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BACKGROUND: We hypothesized that ultraviolet-C (UV-C) irradiation (Surfacide, Waukesha, WI) following use of microfiber cloths (Sanny Shop LLC, Longmont, CO) soaked in water would be noninferior to surface disinfection wipes containing a quaternary ammonium compound and alcohol (PDI Healthcare, Woodcliff Lake, NJ) for the pathogenic Staphylococcus aureus (S. aureus) sequence type 5 (ST5). METHODS: This was a randomized laboratory study of disinfection approaches for S. aureus ST5. A total of 270 polycarbonate slides loaded with ST5 were prepared for the standard surface disinfection group (N=18) and water-soaked microfiber cloths and UV-C treatment group (N=144), along with positive and negative microbiological controls. RESULTS: All 18 samples of S. aureus ST5 bacteria treated with standard chemical wipes showed complete disinfection (colony forming units (CFU) = 0). All 144 treatments with water-soaked microfiber wipes followed by UV-C exposure showed complete disinfection (CFU =0) regardless of soiling, height from the floor, or orientation to the emitters. The upper 95% exact one-sided confidence limit for any CFU >0 was 2.1%. DISCUSSION: These data affirm our hypothesis that surface wiping with a damp cloth followed by triangular UV-C irradiation delivery is noninferior to surface disinfection for S. aureus ST5 using germicidal wipes, even when UV-C is compromised by height from the floor and orientation to the emitters and surface disinfection is targeted. CONCLUSION: Removing bioburden with chemical-free microfiber cloths followed by triangular UV-C delivery is a noninferior strategy to targeted surface disinfection with chemical disinfecting wipes for the pathogenic S. aureus ST5 strain in the laboratory setting.

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AIM: Bacterial biofilms can form on the surfaces in hospital, clinics, farms and food processing plants, representing a possible source of infections and cross-contamination. This study investigates the effectiveness of new commercial wipes against Staphylococcus aureus and Pseudomonas aeruginosa biofilms (early attachment and formed biofilms), assessing LH SALVIETTE wipes (Lombarda H S.r.l) potential for controlling biofilm formation. METHODS AND RESULTS: The wipes efficacy was studied against the early attachment phase and formed biofilm of S. aureus ATCC 6538 and P. aeruginosa ATCC 15442 on a polyvinyl chloride (PVC) surface, following a modified standard test EN 16615:2015, measuring Log10 reduction and cell viability using Live/dead staining. It was also evaluated the wipes anti-adhesive activity over time (3 h, 24 h), calculating CFU.mL-1 reduction. Data were analyzed using t-Student test. The wipes significantly reduced both early phase and formed S. aureus biofilm, preventing dispersion on PVC surfaces. Live/dead imaging showed bacterial cluster disaggregation and killing action. The bacterial adhesive capability decreased after short-time treatment (3 h) with the wipes compared to 24 h. CONCLUSIONS: Results demonstrated decreased bacterial count on PVC surface both for early attachment phase and formed biofilms, also preventing the bacterial biofilm dispersion.

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BACKGROUND: We aimed to evaluate the performance of ceiling-mounted UV-C lamps. METHODS: This study was conducted in an empty room with UV-C lamps in the biocontainment unit of a tertiary care hospital in South Korea. Each pathogen (Staphylococcus aureus, Escherichia coli, Candida krusei, Bacillus cereus, and Mycobacterium peregrinum) was inoculated on blood agar plates and placed in 20 selected places from the UV-C lamp, and irradiation was applied for 15 min. As a control group, the bacterial solution was diluted 10,000 times and UV was not applied. RESULTS: A mean ± SD of 5.95 ± 0.91 log reduction was observed with UV irradiation compared with the control. The log reduction was greatest for S. aureus [median, 7.05 (IQR, 6.49-7.26)] and least for M. peregrinum [median, 4.88 (IQR, 4.58-5.24)]. The degree of log reduction was inversely proportional to the square of the distance from the UV-C lamp (R2 = -0.12, P < .001). CONCLUSIONS: In this study, ceiling-mounted UV-C demonstrated effective disinfection of at least 4-log reduction of the test organisms within a 4-m distance. Mounted UV-C lighting is a considerable option for improving surface disinfection.

