UV-induced inactivation rates for airborne Mycobacterium bovis BCG

Quantifying the effectiveness of ultraviolet-C light at inactivating airborne Mycobacterium abscessus

BACKGROUND

Mycobacterium abscessus (MABS) group are environmental organisms that can cause infection in people with cystic fibrosis (CF) and other suppurative lung diseases. There is potential for person-to-person airborne transmission of MABS among people with CF attending the same care centre. Ultraviolet light (band C, UV-C) is used for Mycobacterium tuberculosis control indoors; however, no studies have assessed UV-C for airborne MABS.

AIM

To determine whether a range of UV-C doses increased the inactivation of airborne MABS, compared with no-UVC conditions.

METHODS

MABS was generated by a vibrating mesh nebulizer located within a 400 L rotating drum sampler, and then exposed to an array of 265 nm UV-C light-emitting diodes (LED). A six-stage Andersen Cascade Impactor was used to collect aerosols. Standard microbiological protocols were used for enumerating MABS, and these quantified the effectiveness of UV-C doses (in triplicate). UV-C effectiveness was estimated using the difference between inactivation with and without UV-C.

FINDINGS

Sixteen tests were performed, with UV-C doses ranging from 276 to 1104 μW s/cm². Mean (±SD) UV-C effectiveness ranged from 47.1% (±13.4) to 83.6% (±3.3). UV-C led to significantly greater inactivation of MABS (all P-values ≤0.045) than natural decay at all doses assessed. Using an indoor model of the hospital environment, it was estimated that UV-C doses in the range studied here could be safely delivered in clinical settings where patients and staff are present.

CONCLUSION

This study provides empirical in-vitro evidence that nebulized MABS are susceptible to UV-C inactivation.

Estimating the tuberculosis incidence using a SARIMAX-NNARX hybrid model by integrating meteorological factors in Qinghai Province, China

Tuberculosis (TB) is recognized as being a major public health concern owing to its increase in Qinghai, China. In this study, we aimed to estimate the long-term effects of meteorological variables on TB incidence and construct an advanced hybrid model with seasonal autoregressive integrated moving average (SARIMA) and a neural network nonlinear autoregression (SARIMAX-NNARX) by integrating meteorological factors and evaluating the model fitting and prediction effect. During 2005-2017, TB experienced an upward trend with obvious periodic and seasonal characteristics, peaking in spring and winter. The results showed that TB incidence was positively correlated with average relative humidity (ARH) with a 2-month lag (β = 1.889, p = 0.003), but negatively correlated with average atmospheric pressure (AAP) with a 1-month lag (β =  - 1.633, p = 0.012), average temperature (AT) with a 2-month lag (β =  - 0.093, p = 0.027), and average wind speed (AWS) with a 0-month lag (β =  - 13.221, p = 0.033), respectively. The SARIMA (3,1,0)(1,1,1)_12, SARIMAX(3,1,0)(1,1,1)₁₂, and SARIMAX(3,1,0)(1,1,1)₁₂-NNARX(15,3) were considered preferred models based on the evaluation criteria. Of them, the SARIMAX-NNARX technique had smaller error values than the SARIMA and SARIMAX models in both fitting and forecasting aspects. The sensitivity analysis also revealed the robustness of the mixture forecasting model. Therefore, the SARIMAX-NNARX model by integrating meteorological variables can be used as an accurate method for forecasting the epidemic trends which would be great importance for TB prevention and control in the coming periods in Qinghai.

