The staphylococcal scalded-skin syndrome

Necrotic activity of ExhC from Mammaliicoccus sciuri is mediated by specific amino acid residues

Mammaliicoccus sciuri, a commensal and pathogenic bacterium of significant clinical and veterinary relevance, expresses exfoliative toxin C (ExhC), a specific glutamyl endopeptidase belonging to the chymotrypsin family as the principal virulence factor. However, unlike most members of this family, ETs are inactive against a wide range of substrates and possess exquisite specificity for desmoglein-1 (Dsg1), a cadherin-like adhesion molecule that is crucial to maintain tissue integrity, thereby preventing the separation of skin cells and the entry of pathogens. ExhC is of clinical importance since in addition to causing exfoliation in pigs and mice, it induces necrosis in multiple mammalian cell lines, a property not observed for other ETs. Previous experiments have implicated the ExhC79-128 fragment in causing necrosis. Site-directed mutagenesis of specific residues within this fragment were studied and led to the design of an ExhC variant containing four-point mutations (ExhCmut4) lacking necrotic potential but retaining nearly wild-type (wt) levels of enzymatic activity. Moreover, the determination of the ExhCwt and ExhCmut4 crystal structures identified the conformation in the necrosis-linked region. These results constitute an important step toward the understanding of the mechanisms underlying the necrotic and epidermolytic activity of ExhC.

Molecular Characteristics and Pathogenicity of Staphylococcus aureus Exotoxins

Staphylococcus aureus stands as one of the most pervasive pathogens given its morbidity and mortality worldwide due to its roles as an infectious agent that causes a wide variety of diseases ranging from moderately severe skin infections to fatal pneumonia and sepsis. S. aureus produces a variety of exotoxins that serve as important virulence factors in S. aureus-related infectious diseases and food poisoning in both humans and animals. For example, staphylococcal enterotoxins (SEs) produced by S. aureus induce staphylococcal foodborne poisoning; toxic shock syndrome toxin-1 (TSST-1), as a typical superantigen, induces toxic shock syndrome; hemolysins induce cell damage in erythrocytes and leukocytes; and exfoliative toxin induces staphylococcal skin scalded syndrome. Recently, Panton-Valentine leucocidin, a cytotoxin produced by community-associated methicillin-resistant S. aureus (CA-MRSA), has been reported, and new types of SEs and staphylococcal enterotoxin-like toxins (SEls) were discovered and reported successively. This review addresses the progress of and novel insights into the molecular structure, biological activities, and pathogenicity of both the classic and the newly identified exotoxins produced by S. aureus.

Staphylococcus aureus Exfoliative Toxin E, Oligomeric State and Flip of P186: Implications for Its Action Mechanism

Staphylococcal exfoliative toxins (ETs) are glutamyl endopeptidases that specifically cleave the Glu381-Gly382 bond in the ectodomains of desmoglein 1 (Dsg1) via complex action mechanisms. To date, four ETs have been identified in different Staphylococcus aureus strains and ETE is the most recently characterized. The unusual properties of ETs have been attributed to a unique structural feature, i.e., the 180° flip of the carbonyl oxygen (O) of the nonconserved residue 192/186 (ETA/ETE numbering), not conducive to the oxyanion hole formation. We report the crystal structure of ETE determined at 1.61 Å resolution, in which P186(O) adopts two conformations displaying a 180° rotation. This finding, together with free energy calculations, supports the existence of a dynamic transition between the conformations under the tested conditions. Moreover, enzymatic assays showed no significant differences in the esterolytic efficiency of ETE and ETE/P186G, a mutant predicted to possess a functional oxyanion hole, thus downplaying the influence of the flip on the activity. Finally, we observed the formation of ETE homodimers in solution and the predicted homodimeric structure revealed the participation of a characteristic nonconserved loop in the interface and the partial occlusion of the protein active site, suggesting that monomerization is required for enzymatic activity.

Management of Infectious Emergencies for the Inpatient Dermatologist

Purpose of Review

There are various dermatologic emergencies stemming from bacterial, viral, and fungal etiologies that can present in the inpatient setting. This review summarizes the pathogenesis and diagnosis of infections with cutaneous involvement and highlights new therapies.

Recent Findings

Clindamycin inhibits toxin formation and can be used as an adjunct therapy for the staphylococcal scalded syndrome. Isavuconazole therapy for mucormycosis infection is a less toxic alternative to amphotericin B.

Summary

Diagnosis of these infections is primarily guided by high clinical suspicion and early recognition can prevent dangerous sequelae. Treatment mainstays have been well-established, but there are adjunctive therapies that may potentially benefit the patient.

