Staphylococcus aureus penetrate the interkeratinocyte spaces created by skin-infiltrating neutrophils 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.

A retrospective analysis of skin bacterial colonisation, susceptibility and resistance in atopic dermatitis and impetigo patients.

Atopic dermatitis (AD) and impetigo are skin conditions where bacterial colonisation and infection, especially with Staphylococcus aureus play an important role. We compared skin bacterial population, resistance patterns and choice of antimicrobial agents in patients diagnosed with AD and impetigo during 2005 and 2011 in our department. Number of positive cultures in the AD group were 40 and 53 in 2005 and 2011, with S. aureus found in 97.5% and 100%, respectively. Differences in resistance were marginal. In impetigo, S. aureus was found in all 70 patients in 2005 and all 40 patients in 2011. Antibiotic resistance to specifically fusidic acid was more common in 2005 impetigo patients (22.8%) versus 2011 (5%) (p = 0.078). The most commonly used oral antimicrobial was cefadroxil (in 57.5% and 52.8% of AD and 58.6% and 35% of impetigo patients in 2005 and 2011, respectively). Our observations confirm the high prevalence of S. aureus in both diseases and, interestingly, show a declining resistance trend in impetigo.

The molecular logic of pemphigus and impetigo: the desmoglein story.

Desmosomes are intercellular adhesive junctions of epithelial cells that contain two major transmembrane components, desmogleins (Dsg) and desmocollins; these are both cadherin-type cell-cell adhesion molecules. Pemphigus is an autoimmune blistering disease caused by IgG autoantibodies that target Dsg1 and Dsg3 in pemphigus foliaceus and pemphigus vulgaris respectively. Bullous impetigo is a common and highly contagious superficial skin infection caused by Staphylococcus aureus. Staphylococcal scalded skin syndrome (SSSS) is a generalized form of bullous impetigo. The blisters in bullous impetigo and SSSS are induced by exfoliative toxin that specifically cleaves Dsg1. Clinical and microscopic localization of blisters in pemphigus, bullous impetigo and SSSS are logically explained at the molecular level by the desmoglein compensation theory; the similarity of lesions among these diseases is underscored by a similar pathogenesis.

Clinical manifestations of staphylococcal scalded-skin syndrome depend on serotypes of exfoliative toxins.

We sought a possible correlation between the clinical manifestations of staphylococcal scalded-skin syndrome (SSSS) and the serotype of exfoliative toxins (ET) by PCR screening of the eta and etb genes in Staphylococcus aureus strains isolated from 103 patients with generalized SSSS and 95 patients with bullous impetigo. The eta gene and the etb gene were detected in, respectively, 31 (30%) and 20 (19%) episodes of generalized SSSS and 57 (60%) and 5 (5%) episodes of bullous impetigo. Both genes were detected in 52 (50%) episodes of generalized SSS and 33 (35%) episodes of bullous impetigo. To explain this link between etb and generalized SSSS, we examined the distribution of ETA- and ETB-specific antibodies in the healthy population (n = 175) and found that the anti-ETB antibody titer was lower than the anti-ETA titer. Thus, ETA is associated with bullous impetigo and ETB is associated with generalized SSSS, possibly owing to a lower titer of anti-ETB neutralizing antibodies in the general population.

Impetigo in soldiers after hand-to-hand combat training.

Bacterial skin infections are very common and trigger destruction of the skin integrity. Impetigo is a consequence of group A beta-hemolytic streptococcus or Staphylococcus aureus infection. The clinical presentation in general is very typical and empiric treatment is usually successful. In cases of close contacts such as between classmates, athletes, or soldiers, the prompt recognition and appropriate treatment of the infection may stop an epidemic. We report a group of six soldiers who shared the same military equipment (physical shields) during hand-to-hand combat training. All of the soldiers had skin lesions and two of them suffered from systemic symptoms. Group A beta-hemolytic streptococcus and S. aureus were cultured from the impetiginous lesions. All patients recovered after systemic and/or local antibiotic treatments. These cases emphasize the need for the maintenance of proper hygiene throughout the training program to prevent spread of the disease and the importance of rapid diagnosis by bacteriological identification.

Desmosomes and disease: pemphigus and bullous impetigo.

