Germicidal Efficiency Research Articles

Mesoporous polydopamine/copper sulfide hybrid nanocomposite for highly efficient NIR-triggered bacterial inactivation

Polydopamine has gained considerable attention in the biomaterial domain owing to its excellent biocompatibility, antioxidant activity, photothermal effect and adhesion property. Herein, copper sulfide (Cu2-xS) wrapped in mesoporous polydopamine (MPDA) was synthesized through in-situ polymerization, followed by the surface modification with cationic polyethyleneimine (PEI). The mussel-inspired MPDA matrix successfully prevented the oxidation and agglomeration of Cu2-xS nanoparticles, and regulated the release of copper ions and reactive oxygen species (ROS) levels. Surface-modified PEI endow MPDA@Cu2-xS with positive charges, facilitating their rapid contact with negatively charged bacteria through electrostatic interactions. The pH-dependent Cu+/Cu2+ release and NIR-responsive ROS generation were confirmed using molecular probes and electron spin resonance (ESR). The MPDA@Cu2-xS/PEI showed significantly enhanced antibacterial activity and reduced cytotoxicity for NIH3T3 cells. Under NIR irradiation (1.0 W/cm2, 10 min), germicidal efficiency against Escherichia coli (E. coli) and Staphyloccocus aureus (S. aureus) could reach 100 % and 99.94 %, respectively. The exceptional antibacterial activities of MPDA@Cu2-xS/PEI was mainly attributed to the synergistic photothermal effect, controlled release of copper ions and ROS generation, as well as electrostatic interaction. More importantly, the MPDA@Cu2-xS/PEI composite exhibited excellent biocompatibility and biosafety. Overall, this organic/inorganic hybrid holds great potential as a promising candidate for wound treatment.

Enhanced antimicrobial efficacy and energy efficiency of low irradiance 405-nm light for bacterial decontamination

Due to its increased safety over ultraviolet light, there is interest in the development of antimicrobial violet-blue light technologies for infection control applications. To ensure compatibility with exposed materials and tissue, the light irradiances and dose regimes used must be suitable for the target application. This study investigates the antimicrobial dose responses and germicidal efficiency of 405 nm violet-blue light when applied at a range of irradiance levels, for inactivation of surface-seeded and suspended bacteria. Bacteria were seeded onto agar surfaces (101–108 CFUplate−1) or suspended in PBS (103–109 CFUmL−1) and exposed to increasing doses of 405-nm light (≤ 288 Jcm−2) using various irradiances (0.5–150 mWcm−2), with susceptibility at equivalent light doses compared. Bacterial reductions ≥ 96% were demonstrated in all cases for lower irradiance (≤ 5 mWcm−2) exposures. Comparisons indicated, on a per unit dose basis, that significantly lower doses were required for significant reductions of all species when exposed at lower irradiances: 3–30 Jcm−2/0.5 mWcm−2 compared to 9–75 Jcm−2/50 mWcm−2 for low cell density (102 CFUplate−1) surface exposures and 22.5 Jcm−2/5 mWcm−2 compared to 67.5 Jcm−2/150 mWcm−2 for low density (103 CFUmL−1) liquid exposures (P ≤ 0.05). Similar patterns were observed at higher densities, excluding S. aureus exposed at 109 CFUmL−1, suggesting bacterial density at predictable levels has minimal influence on decontamination efficacy. This study provides fundamental evidence of the greater energy efficacy of 405-nm light for inactivation of clinically-significant pathogens when lower irradiances are employed, further supporting its relevance for practical decontamination applications.

Effects of environmental factors, measurement and modeling for germicidal efficiency of in-duct ultraviolet germicidal irradiation system

In-duct ultraviolet germicidal irradiation (UVGI) systems effectively decontaminate airborne microorganisms that are present in duct air. In this study, the main objectives were to determine the effects of temperature, relative humidity (RH), air velocity, and measurement on the germicidal efficiency of in-duct UVGI and to analyze three germicidal kinetic models. Staphylococcus albus and Escherichia coli were selected as the test bacteria. The maximum UV disinfection efficacy was observed in the temperature range of 26–28 °C and RH range of 30–40 %. The germicidal efficiency of the in-duct UVGI was negatively corelated with air velocity. When the UV lamps were arranged either parallel or vertical to the airflow, there were no obvious differences in-duct UVGI germicidal efficiency. In addition, three mathematical prediction models (C-W model, C-S model, Hom model) were chosen to predict the efficacy of in-duct UVGI in specific applications. The C-S model was fitted to predict the efficacy of E. coli, and the Hom model was fitted to predict that of Staphylococcus albus.

