Heavy metals such as silver have been used for prophylaxis of conjunctivitis of the newborn, topical therapy for burn wounds, and bonding to indwelling catheters, and the use of heavy metals as antiseptics or disinfectants is again being explored Inactivation of bacteria on stainless steel surfaces by zeolite ceramic coatings containing silver and zinc ions has also been demonstrated , Metals such as silver, iron, and copper could be used for environmental control, disinfection of water, or reusable medical devices or incorporated into medical devices e.
A comparative evaluation of six disinfectant formulations for residual antimicrobial activity demonstrated that only the silver disinfectant demonstrated significant residual activity against S. Preliminary data suggest metals are effective against a wide variety of microorganisms.
Clinical uses of other heavy metals include copperquinolinolate as a fungicide against Aspergillus , copper-silver ionization for Legionella disinfection , organic mercurials as an antiseptic e. The wavelength of UV radiation ranges from nm to nm A to A.
Its maximum bactericidal effect occurs at — nm. Inactivation of microorganisms results from destruction of nucleic acid through induction of thymine dimers. UV radiation has been employed in the disinfection of drinking water , air , titanium implants , and contact lenses Bacteria and viruses are more easily killed by UV light than are bacterial spores UV radiation has several potential applications, but unfortunately its germicidal effectiveness and use is influenced by organic matter; wavelength; type of suspension; temperature; type of microorganism; and UV intensity, which is affected by distance and dirty tubes The application of UV radiation in the health-care environment i.
The effect of UV radiation on postoperative wound infections was investigated in a double-blind, randomized study in five university medical centers. No data support the use of UV lamps in isolation rooms, and this practice has caused at least one epidemic of UV-induced skin erythema and keratoconjunctivitis in hospital patients and visitors Pasteurization is not a sterilization process; its purpose is to destroy all pathogenic microorganisms.
However, pasteurization does not destroy bacterial spores. The water temperature and time should be monitored as part of a quality-assurance program Pasteurization of respiratory therapy , and anesthesia equipment is a recognized alternative to chemical disinfection.
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Published: September 23 Society of Petroleum Engineers. You can access this article if you purchase or spend a download. Sign in Don't already have an account? Personal Account. You could not be signed in. Please check your username and password and try again. Sign In Reset password. Sign in via OpenAthens. This is a source of high energy photons with low cost. Nevertheless, the pulsed nature of this technology would limit its use in continuous air disinfection system.
Ozone is an issue that bothers on safety if it remains in the output of an air treatment system. However, ozone can be easily destroyed before leaving the air treatment system if proper catalyst is adopted [ 4 , 5 ]. Also, some photocatalysts can utilize and destroy ozone in addition to its photocatalytic activity [ 6 ]. VUV has an even stronger ionizing power than UVC light and can generate high concentration reactive species such as ozone and OH radicals [ 7 ].
In other words, apart from direct illumination, VUV can inactivate bacterial growth by the radicals generated during VUV irradiation. Therefore, adopting VUV lamps can enhance the air disinfection capability of air cleaning systems. A previous study [ 4 ] conducted by Huang et al. The result demonstrated that VUV light could be an effective measure for chemical degradation in ventilation systems. When it comes to disinfection, extensive research has been carried out on UVC light and effective destruction of both airborne [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ] and other human pathogens [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] has been shown.
Nevertheless, disinfection using VUV light has attracted very little attention. This would be caused by the relative low prevalence of VUV light sources. Kim et al. Besides, Huang et al. Additionally, some researchers tested the disinfection of water with VUV light and it was reported that the efficiency was quite low compared to disinfection with UVC light [ 31 , 32 ].
The reason is due to the low penetration power of VUV light in water [ 33 ]. Moreover, the disinfection of human pathogens by VUV light was rarely reported.
In our opinion, only Christofi et al. Therefore, the effect of VUV light against human pathogens is yet to be elucidated. Influenza viruses and MTB are inherent airborne pathogens while E. Some suspensions of these bacteria and viruses were absorbed into nitrocellulose filter papers during the experiments and the disinfection under the environment with a moderate barrier to light was evaluated.
To evaluate the biocidal effect of VUV light, bacteria and viruses were irradiated with a pair of hot cathode low pressure mercury vapor lamps. To reduce the leakage of UV light and lamp-generated ozone to the surrounding, the lamps and the microorganisms under test were contained in a metal chamber during the experiments as shown in Fig.
Extended Spectrum Beta-Lactamase-producing E. The concentration of the bacterial suspension was then visually adjusted to McFarland standard 0. Test suspension was prepared by diluting the 0. Actual bacterial count was calculated by back titration of the inoculum suspension.