Desmosomal cadherins are the pathophysiologic targets of autoimmune or toxin-mediated disruption in the human diseases pemphigus and bullous impetigo (including its generalized form, called staphylococcal scalded skin syndrome). Experiments exploiting the production of both pathogenic and nonpathogenic antidesmoglein antibodies in pemphigus patients' sera have afforded data that make an invaluable contribution towards identifying the functional domains of the desmogleins involved in intercellular adhesion. Conformational epitopes of antidesmoglein autoantibodies in pemphigus patients' sera and the specific cleavage site of desmoglein 1 by exfoliative toxin have been identified, implicating the N-terminal extracellular domains of the desmogleins as critical regions for controlling intercellular adhesion. Furthermore, the development of active autoimmune mouse models for pemphigus allows in vivo characterization of the disease and its pathogenesis. These studies offer new insight into the potential mechanisms of acantholysis in pemphigus and staphylococcal-associated blistering disease, with implications for the role of desmogleins in desmosomal structure and function.

Severity of nonbullous Staphylococcus aureus impetigo in children is associated with strains harboring genetic markers for exfoliative toxin B, Panton-Valentine leukocidin, and the multidrug resistance plasmid pSK41.

Nonbullous impetigo is a common skin infection in children and is frequently caused by Staphylococcus aureus. Staphylococcal toxins and especially exfoliative toxin A are known mediators of bullous impetigo in children. It is not known whether this is also true for nonbullous impetigo. We set out to analyze clonality among clinical isolates of S. aureus from children with nonbullous impetigo living in a restricted geographical area in The Netherlands. We investigated whether staphylococcal nasal carriage and the nature of the staphylococcal strains were associated with the severity and course of impetigo. Bacterial isolates were obtained from the noses and wounds of children suffering from impetigo. Strains were genetically characterized by pulsed-field gel electrophoresis-mediated typing and binary typing, which was also used to assess toxin gene content. In addition, a detailed clinical questionnaire was filled in by each of the participating patients. Staphylococcal nasal carriage seems to predispose the patients to the development of impetigo, and 34% of infections diagnosed in the Rotterdam area are caused by one clonal type of S. aureus. The S. aureus strains harbor the exfoliative toxin B (ETB) gene as a specific virulence factor. In particular, the numbers (P = 0.002) and sizes (P < 0.001) of the lesions were increased in patients infected with an ETB-positive strain. Additional predictors of disease severity and development could be identified. The presence of a staphylococcal plasmid encoding multiple antibiotic resistance traits, as detected by binary typing, was associated with a reduction in the cure rate. Our results recognize that a combination of staphylococcal virulence and resistance genes rather than a single gene determines the development and course of nonbullous impetigo. The identification of these microbial genetic markers, which are predictive of the severity and the course of the disease, will facilitate guided individualized antimicrobial therapy in the future.

Staphylococcal epidermolysins.

PURPOSE OF REVIEW: Staphylococcal epidermolysins are the major causative toxins of bullous impetigo and staphylococcal scalded skin syndrome. This disease is characterized by the splitting of the epidermis between two cell layers resulting in exfoliation. It predominantly affects newborn babies and exposes them to secondary infections. This leads to the risk of epidemics, especially in nurseries. With only an experimental model which consists of skin injections in newborn mice and the recent determination of three-dimensional structures, the essential function of these toxins remained controversial, split between that of specific proteases and that of superantigens. RECENT FINDINGS: Staphylococcal epidermolysins now constitute a family of toxins, with the recent characterizations of two new serotypes: ETC and ETD. They may be secreted by sensitive or methicillin-resistant strains. Four molecules were also identified in Staphylococcus hyicus responsible for exudative epidermitis in swine. While different observations suggested a proteolytic action to these toxins, the histological parallel made with pemphigus foliaceus greatly helped in the characterization of the targets for epidermolysins ETA, ETB, ETD: desmoglein-1, a desmosome-constitutive protein, and incidentally melanocyte-stimulating hormones, which accounts for the blisters observed clinically. SUMMARY: The growing complexity in staphylococcal toxins has to be taken into account both for their association with diseases and for diagnosis purposes. Even though cases of staphylococcal scalded skin syndrome in adults are rare, they raise further questions about the pathogenic features of the disease such as individual sensitivity and distribution of the toxins into the body.

Roles of the plasminogen activator streptokinase and the plasminogen-associated M protein in an experimental model for streptococcal impetigo.