Germicidal Efficiency of 272 nm LED in Relation to the Hospital Strain of Klebsiella Pneumoniae

Relevance. Currently, the use of ultraviolet (UV) radiation for the disinfection of objects and the treatment for infectious diseases is considered as a promising alternative to chemical biocides and antibiotics. Shortwave — UV-C and UV-B -light emitting diodes (LED) are a relatively new type of UV radiation sources and potentially able to meet the requirements of current medical technologies. However, their possibilities for the treatment of wounds and infectious diseases have not been practically researched to date, which determines the relevance of experiments aimed at studying the biocidal and therapeutic properties of shortwavelength UV LEDs.Purpose. OF STUDY To evaluate the bactericidal efficacy of 272 nm LED radiation against hospital strains of Klebsiella pneumoniae bacteria characterized by multidrug resistance.Materials and Methods. The studies were carried out with an experimental sample of the LED apparatus for UV irradiation. In the irradiator of the device, 5 LEDs are installed with a maximum radiation at a wavelength of 272 nm and a total electrical power of 10 watts. The UV radiation dose achieved in one irradiation session (12 seconds) at a distance of 10 cm from the irradiator was 8 mJ/cm2 . In the experiments, a hospital strain of the bacterium Klebsiella pneumoniae, isolated from the patient’s blood, was used. The strain was characterized by multidrug resistance. A daily culture suspension of K. pneumoniae with a concentration of 108 CFU/ml in a volume of 100 µl was transferred into a Petri dish with a diameter of 9 cm with meat-peptone agar and evenly distributed over a surface with a diameter of 8 cm. Petri dishes were irradiated from a distance of 10 cm from the irradiator. The change in the dose of UV irradiation from 4 to 80 mJ/cm2 was carried out by varying the exposure time. Studies were carried out in 4 repetitions at each dose. After irradiation, the experimental and control (without irradiation) Petri dishes were placed in a thermostat at 37ºC for 24 hours, then the grown colonies were counted. A total of 60 experiments were carried out.Results. As a result of the research, it was shown that the LED device based on five 272 nm diodes provides deep and prompt disinfection of the surface from hospital strains of K. pneumoniae bacteria characterized by multidrug resistance. A dose of UV radiation of 8 mJ/cm2 reduces surface contamination with K. pneumoniae bacteria by more than a million times (decontamination efficiency over 99.9999%). At doses less than 10 mJ/cm2 , the efficiency of the 272 nm LED device in terms of inactivation of K. pneumoniae bacteria is 3–4 times higher than the bactericidal efficiency of mercury lamps.Conclusion.The prospects of using UV devices based on LEDs with a maximum radiation at a wavelength of 272 nm in systems for the operational disinfection of massively contaminated surfaces, potentially including wound surfaces, have been shown.

Formation of halonitromethanes from glycine during LED-UV265/chlorine disinfection

LED-UV265/chlorine is a promising alternative disinfection technology that emits mono-wavelength light for high germicidal efficiency. Halonitromethanes (HNMs) are highly cytotoxic and genotoxic disinfection byproducts that can be formed during LED-UV265/chlorine disinfection. Thus, this work aimed to investigate the HNMs formation from glycine (Gly) during LED-UV265/chlorine disinfection. The results indicated that the concentrations of chlorinated-HNMs (Cl-HNMs) increased first and then decreased as the reaction proceeded. Besides, the effects of operating parameters (UV intensity, free chlorine dosage, and pH) and coexisting ions (Cu2+ and Br−) on HNMs formation were investigated. It was found that the formation concentrations of Cl-HNMs increased with the increase of LED-UV265 intensity and free chlorine dosage but decreased with increased pH. The presence of Cu2+ promoted the formation of Cl-HNMs. The total concentration of HNMs (at 3 min) with adding 1.5 mg/L Cu2+ was 30.90% higher than that without Cu2+. Notably, nine species of HNMs were detected after adding Br−, and the total concentrations of HNMs were enhanced. Moreover, Cl-HNMs were gradually transformed into brominated (chlorinated)-HNMs and brominated-HNMs as Br− concentration increased. According to the findings, the possible formation mechanism of HNMs from Gly during LED-UV265/chlorine disinfection was deduced. Finally, it was demonstrated that the formation laws of HNMs from Gly in real water samples were basically consistent with those in simulated water. Insights obtained in this study help to comprehend the HNMs formation from Gly and provide strategies for controlling the production of HNMs during LED-UV265/chlorine disinfection.