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Bioaerosols and pathogens in indoor workplaces and residential environments are the primary culprits of several infections. Techniques for sanitizing air and surfaces typically involve the use of UV rays or chemical sanitizers, which may release chemical residues harmful to human health. Essential oils, natural substances derived from plants, which exhibit broad antimicrobial properties, could be a viable alternative for air and surface sanitation. The objective of this study has been to investigate the efficacy of thyme essential oil (TEO) in environmental sanitation processes. In Vitro assays through agar well diffusion, disk volatilization and tube dilution methods revealed significant antimicrobial activity of TEO 100% against foodborne and environmental isolates, with both bacteriostatic/fungistatic and bactericidal/fungicidal effects. Therefore, aqueous solutions of TEO 2.5% and 5% were formulated for air sanitation through nebulization and surface disinfection via direct contact. Bioaerosol samples and surface swabs were analyzed before and after sanitation, demonstrating the efficacy of aqueous solutions of TEO in reducing mesophilic and psychrophilic bacteria and environmental fungi levels in both air and on surfaces. The obtained results prove the antimicrobial potential of aqueous solutions of TEO in improving indoor air quality and surface cleanliness, suggesting thyme essential oil as an effective and safe natural sanitizer with minimal environmental impact compared to dangerous chemical disinfectants.

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BACKGROUND: Standardized efficacy surface tests for disinfectants are performed on pristine surfaces. There is a growing interest in understanding the impact of surface ageing on disinfectant activity, owing for example to the increased usage of ultraviolet (UV) radiation and oxidative chemistries for surface decontamination. This acknowledges that general surface 'wear and tear' following UV radiation and oxidative biocide exposure may impact biocidal product efficacy. METHODS: PVC surfaces were aged through thermal and UV-A radiation (340 nm wavelength) following the use of standard ageing surface protocols to simulate natural surface degradation. Surface roughness, contact angle and scanning electron microscopy were performed to evaluate physical changes in PVC surfaces before and after artificial ageing. The efficacy of five pre-impregnated disinfectant wipes were evaluated using the ASTM E2967-15 on stainless-steel (control) and PVC surfaces (aged and non-aged). RESULTS: The type of formulation and the organism tested remained the most significant factors impacting disinfectant efficacy, compared with surface type. Both thermal ageing and UV-A exposure of PVC surfaces clearly showed signs of surface degradation, notably an increase in surface roughness. Physical changes were observed in the roughness of PVC after artificial ageing. A difference in disinfectant efficacy dependent on aged PVC surfaces was observed for some, but not all formulations. CONCLUSION: We showed that surface type and surface ageing can affect biocidal product efficacy, although in a non-predictable manner. More research is needed in this field to ascertain whether surface types and aged surfaces should be used in standardized efficacy testing.

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This recommendation of the Commission for Hospital Hygiene and Infection Prevention (KRINKO) addresses not only hospitals, but also outpatient health care facilities and compiles current evidence. The following criteria are the basis for the indications for cleaning and disinfection: Infectious bioburden and tenacity of potential pathogens on surfaces and their transmission routes, influence of disinfecting surface cleaning on the rate of nosocomial infections, interruption of cross infections due to multidrug-resistant organisms, and outbreak control by disinfecting cleaning within bundles. The criteria for the selection of disinfectants are determined by the requirements for effectiveness, the efficacy spectrum, the compatibility for humans and the environment, as well as the risk potential for the development of tolerance and resistance. Detailed instructions on the organization and implementation of cleaning and disinfection measures, including structural and equipment requirements, serve as the basis for their implementation. Since the agents for surface disinfection and disinfecting surface cleaning have been classified as biocides in Europe since 2013, the regulatory consequences are explained. As possible addition to surface disinfection, probiotic cleaning, is pointed out. In an informative appendix (only in German), the pathogen characteristics for their acquisition of surfaces, such as tenacity, infectious dose and biofilm formation, and the toxicological and ecotoxicological characteristics of microbicidal agents as the basis for their selection are explained, and methods for the evaluation of the resulting quality of cleaning or disinfecting surface cleaning are presented.

