteins changed significantly after PEF combined with 55 °C mild heat treatment, including several heat shock proteins. Finally, the heat shock protein 104 (Hsp104) of S. cerevisiae was knocked out, which led to a decrease in sub-lethally injured cells and an increase in inactivation rate after PEF treatment. Our findings provide critical information for developing more effective PEF-based microbial inactivation approaches in food processing.

Inactivation of simulated aquaculture stream bacteria at low temperature using advanced UVA- and solar-based oxidation methods

In this work the effect of water temperature (6 ± 1 °C and 22 ± 1 °C) on inactivation of bacteria (104 –106 CFU mL−1; Pseudomonas spp., Aeromonas spp. and Enterobacter spp.) in simulated aquaculture streams (SAS) using UVA based advanced oxidation processes (AOP) (H2O2-assisted UVA; photocatalysis; H2O2-assisted photocatalysis) and solar driven AOPs (H2O2-assisted solar disinfection, SODIS) was studied. Efficiency at 22 °C in terms of inactivation rate was higher using H2O2-assisted photocatalysis (H2O2/UVA-TiO2/polysiloxane) > H2O2-assisted UVA disinfection (UVA/H2O2 – 10 mg L-1) > photocatalysis (UVA-TiO2/polysiloxane) > UVA disinfection. At low temperature (6 °C) the inactivation rate increased with SODIS/H2O2 > SODIS > H2O2-assisted UVA disinfection (UVA/H2O2 – 10 mg L-1) > H2O2-assisted photocatalysis (H2O2/UVA-TiO2/polysiloxane) > photocatalysis (UVA-TiO2/polysiloxane). The main results indicate that the inactivation rates increased when hydrogen peroxide (10 mg L-1) was used during H2O2-assisted UVA disinfection and photocatalysis. In addition, exposure of SAS to hydrogen peroxide for 24 h (in absence of light) at room temperature decreased the subsequent exposure UVA irradiation dose by almost four times.Drastic increase of inactivation rate was observed at low water temperature (6 ± 1 °C) when UVA- and solar-based AOPs were employed compared to 22 ± 1 °C. The treatment with SODIS proved to be more effective in Finland than in Spain. The effect of the low temperature (6 ± 1 °C) was proposed as a critical factor during UVA disinfection (UVA/H2O2 and photocatalysis) that can increase the disinfection rate constant (kmax) by 1.3–5.2 times, leading to a reduction of the treatment costs (€ m−3) by 1.3–3.3 times. The mechanism of observed enhanced disinfection at low water temperature (6 ± 1 °C) when natural solar light and UVA are employed as irradiation sources for UVA/H2O2 and photocatalytic bacteria inactivation was proposed. No regrowth was observed in case of H2O2-assisted AOPs.

Chlorine disinfection of drinking water assessed by flow cytometry: New insights

Abstract The efficacy of chlorine disinfection was assessed for the first time over a range of disinfection conditions using flow cytometry (FCM) to provide new insights into disinfection processes. Inactivation was assessed for pure culture bacteria (Escherichia coli) and micro-organisms in real treated water from operational water treatment works (WTWs). A dose dependent increase in inactivation rate (k) was observed for both test matrices, with values of 0.03 to 0.26 and 0.32 to 3.14 L/mg min for the WTW bacteria and E. coli, respectively. After 2 min, E. coli was reduced by 2 log for all chlorine doses (0.12 to 1.00 mg/L). In the case of the WTW filtrate bacteria, after 2 min log reductions were between 0.54 and 1.14 with increasing chlorine concentration, reaching between 1.32 and 2.33 after 30 min. A decrease in disinfection efficacy was observed as temperature decreased from 19 to 5 °C for both microbial populations. With respect to chlorination at different pH (pH 6, 7, 8), membrane damage was more pronounced at higher pH. This was not consistent with the higher disinfection efficacy seen at lower pH. when culture based methods are used to assess bacterial reductions. This provides evidence that more understanding into the fundamental mechanisms of chlorine disinfection are required and that methodological alterations may be required (e.g. pH standardisation) to fully utilise FCM over the entire range of chlorination conditions observed in operational environments.

Effect of pulsed electric field treatment on enzyme kinetics and thermostability of endogenous ascorbic acid oxidase in carrots (Daucus carota cv. Nantes)

The objective of this research was to study the enzyme kinetics and thermostability of endogenous ascorbic acid oxidase (AAO) in carrot purée (Daucus carota cv. Nantes) after being treated with pulsed electric field (PEF) processing. Various PEF treatments using electric field strength between 0.2 and 1.2kV/cm and pulsed electrical energy between 1 and 520kJ/kg were conducted. The enzyme kinetics and the kinetics of AAO thermal inactivation (55–70°C) were described using Michaelis–Menten model and first order reaction model, respectively. Overall, the estimated Vmax and KM values were situated in the same order of magnitude as the untreated carrot purée after being exposed to pulsed electrical energy between 1 and 400kJ/kg, but slightly changed at pulsed electrical energy above 500kJ/kg. However, AAO presented different thermostability depending on the electric field strength applied. After PEF treatment at the electric field strength between 0.2 and 0.5kV/cm, AAO became thermolabile (i.e. increase in inactivation rate (k value) at reference temperature) but the temperature dependence of k value (Ea value) for AAO inactivation in carrot purée decreased, indicating that the changes in k values were less temperature dependent. It is obvious that PEF treatment affects the temperature stability of endogenous AAO. The changes in enzyme kinetics and thermostability of AAO in carrot purée could be related to the resulting carrot purée composition, alteration in intracellular environment and the effective concentration of AAO released after being subjected to PEF treatment.

