Comparative inactivation of adenovirus serotypes by UV light disinfection

The results of this study confirm that adenoviruses are the most resistant enteric viruses to inactivation by UV light and that adenovirus 40 appears to be the most resistant. The effect of freeze-thawing and storage in water may affect the sensitivity of some adenoviruses to inactivation by UV light.     

Molecular indications of protein damage in adenoviruses after UV disinfection

Adenoviruses are resistant to monochromatic, low-pressure (LP) UV disinfection--but have been shown to be susceptible to inactivation by polychromatic, medium-pressure (MP) UV--when assayed using cell culture infectivity. One possible explanation for the difference between UV lamp types is that the additional UV wavelengths emitted by MP UV enable it to cause greater damage to viral proteins than LP UV. The objective of this study was to examine protein damage in adenoviruses treated with LP and MP UV. Results show that MP UV is more effective at damaging viral proteins at high UV doses, though LP UV caused some damage as well. To our knowledge, this study is the first to investigate protein damage in UV-treated adenovirus, and the overview presented here is expected to provide a basis for further, more detailed work.     

Inactivation of Feline Calicivirus and Adenovirus Type 40 by UV Radiation

Little information regarding the effectiveness of UV radiation on the inactivation of caliciviruses and enteric adenoviruses is available. Analysis of human calicivirus resistance to disinfectants is hampered by the lack of animal or cell culture methods that can determine the viruses' infectivity. The inactivation kinetics of enteric adenovirus type 40 (AD40), coliphage MS-2, and feline calicivirus (FCV), closely related to the human caliciviruses based on nucleic acid organization and capsid architecture, were determined after exposure to low-pressure UV radiation in buffered demand-free (BDF) water at room temperature. In addition, UV disinfection experiments were also carried out in treated groundwater with FCV and AD40. AD40 was more resistant than either FCV or coliphage MS-2 in both BDF water and groundwater. The doses of UV required to achieve 99% inactivation of AD40, coliphage MS-2, and FCV in BDF water were 109, 55, and 16 mJ/cm², respectively. The doses of UV required to achieve 99% inactivation of AD40, coliphage MS-2, and FCV in groundwater were slightly lower than those in BDF water. FCV was inactivated by 99% by 13 mJ/cm² in treated groundwater. A dose of 103 mJ/cm² was required for 99% inactivation of AD40 in treated groundwater. The results of this study indicate that if FCV is an adequate surrogate for human caliciviruses, then their inactivation by UV radiation is similar to those of other single-stranded RNA enteric viruses, such as poliovirus. In addition, AD40 appears to be more resistant to UV disinfection than previously reported.     

Inactivation of feline calicivirus and adenovirus type 40 by UV radiation

Little information regarding the effectiveness of UV radiation on the inactivation of caliciviruses and enteric adenoviruses is available. Analysis of human calicivirus resistance to disinfectants is hampered by the lack of animal or cell culture methods that can determine the viruses' infectivity. The inactivation kinetics of enteric adenovirus type 40 (AD40), coliphage MS-2, and feline calicivirus (FCV), closely related to the human caliciviruses based on nucleic acid organization and capsid architecture, were determined after exposure to low-pressure UV radiation in buffered demand-free (BDF) water at room temperature. In addition, UV disinfection experiments were also carried out in treated groundwater with FCV and AD40. AD40 was more resistant than either FCV or coliphage MS-2 in both BDF water and groundwater. The doses of UV required to achieve 99% inactivation of AD40, coliphage MS-2, and FCV in BDF water were 109, 55, and 16 mJ/cm(2), respectively. The doses of UV required to achieve 99% inactivation of AD40, coliphage MS-2, and FCV in groundwater were slightly lower than those in BDF water. FCV was inactivated by 99% by 13 mJ/cm(2) in treated groundwater. A dose of 103 mJ/cm(2) was required for 99% inactivation of AD40 in treated groundwater. The results of this study indicate that if FCV is an adequate surrogate for human caliciviruses, then their inactivation by UV radiation is similar to those of other single-stranded RNA enteric viruses, such as poliovirus. In addition, AD40 appears to be more resistant to UV disinfection than previously reported.     

Effect of UV Light on Spore Viability and Mosquito Larvicidal Activity of Bacillus sphaericus 1593

UV light from a germicidal lamp rapidly reduced the viability of Bacillus sphaericus 1593 spores, but insecticidal activity was resistant to inactivation by continuous exposure to UV light for 4 h.     

