Article

The inactivation and removal of airborne Bacillus atrophaeus endospores from air circulation systems using UVC and HEPA filters

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Abstract

To (i) evaluate the UV radiation in the 'C' band/high efficient particulate air (UVC/HEPA) instrument's potential to inactivate spores of Bacillus atrophaeus and selected Bacillus species and (ii) test whether a titanium dioxide coating inside the cylindrical HEPA filter improves the system's efficacy. Known amounts of dried spore preparations of B. atrophaeus, Bacillus cereus, Bacillus megaterium, Bacillus stearothermophilus and Bacillus thuringiensis were exposed to the UVC lamp within a cylindrical HEPA filter for different time lengths (30 min to 48 h) and with different air flow speeds (0-235 l s(-1)). The log(10) reduction (range 5-16 logs) of colony forming units for spores exposed to the UVC compared with the unexposed spores was significant (P < 0.0001). The addition of a titanium dioxide (TiO(2)) veneer to the interior surface of the HEPA filter significantly increased the inactivation of spores (P < 0.0001). The UVC/HEPA unit could inactivate spores of B. atrophaeus, B. cereus, B. megaterium, B. stearothermophilus and B. thuringiensis. The UVC/HEPA unit represents an effective method of decontaminating circulating air within an air-duct system as found in a building.

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... Due to their small size and ease of use, paper indicator strips containing Bacillus atrophaeus ATCC 9372 (the bacterial strains of B. atrophaeus from American Type Culture Collection, global biological materials resource and standards organization, no 9372) spores were selected for testing. Although the strain is dedicated primarily to assessing the effectiveness of sterilization with dry hot air, it can also be used in the case of sterilization with UVC radiation [20,21]. Bacillus atrophaeus sporulation occurs as a result of the depletion of essential nutrients. ...
... This process results in extremely stress-resistant spores that can be successfully used to assess the effectiveness of sterilization with dry air, ethylene oxide, or microwaves [22]. B. atrophaeus spores were also used to test the effectiveness of the sterilization of air circulation systems with the use of HEPA and UVC filters [20]. Due to non-pathogenicity, ease of breeding, and at the same time, high resistance, B. atrophaeus spores play a fundamental role in monitoring a series of new sterilization and disinfection products [23]. ...
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... In order to improve indoor air quality, air treatment methods can be categorized into two parts Kim et al., 2014); capturing air pollutants by specialized filters, and diluting polluted air with fresh air. Many literature (Chuaybamroong et al., 2010;Gallego et al., 2013;Hyttinen et al., 2007;Iranpour et al., 2005;Luna et al., 2008;Metts and Batterman, 2006;J. H. Park, Yoon and Hwang, 2011;K. ...
... For instance, if we install high efficient air filters (e.g. carbon filter, HEPA H11-13, F7/8 fine-filter, Electro air filter) (Buccolieri et al., 2018;Chuaybamroong et al., 2010;Gallego et al., 2013;Hyttinen et al., 2007;Iranpour et al., 2005;Luna et al., 2008;Metts and Batterman, 2006;J. H. Park et al., 2011;K. ...
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... Several previous studies on microbial inactivation utilized Bacillus thuringiensis (Bt) and B. atrophaeus (also known as BG)] as simulants of B. anthracis (Faille et al., 1999;Beuchat et al., 2005;Rice et al., 2005;Helfinstine et al., 2005;Luna et al., 2008). Therefore, we have tested these two species as challenge aerosols in this investigation. ...
... Freeze-dried BG spores were obtained from the US Army Edgewood Laboratories, Aberdeen Proving Ground, MD). These two simulants are well-characterized as they have been extensively used as simulants of biowarfare agents (Faille et al., 1999;Beuchat et al., 2005;Rice et al., 2005;Helfinstine et al., 2005;Luna et al., 2008). ...
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... Inactivation of viable airborne microorganisms has also been explored in applications related to indoor air quality control. Methods such as germicidal ultraviolet (UV) radiation, ion emission, and thermal treatment have been studied with respect to their biocidal effects against bacterial spores (Luna et al. 2008;Lin and Li (2002); Jung et al. 2009;Grinshpun et al. 2005Grinshpun et al. , 2007Grinshpun et al. , 2010a. ...
... B. atrophaeus (also known as B. subtilis var. niger and B. globigii [BG]) was chosen as the challenge microorganism for this study because it is well-characterized and has been extensively used as a stimulant of biological warfare agents, including B. anthracis (Johnson et al. 1994;Franz et al. 1997;Hill et al. 1999;Helfinstine et al. 2005;Luna et al. 2008). As a genus-level representative, B. atrophaeus has been utilized to evaluate inactivation techniques such as UV radiation (Shafaat and Ponce 2006), plasma sterilization (Muranyi et al. 2007) and thermal sterilization (Kempf et al. 2008). ...