Contributions of animal studies to the understanding of infectious diseases

Experiments in animals have played an integral role in furthering basic understanding of the pathophysiology, host immune response, diagnosis, and treatment of infectious diseases. However, competing demands of modern-day clinical training and increasingly stringent requirements to perform animal research have reduced the exposure of infectious disease physicians to animal studies. For practitioners of infectious diseases and, especially, for contemporary trainees in infectious diseases, it is important to appreciate this historical body of work and its impact on current clinical practice. In this article, we provide an overview of some major contributions of animal studies to the field of infectious diseases. Areas covered include transmission of infection, elucidation of innate and adaptive host immune responses, testing of antimicrobials, pathogenesis and treatment of endocarditis, osteomyelitis, intraabdominal and urinary tract infection, treatment of infection associated with a foreign body or in the presence of neutropenia, and toxin-mediated disease.

Genome-wide comparison of four MRSA clinical isolates from Germany and Hungary

Staphylococcus aureus is a drug-resistant pathogen, capable of colonizing diverse ecological niches and causing a broad spectrum of infections related to a community and healthcare. In this study, we choose four methicillin-resistant S. aureus (MRSA) clinical isolates from Germany and Hungary based on our previous polyphasic characterization finding. We assumed that the selected strains have a different genetic background in terms of the presence of resistance and virulence genes, prophages, plasmids, and secondary metabolite biosynthesis genes that may play a crucial role in niche adaptation and pathogenesis. To clarify these assumptions, we performed a comparative genome analysis of these strains and observed many differences in their genomic compositions. The Hungarian isolates (SA H27 and SA H32) with ST22-SCCmec type IVa have fewer genes for multiple-drug resistance, virulence, and prophages reported in Germany isolates. Germany isolate, SA G6 acquires aminoglycoside (ant(6)-Ia and aph(3’)-III) and nucleoside (sat-4) resistance genes via phage transduction and may determine its pathogenic potential. The comparative genome study allowed the segregation of isolates of geographical origin and differentiation of the clinical isolates from the commensal isolates. This study suggested that Germany and Hungarian isolates are genetically diverse and showing variation among them due to the gain or loss of mobile genetic elements (MGEs). An interesting finding is the addition of SA G6 genome responsible for the drastic decline of the core/pan-genome ratio curve and causing the pan-genome to open wider. Functional characterizations revealed that S. aureus isolates survival are maintained by the amino acids catabolism and favor adaptation to growing in a protein-rich medium. The dispersible and singleton genes content of S. aureus genomes allows us to understand the genetic variation among the CC5 and CC22 groups. The strains with the same genetic background were clustered together, which suggests that these strains are highly alike; however, comparative genome analysis exposed that the acquisition of phage elements, and plasmids through the events of MGEs transfer contribute to differences in their phenotypic characters. This comparative genome analysis would improve the knowledge about the pathogenic S. aureus strain’s characterization, and responsible for clinically important phenotypic differences among the S. aureus strains.

Staphylococcus aureus Secreted Toxins and Extracellular Enzymes

Staphylococcus aureus is a formidable pathogen capable of causing infections in different sites of the body in a variety of vertebrate animals, including humans and livestock. A major contribution to the success of S. aureus as a pathogen is the plethora of virulence factors that manipulate the host's innate and adaptive immune responses. Many of these immune modulating virulence factors are secreted toxins, cofactors for activating host zymogens, and exoenzymes. Secreted toxins such as pore-forming toxins and superantigens are highly inflammatory and can cause leukocyte cell death by cytolysis and clonal deletion, respectively. Coagulases and staphylokinases are cofactors that hijack the host's coagulation system. Exoenzymes, including nucleases and proteases, cleave and inactivate various immune defense and surveillance molecules, such as complement factors, antimicrobial peptides, and surface receptors that are important for leukocyte chemotaxis. Additionally, some of these secreted toxins and exoenzymes can cause disruption of endothelial and epithelial barriers through cell lysis and cleavage of junction proteins. A unique feature when examining the repertoire of S. aureus secreted virulence factors is the apparent functional redundancy exhibited by the majority of the toxins and exoenzymes. However, closer examination of each virulence factor revealed that each has unique properties that have important functional consequences. This chapter provides a brief overview of our current understanding of the major secreted virulence factors critical for S. aureus pathogenesis.