Improving baculovirus resistance to UV inactivation: increased virulence resulting from expression of a DNA repair enzyme

The use of baculoviruses as biological control agents is hampered by their susceptibility to inactivation by ultraviolet (UV) light. In an attempt to reduce UV inactivation, an algal virus pyrimidine dimer-specific glycosylase, cv-PDG, was expressed in the baculovirus Autographa californica M nucleopolyhedrovirus (AcMNPV), and the infectivity of recombinant viruses expressing cv-PDG was measured after exposure to UV light. Expression of cv-PDG resulted in a 3-fold decrease in inactivation of budded virus by UV as measured by plaque assay in Spodoptera frugiperda Sf21 cells. However, occluded viruses expressing cv-PDG were not more resistant to UV inactivation than wild type AcMNPV when fed to either S. frugiperda or Trichoplusia ni neonate larvae. Surprisingly, however, viruses expressing cv-PDG showed a significant decrease in both the dose of occluded virus required for oral lethality and the time required for lethality compared to control virus, but these effects were only seen in S. frugiperda and not in T. ni larvae.     

Assessing the effectiveness of low‐pressure ultraviolet light for inactivating Mycobacterium avium complex (MAC) micro‐organisms

Aims: To assess low‐pressure ultraviolet light (LP‐UV) inactivation kinetics of Mycobacterium avium complex (MAC) strains in a water matrix using collimated beam apparatus. Methods and Results: Strains of M. avium (n = 3) and Mycobacterium intracellulare (n = 2) were exposed to LP‐UV, and log₁₀ inactivation and inactivation kinetics were evaluated. All strains exhibited greater than 4 log₁₀ inactivation at fluences of less than 20 mJ cm^?2. Repair potential was evaluated using one M. avium strain. Light repair was evaluated by simultaneous exposure using visible and LP‐UV irradiation. Dark repair was evaluated by incubating UV‐exposed organisms in the dark for 4 h. The isolate did not exhibit light or dark repair activity. Conclusions: Results indicate that MAC organisms are readily inactivated at UV fluences typically used in drinking water treatment. Differences in activation kinetics were small but statistically significant between some tested isolates. Significance and Impact of the Study: Results provide LP‐UV inactivation kinetics for isolates from the relatively resistant MAC. Although UV inactivation of Mycobaterium species have been reported previously, data collected in this effort are comparable with recent UV inactivation research efforts performed in a similar manner. Data were assessed using a rigorous statistical approach and were useful towards modelling efforts.     

Photoreactivation in airborne Mycobacterium parafortuitum

Photoreactivation was observed in airborne Mycobacterium parafortuitum exposed concurrently to UV radiation (254 nm) and visible light. Photoreactivation rates of airborne cells increased with increasing relative humidity (RH) and decreased with increasing UV dose. Under a constant UV dose with visible light absent, the UV inactivation rate of airborne M. parafortuitum cells decreased by a factor of 4 as RH increased from 40 to 95%; however, under identical conditions with visible light present, the UV inactivation rate of airborne cells decreased only by a factor of 2. When irradiated in the absence of visible light, cellular cyclobutane thymine dimer content of UV-irradiated airborne M. parafortuitum and Serratia marcescens increased in response to RH increases. Results suggest that, unlike in waterborne bacteria, cyclobutane thymine dimers are not the most significant form of UV-induced DNA damage incurred by airborne bacteria and that the distribution of DNA photoproducts incorporated into UV-irradiated airborne cells is a function of RH.     

Assessment of DNA damage and repair in Mycobacterium terrae after exposure to UV irradiation

