Effects of Relative Humidity on the Ultraviolet Induced Inactivation of Airborne Bacteria
TLDR
Cell water sorption and inactivation response was similar for each of the pure cultures tested: when RH exceeded approximately 50%, sorption increased markedly and a sharp concurrent drop in UV-induced inactivation rate was observed.Abstract:
Ultraviolet germicidal irradiation (UVGI) as an engineering control against infectious bioaerosols necessitates a clear understanding of environmental effects on inactivation rates. The response of aerosolized Serratia marcescens, Bacillus subtilis, and Mycobacterium parafortuitum to ultraviolet irradiation was assessed at different relative humidity (RH)levels in a 0.8 m3 completely-mixed chamber. Bioaerosol response was characterized by physical factors including median cell aerodynamic diameter and cell water sorption capacity and by natural decay and UV-induced inactivation rate as determined by direct microscopic counts and standard plate counts. All organisms tested sorbed water from the atmosphere at RH levels between 20% and 95% (up to 70% of dry cell mass at 95% RH); however, no concomitant change in median aerodynamic diameter in this same RH range was observed. Variations in ultraviolet spherical irradiance were minor and not statistically significant in the 20-95% RH range. Cell water sorption...read more
Citations
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Guidelines for preventing the transmission of Mycobacterium tuberculosis in health-care settings, 2005
TL;DR: The threat of MDR TB is decreasing, and the transmission of M. tuberculosis in health-care settings continues to decrease because of implementation of infection-control measures and reductions in community rates of TB.
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Microbiology and atmospheric processes: the role of biological particles in cloud physics
TL;DR: In this article, the potential role of biological particles in atmospheric clouds is discussed, and a short summary of previous laboratory, field and modelling work which investigated the CCN and IN activity of bacterial cells and pollen are also briefly discussed.
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Size-resolved emission rates of airborne bacteria and fungi in an occupied classroom.
Jing Qian,Jing Qian,Denina Hospodsky,Naomichi Yamamoto,Naomichi Yamamoto,William W. Nazaroff,Jordan Peccia +6 more
TL;DR: The first size-resolved, per person emission rate estimates of bacterial and fungal genomes for a common occupied indoor space are presented and suggest that size-dependent aerosol models that use total particles as a surrogate for microbial particles incorrectly assess the fate of and human exposure to airborne bacteria.
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The history of ultraviolet germicidal irradiation for air disinfection.
TL;DR: The history of UVGI for air disinfection is reviewed, starting with its biological basis, moving to its application in the real world, and ending with its current status.
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Effect of Ultraviolet Germicidal Irradiation on Viral Aerosols
Christopher Walker,GwangPyo Ko +1 more
TL;DR: It is confirmed that the UV disinfection rate differs greatly between viral aerosols and viruses suspended in liquid, and there was no significant protective effect of high RH on UV susceptibility of the tested viral aerosol.
References
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TL;DR: Polycarbonate Nuclepore filters are better than cellulose filters for the direct counting of bacteria because they have uniform pore size and a flat surface that retains all of the bacteria on top of the filter.
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TL;DR: Survival was measured as a function of the dose of germicidal UV light for the bacteria Escherichia coli, Salmonella typhi, Shigella sonnei, Streptococcus faecalis, Staphylococcus aureus, and Bacillus subtilis spores, the enteric viruses poliovirus type 1 and simian rotavirus SA11, the cysts of the protozoan Acanthamoeba castellanii, as
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Potassium Iodide as a Chemical Actinometer for 254 nm Radiation: Use of Iodate as an Electron Scavenger
TL;DR: In this paper, a solution of 0.6 M iodide and 0.1 M iodate in 0.01 M borate buffer (pH 9.25) was used as a chemical actinometer to measure the incident fluence from a low-pressure mercury lamp that puts out more than 85% of its energy at 254 nm.