Current Perspectives on Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are considered a delayed-type hypersensitivity reaction to drugs. They represent true medical emergencies and an early recognition and appropriate management is decisive for the survival. SJS/TEN manifest with an "influenza-like" prodromal phase (malaise, fever), followed by painful cutaneous and mucous membrane (ocular, oral, and genital) lesions, and other systemic symptoms. The difference between SJS, SJS/TEN overlap, and TEN is defined by the degree of skin detachment: SJS is defined as skin involvement of < 10%, TEN is defined as skin involvement of > 30%, and SJS/TEN overlap as 10-30% skin involvement. The diagnosis of different degrees of epidermal necrolysis is based on the clinical assessment in conjunction with the corresponding histopathology. The mortality rates for SJS and TEN have decreased in the last decades. Today, the severity-of-illness score for toxic epidermal necrolysis (SCORTEN) is available for SJS/TEN severity assessment. Drugs with a high risk of causing SJS/TEN are anti-infective sulfonamides, anti-epileptic drugs, non-steroidal anti-inflammatory drugs of the oxicam type, allopurinol, nevirapine, and chlormezanone. Besides conventional drugs, herbal remedies and new biologicals should be considered as causative agents. The increased risk of hypersensitivity reactions to certain drugs may be linked to specific HLA antigens. Our understanding of the pathogenesis of SJS/TEN has improved: drug-specific T cell-mediated cytotoxicity, genetic linkage with HLA- and non-HLA-genes, TCR restriction, and cytotoxicity mechanisms were clarified. However, many factors contributing to epidermal necrolysis still have to be identified, especially in virus-induced and autoimmune forms of epidermal necrolysis not related to drugs. In SJS/TEN, the most common complications are ocular, cutaneous, or renal. Nasopharyngeal, esophageal, and genital mucosal involvement with blisters, erosions as well as secondary development of strictures also play a role. However, in the acute phase, septicemia is a leading cause of morbidity and fatality. Pulmonary and hepatic involvement is frequent. The acute management of SJS/TEN requires a multidisciplinary approach. Immediate withdrawal of potentially causative drugs is mandatory. Prompt referral to an appropriate medical center for specific supportive treatment is of utmost importance. The most frequently used treatments for SJS/TEN are systemic corticosteroids, immunoglobulins, and cyclosporine A.

Staphylococcal-scalded skin syndrome: evaluation, diagnosis, and management

BACKGROUND

Staphylococcal-scalded skin syndrome (SSSS), also known as Ritter disease, is a potentially life-threatening disorder and a pediatric emergency. Early diagnosis and treatment is imperative to reduce the morbidity and mortality of this condition. The purpose of this article is to familiarize physicians with the evaluation, diagnosis, and treatment of SSSS.

DATA SOURCES

A PubMed search was completed in Clinical Queries using the key terms "Staphylococcal scalded skin syndrome" and "Ritter disease".

RESULTS

SSSS is caused by toxigenic strains of Staphylococcus aureus. Hydrolysis of the amino-terminal extracellular domain of desmoglein 1 by staphylococcal exfoliative toxins results in disruption of keratinocytes adhesion and cleavage within the stratum granulosum which leads to bulla formation. The diagnosis is mainly clinical, based on the findings of tender erythroderma, bullae, and desquamation with a scalded appearance especially in friction zones, periorificial scabs/crusting, positive Nikolsky sign, and absence of mucosal involvement. Prompt empiric treatment with intravenous anti-staphylococcal antibiotic such as nafcillin, oxacillin, or flucloxacillin is essential until cultures are available to guide therapy. Clarithromycin or cefuroxime may be used should the patient have penicillin allergy. If the patient is not improving, critically ill, or in communities where the prevalence of methicillin-resistant S. aureus is high, vancomycin should be used.

CONCLUSION

A high index of suspicion is essential for an accurate diagnosis to be made and treatment promptly initiated.

Epidemiology of staphylococcal scalded skin syndrome in U.S. children

BACKGROUND

Staphylococcal scalded skin syndrome (SSSS) is a blistering dermatosis caused by exfoliative toxins released from Staphylococcus aureus.

OBJECTIVES

To describe the incidence, costs, length of stay (LOS), comorbidities and mortality of SSSS in U.S. children.

METHODS

The Nationwide Inpatient Sample 2008-2012 was analysed, including a 20% sample of U.S. hospitalizations and 589 cases of SSSS.

RESULTS

The mean annual incidence of SSSS was 7·67 (range 1·83-11·88) per million U.S. children, with 45·1 cases per million U.S. infants age < 2 years. In multivariable logistic regression models, SSSS was significantly associated with the following (shown as adjusted odds ratio and 95% confidence interval): female sex (1·12, 1·00-1·25), age (2-5 years: 13·31, 11·82-14·99; 6-10 years: 2·93, 2·35-3·66; 11-17 years: 0·44, 0·31-0·63); race/ethnicity (black: 0·69, 0·58-0·84) and season (winter: 2·04, 1·66-2·50; summer: 3·47, 2·86-4·22; autumn: 3·04, 2·49-3·70), with increasing odds over time (2010-2011: 2·28, 2·07-2·51; 2012: 2·98, 2·69-3·30). The geometric mean (95% confidence interval) LOS and cost of hospitalization for patients with vs. without SSSS were 3·2 (3·0-3·4) vs. 2·4 (2·4-2·5) days and $4624·0 ($4250-$5030) vs. $1872 ($1782·7-$1965). Crude inpatient mortality rates (with 95% confidence intervals) were similar for children with vs. without SSSS (0·33%, 0·00-0·79% vs. 0·36%, 0·34-0·39%). SSSS was associated with other infections, including in the upper respiratory tract and skin.

CONCLUSIONS

The prevalence of SSSS appears to be increasing over time, and was associated with a number of sociodemographic factors and other infections. Further studies are needed to confirm these findings and reduce rising rates of SSSS.