AIM: Ultraviolet (UV) irradiation for drinking water treatment was examined for inactivation and subsequent dark and photo-repair of Mycobacterium terrae. METHODS AND RESULTS: UV sources tested were low pressure (monochromatic, 254 nm) and medium pressure (polychromatic UV output) Hg lamps. UV exposure resulted in inactivation, and was followed by dark or photo-repair experiments. Inactivation and repair were quantified utilizing a molecular-based endonuclease sensitive site (ESS) assay and conventional colony forming unit (CFU) viability assay. Mycobacterium terrae was more resistant to UV disinfection compared to many other bacteria, with approximately 2-log reduction at a UV fluence of 10 mJ cm(-2) ; similar to UV inactivation of M. tuberculosis. There was no difference in inactivation between monochromatic or polychromatic UV lamps. Mycobacterium terrae did not undergo detectable dark repair. Photo-repair resulted in recovery from inactivation by approximately 0.5-log in less than 30 min for both UV lamp systems. CONCLUSIONS: Mycobacterium terrae is able to photo-repair DNA damage within a short timeframe. The number of pyrimidine dimers induced by UV light were similar for Escherichia coli and M. terrae, however, this similarity did not hold true for viability results. SIGNIFICANCE AND IMPACT OF THE STUDY: There is no practical difference between UV sources for disinfection or prevention of DNA repair for M. terrae. The capability of M. terrae to photo-repair UV damage fairly quickly is important for wastewater treatment applications where disinfected effluent is exposed to sunlight. Finally, molecular based assay results should be evaluated with respect to differences in the nucleic acid content of the test micro-organism.     

Low-pressure UV inactivation and DNA repair potential of Cryptosporidium parvum oocysts.

Because Cryptosporidium parvum oocysts are very resistant to conventional water treatment processes, including chemical disinfection, we determined the kinetics and extent of their inactivation by monochromatic, low-pressure (LP), mercury vapor lamp UV radiation and their subsequent potential for DNA repair of UV damage. A UV collimated-beam apparatus was used to expose suspensions of purified C. parvum oocysts in phosphate-buffered saline, pH 7.3, at 25 degrees C to various doses of monochromatic LP UV. C. parvum infectivity reductions were rapid, approximately first order, and at a dose of 3 mJ/cm(2) (=30 J/m(2)), the reduction reached the cell culture assay detection limit of approximately 3 log(10). At UV doses of 1.2 and 3 mJ/cm(2), the log(10) reductions of C. parvum oocyst infectivity were not significantly different for control oocysts and those exposed to dark or light repair conditions for UV-induced DNA damage. These results indicate that C. parvum oocysts are very sensitive to inactivation by low doses of monochromatic LP UV radiation and that there is no phenotypic evidence of either light or dark repair of UV-induced DNA damage.     

Genetic studies on the yeast Saccharomycopsis lipolytica. Inactivation and mutagenesis

Spontaneous mutants of Saccharomycopsis lipolytica were selected and partially characterized. Several antibiotics and antimetabolites were used for selection of spontaneous resistant mutants from Saccharomycopsis lipolytica. The frequencies of such mutants were mainly arranged between 1 X 10(-7) and 5 X 10(-6) mutants per cell. But one class of glucosamine resistant mutants (GAMRA) occurred more frequently. Among the resistant mutants different types of dominant and recessive resistant mutants could be observed. UV light was used for inactivation of cells and induction of mutants from S. lipolytica. Comparing four haploid strains only small differences were detected in sensitivity to UV light. UV light at a dosage of 135 J/m2 was applied to increase the mutant frequencies in three haploid strains. Besides auxotrophic, temperature sensitive and colony morphology mutants, some new mutant types like small colony forming mutants, red-brown coloured mutants, some new mutant types like small colony forming mutants, red-brown coloured mutants, allylalcohol, glucosamine, 2-deoxyglucose or nystatin resistant mutants, hitherto not described for S. lipolytica, were isolated and partially characterized.     

Inactivation of carotenoid-producing and albino strains of Neurospora crassa by visible light, blacklight, and ultraviolet radiation.

Suspensions of Neurospora crassa conidia were inactivated by blacklight (BL) radiation (300 to 425 nm) in the absence of exogenous photosensitizing compounds. Carotenoid-containing wild-type conidia were less sensitive to BL radiation than albino conidia, showing a dose enhancement factor (DEF) of 1.2 for dose levels resulting in less than 10% survival. The same strains were about equally sensitive to shortwave ultraviolet (UV) inactivation. The kinetics of BL inactivation are similar to those of photodynamic inactivation by visible light in the presence of a photosensitizing dye (methylene blue). Only limited inactivation by visible light in the absence of exogenous photosensitizers was observed. BL and UV inactivations are probably caused by different mechanisms since wild-type conidia are only slightly more resistant to BL radiation (DEF = 1.2 at 1.0% survival) than are conidia from a UV-sensitive strain (upr-1, uvs-3). The BL-induced lethal lesions are probably no cyclobutyl pyrimidine dimers since BL-inactivated Haemophilus influenzae transforming deoxyribonucleic acid is not photoreactivated by N. crassa wild-type enzyme extracts, whereas UV-inactivated transforming deoxyribonucleic acid is photoreactivable with this treatment.     