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Candida auris has emerged as a global healthcare threat, displaying resistance to important healthcare antifungal therapies. Infection prevention and control protocols have become paramount in reducing transmission of C. auris in healthcare, of which cleaning and disinfection plays an important role. Candida albicans is used as a surrogate yeast for yeasticidal claims of disinfection products, but reports have been made that sensitivity to disinfectants by C. auris differs from its surrogate. In this review, we aimed to compile the information reported for products used for skin and hard surface disinfection against C. auris in its planktonic or biofilm form. A comparison was made with other Candida species, and information were gathered from laboratory studies and observations made in healthcare settings.

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The contamination of indoor areas is a global health problem that can cause the dispersion of infectious diseases. In that sense, it is urgent to find new strategies applying a lower concentration of the traditional chemicals used for cleaning and disinfection. Ultraviolet radiation (UV), in particular far-UV-C (200-225 nm), has emerged as a successful, powerful, easy-to-apply, and inexpensive approach for bacterial eradication that still requires scientific assessment. This study investigated new strategies for disinfection based on far-UV-C (222 nm) combined with chlorine and mechanical cleaning, providing an innovative solution using low doses. The bactericidal activity of far-UV-C (222 nm) was tested at an intensity of irradiation from 78.4 µW/cm2 to 597.7 µW/cm2 (for 1 min) against Escherichia coli and Staphylococcus epidermidis adhered on polystyrene microtiter plates. It was further tested in combination with mechanical cleaning (ultrasounds for 1 min) and free chlorine (0.1, 0.5, and 1 mg/L for 5 min). The triple combination consisting of mechanical cleaning + free chlorine (0.5 mg/L) + far-UV-C (54 mJ/cm2) was tested against cells adhered to materials found in hospital settings and other public spaces: polyvinyl chloride (PVC), stainless steel (SS), and polyetheretherketone (PEEK). Disinfection with far-UV-C (54 mJ/cm2) and free chlorine at 0.5 mg/L for 5 min allowed a total reduction of culturable E. coli cells and a logarithmic reduction of 2.98 ± 0.03 for S. epidermidis. The triple combination of far-UV-C, free chlorine, and mechanical cleaning resulted in a total reduction of culturable cells for both adhered bacteria. Bacterial adhesion to PVC, SS, and PEEK occurred at distinct extents and influenced the bactericidal activity of the triple combination, with logarithmic reductions of up to three. The overall results highlight that, based on culturability assessment, far-UV-C (54 mJ/cm2) with chlorine (0.5 mg/L; 5 min) and mechanical cleaning (1 min) as an efficient disinfection strategy using mild conditions. The combination of culturability and viability assessment of disinfection is recommended to detect regrowth events and increase the effectiveness in microbial growth control.

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BACKGROUND: For healthcare workers, surface disinfections are daily routine tasks. An assessment of the inhalation exposure to hazardous substances, in this case the disinfectant´s active ingredients, is necessary to ensure workers safety. However, deciding which exposure model is best for exposure assessment remains difficult. OBJECTIVE: The aim of the study was to evaluate the applicability of different exposure models for disinfection of small surfaces in healthcare settings. METHODS: Measurements of the air concentration of active ingredients in disinfectants (ethanol, formaldehyde, glutaraldehyde, hydrogen peroxide, peroxyacetic acid) together with other exposure parameters were recorded in a test chamber. The measurements were performed using personal and stationary air sampling. In addition, exposure modelling was performed using three deterministic models (unsteady 1-zone, ConsExpo and 2-component) and one modifying-factor model (Stoffenmanager®). Their estimates were compared with the measured values using various methods to assess model quality (like accuracy and level of conservatism). RESULTS: The deterministic models showed overestimation predominantly in the range of two- to fivefold relative to the measured data and high conservatism for all active ingredients of disinfectants with the exception of ethanol. With Stoffenmanager® an exposure distribution was estimated for ethanol, which was in good accordance with the measured data. IMPACT STATEMENT: To date, workplace exposure assessments often involve expensive and time consuming air measurements. Reliable exposure models can be used to assess occupational inhalation exposure to hazardous substances, in this case surface disinfectants. This study describes the applicability of three deterministic and one modifying-factor model for disinfection of small surfaces in healthcare settings, in direct comparison to measurements performed and will facilitate future exposure assessments at these workplaces.