The Effectiveness of Ultraviolet-C (UV-C) Irradiation on the Viability of Airborne Pseudomonas aeruginosa

Pseudomonas aeruginosa (Pa) is the predominant bacterial pathogen in people with cystic fibrosis (CF) and can be transmitted by airborne droplet nuclei. Little is known about the ability of ultraviolet band C (UV-C) irradiation to inactivate Pa at doses and conditions relevant to implementation in indoor clinical settings. We assessed the effectiveness of UV-C (265 nm) at up to seven doses on the decay of nebulized Pa aerosols (clonal Pa strain) under a range of experimental conditions. Experiments were done in a 400 L rotating sampling drum. A six-stage Andersen cascade impactor was used to collect aerosols inside the drum and the particle size distribution was characterized by an optical particle counter. UV-C effectiveness was characterized relative to control tests (no UV-C) of the natural decay of Pa. We performed 112 tests in total across all experimental conditions. The addition of UV-C significantly increased the inactivation of Pa compared with natural decay alone at all but one of the UV-C doses assessed. UV-C doses from 246-1968 µW s/cm² had an estimated effectiveness of approximately 50-90% for airborne Pa. The effectiveness of doses ≥984 µW s/cm² were not significantly different from each other (p-values: 0.365 to ~1), consistent with a flattening of effectiveness at higher doses. Modelling showed that delivering the highest dose associated with significant improvement in effectiveness (984 µW s/cm²) to the upper air of three clinical rooms would lead to lower room doses from 37-49% of the 8 h occupational limit. Our results suggest that UV-C can expedite the inactivation of nebulized airborne Pa under controlled conditions, at levels that can be delivered safely in occupied settings. These findings need corroboration, but UV-C may have potential applications in locations where people with CF congregate, coupled with other indoor and administrative infection control measures.

UV222 disinfection of SARS-CoV-2 in solution

There is an urgent need for evidence-based engineering controls to reduce transmission of SARS-CoV-2, which causes COVID-19. Although ultraviolet (UV) light is known to inactivate coronaviruses, conventional UV lamps contain toxic mercury and emit wavelengths (254 nm) that are more hazardous to humans than krypton chlorine excimer lamps emitting 222 nm (UV222). Here we used culture and molecular assays to provide the first dose response for SARS-CoV-2 solution exposed to UV222. Culture assays (plaque infectivity to Vero host) demonstrated more than 99.99% disinfection of SARS-CoV-2 after a UV222 dose of 8 mJ/cm2 (pseudo-first order rate constant = 0.64 cm2/mJ). Immediately after UV222 treatment, RT-qPCR assays targeting the nucleocapsid (N) gene demonstrated ~ 10% contribution of N gene damage to disinfection kinetics, and an ELISA assay targeting the N protein demonstrated no contribution of N protein damage to disinfection kinetics. Molecular results suggest other gene and protein damage contributed more to disinfection. After 3 days incubation with host cells, RT-qPCR and ELISA kinetics of UV222 treated SARS-CoV-2 were similar to culture kinetics, suggesting validity of using molecular assays to measure UV disinfection without culture. These data provide quantitative disinfection kinetics which can inform implementation of UV222 for preventing transmission of COVID-19.

Evaluation of the Antimicrobial Effect of Graphene Oxide Fiber on Fish Bacteria for Application in Aquaculture Systems

The growing importance of the domestic aquaculture industry has led not only to its continuous development and expansion but also to an increase in the production of wastewater containing pathogenic microorganisms and antibiotic-resistant bacteria. As the existing water purification facilities have a high initial cost of construction, operation, and maintenance, it is necessary to develop an economical solution. Graphene oxide (GO) is a carbon-based nanomaterial that is easy to manufacture, inexpensive and has excellent antimicrobial properties. In this study, the antimicrobial effect of GO polyester fibers on seven species of fish pathogenic bacteria was analyzed to evaluate their effectiveness in water treatment systems and related products. As a result of incubating GO polyester fibers with seven types of fish pathogenic bacteria for 1, 6, and 12 h, there was no antimicrobial effect in Vibrio harveyi, V. scopthalmi, and Edwardsiella tarda. In contrast, GO fibers showed antimicrobial effects of more than 99% against A. hydrophila, S. parauberis, S. iniae, and P. piscicola, suggesting the potential use of GO fibers in water treatment systems.