Inactivation of murine norovirus, feline calicivirus and echovirus 12 as surrogates for human norovirus (NoV) and coliphage (F+) MS2 by ultraviolet light (254 nm) and the effect of cell association on UV inactivation

Aims: To determine inactivation profiles of three human norovirus (NoV) surrogate viruses and coliphage MS2 by ultraviolet (UV) irradiation and the protective effect of cell association on UV inactivation. Methods and Results: The inactivation rate for cell‐free virus or intracellular echovirus 12 was determined by exposure to 254‐nm UV light at fluence up to 100 mJ cm^?2. The infectivity of murine norovirus (MNV), feline calicivirus (FCV) and echovirus 12 was determined by cell culture infectivity in susceptible host cell lines, and MS2 infectivity was plaque assayed on Escherichia coli host cells. The UV fluencies to achieve 4‐log₁₀ inactivation were 25, 29, 30 and 70 (mJ cm^?2) for cell‐free FCV, MNV, echovirus 12 and MS2, respectively. However, a UV fluence of 85 mJ cm^?2 was needed to inactivate intracellular echovirus 12 by 4 log₁₀. Conclusions: Murine norovirus and echoviruses 12 are more conservative surrogates than FCV to predict the UV inactivation response of human NoV. Intracellular echovirus 12 was 2·8‐fold more resistant to UV irradiation than cell‐free one. Significance and Impact of the Study: Variation in UV susceptibilities among NoV surrogate viruses and a likely protective effect of cell association on virus susceptibility to UV irradiation should be considered for effective control of human NoV in water.     

Biofouling control in water by various UVC wavelengths and doses

UV light irradiation is being increasingly applied as a primary process for water disinfection, effectively used for inactivation of suspended (planktonic) cells. In this study, the use of UV irradiation was evaluated as a pretreatment strategy to control biofouling. The objective of this research was to elucidate the relative effectiveness of various targeted UV wavelengths and a polychromatic spectrum on bacterial inactivation and biofilm control. In a model system using Pseudomonas aeruginosa, the inactivation spectra corresponded to the DNA absorption spectra for all wavelengths between 220 and 280 nm, while wavelengths between 254 nm and 270 nm were the most effective for bacterial inactivation. Similar wavelengths of 254-260-270 nm were also more effective for biofilm control in most cases than targeted 239 and 280 nm. In addition, the prevention of biofilm formation by P. aeruginosa with a full polychromatic lamp was UV dose-dependent. It appears that biofilm control is improved when larger UV doses are given, while higher levels of inactivation are obtained when using a full polychromatic MP lamp. However, no significant differences were found between biofilms produced by bacteria that survived UV irradiation and biofilms produced by control bacteria at the same microbial counts. Moreover, the experiments showed that biofilm prevention depends on the post-treatment incubation time and nutrient availability, in addition to targeted wavelengths, UV spectrum and UV dose.     

Analysis of Minimal Functions of Simian Virus 40 III. Evidence for “Host Cell Repair” of Oncogenicity and Infectivity of UV-Irradiated Simian Virus 40

The in vitro transforming capacity of simian virus 40 (SV40) for Syrian hamster cells is highly resistant to inactivation by UV light in comparison to infectivity. In the same cell system, we demonstrated a "host cell repair mechanism" sensitive to caffeine which is, to a large extent, responsible for the high resistance to UV inactivation of the transforming capacity of SV40. The survival of infectivity of UV-irradiated SV40 in CV-1 cells was also sensitive to caffeine, again indicating host cell repair. On the other hand, depression of normal cell DNA synthesis by hydroxyurea during the first 24 h postinfection only modestly reduced, and to a similar extent, the transforming capacity of UV-irradiated and nonirradiated SV40.     

