RESEARCH ARTICLE
Environmental Persistence of Bacillus anthracis and Bacillus subtilis Spores Joseph P. Wood1*, Kathryn M. Meyer2, Thomas J. Kelly3, Young W. Choi3, James V. Rogers3, Karen B. Riggs3, Zachary J. Willenberg3 1 United States Environmental Protection Agency, Office of Research and Development, National Homeland Security Research Center, Research Triangle Park, North Carolina, United States of America, 2 Oak Ridge Institute for Science and Education, Research Triangle Park, NC, United States of America, 3 Battelle Memorial Institute, Columbus, Ohio, United States of America * [email protected]
Abstract
Published: September 15, 2015
There is a lack of data for how the viability of biological agents may degrade over time in different environments. In this study, experiments were conducted to determine the persistence of Bacillus anthracis and Bacillus subtilis spores on outdoor materials with and without exposure to simulated sunlight, using ultraviolet (UV)-A/B radiation. Spores were inoculated onto glass, wood, concrete, and topsoil and recovered after periods of 2, 14, 28, and 56 days. Recovery and inactivation kinetics for the two species were assessed for each surface material and UV exposure condition. Results suggest that with exposure to UV, decay of spore viability for both Bacillus species occurs in two phases, with an initial rapid decay, followed by a slower inactivation period. The exception was with topsoil, in which there was minimal loss of spore viability in soil over 56 days, with or without UV exposure. The greatest loss in viable spore recovery occurred on glass with UV exposure, with nearly a four log10 reduction after just two days. In most cases, B. subtilis had a slower rate of decay than B. anthracis, although less B. subtilis was recovered initially.
Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
Introduction
OPEN ACCESS Citation: Wood JP, Meyer KM, Kelly TJ, Choi YW, Rogers JV, Riggs KB, et al. (2015) Environmental Persistence of Bacillus anthracis and Bacillus subtilis Spores. PLoS ONE 10(9): e0138083. doi:10.1371/ journal.pone.0138083 Editor: Adam Driks, Loyola University Chicago, UNITED STATES Received: May 4, 2015 Accepted: August 25, 2015
Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: The US EPA funded Battelle Memorial Institute to perform this work via contract GS23F001L-3. Kathryn Meyer was funded as a postdoc through the Oak Ridge Institute for Science and Education. Joseph Wood of the EPA was the sponsor and technical director of the study, and was involved in the study design, data analysis, decision to publish, and preparation of manuscript. Competing Interests: The authors have declared that no competing interests exist.
Following the intentional release of virulent Bacillus anthracis spores via the United States Postal Service in 2001 [1], a need for effective remediation methods has emerged. Inactivation of biological agents through natural attenuation processes may be a potential option for remediation of contaminated outdoor areas following a wide area bioterrorism event, depending on the type of microorganism and environmental conditions. For example, bacterial spores are most resistant to viability decay in the environment, whereas vegetative bacteria are least resistant, and the sensitivity of viruses to environmental conditions is intermediate [2]. Further, since ultraviolet radiation (UV) in sunlight is bactericidal [3], exposure to solar radiation could limit bacterial spore (such as those of B. anthracis) persistence in the environment [4]. However, there is a lack of data and a need for predictive understanding of biological agent viability in different environments [2].