Short-Term Inactivation Rates of Selected Gram-Positive and Gram-Negative Bacteria Attached to Metal Oxide Mineral Surfaces: Role of Solution and Surface Chemistry

Metal oxides such as ferric or aluminum oxides can play an important role in the retention of bacteria in granular aquatic environments; however, their role in bacterial inactivation is not well understood. Herein, we examined the role of water chemistry and surface chemistry on the short-term inactivation rates of three bacteria when adhered to surfaces. To evaluate the role of water chemistry on the inactivation of attached bacteria, the loss in membrane integrity of bacteria attached to an iron oxide (Fe2O3) surface was measured over a range of water ionic strengths of either monovalent or divalent salts in the absence of a growth substrate. The influence of surface chemistry on the inactivation of attached bacteria was examined by measuring the loss in membrane integrity of cells attached to three surfaces (SiO2, Fe2O3, and Al2O3) at a specific water chemistry (10 mM KCl). Bacteria were allowed to attach onto the SiO2 or metal oxide coated slides mounted in a parallel-plate flow cell, and their inactivation rate (loss in membrane integrity) was measured directly without removing the cells from the surface and without disturbing the system. X-ray photoelectron spectroscopy analysis revealed a high correlation between the amounts of C-metal or O-metal bonds and the corresponding bacterial inactivation rates for each surface. Finally, for all three surfaces, a consistent increase in inactivation rate was observed with the type of bacterium in the order: Enterococcus faecalis, Escherichia coli O157:H7, and Escherichia coli D21f2.

Protein kinase C-independent inhibition of arterial smooth muscle K+channels by a diacylglycerol analogue

Analogues of the endogenous diacylglycerols have been used extensively as pharmacological activators of protein kinase C (PKC). Several reports show that some of these compounds have additional effects that are independent of PKC activation, including direct block of K(+) and Ca(2+) channels. We investigated whether dioctanoyl-sn-glycerol (DiC8), a commonly used diacylglycerol analogue, blocks K(+) currents of rat mesenteric arterial smooth muscle in a PKC-independent manner. Conventional whole-cell and inside-out patch clamp was used to measure the inhibition of K(+) currents of rat isolated mesenteric smooth muscle cells by DiC8 in the absence and presence of PKC inhibitor peptide. Mesenteric artery smooth muscle K(v) currents inactivated very slowly with a time constant of about 2 s following pulses from -65 to +40 mV. Application of 1 µM DiC8 produced an approximate 40-fold increase in the apparent rate of inactivation. Pretreatment of the cells with PKC inhibitor peptide had a minimal effect on the action of DiC8, and substantial inactivation still occurred, indicating that this effect was mainly independent of PKC. We also found that DiC8 blocked BK and K(ATP) currents, and again a significant proportion of these blocks occurred independently of PKC activation. These results show that DiC8 has a direct effect on arterial smooth muscle K(+) channels, and this precludes its use as a PKC activator when investigating PKC-mediated effects on vascular K(+) channels.

Lysozyme as a barrier to growth of Bacillus anthracis strain Sterne in liquid egg white, milk and beef

In this study, we investigated the role of lysozyme on the viability of Bacillus cereus, Bacillus subtilis, Bacillus pumilus and Bacillus anthracis (Sterne) in egg white (EW), ground beef and milk. At 35 °C in EW, growth rates (GR) for B. cereus, B. subtilis, B. pumilus and B. anthracis were 0.005, −0.018, −0.028 and −0.029 OD600/h, respectively. Heat-treating EW at 55 and 60 °C reduced the inactivating effect of EW by 3.1 and 10.5-fold, respectively. Addition of lysozyme (2 mg/ml) to 60 °C-treated EW increased the inactivation rate 5.76-fold, indicating involvement of lysozyme in B. anthracis inactivation. B. anthracis inactivation was influenced by pH, as shown by a progressive increase in inactivation rate from 0.25 to −4.42 logs CFU/h over a pH range of 6.0–8.5. Adding 2 mg/ml lysozyme to milk and ground beef also suppressed the growth of B. anthracis 3.3 and 6.5-fold, respectively. These data indicate that lysozyme, as a natural component of EW or potential additive in other foods, could reduce biothreat risks presented by bioterror agents.