A Systematic Literature Review of Indoor Air Disinfection Techniques for Airborne Bacterial Respiratory Pathogens

Interrupting the transmission of airborne (<≈5 µm) respiratory pathogens indoors is not a new challenge, but it has attracted unprecedented interest due to the COVID-19 pandemic during 2020–2021. However, bacterial respiratory pathogens with known or potential airborne transmission account for an appreciable proportion of the communicable disease burden globally. We aimed to systematically review quantitative, laboratory-based studies of air disinfection techniques for airborne respiratory bacteria. Three databases (PubMed, Web of Science, Scopus) were searched, following PRISMA guidelines. A total of 9596 articles were identified, of which 517 were assessed in detail and of which 26 met the inclusion and quality assessment criteria. Seven air disinfection techniques, including UV-C light, filtration, and face masks, among others, were applied to 13 different bacterial pathogens. More than 80% of studies suggested that air disinfection techniques were more effective at inactivating or killing bacteria than the comparator or baseline condition. However, it was not possible to compare these techniques because of methodological heterogeneity and the relatively small number of the studies. Laboratory studies are useful for demonstrating proof-of-concept and performance under controlled conditions. However, the generalisability of their findings to person-to-person transmission in real-world settings is unclear for most of the pathogens and techniques we assessed.

The efficacy of vacuum-ultraviolet light disinfection of some common environmental pathogens

Background

This study is to elucidate the disinfection effect of ozone producing low-pressure Hg vapor lamps against human pathogens. Ozone producing low-pressure Hg vapor lamps emit mainly 254 nm ultraviolet light C (UVC) with about 10% power of Vacuum-ultraviolet (VUV) light at 185 nm. The combination of UVC and VUV can inactivate airborne pathogens by disrupting the genetic materials or generation of reactive oxygen species, respectively. In this study, inactivation of common bacteria including Escherichia coli ATCC25922 (E. coli), Extended Spectrum Beta-Lactamase-producing E. coli (ESBL), Methicillin-resistant Staphylococcus aureus (MRSA) and Mycobacterium tuberculosis (MTB), and that of influenza A viruses H1N1 and H3N2 under the radiation from ozone producing low-pressure Hg vapor lamps was examined. Log reduction values at different treatment durations were determined.

Methods

In vitro tests were carried out. Various bacterium and virus suspensions were added onto nitrocellulose filter papers and subjected to the illumination from ozone producing low-pressure Hg vapor lamps. The extents of pathogen inactivation at different illumination times were investigated by conducting a series of experiments with increasing duration of illumination. log10 reduction in CFU/ml and reduction at log10(TCID₅₀) were respectively measured for bacteria and viruses. The disinfection effectiveness of this type of lamps against the pathogens under the environment with a moderate barrier to light was therefore evaluated.

Results

Ozone producing low-pressure Hg vapor lamp successfully inactivated these human pathogens. Nevertheless, among these pathogens, disinfection of MTB required more intense treatment. In the best tested situation, 3-log10 inactivation of pathogens can be achieved with ≤10 min of VUV treatment except MTB which needed about 20 min. This demonstrated the high resistance against UV disinfection of MTB.

Conclusions

Following the criteria that valid germicidal results can be reflected with 3-log10 inactivation for bacteria, 4-log10 inactivation for viruses and 5-log10 inactivation for MTB, most of the bacteria required ≤10 min of VUV treatment, 20 min for the influenza viruses while MTB needed about 30 min VUV treatment. This indicated that VUV light is an effective approach against different environmental microorganisms.

Spatial distribution of tuberculosis and its association with meteorological factors in mainland China

BACKGROUND

The incidence of tuberculosis (TB) remains high worldwide. Current strategies will not eradicate TB by 2035; instead, by 2182 is more likely. Therefore, it is urgent that new risk factors be identified.

METHODS

An ecological study was conducted in 340 prefectures in China from 2005 to 2015. The spatial distribution of TB incidence was shown by clustering and hotspot analysis. The relationship between the distribution patterns and six meteorological factors was evaluated by the geographically weighted regression (GWR) model.

