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      An integrated experimental-computational approach for predicting virulence in New Zealand white rabbits and humans following inhalation exposure to Bacillus anthracis spores

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          Abstract

          Inhalation of Bacillus anthracis spores can lead to an anthrax infection that can be fatal. Previously published mathematical models have extrapolated kinetic rates associated with bacterial growth in New Zealand White (NZW) rabbits to humans, but to date, actual measurements of the underlying processes associated with anthrax virulence between species have not been conducted. To address this knowledge gap, we have quantified species-specific rate constants associated with germination, proliferation, and immune cell inactivation of B. anthracis Sterne using an in vitro test platform that includes primary lung epithelial and immune cells. The generated data was then used to develop a physiologically based biokinetic model (PBBK) which quantitatively compares bacterial growth and mean time to death under lethal conditions in rabbits and humans. Simulations based upon our in vitro data and previously published in vivo data from rabbits indicate that disease progression is likely to be faster in humans than in NZW rabbits under comparable total deposited dose conditions. With the computational framework established, PBBK parameters can now be refined using experimental data for lethal B. anthracis strains (e.g. Ames) under identical conditions in future studies. The PBBK model can also be linked to existing aerosol dosimetry models that account for species-specific differences in aerosol deposition patterns to further improve the human health risk assessment of inhalation anthrax.

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          Most cited references15

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          A dynamic approach to predicting bacterial growth in food.

          A new member of the family of growth models described by Baranyi et al. (1993a) is introduced in which the physiological state of the cells is represented by a single variable. The duration of lag is determined by the value of that variable at inoculation and by the post-inoculation environment. When the subculturing procedure is standardized, as occurs in laboratory experiments leading to models, the physiological state of the inoculum is relatively constant and independent of subsequent growth conditions. It is shown that, with cells with the same pre-inoculation history, the product of the lag parameter and the maximum specific growth rate is a simple transformation of the initial physiological state. An important consequence is that it is sufficient to estimate this constant product and to determine how the environmental factors define the specific growth rate without modelling the environment dependence of the lag separately. Assuming that the specific growth rate follows the environmental changes instantaneously, the new model can also describe the bacterial growth in an environment where the factors, such as temperature, pH and aw, change with time.
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            Bacillus anthracis physiology and genetics.

            Bacillus anthracis is a member of the Bacillus cereus group species (also known as the "group 1 bacilli"), a collection of Gram-positive spore-forming soil bacteria that are non-fastidious facultative anaerobes with very similar growth characteristics and natural genetic exchange systems. Despite their close physiology and genetics, the B. cereus group species exhibit certain species-specific phenotypes, some of which are related to pathogenicity. B. anthracis is the etiologic agent of anthrax. Vegetative cells of B. anthracis produce anthrax toxin proteins and a poly-d-glutamic acid capsule during infection of mammalian hosts and when cultured in conditions considered to mimic the host environment. The genes associated with toxin and capsule synthesis are located on the B. anthracis plasmids, pXO1 and pXO2, respectively. Although plasmid content is considered a defining feature of the species, pXO1- and pXO2-like plasmids have been identified in strains that more closely resemble other members of the B. cereus group. The developmental nature of B. anthracis and its pathogenic (mammalian host) and environmental (soil) lifestyles of make it an interesting model for study of niche-specific bacterial gene expression and physiology.
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              The pathology of experimental anthrax in rabbits exposed by inhalation and subcutaneous inoculation.