Auxiliary activation of the complement system and its importance for the pathophysiology of clinical conditions

Activation and regulation of the cascade systems of the blood (the complement system, the coagulation/contact activation/kallikrein system, and the fibrinolytic system) occurs via activation of zymogen molecules to specific active proteolytic enzymes. Despite the fact that the generated proteases are all present together in the blood, under physiological conditions, the activity of the generated proteases is controlled by endogenous protease inhibitors. Consequently, there is remarkable little crosstalk between the different systems in the fluid phase. This concept review article aims at identifying and describing conditions where the strict system-related control is circumvented. These include clinical settings where massive amounts of proteolytic enzymes are released from tissues, e.g., during pancreatitis or post-traumatic tissue damage, resulting in consumption of the natural substrates of the specific proteases and the available protease inhibitor. Another example of cascade system dysregulation is disseminated intravascular coagulation, with canonical activation of all cascade systems of the blood, also leading to specific substrate and protease inhibitor elimination. The present review explains basic concepts in protease biochemistry of importance to understand clinical conditions with extensive protease activation.

Staphylococcus aureus-Associated Skin and Soft Tissue Infections: Anatomical Localization, Epidemiology, Therapy and Potential Prophylaxis

Skin and soft tissue infections (SSTIs) are among the most common infections worldwide. They range in severity from minor, self-limiting, superficial infections to life-threatening diseases requiring all the resources of modern medicine. Community (CA) and healthcare (HA) acquired SSTIs are most commonly caused by Staphylococcus aureus . They have variable presentations ranging from impetigo and folliculitis to surgical site infections (SSIs). Superficial SSTIs may lead to even more invasive infections such as bacteraemia and osteomyelitis. Here we describe the anatomical localization of the different SSTI associated with S. aureus, the virulence factors known to play a role in these infections, and their current epidemiology. Current prevention and treatment strategies are also discussed. Global epidemiological data show increasing incidence and severity of SSTIs in association with methicillin-resistant S. aureus strains (MRSA). CA-SSTIs are usually less morbid compared to other invasive infections caused by S. aureus, but they have become the most prevalent, requiring a great number of medical interventions, extensive antibiotic use, and therefore a high cost burden. Recurrence of SSTIs is common after initial successful treatment, and decolonization strategies have not been effective in reducing recurrence. Furthermore, decolonization approaches may be contributing to the selection and maintenance of multi-drug resistant strains. Clinical studies from the early 1900s and novel autovaccination approaches suggest an alternative strategy with potential effectiveness: using vaccines to control S. aureus cutaneous infections.

Virulence Plasmids of Nonsporulating Gram-Positive Pathogens

Gram-positive bacteria are leading causes of many types of human infection, including pneumonia, skin and nasopharyngeal infections, as well as urinary tract and surgical wound infections among hospitalized patients. These infections have become particularly problematic because many of the species causing them have become highly resistant to antibiotics. The role of mobile genetic elements, such as plasmids, in the dissemination of antibiotic resistance among Gram-positive bacteria has been well studied; less well understood is the role of mobile elements in the evolution and spread of virulence traits among these pathogens. While these organisms are leading agents of infection, they are also prominent members of the human commensal ecology. It appears that these bacteria are able to take advantage of the intimate association between host and commensal, via virulence traits that exacerbate infection and cause disease. However, evolution into an obligate pathogen has not occurred, presumably because it would lead to rejection of pathogenic organisms from the host ecology. Instead, in organisms that exist as both commensal and pathogen, selection has favored the development of mechanisms for variability. As a result, many virulence traits are localized on mobile genetic elements, such as virulence plasmids and pathogenicity islands. Virulence traits may occur within a minority of isolates of a given species, but these minority populations have nonetheless emerged as a leading problem in infectious disease. This chapter reviews virulence plasmids in nonsporulating Gram-positive bacteria, and examines their contribution to disease pathogenesis.

Staphylococcal scalded skin syndrome: diagnosis and management in children and adults

Staphylococcal scalded skin syndrome is a potentially life-threatening disorder caused most often by a phage group II Staphylococcus aureus infection. Staphylococcal scalded skin syndrome is more common in newborns than in adults. Staphylococcal scalded skin syndrome tends to appear abruptly with diffuse erythema and fever. The diagnosis can be confirmed by a skin biopsy specimen, which can be expedited by frozen section processing, as staphylococcal scalded skin syndrome should be distinguished from life threatening toxic epidermal necrolysis. Histologically, the superficial epidermis is detached, the separation level being at the granular layer. The diffuse skin loss is due to a circulating bacterial exotoxin. The aetiological exfoliating toxin is a serine protease that splits only desmoglein 1. The exfoliative toxins are spread haematogenously from a localized source of infection, causing widespread epidermal damage at distant sites. Sepsis and pneumonia are the most feared complications. The purpose of this review is to summarize advances in understanding of this serious disorder and provide therapeutic options for both paediatric and adult patients. Recent epidemiological studies have demonstrated that paediatric patients have an increased incidence of Staphylococcal scalded skin syndrome during the summer and autumn. Mortality is less than 10% in children, but is between 40% and 63% in adults, despite antibacterial therapy. Previously, intravenous immunoglobulin had been recommended to combat Staphylococcal scalded skin syndrome, but a recent study associates its use with prolonged hospitalization.