Photoreactivation in Airborne Mycobacterium parafortuitum

Photoreactivation was observed in airborne Mycobacterium parafortuitum exposed concurrently to UV radiation (254 nm) and visible light. Photoreactivation rates of airborne cells increased with increasing relative humidity (RH) and decreased with increasing UV dose. Under a constant UV dose with visible light absent, the UV inactivation rate of airborne M. parafortuitum cells decreased by a factor of 4 as RH increased from 40 to 95%; however, under identical conditions with visible light present, the UV inactivation rate of airborne cells decreased only by a factor of 2. When irradiated in the absence of visible light, cellular cyclobutane thymine dimer content of UV-irradiated airborne M. parafortuitum and Serratia marcescens increased in response to RH increases. Results suggest that, unlike in waterborne bacteria, cyclobutane thymine dimers are not the most significant form of UV-induced DNA damage incurred by airborne bacteria and that the distribution of DNA photoproducts incorporated into UV-irradiated airborne cells is a function of RH.     

Inactivation of adenovirus and simian virus 40 tumorigenicity in hamsters by vaccine processing methods

The effectiveness of the adenovirus vaccine inactivation process in destroying the tumorigenic potential for hamsters of adenoviruses, simian virus 40 (SV-40), and adenovirus-SV-40 hybrids was studied. Baby hamsters injected with untreated virus and with samples subjected to the complete inactivation process and to portions of the process were observed for tumor development for periods in excess of 300 days. Over 20,000 hamsters were injected. From 1 to 7 hr of exposure to formaldehyde at a concentration of 0.031 m at 37 C was sufficient to destroy the tumorigenicity observed in the nontreated preparations. Since the inactivation process included 48 hr of exposure at 37 C to 0.031 m formaldehyde plus treatment with ultraviolet (UV) and with beta-propiolactone (BPL), it was concluded that the process has a large margin of safety. Adenovirus isolates free from tumorigenic potential are difficult, if not impossible, to obtain. Therefore, a proven inactivation process appears to provide the best assurance for obtaining adenovirus vaccines free from such potential. Data presented suggest that the tumorigenic property of the viruses studied might be independent of the infectivity of the preparation. The tumorigenic property was found to be highly susceptible to formaldehyde, but less sensitive to BPL or UV treatment. In contrast, treatment with UV or BPL decreased viral infectivity more readily than tumorigenicity. The three-stage inactivation process (formaldehyde, UV, and BPL) inactivated both tumorigenicity and infectivity.     

Interactions between humic matter and bacteria when disinfecting water with UV light

Aims:  To investigate the impact of aquatic humic matter on the inactivation of Escherichia coli and Bacillus subtilis by ultraviolet (UV) light.
Methods and Results:  A bench-scale study investigated the potential for Aldrich^® humic acid (AHA) and Suwannee River natural organic matter (SR-NOM) to coat the surface of E. coli and B. subtilis and offer protection from low-pressure UV light. UV doses of 5 and 14 mJ cm⁻² were applied using a collimated beam at four concentrations of humic matter (0, 10, 50 and 120 mg l⁻¹) in reagent grade water. Both AHA and SR-NOM were found to offer statistically significant protection of both E. coli and B. subtilis at concentrations of 50 and 120 mg l⁻¹ for a UV dose of 14 mJ cm⁻².
Conclusions:  Both E. coli and B. subtilis are susceptible to coating by humic matter which can reduce the sensitivity of the cells to UV light.
Significance and impact of the study:  Micro-organisms in the environment may acquire characteristics through interaction with humic matter that render them more resistant to UV disinfection than would be predicted based on laboratory inactivation studies using clean cells.     

Ultraviolet Inactivation Dichroic Ratio of Oriented fd Bacteriophage

Polarized UV light irradiation of flow-oriented fd bacteriophage indicates that the degree of damage (inactivation) depends on the relative orientation of the light polarization vector and the plane of the DNA bases. The technique of anisotropic UV inactivation was evaluated, and further information on the orientation in this virus was gained. The fd bacteriophage were aligned and irradiated with plane-polarized monochromatic UV light either parallel or perpendicular to the virus axis. Variation of the inactivation dichroic ratio with wavelength implicated virus inactivation by light absorbed in both the DNA and protein. Analysis of the wavelength variation of inactivation dichroic ratios gave molecular dichroic ratios of 0.76 and 1.48 for the DNA and protein components, respectively. On the basis of these anisotropic inactivation studies, the average angle of DNA base tilt in fd was calculated to be 29-32°, a value in agreement with the absorption dichroism studies of Bendet and Mayfield.