Impact of Environmental Factors on Efficacy of Upper-Room Air Ultraviolet Germicidal Irradiation for Inactivating Airborne Mycobacteria

This study evaluated the efficacy of an upper-room air ultraviolet germicidal irradiation (UVGI) system for inactivating airborne bacteria, which irradiates the upper part of a room while minimizing radiation exposure to persons in the lower part of the room. A full-scale test room (87 m3), fitted with a UVGI system consisting of 9 louvered wall and ceiling fixtures (504 W all lamps operating) was operated at 24 and 34 degrees C, between 25 and 90% relative humidity, and at three ventilation rates. Mycobacterium parafortuitum cells were aerosolized into the room such that their numbers and physiologic state were comparable both with and without the UVGI system operating. Airborne bacteria were collected in duplicate using liquid impingers and quantified with direct epifluorescent microscopy and standard culturing assay. Performance of the UVGI system degraded significantly when the relative humidity was increased from 50% to 75-90% RH, the horizontal UV fluence rate distribution was skewed to one side compared to being evenly dispersed, and the room air temperature was stratified from hot at the ceiling to cold at the floor. The inactivation rate increased linearly with effective UV fluence rate up to 5 microW cm(-2); an increase in the fluence rate above this level did not yield a proportional increase in inactivation rate.

The interaction between biologically inactive tRNA conformers and leucyl-tRNA synthetase from rabbit liver.

The interaction between tRNA conformers inactive in aminoacylation and leucyl-tRNA synthetase has been investigated. Heat inactivation of the enzyme in the presence of inactive tRNA conformers is shown to lead to a marked increase of inactivation rate while active tRNA conformers, on the other hand, reveal a protecting effect. To study the properties of the enzyme complexed with different tRNA conformers limited proteolysis has been used. Active tRNA conformers are found to protect leucyl-tRNA synthetase against hydrolysis while inactive ones tend to intensify it. Inactive tRNA conformers are also shown to inhibit the aminoacylation of native tRNA in vitro. On the basis of these data biologically inactive conformers of animal tRNA are assumed to form an unproductive complex with leucyl-tRNA synthetase and the structure of the enzyme involved in such interaction is supposed to be more labile and 'extended' than that in complex with active tRNA conformers.

Determinants of the Formation and Activity of Factor V-phospholipid Complexes II. Molecular Properties of the Complexes

The stability, buoyancy, and intrinsic activity for factor V-phospholipid complexes were investigated. The decay of factor V activity in the absence of phospholipid followed first order kinetics; however, in the presence of several phospholipids a biphasic decay curve was observed. The addition of phosphatidylethanolamine to factor V produced only a small loss of activity in the first 2 minutes but decreased the subsequent rate of inactivation fourfold. A PE-factor V complex with a low bouyant density was separated from uncomplexed factor V by sucrose density ultracentrifugation. The association constant for this complex was 5 X 10(6) M-1 with approximately 2 moles of factor V bound per mole of lipid micelle. The isolated complex was capable of increasing prothrombin conversion 10-fold without additional phospholipid. A still lighter complex increased the rate of prothrombin conversion 18-fold. Phosphatidyl serine produced a concentration-dependent loss of up to 95% of the factor V activity in the first 2 minutes. After ultracentrifugation on a sucrose density gradient, a PS-factor V complex of increased density was detected. This complex failed to accelerate prothrombin conversion in the intrinsic two-stage assay. Except at very high concentrations, phosphatidylcholine did not alter the kinetics of inactivation of factor V. A factor V-phosphatidylcholine complex could not be detected after ultracentrifugation. When added to factor V, cardiolipin (200 mug/ml), produced a rapid 50% decline in activity with a subsequent three-fold increase in the rate of inactivation. No activity was recovered after ultracentrifugation of factor V in the presence of cardiolipin. Saturated phosphatidylethanolamine produced a concentration dependent initial loss of activity, but only a minimal increase in the subsequent rate of inactivation. At 200 mug/ml almost no light complex was detected after ultracentrifugation, but at 800 mug/ml a light complex was observed. This behavior corresponds to the ability of saturated phosphatidylethanolamine to accelerate prothrombin conversion only at very high concentrations. Thus, phospholipids combine with factor V to form complexes which differ in their ability to accelerate prothrombin conversion. The most active species are stable lipoprotein complexes of lower buoyant density than factor V.

Effect of pH on Heat Inactivation of Bacteriophage.

It has been shown by Krueger1 and confirmed by Dreyer and Campbell-Renton2 that the heat inactivation of bacteriophage follows the course of a monomolecular reaction. In Krueger's data the increase in rate of inactivation with rise in temperature was very rapid (μ in the van't Hoff-Arrhenius equation = 101,000). Critical thermal increments of this order of magnitude are uniquely characteristic of protein denaturation and the experimental results with phage were consequently interpreted as indicating that inactivation involved denaturation as a significant factor. The present paper deals with the effect of pH on the heat inactivation of the same anti-Staphylococcus phage used in previous work.2.5 ml. of standard anti-Staphylococcus phage containing 1 × 1010 activity units per ml.3 was added to 2.5 ml. of beef infusion broth containing sufficient normal HCl to bring the final pH to the desired point. The samples were placed in a water bath adjusted to 57°C. for one-half hour and the residual (Phage) determi...