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Far-ultraviolet C (UVC) light has demonstrated its ability to inactivate microbes on surfaces. However, the factors influencing the efficacy of far-UVC surface disinfection remain unclear. This study aimed to explore the effects of material properties on far-UVC disinfection of bioaerosols (represented by Escherichia coli (E. coli)) deposited on surfaces. The susceptibility constants (Z-values) of E. coli on 14 common materials were measured and analyzed. Additionally, five possible influencing factors (roughness, pores, electrostatic charge, wetness, and temperature) related to surface properties were investigated by control experiments. The results show that far-UVC light effectively disinfected E. coli on the 14 materials, with disinfection efficiencies ranging from 69.1% to 98.9% under a dose of 100.8 J/m2. Surface roughness and electrostatic charges had negligible influence on far-UVC disinfection of E. coli on surfaces. However, for porous materials, pore sizes larger than the E. coli size resulted in lower Z-values. Higher surface wetness decreased both the Z-value and natural decay rate. Meanwhile, a higher surface temperature of 40 °C resulted in a higher Z-value and natural decay rate. The results can improve our understanding of far-UVC disinfection of microbes on surfaces, and the database can be used for numerical models.

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Effective disinfection of contaminated surfaces is essential for preventing the transmission of pathogens. In this study, we investigated the UV irradiance and wavelength distribution of a 222-nm ultraviolet C (UVC) excimer lamp and its disinfection efficacy against microorganisms in laboratory conditions. By using a carrier quantitative germicidal test with stainless steel sheets as carriers, we examined the disinfection effect of the 222-nm UVC lamp on three standard strains-Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. We tested the disinfection efficacy under different conditions by adjusting irradiation time, as well as the state and temperature of the stainless steel carriers. Our results indicated that a bacterial suspension in PBS and not-dried stainless steel carriers yielded better disinfection than in TSB and dried carriers. Additionally, carrier temperature had no significant impact on disinfection efficacy. When utilizing a bacterial suspension in PBS and non-dried carriers at a temperature of 20 °C, the three bacteria were eliminated by 222-nm UVC excimer lamp irradiation in just 15 s. In contrast, when using a bacterial suspension in TSB and dried carriers at temperatures of 20 °C, 4 °C, or - 20 °C, the three bacteria were eradicated by 222-nm UVC excimer lamp irradiation in 60 s. Comparatively, the LPM lamp required more than 10 min to achieve the same disinfection effect. Our data demonstrate that the 222-nm UVC excimer lamp has higher irradiance and a more potent microbial disinfection effect than the LPM lamp, requiring significantly less irradiation time to achieve the same disinfection effect under identical conditions. Furthermore, the 222-nm UVC excimer lamp exhibited a substantial disinfection effect on bacterial propagules at low temperatures. Our findings support the optimization of "tunnel-type" cold-chain goods disinfection devices, providing an alternative, highly efficient, and practical tool to combat the spread of SARS-CoV-2 through cold-chain systems.