PLOS ONE | DOI:10.1371/journal.pone.0138083 September 15, 2015
1 / 17
Bacillus anthracis Persistence
Historically, most laboratory studies of Bacillus spore photochemistry and resistance mechanisms have used 254 nm UV radiation (UV-C) [5–9], as this wavelength was predominantly tested because of its germicidal properties [10,11]. However, natural solar radiation, or sunlight, is considerably more complex than this monochromatic 254 nm UV wavelength. Solar radiation is a mixture of UV, visible, and infrared radiation, with only those UV wavelengths longer than 290 nm reaching the Earth’s surface [4]. That is, solar UV radiation reaching the Earth’s surface is comprised of both UV-A (380–320 nm) and UV-B (320–290 nm) regions, with no UV-C (95% refractile spores with 95% refractile spores with
Environmental Persistence of Bacillus anthracis and Bacillus subtilis Spores Joseph P. Wood1*, Kathryn M. Meyer2, Thomas J. Kelly3, Young W. Choi3, James V. Rogers3, Karen B. Riggs3, Zachary J. Willenberg3 1 United States Environmental Protection Agency, Office of Research and Development, National Homeland Security Research Center, Research Triangle Park, North Carolina, United States of America, 2 Oak Ridge Institute for Science and Education, Research Triangle Park, NC, United States of America, 3 Battelle Memorial Institute, Columbus, Ohio, United States of America * [email protected]
Abstract
Published: September 15, 2015
There is a lack of data for how the viability of biological agents may degrade over time in different environments. In this study, experiments were conducted to determine the persistence of Bacillus anthracis and Bacillus subtilis spores on outdoor materials with and without exposure to simulated sunlight, using ultraviolet (UV)-A/B radiation. Spores were inoculated onto glass, wood, concrete, and topsoil and recovered after periods of 2, 14, 28, and 56 days. Recovery and inactivation kinetics for the two species were assessed for each surface material and UV exposure condition. Results suggest that with exposure to UV, decay of spore viability for both Bacillus species occurs in two phases, with an initial rapid decay, followed by a slower inactivation period. The exception was with topsoil, in which there was minimal loss of spore viability in soil over 56 days, with or without UV exposure. The greatest loss in viable spore recovery occurred on glass with UV exposure, with nearly a four log10 reduction after just two days. In most cases, B. subtilis had a slower rate of decay than B. anthracis, although less B. subtilis was recovered initially.
Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
Introduction
OPEN ACCESS Citation: Wood JP, Meyer KM, Kelly TJ, Choi YW, Rogers JV, Riggs KB, et al. (2015) Environmental Persistence of Bacillus anthracis and Bacillus subtilis Spores. PLoS ONE 10(9): e0138083. doi:10.1371/ journal.pone.0138083 Editor: Adam Driks, Loyola University Chicago, UNITED STATES Received: May 4, 2015 Accepted: August 25, 2015
Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: The US EPA funded Battelle Memorial Institute to perform this work via contract GS23F001L-3. Kathryn Meyer was funded as a postdoc through the Oak Ridge Institute for Science and Education. Joseph Wood of the EPA was the sponsor and technical director of the study, and was involved in the study design, data analysis, decision to publish, and preparation of manuscript. Competing Interests: The authors have declared that no competing interests exist.
Following the intentional release of virulent Bacillus anthracis spores via the United States Postal Service in 2001 [1], a need for effective remediation methods has emerged. Inactivation of biological agents through natural attenuation processes may be a potential option for remediation of contaminated outdoor areas following a wide area bioterrorism event, depending on the type of microorganism and environmental conditions. For example, bacterial spores are most resistant to viability decay in the environment, whereas vegetative bacteria are least resistant, and the sensitivity of viruses to environmental conditions is intermediate [2]. Further, since ultraviolet radiation (UV) in sunlight is bactericidal [3], exposure to solar radiation could limit bacterial spore (such as those of B. anthracis) persistence in the environment [4]. However, there is a lack of data and a need for predictive understanding of biological agent viability in different environments [2].
PLOS ONE | DOI:10.1371/journal.pone.0138083 September 15, 2015
1 / 17
Bacillus anthracis Persistence
Historically, most laboratory studies of Bacillus spore photochemistry and resistance mechanisms have used 254 nm UV radiation (UV-C) [5–9], as this wavelength was predominantly tested because of its germicidal properties [10,11]. However, natural solar radiation, or sunlight, is considerably more complex than this monochromatic 254 nm UV wavelength. Solar radiation is a mixture of UV, visible, and infrared radiation, with only those UV wavelengths longer than 290 nm reaching the Earth’s surface [4]. That is, solar UV radiation reaching the Earth’s surface is comprised of both UV-A (380–320 nm) and UV-B (320–290 nm) regions, with no UV-C (95% refractile spores with 95% refractile spores with