RESULTS

During the 11 years of the study period, TB incidence was persistently low in the east and high in the west. Local coefficients from the GWR model showed a positive correlation between TB incidence and yearly average rainfall (AR) but a negative correlation with other meteorological factors. Average relative humidity (ARH) was negatively correlated with the incidence of TB in all prefectures (p < 0.05).

CONCLUSION

Meteorological factors may play an important role in the prevention and control of TB.

Herbal Extract Incorporated Nanofiber Fabricated by an Electrospinning Technique and its Application to Antimicrobial Air Filtration

Recently, with the increased attention to indoor air quality, antimicrobial air filtration techniques have been studied widely to inactivate hazardous airborne microorganisms effectively. In this study, we demonstrate herbal extract incorporated (HEI) nanofibers synthesized by an electrospinning technique and their application to antimicrobial air filtration. As an antimicrobial herbal material, an ethanolic extract of Sophora flavescens, which exhibits great antibacterial activity against pathogens, was mixed with the polymer solution for the electrospinning process. We measured various characteristics of the synthesized HEI nanofibers, such as fiber morphology, fiber size distribution, and thermal stability. For application of the electrospun HEI nanofibers, we made highly effective air filters with 99.99% filtration efficiency and 99.98% antimicrobial activity against Staphylococcus epidermidis. The pressure drop across the HEI nanofiber air filter was 4.75 mmH2O at a face air velocity of 1.79 cm/s. These results will facilitate the implementation of electrospun HEI nanofiber techniques to control air quality and protect against hazardous airborne microorganisms.

Synthesis of hybrid carbon nanotube structures coated with Sophora flavescens nanoparticles and their application to antimicrobial air filtration

Controlling airborne microorganisms has become increasingly important with increase in human indoor activities, epidemic disease outbreaks, and airborne pathogen transmission. Treatments using antimicrobial nanoparticles have shown promise because of the high surface-to-volume ratio of nanoparticles compared to their bulk counterparts, and their unique physical and chemical properties. In this study, hybrid nanostructures of multi-walled carbon nanotubes (MWCNTs) coated with antimicrobial, natural product (NP) nanoparticles were synthesized using a twin-head electrospray system (THES). The coated nanoparticles were then used in antimicrobial air filters to increase their antimicrobial efficiency. Electrosprayed droplets were converted to NP nanoparticles and MWCNTs through ethanol evaporation. Oppositely charged NP nanoparticles and MWCNTs were coagulated via Coulombic collisions to form hybrid nanoparticles that were deposited continuously onto an air filter medium. The size distribution and composition of the hybrid NP/MWCNT particles were characterized using a wide-range particle spectrometer (WPS) and transmission electron microscope (TEM). The concentration of hybrid NP/MWCNT nanoparticles was lower than that of NP nanoparticles but higher than that of MWCNTs and showed a bimodal size distribution with peak diameters of 21.1 and 49 nm. TEM analyses confirmed that the NP nanoparticles were attached to the MWCNT surface with a density of ~4-9 particles/MWCNT. When deposited onto the filter medium, NP/MWCNT particles formed dendrites on the filter׳s fiber surface. The filtration efficiency and pressure drop of the NP/MWCNT-coated filters were higher than those of pristine, NP nanoparticles-coated or MWCNTs-coated filters. The hybrid filter also exhibited stronger antimicrobial activity than those of NP or MWCNT-coated filters at identical deposited volumes (1.1×10-2 cm3/cm2 filter). Ninety-five percent of the tested bacterial aerosols were inactivated on the NP/MWCNTs filter while only <70% were inactivated on NP- or MWCNT-coated filters.