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... Similar to the results of this study, Lin and Li (2002) reported that low UV doses can produce comparable inactivation levels in aerosolized bacterial and fungal spores. The inactivation effect of UV irradiation is expected to increase at a longer treatment time or higher UV irradiance intensity for both species (Chang et al., 1985;Kujundzic et al., 2006;Levetin et al., 2001;Lin and Li, 2002;Luna et al., 2008;Ozcelik, 2007). ...
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... Role of SASP and spore water content in air-dried spore UV resistance to 254-nm UV-C radiation. Because germicidal (254-nm) UV is often used to disinfect dry surfaces and building air (18,31), it was of interest to understand the UV resistance of spores in the air-dried state. In order to extend results from previous studies of spore resistance to 254-nm UV in aqueous suspension, quadruplicate samples of the isogenic air-dried spores were exposed to 254-nm UV-C and spore inactivation kinetics plotted and fitted to exponential best-fit lines (Fig. 1A). ...
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The present study demonstrated the antibacterial effect of photocatalytic oxidation in indoor air using titanium dioxide as the catalyst. Through a series of experiments, it was determined that titanium dioxide did enhance the inactivation rate of the microorganisms under certain conditions. In these experiments the air velocity, relative humidity, and UV (350 nm) intensity were varied. It was found that higher velocities retarded the destruction rate due to the low retention time in the reactor. TiO2 also did not accelerate the reaction at low humidities (30 percent). At a relative humidity of 50 percent, there was complete inactivation of the organisms, bur at higher humidities (85 percent), 10 percent of the organisms were still viable. The experiments showed that at higher UV intensifies, most of the inactivation was done by the UV photons. However, the photons were not able to completely inactivate the microorganisms. In the photocatalysis experiments there was complete inactivation of the bacteria.
Article
Solar ultraviolet (UV) photocatalyzed oxidation of chemicals with titanium dioxide (TiOâ) has received considerable attention. Much less recognized, however, is the ability of the same system to destroy bacteria. This study examined this phenomenon and the conditions that effect it. Bacteria in aqueous solution were given solar exposure with titanium dioxide and their survival with time was detected. Lamps with a predominantly solar ultraviolet spectrum were also used in the experiments. Without exposure to UV light, TiOâ does not affect the bacteria. However, several common bacteria were killed in just a few minutes on solar exposure in the presence of TiOâ. Whereas without TiOâ it took more than an hour to destroy them. A concentration of 0.01 percent TiOâ was most effective in killing bacteria and tenfold concentrations lower or higher were successively less effective. Inorganic and organic compounds in solution, even in small amounts, interfered with the efficiency of killing. An alkaline solution also reduced the bactericidal activity. Circulation and agitation provided by stirring to keep the TiOâ particles suspended reduced the time necessary to kill the bacteria. Time-intensity curves for killing bacteria were the same general shape with or without TiOâ. This suggests that TiOâ served merely as a catalyst to increase the rate of the reaction but that the mechanism of action was not changed. The shape of the curves shows that the organisms are sensitized with a minimum intensity of radiation and that an increase doesn`t greatly increase the rate of the kill. Below this critical intensity, however, the time required for killing markedly increases as the intensity is decreased.
Article
Use of solar radiation for photocatalytic detoxification and disinfection is a very fascinating and fast-developing area. Although scientific research on these processes, especially photocatalytic oxidation, has been conducted for at least the last three decades, the development of industrial/commercial applications, engineering systems and engineering design methodologies have occurred only recently. A number of reactor concepts and designs, including concentrating and non-concentrating types and various methods of catalyst deployment have been developed. Some of these reactors have been used in field demonstrations of groundwater and wastewater remediation. Recent research has been focused on improvements of catalysts to increase the reaction rates, as well as finding new applications of the process. This paper reviews the latest developments of solar detoxification and disinfection including catalyst development, industrial/commercial applications, reactor design and engineering system design methodologies. 80 refs., 20 figs., 3 tabs.
Article
The effectiveness of duct-mounted and console wall-mounted germicidal air cleaning units on the reduction of airborne microbes was determined. Preliminary air samples were collected and airborne bacteria and molds were monitored over time in the retail sales room, processing room, aging cooler and chill cooler of the Auburn Univ. Meat Laboratory. Log10 cfu/m3 bacteria and molds were not reduced by filtration of fresh air in the air duct of the sales room(P > 0.05). After at least 18 h of filtration, 3 or 4 console filtration units operated simultaneously were effective (P ≤ 0.05) at reducing airborne bacteria and molds under controlled conditions in the processing room, aging cooler, and chill cooler. Three console filtration units reduced (P ≤ 0.05) airborne molds under production conditions in the processing room. These data suggest that an electrostatically polarized filter medium combined with scanning UV light is effective in reducing airborne microorganisms in a small processing plant.