Antimicrobial 405nm violet-blue light treatment of ex vivo human platelets leads to mitochondrial metabolic reprogramming and potential alteration of Phospho-proteome.

Continued efforts to reduce the risk of transfusion-transmitted infections (TTIs) through blood and blood components led to the development of ultraviolet (UV) light irradiation technologies known as pathogen reduction technologies (PRT) to enhance blood safety. While these PRTs demonstrate germicidal efficiency, it is generally accepted that these photoinactivation techniques have limitations as they employ treatment conditions shown to compromise the quality of the blood components. During ex vivo storage, platelets having mitochondria for energy production suffer most from the consequences of UV irradiation. Recently, application of visible violet-blue light in the 400-470nm wavelength range has been identified as a relatively more compatible alternative to UV light. Hence, in this report, we evaluated 405nm light-treated platelets to assess alterations in energy utilization by measuring different mitochondrial bioenergetic parameters, glycolytic flux, and reactive oxygen species (ROS). Furthermore, we employed untargeted data-independent acquisition mass spectrometry to characterize platelet proteomic differences in protein regulation after the light treatment. Overall, our analyses demonstrate that ex vivo treatment of human platelets with antimicrobial 405nm violet-blue light leads to mitochondrial metabolic reprogramming to survive the treatment, and alters a fraction of platelet proteome.

Enhanced the dispersibility and permeability of silver nanoparticles over rGO grafted by positively-charged polyethyleneimine toward broad-spectrum sterilization

Silver nanoparticles (Ag NPs) are used as antimicrobial agents due to their high-efficiency, broad-spectrum disinfection activity. However, the agglomeration and stability problems caused by excessive release of silver ions (Ag+) have severely restricted their developments. Herein, a novel silver/polyethyleneimine/reduced graphene oxide (Ag/PEI/rGO) antibacterial material featuring good dispersibility and permeability was rationally designed, thus benefiting for the capture of bacteria due to the introducing of highly-cationic PEI modifier and controllable release of biocidal agents (Ag+). Compared with Ag/rGO, the Ag/PEI/rGO has excellent stability and shows a more efficient sterilization efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) with 100% germicidal efficiency with low orders of dozens of ppm. In addition, the outstanding biocompatibility of this Ag/PEI/rGO antibacterial material endows it with promising potential in sterilization applications, which is expected to solve the infection problem caused by bacterial biofilm formation.

Viricidal Efficacy of a 405-nm Environmental Decontamination System for Inactivation of Bacteriophage Phi6: Surrogate for SARS-CoV-2.

The highly transmittable nature of SARS-CoV-2 has increased the necessity for novel strategies to safely decontaminate public areas. This study investigates the efficacy of a low irradiance 405-nm light environmental decontamination system for the inactivation of bacteriophage phi6 as a surrogate for SARS-CoV-2. Bacteriophage phi6 was exposed to increasing doses of low irradiance (~0.5 mW cm-2 ) 405-nm light while suspended in SM buffer and artificial human saliva at low (~103-4 PFU mL-1 ) and high (~107-8 PFU mL-1 ) seeding densities, to determine system efficacy for SARS-CoV-2 inactivation and establish the influence of biologically relevant suspension media on viral susceptibility. Complete/near-complete (≥99.4%) inactivation was demonstrated in all cases, with significantly enhanced reductions observed in biologically relevant media (P < 0.05). Doses of 43.2 and 172.8 J cm-2 were required to achieve ~3 log10 reductions at low density, and 97.2 and 259.2 J cm-2 achieved ~6 log10 reductions at high density, in saliva and SM buffer, respectively: 2.6-4 times less dose was required when suspended in saliva compared to SM buffer. Comparative exposure to higher irradiance (~50 mW cm-2 ) 405-nm light indicated that, on a per unit dose basis, 0.5 mW cm-2 treatments were capable of achieving up to 5.8 greater log10 reductions with up to 28-fold greater germicidal efficiency than that of 50 mW cm-2 treatments. These findings establish the efficacy of low irradiance 405-nm light systems for inactivation of a SARS-CoV-2 surrogate and demonstrate the significant enhancement in susceptibility when suspended in saliva, which is a major vector in COVID-19 transmission.