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BACKGROUND: In the clinical setting, surface disinfection is an important measure to reduce the risk of cross transmission of micro-organisms and the risk of nosocomial infections. Standardized methods can be used to evaluate disinfection procedures, as well as the effectiveness of the active ingredients used for disinfection. However, despite standardization, the results of such methodologies are still determined by several factors, and incorrect results may lead to invalid assumptions about the effectiveness of a disinfectant, posing significant health risks for patients and health personnel. AIM: The objective of this study was to evaluate several determinants for the recovery of Pseudomonas aeruginosa and other test organisms to establish their influence on the results of standardized disinfection methodologies, and to find Gram-negative strains that can be used as suitable replacements for P. aeruginosa. METHODS: The effects of inoculum application method, drying time, temperature and carrier material on the survival and recovery of the test organisms were evaluated using Student's t-test, one-way analysis of variance and Tukey's multiple comparison test. FINDINGS AND CONCLUSIONS: Temperature, drying time, application method and carrier material were found to affect the recovery of P. aeruginosa cells significantly, and therefore influence the outcome of the methodologies used. This study also showed thatP. aeruginosa could be replaced with the Gram-negative species Acinetobacter baumannii, a test organism used in many standardized methodologies, which responds better under the same circumstances and has a behaviour similar to that of P. aeruginosa in disinfectant efficacy tests.

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Aerosolized anthrax (Bacillus anthracis) spores are of extreme health concern and can remain airborne for hours and contaminate all kinds of surfaces, constituting reservoirs from which resuspension is easily produced. The assessment of decontamination techniques must therefore consider both air and surfaces. In the present study, several kinds of disinfecting fogs were experimentally tested against Bacillus thuringiensis spores, which served as a surrogate for Bacillus anthracis, both as aerosols released into the air and spread on porous and non-porous surfaces with different positions and orientations. This technology removed Bacillus thuringiensis spores from the air in 20 min with just a 1 min application of fog. The dynamics and characteristics of the fog, related to aerosol and surface interactions, proved to be critical for optimal performance and decontamination. An optimal configuration could provide effective disinfection even on indirectly reached surfaces. In all cases, 8% hydrogen peroxide (H2O2) provided a higher disinfection rate than 2% glutaraldehyde.

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Ultraviolet (UV)-C irradiation is a promising method for microbial eradication on surfaces. Major developments have taken place in UV-C light-emitting diodes (LEDs) technology. In this study, we examined the suitability of UV-C LED-based surface disinfection in hospitals. We tested the efficacy of UV-C LED surface treatment on different microorganisms dried on a carrier surface or in a liquid solution. The influences of soiling, shading, surface material, radiation wavelength, microbial load and species on the disinfection performance were investigated. UV-C LED caused a reduction of >5 log10 levels of E. coli, S. aureus and C. albicans, whereas 3 log10 reduction was observed for G. stearothermophilus spores. The components of the medium led to a reduced UV-C LED efficiency compared to buffered solutions. We observed that the microbial load and the roughness of the carrier surface had a major influence on the UV-C LED disinfection efficiencies, whereas shading had no impact on inactivation. This study showed that UV-C is suitable for surface disinfection, but only under certain conditions. We showed that the main factors influencing microbial inactivation through UV-C light (e.g., intrinsic and extrinsic factors) had a similar impact when using a UV-C LED radiation source compared to a conventional UV-C lamp. However, the potential of LEDs is contributed by their adjustable wavelength and customizable geometry for the decontamination of medical devices and surfaces, and thereby their ability to overcome shading effects.

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BACKGROUND: Polymerase chain reaction (PCR) is an essential tool for rapid detection of pathogens, but is susceptible to cross-contamination by residual nucleic acid, leading to false-positive results. Adequate surface decontamination would help prevent this, but most protocols target infectious microbes rather than free nucleic acid. The aim of this study was to evaluate the ability of commercial surface disinfectants to degrade different representative classes of nucleic acid. METHODS: Commercial surface disinfectants with various active ingredients, as well as 10% chlorine bleach, were tested. Nucleic acid was dried on to stainless steel coupons and treated with disinfectant for 0-4 min prior to neutralization and quantification by quantitative reverse transcription PCR. The effective disinfectants were also evaluated in the presence of organic load. RESULTS: Only dilute chlorine bleach and the hypochlorite-based commercial disinfectant significantly degraded any type of free nucleic acid. Hydrogen-peroxide- and quaternary-ammonium-based disinfectants gave <1 log reduction after 4 min for all targets. Results were time-dependent for each target, which underscores the importance of adequate contact time. Organic load appeared to have little impact on the efficacy of hypochlorite-based disinfectants for nucleic acid degradation. CONCLUSIONS: This study demonstrates the importance of proper selection and application of disinfectant to remove residual nucleic acid when processing samples for molecular diagnostic testing.