Article
The loss of stratospheric ozone and the accompanying increase in solar UV flux have led to concerns regarding decreases in global microbial productivity. Central to understanding this process is determining the types and amounts of DNA damage in microbes caused by solar UV irradiation. While UV irradiation of dormant Bacillus subtilis endospores results mainly in formation of the "spore photoproduct" 5-thyminyl-5,6-dihydrothymine, genetic evidence indicates that an additional DNA photoproduct(s) may be formed in spores exposed to solar UV-B and UV-A radiation (Y. Xue and W. L. Nicholson, Appl. Environ. Microbiol. 62:2221-2227, 1996). We examined the occurrence of double-strand breaks, single-strand breaks, cyclobutane pyrimidine dimers, and apurinic-apyrimidinic sites in spore DNA under several UV irradiation conditions by using enzymatic probes and neutral or alkaline agarose gel electrophoresis. DNA from spores irradiated with artificial 254-nm UV-C radiation accumulated single-strand breaks, double-strand breaks, and cyclobutane pyrimidine dimers, while DNA from spores exposed to artificial UV-B radiation (wavelengths, 290 to 310 nm) accumulated only cyclobutane pyrimidine dimers. DNA from spores exposed to full-spectrum sunlight (UV-B and UV-A radiation) accumulated single-strand breaks, double-strand breaks, and cyclobutane pyrimidine dimers, whereas DNA from spores exposed to sunlight from which the UV-B component had been removed with a filter ("UV-A sunlight") accumulated only single-strand breaks and double-strand breaks. Apurinic-apyrimidinic sites were not detected in spore DNA under any of the irradiation conditions used. Our data indicate that there is a complex spectrum of UV photoproducts in DNA of bacterial spores exposed to solar UV irradiation in the environment.
Article
Recent bioterrorism concerns have prompted renewed efforts towards understanding the biology of bacterial spore resistance to radiation with a special emphasis on the spores of Bacillus anthracis. A review of the literature revealed that B. anthracis Sterne spores may be three to four times more resistant to 254-nm-wavelength UV than are spores of commonly used indicator strains of Bacillus subtilis. To test this notion, B. anthracis Sterne spores were purified and their UV inactivation kinetics were determined in parallel with those of the spores of two indicator strains of B. subtilis, strains WN624 and ATCC 6633. When prepared and assayed under identical conditions, the spores of all three strains exhibited essentially identical UV inactivation kinetics. The data indicate that standard UV treatments that are effective against B. subtilis spores are likely also sufficient to inactivate B. anthracis spores and that the spores of standard B. subtilis strains could reliably be used as a biodosimetry model for the UV inactivation of B. anthracis spores.
Article
Particularly in microbiological laboratories and areas in intensive medical use, regular and thorough disinfection of surfaces is required in order to reduce the numbers of bacteria and to prevent bacterial transmission. The conventional methods of disinfection with wiping are not effective in the longer term, cannot be standardized, are time- and staff-intensive and use aggressive chemicals. Disinfection with hard ultraviolet C (UVC) light is usually not satisfactory, as the depth of penetration is inadequate and there are occupational medicine risks. Photocatalytic oxidation on surfaces coated with titanium dioxide (TiO2) might offer a possible alternative. In the presence of water and oxygen, highly reactive OH-radicals are generated by TiO2 and mild ultraviolet A (UVA). These radicals are able to destroy bacteria, and may therefore be effective in reducing bacterial contamination. Direct irradiation with UVC however can produce areas of shadow in which bacteria are not inactivated. Using targeted light guidance and a light-guiding sheet (out of a UVA-transmittant, Plexiglas, for example), as in the method described in the present study, bacterial inactivation over the entire area is possible. The effectiveness of the method was demonstrated using bacteria relevant to hygiene such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus faecium. For these bacteria, a reduction efficiency (RE) more than 6log10 steps in 60 min was observed. Using Candida albicans, a RE of 2log10 steps in 60 min was seen. Light and scanning electron microscopic examinations suggest that the germ destruction achieved takes place through direct damage to cell walls caused by OH-radicals.