Surface dielectric barrier discharge plasma–treated pork cut parts: bactericidal efficacy and physiochemical characteristics

Maintaining agro-food product safety remains a significant challenge for satisfying local and global consumers in tropical countries. This issue has been growing due to new pathogen strains, low infectious doses, increased virulence, antibiotic resistance, cross-contamination or recontamination of foods, food-contact surfaces, and biocontamination of water within the food production chain. To respond to this situation, we studied the inactivation efficacy of surface dielectric barrier discharge (SDBD) plasma against pathogens on the surface of various pork cut parts, including the loin, hip, belly, liver, and intestine. The SDBD plasma was operated at 0.30 W/cm2 in ambient air, with a gap of 5.0 mm between the plasma generator and the sample surface. Up to 96% germicidal efficiency against surface pathogens were observed, showing after 1 min of SDBD plasma exposure. Visualization of reactive species deposition on the treated surface using KI–starch agar gel reagent indicated a non-uniform distribution of the SDBD-generated reactive species on the treated surface. Following the indirect plasma treatment by the SDBD reactor, the overall color of pork cut samples after plasma treatment was significantly different compared with before. However, the surface morphology and structural characterization of the treated pork cut samples were not significantly altered, and residual nitrites and nitrates were lower than the restriction level for safe consumption. The SDBD reactor should be developed further to produce a uniform distribution of reactive species on the meat surface for the improvement of the decontamination effect without undesirable effects on meat quality parameters.

Comparison of the Antimicrobial Efficacy and Germicidal Efficiency of 405-nm Light for Surface Decontamination

Background The persistence of infectious organisms on hospital surfaces presents a significant challenge to healthcare environments. Low irradiance visible 405-nm light has recently been developed as a method for environmental decontamination, with studies demonstrating successful reductions of environmental bacteria in wards and operating theatres. This study investigates the antimicrobial efficacy of 405-nm light for decontamination of surfaces, and how the dose-response kinetics are affected by use of differing light irradiances. Methods Surface-seeded Staphylococcus aureus and Pseudomonas aeruginosa (selected as model Gram-positive and Gram-negative species) were exposed to increasing doses of 405-nm light (≤ 90 Jcm-2) at three discrete irradiances (0.5, 5 and 50 mWcm-2). For both species, inactivation kinetics at each respective irradiance was established and susceptibility at equivalent light doses compared. Results Results demonstrate increased bacterial susceptibility to 405-nm light inactivation when exposed at lower irradiance treatments. For both species, 3 Jcm-2 was required when exposed using 0.5 mWcm-2 irradiance to achieve significant bacterial inactivation (P &lt; 0.05; 26.7-73.7% reduction). When exposed at 5 mWcm-2, double the energy (6 Jcm-2) was required to achieve similar reductions. Exposure at the highest irradiance (50 mWcm-2) required 3-5 times greater dose (9-15 Jcm-2) to achieve similar reductions to the lowest irradiance tested (0.5 mWcm-2). Conclusion This study provides evidence of the enhanced germicidal efficiency of low irradiance 405-nm light, highlighting its efficacy for continuous environmental decontamination applications. Further investigation into the photo-chemical inactivation mechanisms will be crucial for its optimisation for a range of infection control applications.

Glycosylation increases the anti-QS as well as anti-biofilm and anti-adhesion ability of the cyclo (L-Trp-L-Ser) against Pseudomonas aeruginosa

Pseudomonas aeruginosa infections pose a huge threat to cystic fibrosis patients, as well as those suffering from immunodeficiency. Antimicrobial resistance, especially multi-drug resistance, due to its ability to aggregate the compact biofilm, makes it more inefficient to treat this pathogen with traditional antibiotics. Biofilm and quorum sensing (QS) have become the alternative targets for treating P. aeruginosa infections. Previously, a cyclic dipeptide cyclo(L-Trp-L-Ser) has been identified as a QS inhibitor of P. aeruginosa. On the other hand, some monosaccharides have been proved lectin-targeting behavior and to mediate biofilm formation and adhesion of P. aeruginosa. We constructed novel cyclic dipeptide-carbohydrate conjugates as a low molecular weight dual-functional QS inhibitor, which can not only enhance its anti-QS activity but also enable good anti-biofilm and anti-adhesion ability. The IC50 of galactosylated c(WS) on biofilm formation and glass adhesion was 1/6 and 1/4 of that of the unmodified cyclic dipeptide, respectively. And the ability to eliminate the preformed biofilm was increased 10-fold. Furthermore, the carbohydrate conjugates can increase the germicidal efficiency of clinical antibiotic azithromycin when used synergistically. Our results provide a novel scaffold for developing anti-virulence adjuvants when taken with clinical antibiotics.

