Ichiro Imanishi1, Shinpei Hattori1,2, Junzo Hisatsune3, Kaori Ide1, Motoyuki Sugai3, Koji Nishifuji1. 1. Laboratory of Veterinary Internal Medicine, Division of Animal Life Science, Graduate School, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo, 183-8509, Japan. 2. Kariya Animal Hospital, 5-20-2 Morishita, Koto-ku, Tokyo, 135-0004, Japan. 3. Department of Bacteriology, Graduate school of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8551, Japan.
Abstract
BACKGROUND: Impetigo is a bacterial skin disease characterized by intraepidermal neutrophilic pustules. Previous studies have demonstrated that exfoliative toxin producing staphylococci are isolated in the cutaneous lesions of human and canine impetigo. However, the mechanisms of intraepidermal splitting in impetigo remain poorly understood. OBJECTIVE: To determine how staphylococci penetrate the living epidermis and create intraepidermal pustules in vivo using a mouse model of impetigo. METHODS: Three Staphylococcus aureus strains harbouring the etb gene and three et gene negative strains were epicutaneously inoculated onto tape-stripped mouse skin. The skin samples were subjected to time course histopathological and immunofluorescence analyses to detect intraepidermal neutrophils and infiltrating staphylococci. To determine the role of neutrophils on intraepidermal bacterial invasion, cyclophosphamide (CPA) was injected intraperitoneally into the mice to cause leucopenia before the inoculation of etb gene positive strains. RESULTS: In mice inoculated with etb gene positive S. aureus, intraepidermal pustules resembling impetigo were detected as early as 4 h post-inoculation (hpi). Neutrophils in the epidermis were detected from 4 hpi, whereas intraepidermal staphylococci was detected from 6 hpi. The dimensions of the intraepidermal clefts created in mice inoculated with etb gene positive strains at 6 hpi were significantly larger than those in mice inoculated with et gene negative strains. In CPA treated mice, staphylococci or neutrophils were not detected in the deep epidermis until 6 hpi. CONCLUSION: Our findings indicate that intraepidermal neutrophils play an important role in S. aureus invasion into the living epidermis in a mouse model of impetigo.
BACKGROUND: Impetigo is a bacterial skin disease characterized by intraepidermal neutrophilic pustules. Previous studies have demonstrated that exfoliative toxin producing staphylococci are isolated in the cutaneous lesions of human and canine impetigo. However, the mechanisms of intraepidermal splitting in impetigo remain poorly understood. OBJECTIVE: To determine how staphylococci penetrate the living epidermis and create intraepidermal pustules in vivo using a mouse model of impetigo. METHODS: Three Staphylococcus aureus strains harbouring the etb gene and three et gene negative strains were epicutaneously inoculated onto tape-stripped mouse skin. The skin samples were subjected to time course histopathological and immunofluorescence analyses to detect intraepidermal neutrophils and infiltrating staphylococci. To determine the role of neutrophils on intraepidermal bacterial invasion, cyclophosphamide (CPA) was injected intraperitoneally into the mice to cause leucopenia before the inoculation of etb gene positive strains. RESULTS: In mice inoculated with etb gene positive S. aureus, intraepidermal pustules resembling impetigo were detected as early as 4 h post-inoculation (hpi). Neutrophils in the epidermis were detected from 4 hpi, whereas intraepidermal staphylococci was detected from 6 hpi. The dimensions of the intraepidermal clefts created in mice inoculated with etb gene positive strains at 6 hpi were significantly larger than those in mice inoculated with et gene negative strains. In CPA treated mice, staphylococci or neutrophils were not detected in the deep epidermis until 6 hpi. CONCLUSION: Our findings indicate that intraepidermal neutrophils play an important role in S. aureus invasion into the living epidermis in a mouse model of impetigo.