Article
Despite the increasing number of screening tests being introduced, ensuring the inactivation of blood-borne pathogens in blood-derived therapeutic material is a major concern. Dynamic continuous-flow UVC irradiation is a new way to inactivate a large range of pathogens without adding any photosentizers. The efficacy of different methods was evaluated against the following viruses: murine parvovirus MVMp, human B19, the encephalomyocarditis virus (EMC, a picornavirus used as a model for model for hepatitis A virus), and bovine herpes virus type 1 (BHV, a model for enveloped viruses such as hepatitis B virus). We show that continuous-flow UVC irradiation is very effective, particularly against resistant pathogens (e.g. parvoviruses and bacteria) at UVC doses preserving protein activity. It may be applicable to newly emerging related viruses or variants.
Article
The impacts of UV irradiation, gamma irradiation, and a combination of both on Escherichia coli inactivation in primary and secondary wastewater effluents were investigated. UV doses of 35 and 62 J/m(2) were required for a 1-log inactivation of E. coli in the primary and secondary wastewater samples, respectively. A gamma dose of 170 Gy (J/kg) was required for a 1-log inactivation of E. coli in both wastewater samples. Variation in gamma radiation dose rates did not have a significant impact on the extent of inactivation at a given total dose. Gamma irradiation of previously UV-irradiated samples indicated that particle-associated microorganisms, which are protected from UV, can be inactivated by ionizing radiation at a rate similar to that for free microorganism inactivation. An estimation of the energy required for disinfection indicated that, in general, the required energy and the energy cost for E. coli inactivation using ionizing radiation are considerably higher than those for UV radiation.
Article
The ability of solar disinfection (SODIS) and solar photocatalytic (TiO(2)) disinfection (SPC-DIS) batch-process reactors to inactivate waterborne protozoan, fungal and bacterial microbes was evaluated. After 8 h simulated solar exposure (870 W/m(2) in the 300 nm-10 microm range, 200 W/m(2) in the 300-400 nm UV range), both SPC-DIS and SODIS achieved at least a 4 log unit reduction in viability against protozoa (the trophozoite stage of Acanthamoeba polyphaga), fungi (Candida albicans, Fusarium solani) and bacteria (Pseudomonas aeruginosa, Escherichia coli). A reduction of only 1.7 log units was recorded for spores of Bacillus subtilis. Both SODIS and SPC-DIS were ineffective against the cyst stage of A. polyphaga.
Article
The relative disinfection efficiencies of peracetic acid (PAA), hydrogen peroxide (H2O2) and sodium hypochlorite (NaOCl) against Escherichia coli, Enterococcus faecalis, Salmonella enteritidis and coliphage MS2 virus were studied in laboratory-scale experiments. This study also evaluated the efficiency of combined PAA/ultraviolet irradiation (UV) and H2O2/UV treatments to determine if the microbial inactivation was synergistic. Microbial cultures were added into a synthetic wastewater-like test medium and treated by chemical disinfectants with a 10 min contact time, UV irradiation or the combination of chemical and UV treatments. A peracetic acid dose of 3 mg/l resulted in approximately 2-3 log enteric bacterial reductions, whereas 7-15 mg/l PAA was needed to achieve 1-1.5 log coliphage MS2 reductions. Doses of 3-150 mg/l hydrogen peroxide achieved below 0.2 log microbial reductions. Sodium hypochlorite treatments caused 0.3-1 log microbial reductions at an 18 mg/l chlorine dose, while 2.6 log reductions of E. faecalis were achieved at a 12 mg/l chlorine dose. The results indicate that PAA could represent a good alternative to chlorine compounds in disinfection procedures, especially in wastewaters containing easily oxidizable organic matter. Hydrogen peroxide is not an efficient disinfectant against enteric microorganisms in wastewaters. The combined PAA/UV disinfection showed increased disinfection efficiency and synergistic benefits with all the enteric bacteria tested but lower synergies for the coliphage MS2. This suggests that this method could improve the efficiency and reliability of disinfection in wastewater treatment plants. The combined H2O2/UV disinfection only slightly influenced the microbial reductions compared to UV treatments and showed some antagonism and no synergies.
Article
Commercial titanium dental implants are coated with nanostructured TiO2. The aim of the research reported in this paper was to assess whether the TiO2 at the surface of a dental implant is sufficiently photoactive to eradicate bacteria when illuminated with low intensity light. The photoactivity of dental implants was established by studies of the photoenhanced decomposition of Rhodamine B. In vitro studies to establish the influence of irradiating with UV light an implant that is immersed in a solution containing Escherichia Coli were performed. It was demonstrated that under low UV intensity irradiation, 49 microW cm(-2), bacteria are killed at a rate of approximately 650 million per cm2 of implant per minute. The results indicate that illumination of dental implants with UV light may be a suitable treatment for periimplantitis.