Development And Testing Of Combined germicidal Recirculator

The important problem of the poultry farming is the prevention of infectious diseases causing poultry deaths and unplanned financial losses. The article authors represent an overview of the air disinfection methods and the selection criteria for the disinfection methods being the most effective among other methods applicable for poultry facilities. There were determined the main factors influencing the germicidal efficiency of the ultraviolet (UV) irradiance sources. Studies were considered, where influence on the germicidal efficiency was discussed in terms of the UV irradiation exposure time in poultry facilities with floor conditions. The theoretical parameters substantiation is given for the device combining the two main disinfection components; it is done by development of both the mathematical model for the average irradiance rate calculation and the calculation method of the highspeed air flow parameters. Also, the method has been developed for determination of the needed number of the combined germicidal aerosol units in poultry keeping premises. The authors present the results of the experiments conducted for determination of the germicidal efficiency of the disinfection fulfilled against such microorganisms as Coli bacteria, Kochii bacilli, etc. with use of the developed combined recirculator. The experimental comparison with a prototype was carried out for the decontamination efficiency achieved with aid of the newly developed combined germicidal aerosol recirculator used in the following mode: the exposure time made 1 hour of work, then 2 hours of break on condition of the process cycling throughout the entire daylight hours. Here presented is the recommended layout of a number of the combined germicidal aerosol units in box-type rooms with poultry keeping on floor in a case of the ideal air flow direction. The increase by 20 % was found in the disinfection efficiency as well as the growth by 7 % in the additional live weight gain of the poultry.

On‐Chip Mercury‐Free Deep‐UV Light‐Emitting Sources with Ultrahigh Germicidal Efficiency

AbstractIn the current COVID‐19 scenario, there is an urgent need for developing efficient and mercury‐free deep‐ultraviolet (deep‐UV) light sources for disinfection applications. AlGaN‐based light‐emitting diodes (LEDs) may be considered as an alternative, but due to their inherent low efficiencies in the deep‐UV spectral region, significant developments are required to address efficiency issues. Here, a mercury‐free chip‐size deep‐UV light source is shown which is enabled by high‐vacuum chip‐scale cavity sealing overcoming the limitations of both mercury lamps and deep‐UV LEDs. These deep‐UV chips are cathodoluminescence based, in which a cavity is created with high vacuum integrity for efficient field‐emission. These chips demonstrate optical output power ≥20 mW (efficiency ≈4%) and, owing to the spectral overlap of phosphor cathodoluminescence spectra and germicidal effectiveness curve, resulted in log 6 (99.9999%) germicidal efficiency. Additionally, these chips offer high reliability, “instant” ON/OFF capability, high operational lifetimes, and low‐temperature dependence with complete design freedom.

Multi-Hollow Surface Dielectric Barrier Discharge for Bacterial Biofilm Decontamination

The plasma-activated gas is capable of decontaminating surfaces of different materials in remote distances. The effect of plasma-activated water vapor on Staphylococcus epidermidis, methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli biofilm contamination was investigated on the polypropylene nonwoven textile surface. The robust and technically simple multi-hollow surface dielectric barrier discharge was used as a low-temperature atmospheric plasma source to activate the water-based medium. The germicidal efficiency of short and long-time exposure to plasma-activated water vapor was evaluated by standard microbiological cultivation and fluorescence analysis using a fluorescence multiwell plate reader. The test was repeated in different distances of the contaminated polypropylene nonwoven sample from the surface of the plasma source. The detection of reactive species in plasma-activated gas flow and condensed activated vapor, and thermal and electrical properties of the used plasma source, were measured. The bacterial biofilm decontamination efficiency increased with the exposure time and the plasma source power input. The log reduction of viable biofilm units decreased with the increasing distance from the dielectric surface.