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BACKGROUND: Global sustainability is a major health concern facing our planet today. The healthcare sector is a significant contributor to environmentally damaging activity. Reusable cloths should be considered as an environmentally friendly alternative to the predominantly used single-use surface wipes in cleaning and disinfection of environmental surfaces in healthcare settings. AIM: To conduct a rapid review of current policies on surface decontamination in healthcare settings; then to carry out a life cycle impact assessment (LCIA) of reusable cotton and microfibre cloths versus conventional single-use cloths, with three compatible disinfectants. METHODS: Seven countries were included in the rapid review of policies. For the LCIA, inputs, outputs, and processes across the life cycle were included, using EcoInvent database v3.7.1 and open LCIA software. Sixteen European-recommended environmental impact categories and eight human health categories were considered. FINDINGS: Infection prevention policies examined do not require single-use wipes for cleaning and disinfection. The disinfectant with the highest environmental impact was isopropyl alcohol. The most environmentally sustainable option for clinical surface decontamination was the microfibre cloth when used with a quaternary ammonium compound. The least environmentally sustainable option was cotton with isopropyl alcohol. CONCLUSION: Impacts were primarily attributed with the use of the disinfectant agent and travel processes.

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(1) Background: Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) continues to cause profound health, economic, and social problems worldwide. The management and disinfection of materials used daily in health centers and common working environments have prompted concerns about the control of coronavirus disease 2019 (COVID-19) infection risk. Ozone is a powerful oxidizing agent that has been widely used in disinfection processes for decades. The aim of this study was to assess the optimal conditions of ozone treatment for the elimination of heat-inactivated SARS-CoV-2 from office supplies (personal computer monitors, keyboards, and computer mice) and clinical equipment (continuous positive airway pressure tubes and personal protective equipment) that are difficult to clean. (2) Methods: The office supplies and clinical equipment were contaminated in an area of 1 cm2 with 1 × 104 viral units of a heat-inactivated SARS-CoV-2 strain, then treated with ozone using two different ozone devices: a specifically designed ozonation chamber (for low-medium ozone concentrations over large volumes) and a clinical ozone generator (for high ozone concentrations over small volumes). SARS-CoV-2 gene detection was carried out using quantitative real-time polymerase chain reaction (RT-qPCR). (3) Results: At high ozone concentrations over small surfaces, the ozone eliminated SARS-CoV-2 RNA in short time periods-i.e., 10 min (at 4000 ppm) or less. The optimum ozone concentration over large volumes was 90 ppm for 120 min in ambient conditions (24 °C and 60-75% relative humidity). (4) Conclusions: This study showed that the appropriate ozone concentration and exposure time eliminated heat-inactivated SARS-CoV-2 RNA from the surfaces of different widely used clinical and office supplies, decreasing their risk of transmission, and improving their reutilization. Ozone may provide an additional tool to control the spread of the COVID-19 pandemic.