Antimicrobial Air Filters Using Natural Euscaphis japonica Nanoparticles

Controlling bioaerosols has become more important with increasing participation in indoor activities. Treatments using natural-product nanomaterials are a promising technique because of their relatively low toxicity compared to inorganic nanomaterials such as silver nanoparticles or carbon nanotubes. In this study, antimicrobial filters were fabricated from natural Euscaphis japonica nanoparticles, which were produced by nebulizing E. japonica extract. The coated filters were assessed in terms of pressure drop, antimicrobial activity, filtration efficiency, major chemical components, and cytotoxicity. Pressure drop and antimicrobial activity increased as a function of nanoparticle deposition time (590, 855, and 1150 µg/cm2(filter) at 3-, 6-, and 9-min depositions, respectively). In filter tests, the antimicrobial efficacy was greater against Staphylococcus epidermidis than Micrococcus luteus; ~61, ~73, and ~82% of M. luteus cells were inactivated on filters that had been coated for 3, 6, and 9 min, respectively, while the corresponding values were ~78, ~88, and ~94% with S. epidermidis. Although statistically significant differences in filtration performance were not observed between samples as a function of deposition time, the average filtration efficacy was slightly higher for S. epidermidis aerosols (~97%) than for M. luteus aerosols (~95%). High-performance liquid chromatography (HPLC) and electrospray ionization-tandem mass spectrometry (ESI/MS) analyses confirmed that the major chemical compounds in the E. japonica extract were 1(ß)-O-galloyl pedunculagin, quercetin-3-O-glucuronide, and kaempferol-3-O-glucoside. In vitro cytotoxicity and disk diffusion tests showed that E. japonica nanoparticles were less toxic and exhibited stronger antimicrobial activity toward some bacterial strains than a reference soluble nickel compound, which is classified as a human carcinogen. This study provides valuable information for the development of a bioaerosol control system that is environmental friendly and suitable for use in indoor environments.

Antimicrobial durability of air filters coated with airborne Sophora flavescens nanoparticles

Airborne biological particles containing viruses, bacteria, and/or fungi can be toxic and cause infections and allergy symptoms. Recently, natural materials such as tea tree oil and Sophora flavescens have shown promising antimicrobial activity when applied as air filter media. Although many of these studies demonstrated excellent antimicrobial efficacy, only a few of them considered external environmental effects such as the surrounding humidity, temperature, and natural degradation of chemicals, all of which can affect the antimicrobial performance of these natural materials. In this study, we investigated the antimicrobial durability of air filters containing airborne nanoparticles from S. flavescens for 5 months. Antimicrobial tests and quantitative chemical analyses were performed every 30 days. Morphological changes in the nanoparticles were also evaluated by scanning electron microscopy. The major antimicrobial compounds remained stable and active for ~90 days at room temperature. After about 90 days, the quantities of major antimicrobial compounds decreased noticeably with a consequent decrease in antimicrobial activity. These results are promising for the implementation of new technologies using natural antimicrobial products and provide useful information regarding the average life expectancy of antimicrobial filters using nanoparticles of S. flavescens.

Effects of ultraviolet germicidal irradiation and swirling motion on airborne Staphylococcus aureus, Pseudomonas aeruginosa and Legionella pneumophila under various relative humidities

Staphylococcus aureus, Pseudomonas aeruginosa, and Legionella pneumophila have been detected in indoor air and linked to human infection. It is essential to adopt control methods to inactivate airborne pathogens. By passing bioaerosols horizontally into a UV device at two flow rates (Qs) and moving cells around a central UVC lamp at relative humidity (RH) of 12.7-16.7%, 58.7-59.6%, and 87.3-90%, the effects of swirling motion and 254-nm ultraviolet germicidal irradiation (UVGI) against bioaerosols were assessed under UV-off and UV-on settings, respectively. An inverse relationship between RH and UVGI effectiveness was observed for every test bioaerosol (r = -0.74 ∼ -0.81, P < 0.0001). Increased UV resistance with RH is likely associated with the hygroscopicity of bioaerosols, evident by increased aerodynamic diameters at high RH (P < 0.05). UVGI effectiveness was significantly increased with decreasing Q (P < 0.0001). Moreover, P. aeruginosa was the most susceptible to UVGI, while the greatest UV resistance occurred in L. pneumophila at low RH and S. aureus at medium and high RH (P < 0.05). Results of UV off show P. aeruginosa and L. pneumophila were more sensitive to air-swirling motion than S. aureus (P < 0.05). Overall, test bioaerosols were reduced by 1.7-4.9 and 0.2-1.7 log units because of the UVGI and swirling movement, respectively.