Inactivation of microorganisms by newly emerged microplasma UV lamps

Pathogenic microbes are becoming one of the biggest health-threatening challenges leading to a global need for sustainable solutions. Ultraviolet (UV) radiation enables the control of microorganismal replication. However, microbes with protected and/or repairable nucleic acids have challenged the inactivation efficacy of current UV sources. Targeting proteins responsible for nucleic acid protection and repair or microbial infection can be game-changing. Here, we identified and kinetic-modelled the efficiency of a new mercury-free radiation technology: microplasma UV, which radiates around proteins’ UV-absorption and decomposition peak with unique spectral power distributions. Surrogates for challenging microorganisms were studied: Escherichia coli (E. coli) bacterium that contains nucleic acid reactivation proteins, and bacteriophage-MS2 virus that possesses viral proteins responsible for protecting nucleic acid (capsid) and initiating infection (maturation). The microplasma UV lamp photons, at wavelengths below 240 nm, induced nucleic acid repair-deficiency disorder and enhanced inactivation of viral infectivity. Both studied microplasma UV sources presented higher germicidal efficiency for MS2 and significantly lower repair for E. coli compared with the standard values reported for mercury UVC lamps and UVC light emitting diodes (UVC-LEDs) in the literature. The reactive oxygen species were found to not play a role in this enhancement. The present results introduce promising UV sources for efficient and long-lasting microbial inactivation, thereby paving the way toward sustainable disinfection systems.

Efficient photocatalytic inactivation of E. coli by Mn-CdS/ZnCuInSe/CuInS2 quantum dots-sensitized TiO2 nanowires

A novel visible light-driven photocatalyst (represented as Mn-CdS/ZCISe/CIS/TiO2) for the passivation of E. coli was prepared with TiO2 nanowires as support and using CuInS2 (CIS) and ZnCuInSe (ZCISe) quantum dots (QDs), as well as Mn-doped CdS (Mn-CdS) nanoparticles (NPs) as sensitizers. The use of CIS and ZCISe QDs and Mn-CdS NPs extends the light harvest region to visible light. The photoelectric conversion efficiency was consequently improved, with a photocurrent density of 12.5 mA cm−2, about 60 times that of pure TiO2 nanowires. The germicidal efficiency of the photocatalyst was assessed by passivation of E. coli, 96% bacteria in 50 ml 105 colony forming units (CFU) ml−1 solution were killed within 50 min. Besides the high efficiency, the composite has good stability and satisfactory recycling performance. The antibiotic mechanism was also performed by using photoluminescence and a scavenging agent of different active matter, revealing that the photo-generated holes play a major role in the sterilization process.

405-nm Light for Bacterial Reduction in Blood Plasma: Preliminary investigations into antimicrobial efficacy and plasma protein integrity

Background: Pathogen reduction technologies (PRT) for blood products can reduce the incidence of transfusion-transmitted infection and associated wastage of blood products. Visible 405nm-light has been shown to inactivate bacteria in situ in bagged blood plasma without the addition of photo-sensitive chemicals. However, threshold levels for plasma protein compatibility and optimal bactericidal activity are currently unknown. This study investigates different treatment conditions and their suitability for safely inactivating bacteria in blood plasma. Method: Plasma seeded with Staphylococcus aureus (102–105CFU/ml) was exposed to 405nm-light at low and high irradiances (10, 100mW/cm2) with treatment times ranging between 0.2–7-hr (≤252 Jcm-2). SDS-PAGE was then used to assess the light effect in terms of antimicrobial treatment levels on plasma protein integrity. Results: High and low intensity treatment regimens achieved significant bacterial inactivation (P=&lt;0.05) with doses of 252 Jcm-2 achieving ≥99.3% reduction. Results suggest that lower irradiances have greater germicidal efficiency, with use of 10mWcm-2 achieving up to 30% greater inactivation than equivalent doses using 100mWcm-2. SDS-PAGE analysis demonstrated no major detrimental impact on protein integrity with any of the treatment conditions investigated. Minimal changes in protein bands (≈28kDa) were observed relative to positive control samples after application of doses &gt;144 Jcm-2. Conclusion: The results of this study have highlighted the safety potential of 405nm-light treatment on blood plasma. Further research is required to determine the upper and lower threshold treatment levels and functionality of plasma proteins post-exposure for further development of this technology as a PRT tool for application in transfusion medicine.