Primary infection by group A streptococci (GAS) takes place at either the throat or skin of the human host, often leading to pharyngitis or impetigo, respectively. Many GAS strains differ in their preference for throat and skin tissue sites. Previous epidemiological findings show that many of the strains displaying strong tropism for the skin have a high-affinity binding site for plasminogen, located within M protein (PAM), a prominent surface fibril. Plasminogen bound by PAM interacts with streptokinase, a plasminogen activator secreted by GAS, to yield bacterial-bound plasmin activity. In this study, PAM and streptokinase were tested for their roles in infection using an experimental model that closely mimics human impetigo. Inactivation of genes encoding either PAM or streptokinase led to a partial, but significant, loss of virulence in vivo, as measured by net growth of the bacteria and pathological alterations. The relative loss in virulence in vivo was greater for the streptokinase mutant than for the PAM mutant. However, the PAM mutant, but not the streptokinase mutant, displayed a partial loss in resistance to phagocytosis in vitro. The combined experimental and epidemiological data provide evidence that PAM and streptokinase play a key role in mediating skin-specific infection by GAS. In addition, secreted cysteine proteinase activity due to SpeB leads to degradation of streptokinase in stationary phase broth cultures. Since SpeB is also a determinant of tissue-specific GAS infection at the skin, direct interactions between these two proteolytic pathways may constitute an important pathogenic mechanism. An integrated model for superficial infection at the skin is presented.

Toxin in bullous impetigo and staphylococcal scalded-skin syndrome targets desmoglein 1.

Exfoliative toxin A, produced by Staphylococcus aureus, causes blisters in bullous impetigo and its more generalized form, staphylococcal scalded-skin syndrome. The toxin shows exquisite specificity in causing loss of cell adhesion only in the superficial epidermis. Although exfoliative toxin A has the structure of a serine protease, a target protein has not been identified. Desmoglein (Dsg) 1, a desmosomal cadherin that mediates cell-cell adhesion, may be the target of exfoliative toxin A, because it is the target of autoantibodies in pemphigus foliaceus, in which blisters form with identical tissue specificity and histology. We show here that exfoliative toxin A cleaved mouse and human Dsg1, but not closely related cadherins such as Dsg3. We demonstrate this specific cleavage in cell culture, in neonatal mouse skin and with recombinant Dsg1, and conclude that Dsg1 is the specific receptor for exfoliative toxin A cleavage. This unique proteolytic attack on the desmosome causes a blister just below the stratum corneum, which forms the epidermal barrier, presumably allowing the bacteria in bullous impetigo to proliferate and spread beneath this barrier.

Current aspects of bacterial infections of the skin.

The practicing dermatologist is faced with an ever-changing epidemiologic spectrum of cutaneous bacterial diseases. Studies have stated that bacterial skin infections may account for up to 17% of clinical visits. It is hoped that the information presented in this article will enable the practicing dermatologist to provide improved patient care in the diagnosis and management of bacterial infections of the skin.

Impetigo: an overview.

This article reviews in detail the pathogenesis, clinical characteristics and management of impetigo in children. Impetigo is the most common bacterial skin infection of children. Most cases of nonbullous impetigo and all cases of bullous impetigo are caused by Staphylococcus aureus. The remainder of cases of nonbullous impetigo are due to group A beta hemolytic streptococci (GABHS). GABHS colonize the skin directly by binding to sites on fibronectin that are exposed by trauma. In contrast, S. aureus colonizes the nasal epithelium first; from this reservoir, colonization of the skin occurs. Patients with recurrent impetigo should be evaluated for carriage of S. aureus. Superficial, localized impetigo may be treated successfully in more than 90% of cases with topical application of mupirocin ointment. Impetigo that is widespread or involves deeper tissues should be treated with a beta-lactamase-resistant oral antibiotic. The choice of antibiotics is affected by the local prevalence of resistance to erythromycin among strains of S. aureus, antibiotic cost and availability, and issues of compliance.

Infecciones bacterianas cutáneas superficiales o impétigos: aspectos clínicos y terapéuticos / Superficial bacterial skin infections or impetigo: clinical and therapeutic aspects

Impétigo es una infección bacteriana, cutánea, superficial causada sobre todo por estafilococo dorado por estreptococo o por ambos. Es el padecimiento cutáneo infecto-contagioso más frecuente. Predomina en niños de estrato socioeconómicocultural bajo, en regiones húmedas y cálidas. Las lesiones son vesículas frágiles que se transforman en costras, preferentemente vecinas a los orificios naturales de la cara. El tratamiento consiste en antimicrobianos tópicos y/o sistémicos. La prevención consiste en el aseo y antisepsia de todo traumatismo que cause pérdida de la continuidad de la piel