PRACTICAL IMPLICATIONS

The studied UV device, with a combination of swirling motion and UVGI, is effective to inactivate airborne S. aureus, P. aeruginosa, and L. pneumophila. This study also explores the factors governing the UVGI and swirling motion against infectious bioaerosols. With understanding the environmental and operational parameters, the studied UV device has the potential to be installed indoors where people are simultaneously present, for example, hospital wards and nursing homes, to prevent the humans from acquiring infectious diseases.

Short-term effect of humid airflow on antimicrobial air filters using Sophora flavescens nanoparticles

Bioaerosols have received social and scientific attention because they can be hazardous to human health. Recently, antimicrobial treatments using natural products have been used to improve indoor air quality (IAQ) since they are typically less toxic to humans compared to other antimicrobial substances such as silver, carbon nanotubes, and metal oxides. Few studies, however, have examined how environmental conditions such as the relative humidity (RH), surrounding temperature, and retention time of bacteria on filters affect the filtration and antimicrobial characteristics of a filter treated with such natural products. In this study, we investigated changes in the morphology of the natural nanoparticles, pressure drop, filtration efficiency, and the inactivation rate caused by the short-term effect of humid airflow on antimicrobial fiber filters. Nanoparticles of Sophora flavescens were deposited on the filter media surface using an aerosol process. We observed coalescence and morphological changes of the nanoparticles on fiber filters under humid conditions of an RH >50%. The level of coalescence in these nanoparticles increased with increasing RH. Filters exposed to an RH of 25% have a higher pressure drop than those exposed to an RH >50%. In an inactivation test against Staphylococcus epidermidis bacterial aerosol, the inactivation efficiency at an RH of 25% was higher than that at an RH of 57% or 82%. To effectively apply antimicrobial filters using natural products in the environment, one must characterize the filters under various environmental conditions. Thus, this study provides important information on the use of antimicrobial filters made of natural products.

Effect of hybrid UV-thermal energy stimuli on inactivation of S. epidermidis and B. subtilis bacterial bioaerosols

Bioaerosols have become an increasingly important issue due to their harmful effects on human health. As the concern over airborne microorganisms grows, so does the need to develop and study efficient methods of controlling them. In this study, we designed a hybrid system involving ultraviolet (UV) irradiation and thermal energy and investigated its effects on bacterial bioaerosols, followed by a comparison with thermal energy alone and UV irradiation alone. The results show that the hybrid effect caused no variation in the shape of the normalized particle size distributions of S. epidermidis and B. subtilis bioaerosols. However, a physical transport loss of bacterial bioaerosols developed as the temperature inside the glass quartz tube increased. When bacterial bioaerosols were simultaneously exposed to UV irradiation and thermal energy for less than 1.05 s, more than 99% of S. epidermidis bioaerosols were inactivated at 120 °C with exposure to one UV lamp and at 80 °C with exposure to two UV lamps; and 93.5% and 98.5% of B. subtilis bioaerosols were inactivated at 280 °C with exposure to one and two UV lamps, respectively. Moreover, the hybrid UV-thermal stimuli significantly reduced the concentration of ozone, which is a secondary UV-induced pollutant. Our results show that to obtain the same inactivation efficiency, the hybrid UV-thermal stimuli were more efficient than thermal energy alone in terms of energy consumption and produced significantly less ozone than UV irradiation alone. The hybrid stimuli also had higher inactivation efficiency than UV alone. Therefore, these results provide valuable information for the development of new methods for controlling bioaerosols.

