Experimental cutaneous Bacillus anthracis infections in hairless HRS/J mice

Division of Infectious Diseases, Medical College of Wisconsin, Milwaukee, Wisconsin, United States
International Journal of Experimental Pathology (Impact Factor: 2.17). 03/2007; 88(1):75-84. DOI: 10.1111/j.1365-2613.2006.00519.x
Source: PubMed


Previous studies of experimental Bacillus anthracis cutaneous infections in mice have implicated hair follicles as a likely entry site. Hairless HRS/J mice were used to investigate this possibility because of their non-functional hair follicles that lack penetrating hair shafts. These mice also have diminished macrophage function, increased susceptibility to Listeria, and enhanced neutrophil responses. HRS/J and Balb/c mice were found to be resistant to epicutaneous inoculation with Bacillus anthracis (Sterne) spores onto abraded skin when compared with DBA/2 mice or leucopenic C57BL/6 mice. The HRS/J mice also resisted spore injections that bypassed hair follicles. Haired HRS/J heterozygote mice demonstrated similar reduced susceptibility to B. anthracis spores. Hairless HRS/J mice that were made leucopenic did become susceptible to the epicutaneous spore inoculations. Histologically, the hairless and haired HRS/J mice showed markedly reduced numbers of organisms in hair follicles and the interfollicular dermis when compared even with the resistant Balb/c mice; inflammatory cell infiltrates in the superficial dermis were increased in the HRS/J mice compared with more sensitive strains. Therefore, resistance in the HRS/J mice was apparent at the initial site of epicutaneous inoculation and seemed related to an accumulation of dermal neutrophils rather than to a lack of functional hair follicles.

