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Characterization of Bacillus anthracis persistence in vivo.

Jenkins SA, Xu Y - PLoS ONE (2013)

Bottom Line: Immunofluorescence staining of lung sections showed that spores associated with the alveolar and airway epithelium.We also showed that the anthrax toxins did not play a role in persistence.Together, the results suggest that B. anthracis spores have special properties that promote their persistence in the lung, and that there may be multiple mechanisms contributing to spore persistence.

View Article: PubMed Central - PubMed

Affiliation: Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M Health Science Center, Houston, Texas, USA.

ABSTRACT
Pulmonary exposure to Bacillus anthracis spores initiates inhalational anthrax, a life-threatening infection. It is known that dormant spores can be recovered from the lungs of infected animals months after the initial spore exposure. Consequently, a 60-day course antibiotic treatment is recommended for exposed individuals. However, there has been little information regarding details or mechanisms of spore persistence in vivo. In this study, we investigated spore persistence in a mouse model. The results indicated that weeks after intranasal inoculation with B. anthracis spores, substantial amounts of spores could be recovered from the mouse lung. Moreover, spores of B. anthracis were significantly better at persisting in the lung than spores of a non-pathogenic Bacillus subtilis strain. The majority of B. anthracis spores in the lung were tightly associated with the lung tissue, as they could not be readily removed by lavage. Immunofluorescence staining of lung sections showed that spores associated with the alveolar and airway epithelium. Confocal analysis indicated that some of the spores were inside epithelial cells. This was further confirmed by differential immunofluorescence staining of lung cells harvested from the infected lungs, suggesting that association with lung epithelial cells may provide an advantage to spore persistence in the lung. There was no or very mild inflammation in the infected lungs. Furthermore, spores were present in the lung tissue as single spores rather than in clusters. We also showed that the anthrax toxins did not play a role in persistence. Together, the results suggest that B. anthracis spores have special properties that promote their persistence in the lung, and that there may be multiple mechanisms contributing to spore persistence.

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Related in: MedlinePlus

Bacterial and spore burden in the lungs of mice infected with toxin-deficient B. anthracis mutants.Mice were inoculated i.n. with ∼1.5×107 spores. Lungs were harvested at 2 and 4 weeks post inoculation, homogenized and plated with or without heat treatment. The results were combined from two independent experiments. Closed circles represent total viable bacteria and open circles heat-resistant dormant spores.
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pone-0066177-g009: Bacterial and spore burden in the lungs of mice infected with toxin-deficient B. anthracis mutants.Mice were inoculated i.n. with ∼1.5×107 spores. Lungs were harvested at 2 and 4 weeks post inoculation, homogenized and plated with or without heat treatment. The results were combined from two independent experiments. Closed circles represent total viable bacteria and open circles heat-resistant dormant spores.

Mentions: Minimal inflammation observed in the lung from the H&E stained sections suggested that there was a subdued immune response in the presence of spores. B. anthracis lethal factor (LF) is a Zn2+-dependent metalloprotease that cleaves mitogen-activated protein kinase kinases (MEKs) and plays an important role in suppressing the host immune responses during anthrax infections [20]. We observed a low level of spore germination in the lung during the studies described above. LF was reported to be secreted shortly after spores germinate [21]. We investigated the possibility that LF secreted by the germinated spores suppressed the immune response and contributed to spore persistence in the lung. We compared the persistence of spores from the Sterne strain 7702 with that from the isogenic LF-deficient strain (Δlef) [22] as well as a plasmid-free Sterne strain 9131, which does not produce any anthrax toxins. We did not observe any significant difference in either the total bacteria or the spore counts between the three strains at 2 or 4 weeks post-inoculation (Fig. 9, A and B), indicating that the anthrax toxins do not play a role in the persistence of spores in the mouse lung.


Characterization of Bacillus anthracis persistence in vivo.

Jenkins SA, Xu Y - PLoS ONE (2013)

Bacterial and spore burden in the lungs of mice infected with toxin-deficient B. anthracis mutants.Mice were inoculated i.n. with ∼1.5×107 spores. Lungs were harvested at 2 and 4 weeks post inoculation, homogenized and plated with or without heat treatment. The results were combined from two independent experiments. Closed circles represent total viable bacteria and open circles heat-resistant dormant spores.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672131&req=5

pone-0066177-g009: Bacterial and spore burden in the lungs of mice infected with toxin-deficient B. anthracis mutants.Mice were inoculated i.n. with ∼1.5×107 spores. Lungs were harvested at 2 and 4 weeks post inoculation, homogenized and plated with or without heat treatment. The results were combined from two independent experiments. Closed circles represent total viable bacteria and open circles heat-resistant dormant spores.
Mentions: Minimal inflammation observed in the lung from the H&E stained sections suggested that there was a subdued immune response in the presence of spores. B. anthracis lethal factor (LF) is a Zn2+-dependent metalloprotease that cleaves mitogen-activated protein kinase kinases (MEKs) and plays an important role in suppressing the host immune responses during anthrax infections [20]. We observed a low level of spore germination in the lung during the studies described above. LF was reported to be secreted shortly after spores germinate [21]. We investigated the possibility that LF secreted by the germinated spores suppressed the immune response and contributed to spore persistence in the lung. We compared the persistence of spores from the Sterne strain 7702 with that from the isogenic LF-deficient strain (Δlef) [22] as well as a plasmid-free Sterne strain 9131, which does not produce any anthrax toxins. We did not observe any significant difference in either the total bacteria or the spore counts between the three strains at 2 or 4 weeks post-inoculation (Fig. 9, A and B), indicating that the anthrax toxins do not play a role in the persistence of spores in the mouse lung.

Bottom Line: Immunofluorescence staining of lung sections showed that spores associated with the alveolar and airway epithelium.We also showed that the anthrax toxins did not play a role in persistence.Together, the results suggest that B. anthracis spores have special properties that promote their persistence in the lung, and that there may be multiple mechanisms contributing to spore persistence.

View Article: PubMed Central - PubMed

Affiliation: Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M Health Science Center, Houston, Texas, USA.

ABSTRACT
Pulmonary exposure to Bacillus anthracis spores initiates inhalational anthrax, a life-threatening infection. It is known that dormant spores can be recovered from the lungs of infected animals months after the initial spore exposure. Consequently, a 60-day course antibiotic treatment is recommended for exposed individuals. However, there has been little information regarding details or mechanisms of spore persistence in vivo. In this study, we investigated spore persistence in a mouse model. The results indicated that weeks after intranasal inoculation with B. anthracis spores, substantial amounts of spores could be recovered from the mouse lung. Moreover, spores of B. anthracis were significantly better at persisting in the lung than spores of a non-pathogenic Bacillus subtilis strain. The majority of B. anthracis spores in the lung were tightly associated with the lung tissue, as they could not be readily removed by lavage. Immunofluorescence staining of lung sections showed that spores associated with the alveolar and airway epithelium. Confocal analysis indicated that some of the spores were inside epithelial cells. This was further confirmed by differential immunofluorescence staining of lung cells harvested from the infected lungs, suggesting that association with lung epithelial cells may provide an advantage to spore persistence in the lung. There was no or very mild inflammation in the infected lungs. Furthermore, spores were present in the lung tissue as single spores rather than in clusters. We also showed that the anthrax toxins did not play a role in persistence. Together, the results suggest that B. anthracis spores have special properties that promote their persistence in the lung, and that there may be multiple mechanisms contributing to spore persistence.

Show MeSH
Related in: MedlinePlus