DNA repair systems and the pathogenesis of Mycobacterium tuberculosis: varying activities at different stages of infection

Mycobacteria, including most of all MTB (Mycobacterium tuberculosis), cause pathogenic infections in humans and, during the infectious process, are exposed to a range of environmental insults, including the host's immune response. From the moment MTB is exhaled by infected individuals, through an active and latent phase in the body of the new host, until the time they reach the reactivation stage, MTB is exposed to many types of DNA-damaging agents. Like all cellular organisms, MTB has efficient DNA repair systems, and these are believed to play essential roles in mycobacterial pathogenesis. As different stages of infection have great variation in the conditions in which mycobacteria reside, it is possible that different repair systems are essential for progression to specific phases of infection. MTB possesses homologues of DNA repair systems that are found widely in other species of bacteria, such as nucleotide excision repair, base excision repair and repair by homologous recombination. MTB also possesses a system for non-homologous end-joining of DNA breaks, which appears to be widespread in prokaryotes, although its presence is sporadic within different species within a genus. However, MTB does not possess homologues of the typical mismatch repair system that is found in most bacteria. Recent studies have demonstrated that DNA repair genes are expressed differentially at each stage of infection. In the present review, we focus on different DNA repair systems from mycobacteria and identify questions that remain in our understanding of how these systems have an impact upon the infection processes of these important pathogens.

Effect of ultraviolet germicidal irradiation on viral aerosols

Ultraviolet (UV) germicidal air disinfection is an engineering method used to control the airborne transmission of pathogenic microorganisms in high-risk settings. Despite the recent emergence of respiratory viral pathogens such as SARS and avian influenza viruses, UV disinfection of pathogenic viral aerosols has not been examined. Hence, we characterized the UV disinfection of viral aerosols using the bacteriophage MS2, adenovirus, and coronavirus. Our objectives were to characterize the effect of nebulization and air sampling on the survival of important viral pathogens, quantitatively characterize and estimate the UV susceptibility of pathogenic viral aerosols, and evaluate the effect of relative humidity (RH) on the susceptibility of viral aerosols, to 254 nm UV-C. The viruses were aerosolized into an experimental chamber using a six-jet Collison nebulizer, exposed to 254 nm UV, and sampled using an AGI-30 liquid impinger. Both the MS2 and adenovirus aerosols were very resistant to UV air disinfection, with a reduction of less than 1 logarithm in viable viral aerosols at a UV dose of 2608 microW s/cm2. The susceptibility of coronavirus aerosols was 7-10 times that of the MS2 and adenovirus aerosols. Unlike bacterial aerosols, there was no significant protective effect of high RH on UV susceptibility of the tested viral aerosols. We confirmed that the UV disinfection rate differs greatly between viral aerosols and viruses suspended in liquid.

UV light inactivation of Mycobacterium avium subsp. paratuberculosis in milk as assessed by FASTPlaqueTB phage assay and culture

UV light inactivation of Mycobacterium avium subsp. paratuberculosis in Middlebrook 7H9 broth and whole and semiskim milk was investigated using a laboratory-scale UV machine that incorporated static mixers within UV-penetrable pipes. UV treatment proved to be less effective in killing M. avium subsp. paratuberculosis suspended in milk (0.5- to 1.0-log(10) reduction per 1,000 mJ/ml) than that suspended in Middlebrook 7H9 broth (2.5- to 3.3-log(10) reduction per 1,000 mJ/ml). The FASTPlaqueTB phage assay provided more rapid enumeration of surviving M. avium subsp. paratuberculosis (within 24 h) than culture on Herrold's egg yolk medium (6 to 8 weeks). Despite the fact that plaque counts were consistently 1 to 2 log(10) lower than colony counts throughout the study, UV inactivation rates for M. avium subsp. paratuberculosis derived using the phage assay and culture results were not significantly different (P = 0.077).

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.