Skin findings of Staphylococcus aureus toxin-mediated infection in relation to toxin encoding genes

BACKGROUND

Staphylococcal scalded skin syndrome and toxic shock syndrome are associated with exfoliatins and superantigens, respectively; and are easy to distinguish in their usual presentation. However, there is confusion about the mild forms of these 2 staphylococcal diseases. These mild forms are both designated as "staphylococcal scarlet fever" despite differences in their pathophysiology and clinical presentation. Our study aimed to distinguish between the clinical characteristics of the rash associated with exfoliatins and the rash associated with superantigens.

METHODS

Patients were selected from the French National Reference Center for Staphylococci. We retrospectively compared the clinical characteristics of patients with a generalized rash during Staphylococcus aureus infection. Patients who met the criteria of staphylococcal scalded skin syndrome or toxic shock syndrome were excluded. The patients were classified into 2 groups depending on the presence of a gene coding for exfoliatin or for superantigenic toxin.

RESULTS

We included 13 cases with exfoliatin and 9 with superantigens. The patients of the exfoliatin group were more likely to have facial involvement, fold involvement and a superficial focus of infection. In the second group, S. aureus was isolated from a deeper focus in 8 of 9 patients.

CONCLUSION

Mild forms of S. aureus toxin-mediated infection affect the pediatric population. Examination made it possible to distinguish an exanthema associated with an exfoliatin from one associated with a superantigen. This early clinical distinction results in differences in management.

Desmoglein as a target in skin disease and beyond

Much of the original research on desmosomes and their biochemical components was through analysis of skin and mucous membranes. The identification of desmogleins 1 and 3, desmosomal adhesion glycoproteins, as targets in pemphigus, a fatal autoimmune blistering disease of the skin and mucous membranes, provided the first link between desmosomes, desmogleins, and human diseases. The clinical and histological similarities of staphylococcal scalded skin syndrome or bullous impetigo and pemphigus foliaceus led us to identify desmoglein 1 as the proteolytic target of staphylococcal exfoliative toxins. Genetic analysis of striate palmoplantar keratoderma and hypotrichosis identified their responsible genes as desmogleins 1 and 4, respectively. More recently, these fundamental findings in cutaneous biology were extended beyond the skin. Desmoglein 2, which is expressed earliest among the four isoforms of desmoglein in development and found in all desmosome-bearing epithelial cells, was found to be mutated in arrythmogenic right ventricular cardiomyopathy and has also been identified as a receptor for a subset of adenoviruses that cause respiratory and urinary tract infections. The story of desmoglein research illuminates how dermatological research, originally focused on one skin disease, pemphigus, has contributed to understanding the biology and pathophysiology of many seemingly unrelated tissues and diseases.

Staphylococcal scalded skin syndrome in the Czech Republic: an epidemiological study

OBJECTIVE

To identify the basic epidemiological characteristics of children hospitalized with diagnosis of Staphylococcal scalded skin syndrome in the Czech Republic in the years 1994-2009.

INTRODUCTION

Staphylococcal scalded skin syndrome (SSSS) is a relatively rare disease in childhood. This syndrome was first defined in 1878 by Baron Gottfried Ritter von Rittershainem and belongs to the group of diseases called Burn-like syndromes. It is a bullous skin disease caused by exfoliative toxins which are produced by certain types of Staphyloccocus aureus. Typical structures affected by these toxins are desmosome proteins called Desmoglein-1 located in the stratum granulosum of epidermis. Unlike in Lyell's syndrome or Stevens-Johnson's syndrome, the exfoliation is caused by loss of adhesivity particularly in the stratum granulosum and not by induction of apoptosis in the dermo-epidermal junction.

MATERIAL AND METHODS

This retrospective study was conducted on patients hospitalized in the Czech Republic in the period from 1.1.1994 to 31.12.2009. The basic condition for the inclusion in the retrospective study was age under 1 year and hospitalization due to SSSS. A total of 399 children (177 girls) fulfilled the criteria for inclusion into the study. Information was obtained from a central data depository, the Department of Health Information and Statistics, Czech Republic.

RESULTS

A total of 399 children under 1 year were hospitalized for the diagnosis of SSSS in the study period. The group included 177 girls and 222 boys. M:F ratio was 1.25:1. The average incidence of SSSS in the Czech Republic was 25.11 cases per 100,000 children under 1 year of age. The highest recorded incidence in the followed period was in 1994, when a total of 57 cases of SSSS was reported, namely 53.47 per 100,000 children. By contrast, in 2003, there were reported only 12 cases and the incidence of 12.81 per 100,000 children. The average length of hospitalization was 6.39 days. In 1995, the highest average length of hospitalization was reported, which was 8.1 days, and then in 2007, the lowest average length of hospitalization, 4.4 days. There was no significant difference in the length of hospitalization in boys and girls. None of the 399 children in the population died.