Mycobacterial colonies were resuspended into glass-bead Phospate-Buffered Saline with 0. Two test suspensions were prepared, which were 0. Actual MTB count was calculated by back titration of the inoculum suspension on Middlebrook 7H11 agar. Purity of MTB was checked by culturing the inoculums on blood agar to ensure no fungal and bacterial contamination, and on non-selective Middlebrook 7H11 agar to ensure there was no contamination by nontuberculous mycobacteria.
H3N2, a seasonal flu in Hong Kong, was generously provided by Prof. Virus-infected cells were harvested when almost all MDCK cells exhibited cytopathic effects. Infected cells and the conditioned media underwent one freeze-thaw cycle to release viral particles. This distance was selected based on the consideration of the time of disinfection and temperature rise of the agar during the course of experiments.
The resultant CFU in each test suspension reflected the viable bacterial count after different disinfection durations.
The disinfection assay was carried out in triplicate for each bacterial strain. Bacterial inoculum without VUV illumination was used as MTB growth control and to determine the original viable bacterial count. Each test set was conducted in triplicate. The end point of cytopathic effects CPE as small, round and degeneration was recorded. Each test was conducted in triplicate.
MS Excel was used in all calculations and graph generation. A spreadsheet file containing raw data and intermediate calculations is provided in as a supplementary information file. Initial inoculum sizes for E. The results suggested that VUV light disinfection is much more effective against lower E. VUV light disinfection against E. Both fold a and fold b diluted 0. Initial bacterial counts of ESBL for fold diluted and fold diluted 0.
It was observed that after min disinfection, both fold diluted and fold diluted 0. However, at min of disinfection time, although, the device was able to produce at least 6-log10 reduction of bacterial growth for the fold diluted inoculum, VUV light was only able to produce a borderline to insufficient bactericidal effect for the fold diluted 0.
The test only demonstrated an average of 2. Initial bacterial counts of MRSA for fold diluted and fold diluted 0. As defined in previous sections, disinfection time against bacteria was considered sufficient when a minimum 3-log10 reduction of viable bacterial count was observed. For mycobactericidal activity, a 5-log10 reduction in viable bacterial load is required due to the highly infectious nature of MTB. In other words, a minimum of 5-log10 viable bacterial load would be required for a valid experimental set.
The average bacterial concentration for McFarland standard 0. The bacterial load could be too low and it was incapable of illustrating 5-log10 growth reduction. The experiment was therefore conducted with a higher bacterial concentration and more detailed disinfection time as compared to the tests of other bacteria. Initial bacterial counts for 0. Gradual reduction in bacterial count was observed with prolonged VUV disinfection time. The experimental sets were conducted on 0.
Previous studies [ 19 , 35 , 36 ] showed that mycobacterial species are generally more resistant to UV disinfection, but are subject to a better disinfection effect under VUV light. Meanwhile for viral disinfection, test results were considered acceptable when the viral-induced cytotoxic effect is indistinguishable from test agent-induced cytotoxic effects.
VUV light disinfection time against viruses would be considered sufficient when a minimum of 3-log10 reduction in viral-induced cytotoxicity in titer was achieved.
To determine the disinfection efficacy of VUV light against seasonal influenza viruses, two common influenza A viruses, H3N2 and H1N1, causing seasonal epidemics were used. High-energy vacuum-UV light is efficient in disinfection.
Similar to other UV disinfection mechanisms, direct illumination of VUV could result in the formation of new bonds between adjacent nucleotides, causing photochemical damage on DNA strands and eventually inactivating the replication of microorganisms.
In addition, the high-energy VUV could also lead to the formation of both OH radicals and O 3 , which diffuse into anywhere that is shielded from direct UV irradiation and inhibit the growth of microorganism.
This explained the excellent bactericidal efficiency of VUV light disinfection even in the presence of the opaque nitrocellulose filter. Our result has further revealed the potential of VUV light to provide a thorough disinfection, even for dust particles and large aerosols contaminated with pathogens where direct UV illumination cannot penetrate.
This is insufficient according to our 5-log10 reduction criterion for mycobacterial disinfection. This is concordant to previous studies [ 19 , 35 , 36 ] where mycobacterial species were generally more resistant to UV disinfection.
This is probably accounted by the thicker lipid cell wall in Mycobacterium species. The tested variations in concentrations of bacteria did not manifest a trend in the rate of inactivation.
For E. Experiments with MTB showed a different trend. Nevertheless, no obvious trend was showed in the experiments with MRSA. From literature, various research teams reported the UV dosages required attaining Most of their experiments were conducted with bacteria and viruses virtually unprotected.
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