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Analysis of epidermal entry in experimental cutaneous Bacillus anthracis infections in mice
Beth L Hahn1, Sonia Sharma, Peter G Sohnle
1Division of Infectious Diseases, Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
Abstract:
Cutaneous infection is the most common form of human anthrax, but little is known of Bacillus anthracis-epidermal interactions. To study the latter, we used experimental inoculations of B. anthracis Sterne spores onto mouse flank skin. In DBA/2 mice (a sensitive strain) 10(7) spores injected intradermally or applied under occlusive dressings to abraded skin produced ipsilateral inguinal edema and rapid death. Epicutaneous application to shaved-only skin produced edema and death in most animals, but at longer times. Mortality after inoculation onto abraded skin was less in C57BL/6 mice (a relatively resistant strain). Inoculations onto shaved-only skin immunized C57BL/6 mice, and they survived later intradermal spore injections. Histology revealed massive organism proliferation in remaining epidermis and hair follicles of inoculated abraded skin, but less growth in the dermis itself. Conversely, no foci could be located by microscopic examination after inoculation onto shaved-only skin. High-dose nonocclusive dressing inoculations onto unshaved skin in DBA/2 mice revealed small numbers of infective foci, all in hair follicles. These results suggest that epidermal damage may increase infection susceptibility to B. anthracis of hair follicle contents and remaining epidermal remnants; the findings also indicate that access may occur through hair follicles and the denuded dermis.
Insights
Bacillus anthracis skin infection is common, but interactions are unclear. Epidermal damage, like abrasions, enhances anthrax susceptibility by allowing spore entry via hair follicles and damaged skin.
Area of Science:
- Microbiology
- Immunology
- Dermatology
Background:
- Cutaneous anthrax, caused by Bacillus anthracis, is the most frequent human infection type.
- Limited knowledge exists regarding the specific interactions between Bacillus anthracis and the epidermis.
- Understanding these interactions is crucial for developing effective prevention and treatment strategies.
Purpose of the Study:
- To investigate the role of the epidermis and hair follicles in Bacillus anthracis cutaneous infection.
- To determine how skin barrier integrity influences anthrax susceptibility and disease progression.
- To elucidate the initial sites of B. anthracis proliferation following experimental skin inoculation.
Main Methods:
- Experimental inoculation of Bacillus anthracis Sterne spores onto mouse skin models (DBA/2 and C57BL/6 strains).
- Varied inoculation methods included intradermal injection, epicutaneous application to abraded skin, and application to shaved-only skin under different dressing conditions.
- Histological examination was performed to identify bacterial proliferation sites and host responses.
Main Results:
- Intradermal inoculation or application to abraded skin led to rapid edema and death in sensitive DBA/2 mice.
- Application to intact, shaved skin caused delayed edema and death, suggesting a role for skin barrier integrity.
- Histology revealed massive B. anthracis proliferation in the epidermis and hair follicles of abraded skin, with limited dermal invasion.
- Inoculation onto intact skin showed infective foci primarily within hair follicles.
Conclusions:
- Epidermal damage significantly increases susceptibility to Bacillus anthracis infection.
- Hair follicles and residual epidermal remnants serve as key entry points and sites for initial B. anthracis proliferation.
- The findings suggest that maintaining skin barrier integrity is important in preventing cutaneous anthrax.
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