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AIM: The present study aimed to assess the bond integrity of curcumin photosensitizer (CPS) Photodynamic therapy (PDT) on fiber post disinfection bonded to radicular dentin in comparison to the conventional fiber post sterilant used. MATERIALS AND METHODS: Fifty human permanent single-rooted premolars were utilized with the crown part sectioned using up to the cementoenamel junction. Root canal preparation was performed followed by canal obturation with gutta-percha (GP) and resin-based sealer. The post space was prepared using peso reamers leaving 4 mm at the apical part of the post space. Fifty glass fiber posts (GFP) were divided into five groups based on the surface disinfectant (n = 10). group 1: Autoclave sterilization (AS) group 2: chlorhexidine digluconate (CHX dig), group 3: CPS solution, group 4: 35% phosphoric acid (PA) gel, and group 5: No disinfection. Cementation was performed using dual-cure self-etch resin cement. Each tooth was sectioned and placed on the universal testing machine. Failure mode was analyzed using a stereomicroscope at 40x magnification. Statistical analysis was performed using one-way analysis of variance (ANOVA) and Tukey multiple comparison tests. (p = 0.05). RESULTS: Intragroup comparison analysis demonstrated that group 2 in which 2% CHX dig was used as a post-surface disinfectant revealed the highest bond integrity at all three levels. Group 5 where no disinfectant was used to decontaminate the post surface exhibited the lowest bond values. In all the investigated groups, PBS values showed a downward trend from coronal to the apical third of the post space. Group 1 in which AS was used to sterilize the fiber post and group 3 in which CPS was smeared to decontaminate the GFPs surface-displayed comparable outcomes of PBS to group 5 specimens at all three levels. (p > 0.05). CONCLUSION: CHX dig and PA post-surface disinfection displayed a positive impact on bond strength with the radicular dentin. However, CPS and AS do not reveal any effect on the PBS when used for post-decontamination.

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The experience of COVID19 pandemic has demonstrated the real concern of biological agents dispersed in the air and surfaces environments. Therefore, the need of a fast and large-scale disinfection method has arisen for prevention of contagion. COUNTERFOG® is an innovative technology developed for large-scale decontamination of air and surfaces. The objective of this study is to assess experimentally the effectiveness of COUNTERFOG® in disinfecting viral-contaminated surfaces. We also aim to measure the necessary time to disinfect said surfaces. Stainless steel surfaces were contaminated with bacteriophage φ29 and disinfected using COUNTERFOG® SDR-F05A+, which uses a sodium hypochlorite solution at different concentrations and for different exposure times. A log reduction over 6 logs of virus titer is obtained in 1 min with 1.2% sodium hypochlorite when the application is direct; while at a radial distance of 5 cm from the point of application the disinfection reaches a reduction of 5.5 logs in 8 min. In the same way, a higher dilution of the sodium hypochlorite concentration (0.7% NaOCl) requires more exposure time (16 min) to obtain the same log reduction (> 6 logs). COUNTERFOG® creates, in a short time and at a distance of 2 m from the point of application, a thin layer of disinfectant that covers the surfaces. The selection of the concentration and exposure time is critical for the efficacy of disinfection. These tests demonstrate that a concentration between 0.7- 1.2% sodium hypochlorite is enough for a fast and efficient ɸ29 phage inactivation. The fact that ɸ29 phage is more resistant to disinfection than SARS-CoV-2 sustains this disinfection procedure.

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The COVID-19 pandemic has raised interest in using devices that generate ultraviolet C (UVC) radiation as an alternative approach for reducing or eliminating microorganisms on surfaces. Studies investigating the efficacy of UVC radiation against pathogens use a wide range of laboratory methods and experimental conditions that can make cross-comparison of results and extrapolation of findings to real-world settings difficult. Here, we use three different UVC-generating sources - a broad-spectrum pulsed xenon light, a continuous light-emitting diode (LED), and a low-pressure mercury vapour lamp - to evaluate the impact of different experimental conditions on UVC efficacy against the coliphage MS2 on surfaces. We find that a nonlinear dose-response relationship exists for all three light sources, meaning that linear extrapolation of doses resulting in a 1-log10 (90%) reduction does not accurately predict the dose required for higher (e.g. 3-log10 or 99.9%) log10 reductions. In addition, our results show that the inoculum characteristics and underlying substrate play an important role in determining UVC efficacy. Variations in microscopic surface topography may shield MS2 from UVC radiation to different degrees, which impacts UVC device efficacy. These findings are important to consider in comparing results from different UVC studies and in estimating device performance in field conditions.

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