CONCLUSION

In our retrospective study, we established basic epidemiological characteristics of a group of children aged under 1 year with diagnosis of SSSS. As epidemiological data show, the occurrence of this syndrome is not sporadic, but steady.

Characterization of Virulence Factors of Staphylococcus aureus: Novel Function of Known Virulence Factors That Are Implicated in Activation of Airway Epithelial Proinflammatory Response

Airway epithelial cells play a major role in initiating inflammation in response to bacterial pathogens. S. aureus is an important pathogen associated with activation of diverse types of infection characterized by inflammation dominated by polymorphonuclear leukocytes. This bacterium frequently causes lung infection, which is attributed to virulence factors. Many of virulence determinants associated with S. aureus-mediated lung infection have been known for several years. In this paper, we discuss recent advances in our understanding of known virulence factors implicated in pneumonia. We anticipate that better understanding of novel functions of known virulence factors could open the way to regulate inflammatory reactions of the epithelium and to develop effective strategies to treat S. aureus-induced airway diseases.

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

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.

Regulatory mechanism for exfoliative toxin production in Staphylococcus aureus

The exfoliative toxin (ET) is a major virulence factor of Staphylococcus aureus that causes bullous impetigo and its disseminated form, staphylococcal scalded-skin syndrome (SSSS). ET selectively digests one of the intracellular adhesion molecules, desmoglein 1, of epidermal keratinocytes and causes blisters due to intraepidermal cell-cell dissociation. Most S. aureus strains that cause blistering disease produce either ETA or ETB. They are serologically distinct molecules, where ETA is encoded on a phage genome and ETB is enocded on a large plasmid. ETA-producing S. aureus strains are frequently isolated from impetigo patients, and ETB-producing S. aureus strains are isolated from SSSS. ET-induced blister formation can be reproduced with the neonatal mouse. To determine the regulatory mechanism of ET production, we investigated the role of the two-component systems and global regulators for eta or etb expression in vitro and in vivo with the mouse model. Western blot and transcription analyses using a series of mutants demonstrate ETA production was downregulated by sigB, sarS, and sarA, while ETB production was downregulated by sigB and sarA but not by sarS. Production of both toxins is upregulated by saeRS, arlRS, and agrCA. Furthermore, by the in vivo neonatal mouse model, sigB and sarS but not sarA negatively regulate the exfoliation activity of the ETA-producing strain, while sarA negatively regulates the ETB-producing strain. In both strains, saeRS, arlRS, and agrCA positively regulate the exfoliation activity in vivo. The data illustrate similar but distinct regulatory mechanisms for ETA and ETB production in S. aureus in vitro as well as in vivo.

Cleavage isn't everything: potential novel mechanisms of exfoliative toxin-mediated blistering

This Commentary describes breakthroughs in understanding the interactions between desmoglein 1 and plakogloben in staphylococcal-mediated blistering skin diseases.

Nosocomial Staphylococcal scalded skin syndrome caused by intra-articular injection

BACKGROUND

The pathogenic role of nasal carriage as a source for cutaneous and soft-tissue Staphylococcus aureus (SA) infections, and Staphylococcal scalded skin syndrome (SSSS) in particular, is unclear.

OBSERVATION

We herein describe a nosocomial outbreak of SSSS in three orthopaedic patients who received intra-articular injections by a single orthopaedic surgeon. Bacteriological samples from the index patients and medical personnel involved in their care were assessed by phage typing, polymerase chain reaction for exfoliative toxin genes, SmaI macro-restriction analysis and molecular spa-typing. These studies first revealed SA cultural growth in synovial fluid of all three patients as well as nasal mucosa of one medical assistant. Moreover, all SA isolates had the same phage typing and antibiotic susceptibilities and were positive for exfoliative toxin ETa by polymerase chain reaction. SmaI macro-restriction and spa-typing further confirmed all proband isolates to be identical.

CONCLUSION

These findings provide evidence that SA nasal colonization of otherwise healthy carriers is a risk factor for SA infections, including SSSS, in predisposed individuals.

Exploring the Nature of Desmosomal Cadherin Associations in 3D

Desmosomes are a complex assembly of protein molecules that mediate adhesion between adjacent cells. Desmosome composition is well established and spatial relationships between components have been identified. Intercellular cell-cell adhesion is created by the interaction of extracellular domains of desmosomal cadherins, namely, desmocollins and desmogleins. High-resolution methods have provided insight into the structural interactions between cadherins. However, there is a lack of understanding about the architecture of the intact desmosomes and the physical principles behind their adhesive strength are unclear. Electron Tomography (ET) studies have offered three-dimensional visual data of desmosomal cadherin associations at molecular resolution. This review discusses the merits of two cadherin association models represented using ET. We discuss the possible role of sample preparation on the structural differences seen between models and the possibility of adaptive changes in the structure as a direct consequence of mechanical stress and stratification.