Article
TiO(2) photocatalysis with ultraviolet (UV-A) light has proven to be a highly effective process for complete inactivation of airborne microbes. However, the overall efficiency of the technology needs to be improved to make it more attractive as a defense against bio-terrorism. The present research investigates the enhancement in the rate of destruction of bacterial spores on metal (aluminum) and fabric (polyester) substrates with metal (silver)-doped titanium dioxide and compares it to conventional photocatalysis (TiO(2) P25/+UV-A) and UV-A photolysis. Bacillus cereus bacterial spores were used as an index to demonstrate the enhanced disinfection efficiency. The results indicate complete inactivation of B. cereus spores with the enhanced photocatalyst. The enhanced spore destruction rate may be attributed to the highly oxidizing radicals generated by the doped TiO(2).
Article
Bacillus endospores show different kinds of pigmentation. Red-pigmented spores of Bacillus atrophaeus DSM 675, dark-gray spores of B. atrophaeus(T) DSM 7264 and light-gray spores of B. subtilis DSM 5611 were used to study the protective role of the pigments in their resistance to defined ranges of environmental UV radiation. Spores of B. atrophaeus DSM 675 possessing a dark-red pigment were 10 times more resistant to UV-A radiation than those of the other two investigated strains, whereas the responses to the more energetic UV-B and UV-C radiation were identical in all three strains. The methanol fraction of the extracted pigment from the spores absorbs in the associated wavelength area. These results indicate that the carotene-like pigment of spores of B. atrophaeus DSM 675 affects the resistance of spores to environmental UV-A radiation.
Article
To compare the relative sensitivity of Bacillus anthracis and spores of other Bacillus spp. deposited on different solid surfaces to inactivation by liquid chemical disinfecting agents. We prepared under similar conditions spores from five different virulent and three attenuated strains of B. anthracis, as well as spores of Bacillus subtilis, Bacillus atrophaeus (previously known as Bacillus globigii), Bacillus cereus, Bacillus thuringiensis and Bacillus megaterium. As spore-surface interactions may bias inactivation experiments, we evaluated the relative binding of different spores to carrier materials. The survival of spores deposited on glass, metallic or polymeric surfaces were quantitatively measured by ASTM standard method E-2414-05 which recovers spores from surfaces by increasing stringency. The number of spores inactivated by each decontaminant was similar and generally within 1 log among the 12 different Bacillus strains tested. This similarity among Bacillus strains and species was observed through a range of sporicidal efficacy on spores deposited on painted metal, polymeric rubber or glass. The data obtained indicate that the sensitivity of common simulants (B. atrophaeus and B. subtilis), as well as spores of B. cereus, B. thuringiensis, and B. megaterium, to inactivation by products that contain either: peroxide, chlorine or oxidants is similar to that shown by spores from all eight B. anthracis strains studied. The comparative results of the present study suggest that decontamination and sterilization data obtained with simulants can be safely extrapolated to virulent spores of B. anthracis. Thus, valid conclusions on sporicidal efficacy could be drawn from safer and less costly experiments employing non-pathogenic spore simulants.
Engineering of solar photocatalytic detoxification and disinfection processes In Advances in Solar Energy; an Annual Review of Research and Develop-ment ed Photocat-alytic disinfection of indoor air
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V.A. Luna et al. UVC-HEPA removal of Bacillus spores ª 2007 The Authors Goswami, D.Y. (1995) Engineering of solar photocatalytic detoxification and disinfection processes. In Advances in Solar Energy; an Annual Review of Research and Develop-ment ed. Vol. 10. Boer, K.W. pp. 165–209 Boulder, CO: American Solar Energy Society, Inc. Goswami, D.Y., Trivedi, D.M. and Block, S.S. (1997) Photocat-alytic disinfection of indoor air. J Solar Energy Eng 119, 92–96.
Engineering of solar photocatalytic detoxification and disinfection processes In Advances in Solar Energy; an Annual Review of Research and Development ed
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Goswami, D.Y. (1995) Engineering of solar photocatalytic detoxification and disinfection processes. In Advances in Solar Energy; an Annual Review of Research and Development ed. Vol. 10. Boer, K.W. pp. 165–209 Boulder, CO: American Solar Energy Society, Inc.
Air-cleaning system effectiveness for control of airborne microbes in a meat-processing plant
  • C J Cundith
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  • D I Kublers
Cundith, C.J., Kerth, C.R., Hones, W.R., McCaskey, T.A. and Kublers, D.I. (2002) Air-cleaning system effectiveness for control of airborne microbes in a meat-processing plant. J Food Sci 67, 1170-1174.
  • Riley R.L.