Germicidal Activities of Some Selected Disinfectants on Staphylococcus aureus and Escherichia Coli

The germicidal efficacy of four common disinfectants used for different purposes was tested against two common pathogens namely Escherichia coli and Staphylococcus aureus . The disinfectants (Dettol, Jik, Izal and Purit) were diluted with sterile distilled water to achieve different concentrations (100%, 50%, 25%, 12.5% and 6.25%) and they were tested on the two organisms using Agar well diffusion method. The plates were allowed to incubate for 24 hours at 37°C.The germicidal efficiency of the disinfectants was evaluated by measuring the zone of inhibition of each disinfectant based on their varying concentrations. Dettol was observed to have the highest inhibition at 100% concentration and was more germicidal on E. coli than S. aureus with Minimal Inhibitory Concentration (MIC) value of 1:16 dilution against the two test organisms. This was closely followed by Jik which also showed more inhibitory activity against E. coli at the initial concentration recording the second highest inhibition rate compared to other disinfectants, but its efficacy decreased as the concentration dropped. Jik exhibited MIC value of 1:8 and 1:2 dilutions for Staphylococcus aureus and Escherichia coli respectively. Purit showed more inhibitory activity on S. aureus with 3.8mm zone of inhibition as against 1.3mm at 100% concentration, recording MIC value of 1:8 dilution on S. aureus and 1:16 dilution for E. coli . The disinfectant Izal was observed to be the lowest as it did not inhibit the growth of any of the organisms, indicating resistance of the organisms to the disinfectant at all concentrations. All the disinfectants apart from Izal inhibited the two test isolates. Only Dettol proved to be best among them. Therefore, Dettol is encouraged to be used in homes to prevent pathogenic infection.

The involvement of superoxide radicals in medium pressure UV derived inactivation

Today, two types of lamp systems dominate the UV disinfection industry: low-pressure (LP) UV lamps and medium-pressure (MP) polychromatic lamps. Both lamp types have their advantages and disadvantages in microorganism inactivation, with LP lamps being cheaper, having longer life, and working at lower temperature, hence reducing fouling, and MP lamps showing better inactivation per germicidal dose for certain microorganisms. Bacterium-based biosensors were used to compare LP and MP irradiation. These biosensors were Escherichia coli bacteria carrying the lux operon genes under the control of different stress-responding promoters, where activation of the specific promoter is manifested as bioluminescence. MP irradiation, considerably more than LP irradiation, resulted in activation of the superoxide dismutase expression, indicating the formation of superoxide radicals inside the cells. Accordingly, pre-exposure (immunization) of the bacteria to an activator that produces superoxide radicals resulted in lower inactivation and increased resistance to MP irradiation, but not to LP irradiation. This study shows that the difference in germicidal efficiency may result from the production of intracellular superoxide radicals by MP irradiation, at wavelengths other than 254 nm, as emitted by LP lamps.

Understanding possible underlying mechanism in declining germicidal efficiency of UV-LED reactor

Since ultraviolet light emitting diodes (UV-LEDs) have emerged as an alternative light source for UV disinfection systems, enhancement of reactor performance is a demanding challenge to promote its practical application in water treatment process. This study explored the underlying mechanism of the inefficiency observed in flow-through mode UV disinfection tests to improve the light utilization of UV-LED applications. In particular, the disinfection performance of UV-LED reactors was evaluated using two different flow channel types, reservoir and pathway systems, in order to elucidate the impact of physical circumstances on germicidal efficiency as the light profile was adjusted. Overall, a significant reduction in germicidal efficiency was observed when exposure time was prolonged or a mixing chamber was integrated. Zeta analysis revealed that the repulsion rate between microorganisms decreased with UV fluence transfer, and that change might cause the shielding effect of UV delivery to target microorganisms. In line with the above findings, the reduction in efficiency intensified when opportunities for microbial collision increased. Thus, UV induced microbial aggregation was implicated as being a disinfection hindering factor, exerting its effect through uneven UV illumination. Ultimately, the results refuted the prevailing belief that UV has a cumulative effect. We found that the reservoir system achieved worse performance than the pathway system despite it providing 15 times higher UV fluence: the differences in germicidal efficiency were 1-log, 1.4-log and 1.7-log in the cases of P.aeruginosa, E.coli and S.aureus, respectively.