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.

Exfoliative toxins of Staphylococcus aureus

Staphylococcus aureus is an important pathogen of humans and livestock. It causes a diverse array of diseases, ranging from relatively harmless localized skin infections to life-threatening systemic conditions. Among multiple virulence factors, staphylococci secrete several exotoxins directly associated with particular disease symptoms. These include toxic shock syndrome toxin 1 (TSST-1), enterotoxins, and exfoliative toxins (ETs). The latter are particularly interesting as the sole agents responsible for staphylococcal scalded skin syndrome (SSSS), a disease predominantly affecting infants and characterized by the loss of superficial skin layers, dehydration, and secondary infections. The molecular basis of the clinical symptoms of SSSS is well understood. ETs are serine proteases with high substrate specificity, which selectively recognize and hydrolyze desmosomal proteins in the skin. The fascinating road leading to the discovery of ETs as the agents responsible for SSSS and the characterization of the molecular mechanism of their action, including recent advances in the field, are reviewed in this article.

Bacteremia in Stevens-Johnson syndrome and toxic epidermal necrolysis: epidemiology, risk factors, and predictive value of skin cultures

Toxic epidermal necrolysis (TEN) is a rare drug-related life-threatening acute condition. Sepsis is the main cause of mortality. Skin colonization on top of impaired barrier function promotes bloodstream infections (BSI). We conducted this study to describe the epidemiology, identify early predictors of BSI, and assess the predictive value for bacteremia of routine skin surface cultures. We retrospectively analyzed the charts of all patients with Stevens-Johnson syndrome (SJS) and TEN hospitalized over an 11-year period. Blood cultures and skin isolates were recovered from the microbiology laboratory database. Early predictors of BSI were identified using a Cox model. Sensitivity, specificity, and negative and positive predictive values of skin cultures for the etiology of BSI were assessed. The study included 179 patients, classified as having SJS (n = 54; 30.2%), SJS/TEN overlap (n = 59; 33.0%), and TEN (n = 66; 36.9%). Forty-eight episodes of BSI occurred, yielding a rate of 15.5/1000 patient days. In hospital mortality was 13.4% (24/179). Overall, 70 pathogens were recovered, mainly Staphylococcus aureus (n = 23/70; 32.8%), Pseudomonas aeruginosa (n = 15/70; 21.4%), and Enterobacteriaceae organisms (n = 17/70; 24.3%). Variables associated with BSI in multivariate analysis included age >40 years (hazard ratio [HR], 2.5; 95% confidence interval [CI], 1.35-4.63), white blood cell count >10,000/mm3 (HR, 1.9; 95% CI, 0.96-3.61), and percentage of detached body surface area >or=30% (HR, 2.5; 95% CI, 1.13-5.47). Skin cultures had an excellent negative predictive value for bacteremia due to S aureus (especially methicillin-resistant strains) and P aeruginosa, but not for those due to Enterobacteriaceae organisms. In contrast, the positive predictive value was low for all pathogens studied.To our knowledge, this is the largest study describing the epidemiology and risk factors of BSI in patients with SJS/TEN. The body surface area involved is the main predictor of BSI. Excellent negative predictive values of skin cultures for S aureus and P aeruginosa bacteremia should help clinicians consider targeted empirical antibiotic choices when appropriate.

Autoimmune and infectious skin diseases that target desmogleins

Desmosomes are intercellular adhesive junctions of epithelial cells that contain two major transmembrane components, the desmogleins (Dsg) and desmocollins (Dsc), which are cadherin-type cell-cell adhesion molecules and are anchored to intermediate filaments of keratin through interactions with plakoglobin and desmoplakin. Desmosomes play an important role in maintaining the proper structure and barrier function of the epidermis and mucous epithelia. Four Dsg isoforms have been identified to date, Dsg1-Dsg4, and are involved in several skin and heart diseases. Dsg1 and Dsg3 are the two major Dsg isoforms in the skin and mucous membranes, and are targeted by IgG autoantibodies in pemphigus, an autoimmune disease of the skin and mucous membranes. Dsg1 is also targeted by exfoliative toxin (ET) released by Staphylococcus aureus in the infectious skin diseases bullous impetigo and staphylococcal scalded skin syndrome (SSSS). ET is a unique serine protease that shows lock and key specificity to Dsg1. Dsg2 is expressed in all tissues possessing desmosomes, including simple epithelia and myocardia, and mutations in this gene are responsible for arrhythmogenic right ventricular cardiomyopathy/dysplasia. Dsg4 plays an important adhesive role mainly in hair follicles, and Dsg4 mutations cause abnormal hair development. Recently, an active disease model for pemphigus was generated by a unique approach using autoantigen-deficient mice that do not acquire tolerance against the defective autoantigen. Adoptive transfer of Dsg3(-/-) lymphocytes into mice expressing Dsg3 induces stable anti-Dsg3 IgG production with development of the pemphigus phenotype. This mouse model is a valuable tool with which to investigate immunological mechanisms of harmful IgG autoantibody production in pemphigus. Further investigation of desmoglein molecules will continue to provide insight into the unsolved pathophysiological mechanisms of diseases and aid in the development of novel therapeutic strategies with minimal side effects.

