Staphylococcus pseudintermedius exfoliative toxin EXI selectively digests canine desmoglein 1 and causes subcorneal clefts in canine epidermis

Abstract

Staphylococcal exfoliative toxins are known to digest desmoglein (Dsg) 1, a desmosomal cell-cell adhesion molecule, thus causing intraepidermal splitting in human bullous impetigo, staphylococcal scalded skin syndrome and swine exudative epidermitis. Recently, a novel exfoliative toxin gene (exi), whose sequence shares significant homology with previously identified exfoliative toxins, was isolated from Staphylococcus pseudintermedius. Little is known about the pathogenic involvement of this toxin in canine pustular diseases such as impetigo. The aim of this study was to determine whether EXI, the product of the exi gene, digests canine Dsg1 and causes intraepidermal splitting in canine skin. An exi gene was isolated from chromosomal DNA of an S. pseudintermedius strain obtained from a pustule of a dog with impetigo, and was used to produce a recombinant EXI by Escherichia coli expression. When purified recombinant EXI was injected intradermally into normal dogs, it caused the development of vesicles or erosions with superficial epidermal splitting. In addition, the EXI abolished immunofluorescence for Dsg1, but not for Dsg3, at the injection sites. Moreover, the EXI directly degraded baculovirus-secreted recombinant extracellular domains of canine Dsg1, but not that of canine Dsg3, in vitro. The EXI also degraded mouse Dsg1α and swine Dsg1, but not human Dsg1, mouse Dsg1β and Dsg1γ. Conversely, recombinant SIET, previously designated as S. intermedius exfoliative toxin, did not cause intraepidermal splitting or degradation of any Dsgs. These findings indicate that EXI has a proteolytic activity that digests canine Dsg1, and this characteristic might be involved in the pathogenesis of intraepidermal splitting in canine impetigo.

Staphylococcus pseudintermedius, both commensal and pathogen

“…Dogs injected with purified SIET developed lesions with positive Nikolsky's sign (exfoliation of skin when rubbed) with erythema and crusting which resemble those of canine pyoderma (104). On the other hand, other studies revealed that intradermal injection of recombinant SIET in dogs did not cause any lesions, either clinically or histopathologically (47). Thus, the biological significance of this toxin remains unclear (47,104,113).…”

“…The authors proposed the renaming of EXI as EXPA (exfoliatin of S. pseudintermedius type A), and the novel protein was named EXPB (exfoliatin of S. pseudintermedius type B). Moreover, it was shown that both EXPA and EXPB could digest canine desmoglein-1 (Dsg-1) and caused subcorneal splits in the epidermis when injected in mice, which resembles mechanisms involved in the pathogenesis of intraepidermal splitting in canine impetigo (46,47).…”

“…In dogs, there is increasing evidence suggesting that some lesions of superficial bacterial skin infections are caused by S. pseudintermedius producing exfoliative toxins (5). Staphylococcal exfoliative toxins are known to digest desmoglein (Dsg) 1, a desmosomal cell-cell adhesion molecule, thus causing intraepidermal splitting in human bullous impetigo, staphylococcal scalded skin syndrome and swine exudative epidermitis ("greasy pig disease") (47). It was proved that Staphylococcus intermedius exfoliative toxin (SIET), which is produced by S. pseudintermedius strains, has a rounding effect in cultured epithelial cells and an exfoliative effect in 1-day-old chickens, hamsters and dogs, but not in rats or mice (104).…”

“…On the other hand, other studies revealed that intradermal injection of recombinant SIET in dogs did not cause any lesions, either clinically or histopathologically (47). Thus, the biological significance of this toxin remains unclear (47,104,113). Futagawa-Saito et al (32) described a novel exfoliative toxin (EXI) produced by S. pseudintermedius.…”

Occurrence of toxin genes in Staphylococcus pseudintermedius from diseased dogs and other domestic and wild species

“…Other diseases such as mastitis, arthritis, atopic dermatitis, inflammatory bowel disease, Kawasaki disease and autoimmune diseases have been associated with enterotoxins [11,12]. S. pseudintermedius exfoliative toxin SIET and exfoliative toxin EXI possibly play a role in the pathogenesis of cutaneous canine lesions and chronic otitis [13,14]. S. intermedius produces a bicomponent leukotoxin (Luk-I) similar to Panton-Valentine Leukocidin (PVL) of S. aureus, which is also encoded by two genes, LukS-I and LukF-I [15].…”