              Although rhesus monkeys are considered to be an appropriate model for inhalational anthrax in humans, an alternative for vaccine and therapeutic efficacy studies is desirable. This study characterized the pathology of lethal anthrax in rabbits challenged by subcutaneous inoculation and aerosol exposure. New Zealand white rabbits were exposed by subcutaneous inoculation or aerosol to lethal doses of Bacillus anthracis spores. The pathology of anthrax in rabbits exposed by either route was similar, with principal findings occurring in the spleen, lymph nodes, lungs, gastrointestinal tract, and adrenal glands. The cardinal changes were hemorrhage, edema, and necrosis, with bacilli and limited leukocytic infiltration. Features that depended on the route of exposure included mediastinitis in aerosol-exposed rabbits, a primary dermal lesion after subcutaneous inoculation, and differences in the pattern of lymph node involvement. Lesions observed in rabbits were comparable to those of inhalational anthrax in humans and rhesus monkeys. Noteworthy differences included the lack of leukocytic infiltration in brain and meningeal lesions, the relatively mild mediastinal lesions, and a lower incidence of anthrax-related pneumonia in rabbits compared with humans. These differences may be attributed to the greater susceptibility of rabbits to anthrax. Increased susceptibility is associated with both reduced leukocytic response to the bacilli and a more rapid progression to death, which further limits development of leukocytic infiltrates in response to the basic lesions of hemorrhage and necrosis. Primary pneumonic foci of inhalational anthrax, which may be influenced by preexisting pulmonary lesions in humans, were not observed in our rabbits, which were free of preexisting pulmonary disease. Anthrax in rabbits may provide a useful model for evaluating prophylaxis and therapy against inhalational anthrax in humans.
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Project administrationRole: SupervisionRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: SoftwareRole: ValidationRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Writing – original draftRole: Writing – review & editing
                Role: Data curationRole: MethodologyRole: Writing – review & editing
                Role: ConceptualizationRole: Funding acquisitionRole: Investigation
                Role: InvestigationRole: Writing – review & editing
                Role: Conceptualization
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: SoftwareRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: Funding acquisitionRole: InvestigationRole: MethodologyRole: SoftwareRole: SupervisionRole: Writing – original draft
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                1 July 2019
                2019
                : 14
                : 7
                : e0219160
                Affiliations
                [1 ] Chemical and Biological Signature Sciences, Pacific Northwest National Laboratory, Richland, WA, United States of America
                [2 ] Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, United States of America
                Laurentian, CANADA
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                [¤a]

                Current address: USDA-ARS National Animal Disease Center, Ames, IA, United States of America

                [¤b]

                Current address: EMD Serono, Billerica, MA, United States of America

                [¤c]

                Current address: Greek Creek Toxicokinetics Consulting, LLC, Boise, ID, United States of America

                Author information
                http://orcid.org/0000-0003-1093-5478
                Article
                PONE-D-19-03982
                10.1371/journal.pone.0219160
                6602573
                31260462
                0a8aed1f-7184-4e1d-beda-472b70efa798
                © 2019 Hess et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 10 February 2019
                : 12 June 2019
                Page count
                Figures: 8, Tables: 6, Pages: 20
                Funding
                Funded by: funder-id http://dx.doi.org/10.13039/100000180, U.S. Department of Homeland Security;
                Award ID: HSHQPM-14-X-00037
                Award Recipient :
                RC and TS received the funding award. The Department of Homeland Security, Science and Technology Directorate provided funding for this research through contract HSHQPM-14-X-00037 to Pacific Northwest National Laboratory. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the United States Department of Energy under contract DE-AC06-76RLO. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology and Life Sciences
                Microbiology
                Bacteriology
                Bacterial Physiology
                Bacterial Spores
                Biology and Life Sciences
                Microbiology
                Microbial Physiology
                Bacterial Physiology
                Bacterial Spores
                Biology and Life Sciences
                Organisms
                Eukaryota
                Animals
                Vertebrates
                Amniotes
                Mammals
                Leporids
                Rabbits
                Research and Analysis Methods
                Animal Studies
                Experimental Organism Systems
                Animal Models
                Rabbits
                Biology and Life Sciences
                Organisms
                Bacteria
                Bacillus
                Bacillus Anthracis
                Biology and Life Sciences
                Microbiology
                Medical Microbiology
                Microbial Pathogens
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                Medicine and Health Sciences
                Pathology and Laboratory Medicine
                Pathogens
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                Biology and Life Sciences
                Cell Biology
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                Immune Cells
                Biology and Life Sciences
                Immunology
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                Medicine and Health Sciences
                Immunology
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                Pharmaceutics
                Dose Prediction Methods
                Biology and Life Sciences
                Cell Biology
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                Animal Cells
                Epithelial Cells
                Biology and Life Sciences
                Anatomy
                Biological Tissue
                Epithelium
                Epithelial Cells
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                Anatomy
                Biological Tissue
                Epithelium
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                Biology and Life Sciences
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