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    • "Epicutaneous inoculation of L. interrogans on the flank skin of guinea pigs was performed using the modified procedure as previously described [20]. Briefly, the guinea pigs were carefully shaved over their left flank one day before inoculation, and then disinfected with iodine, washed with 75% alcohol followed by saline. "
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    ABSTRACT: Leptospires are presumed to enter their host via small abrasions or breaches of the skin. The intraperitoneal route, although commonly used in guinea pig and hamster models of leptospirosis, does not reflect conditions encountered during natural infection. The aim of this study is to develop a novel leptospirosis guinea pig model through epicutaneous route and to elucidate the pathogenesis of leptospirosis in experimental guinea pigs by comparing the data from other studies using different infection routes. The guinea pigs were inoculated with 5 × 108 Leptospira interrogans strain Lai onto either shaved-only or abraded skin. The guinea pigs were sacrificed at 2, 8, 24, 48, 72, 96 and 144 h post-infection (p.i.) followed by harvest of the lungs, liver, kidneys, spleen, and the skin around the inoculated sites for further examinations. Hematoxylin and eosin (HE) staining and electron microscopy were used to detect the pathologic changes. Real time PCR and immunohistochemistry staining were performed to detect dynamic distribution of leptospires in blood and tissues, respectively. In the guinea pigs with abraded skin inoculations, leptospires were detected in blood as early as 2 h post infection (p.i.) and then disseminated to the liver, lungs and kidneys of almost all animals within 96 h p.i.. Leptospires were also detected engulfed in the swelling vascular endothelial cells and were frequently aggregated around the capillaries in the dermis and subcutaneous tissue under the inoculated site. For the guinea pigs with abraded skin inoculations, hemorrhage at the dermis around the inoculated site was found before the appearance of internal organs hemorrhage, severe lesions such as hemorrhages in the lungs, nephritis, jaundice, haematuria were also observed, and two of seven guinea pigs died at 144 h p.i. while no lesions and leptospires were detected in the shaved-only guinea pigs using the same dose of strain Lai. Intact keratinocyte layer is a very efficient barrier against leptospires, and intact skin can prevent the infiltration of leptosipres to the host. Leptospires can penetrate abraded skin and quickly establish a systemic infection by crossing tissue barriers. We have successfully established a novel leptospirosis guinea pig model through epicutaneous inoculations route, which replicates a natural course of infection and appears to be an alternative way to investigate the pathogenesis of leptospirosis, especially in terms of early stage of host-pathogen interactions. This novel model may also be advantageous for studies of the mechanisms involved in cutaneous barriers and epidermal interactions with this organism.
    Full-text · Article · Jan 2012 · BMC Infectious Diseases
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    • "When skin is abraded, as is readily evident from skin window studies in humans, there is a brisk exudation of host inflammatory cells that are primarily neutrophils (Wandall 1980; Yee et al. 1994; Koivuranta-Vaara 1985). We have previously found a similar exudation of inflammatory cells, predominantly neutrophils, in the abraded skin of mouse strains such as C57BL ⁄ 6, DBA ⁄ 2, and HRS ⁄ J hr ⁄ hr (Bischof et al. 2007a). Also, neutrophils from humans and mice have been found to be capable of killing B. anthracis spores and ⁄ or bacilli in vitro (Welkos et al. 1989; Mayer-Scholl et al. 2005); in fact, in one study encapsulated bacilli of the B. anthracis Vollum strain were phagocytosed and killed efficiently by human neutrophils through a mechanism dependent upon a-defensins (Mayer- Scholl et al. 2005). "
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    ABSTRACT: Skin window procedures in humans have shown rapid accumulation of neutrophils into the exuded fluids above abraded skin. The present study was undertaken to determine if similar epicutaneous neutrophil accumulation might explain the extreme resistance of HRS/J mice, both hairless (hr/hr) and haired (hr/+), to experimental cutaneous Bacillus anthracis Sterne infections on abraded skin. In this study, very early (6 h) biopsies demonstrated a lack of bacilli in skin from the HRS/J hr/hr mice, indicating that the organisms never did invade in these animals as opposed to early skin entry and then efficient clearance by host responses in the tissues. Touch preparations of either the inoculation filter or the skin surface revealed more inflammatory cells, fewer bacilli, and a higher percentage of cell-associated bacilli in the HRS/J hr/hr mice than in comparator strains. In the HRS/J mice, cyclophosphamide treatment or separation of inoculated spores from the inflammatory infiltrates by a second filter below both produced marked increases in the number of bacilli observed. Examination of inoculation filter specimens demonstrated ingestion of spores and bacilli by neutrophils inside the filter at 6 h after inoculation. These findings suggest that an early and vigorous inflammatory cell infiltrate in HRS/J mice attacks the inoculated organisms above the skin surface and does not allow them to invade the tissues below.
    Full-text · Article · Jul 2008 · International Journal of Experimental Pathology
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    ABSTRACT: Hair follicles may allow pathogen entry because they represent potential barrier defects and because there is immunological privilege within actively growing follicles. Experimental cutaneous Bacillus anthracis infections in mice have previously shown prominent organism invasion and proliferation within hair follicles. For the present study, C57BL/6 mice were inoculated with B. anthracis (Sterne) spores onto abraded skin with either anagen (actively growing) or telogen (inactive) hair follicles; skin samples were evaluated by histologic methods and electron microscopy. The infections were found to progress similarly in either anagen or telogen hair follicles, with bacilli occasionally invading deeper sites in anagen hair follicles. The infections progressed from the surface inward, rather than growing outward from within the follicles. Infecting bacilli destroyed the hair follicle keratinocytes and were initially not contacted by inflammatory cells within the follicles. However, at 3-4 days after inoculation, inflammatory cells did contact and disperse the massed follicle bacilli and led to apparent resolution of the follicle infections. Therefore, in this model system B. anthracis initially attacks superficial sites in active or inactive hair follicles and then progresses inward, producing destructive infections of the hair follicles; these infections clear when the massed bacilli are eventually contacted and dispersed by inflammatory cells.
    No preview · Article · Jun 2008 · Microbial Pathogenesis
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