The desmosome and pemphigus

Desmosomes are patch-like intercellular adhering junctions ("maculae adherentes"), which, in concert with the related adherens junctions, provide the mechanical strength to intercellular adhesion. Therefore, it is not surprising that desmosomes are abundant in tissues subjected to significant mechanical stress such as stratified epithelia and myocardium. Desmosomal adhesion is based on the Ca(2+)-dependent, homo- and heterophilic transinteraction of cadherin-type adhesion molecules. Desmosomal cadherins are anchored to the intermediate filament cytoskeleton by adaptor proteins of the armadillo and plakin families. Desmosomes are dynamic structures subjected to regulation and are therefore targets of signalling pathways, which control their molecular composition and adhesive properties. Moreover, evidence is emerging that desmosomal components themselves take part in outside-in signalling under physiologic and pathologic conditions. Disturbed desmosomal adhesion contributes to the pathogenesis of a number of diseases such as pemphigus, which is caused by autoantibodies against desmosomal cadherins. Beside pemphigus, desmosome-associated diseases are caused by other mechanisms such as genetic defects or bacterial toxins. Because most of these diseases affect the skin, desmosomes are interesting not only for cell biologists who are inspired by their complex structure and molecular composition, but also for clinical physicians who are confronted with patients suffering from severe blistering skin diseases such as pemphigus. To develop disease-specific therapeutic approaches, more insights into the molecular composition and regulation of desmosomes are required.

Staphylococcal exfoliative toxins: “Molecular scissors” of bacteria that attack the cutaneous defense barrier in mammals

Bullous impetigo and its generalized form, staphylococcal scalded-skin syndrome (SSSS), are highly contagious, blistering skin diseases caused by Staphylococcus aureus infection. Virulent strains of the bacteria produce exfoliative toxins (ETs) that cause the loss of keratinocyte cell-cell adhesion in the superficial epidermis. Recent studies have indicated that the three isoforms of ETs, i.e., ETA, ETB, and ETD, are glutamate-specific serine proteases that specifically and efficiently cleave a single peptide bond in the extracellular region of human and mouse desmoglein 1 (Dsg1), a desmosomal intercellular adhesion molecule. In addition, four isoforms of S. hyicus exfoliative toxin, ExhA, ExhB, ExhC, and ExhD, cleave swine Dsg1, resulting in skin exfoliation similar to that observed in pigs with exudative epidermitis. In this review, we describe recent advances in our knowledge of the mechanisms of action of staphylococcal exfoliative toxins, which act as "molecular scissors" to facilitate percutaneous bacterial invasion of mammalian skin by cleavage of keratinocyte cell-cell adhesion molecules. The species-specificity of staphylococcal exfoliative toxins to cleave Dsg1 in certain mammalian species is discussed.

Épidermolyse staphylococcique et impétigo bulleux chez des jumeaux nouveau-nés contaminés par le lait maternel

Staphylococcus aureus is often responsible for late septic infections, more rarely of toxinic ones, occurring in neonatal period. We report a case of staphylococcal scalded skin syndrome and bullous impetigo in newborn twins infected by breast milk from their asymptomatic mother. This transmission was confirmed by molecular biology method. This case emphasizes the potential part of the mother in staphylococcal nosocomial infections and the complexity of toxinic mechanisms.

[Desmoglein, the target molecule in autoimmunity and infection]

To form the human body and maintain the integrity of its complex tissues, individual cells need to hold tightly to each other. The desmosome is the major type of intercellular adhesive junction, and has desmoglein (Dsg), a cadherin type cell-cell adhesion molecule, as a transmembrane component. Dsg is now known to be targeted in autoimmune diseases, infectious diseases, as well as inherited diseases. Patients with pemphigus, an autoimmune blistering disease of the skin and mucous membrane, have IgG autoantibodies directed against Dsg1 and Dsg3. A subset of patients with pemphigus have Dsg1/Dsg4 crossreacting IgG autoantibodies. Exfoliative toxins produced by Staphylococcal aureus, which causes Staphylococcal Scalded Skin Syndrome (SSSS) and bullous impetigo, specifically digest Dsg1. A subset of patients with SSSS develop a low titer of anti-Dsg1 IgG autoantibodies. A mutation in DSG1 gene causes striate palmoplantar keratoderma and a mutation in DSG4 gene causes inherited hypotrichosis. It is not clear why so many diseases are clustered in desmogleins, but there must be a reason for this. Studies on desmogleins will provide an important framework to understand the mysteries between autoimmunity and infection.

Molecular epidemiology of clinical and carrier strains of methicillin resistant Staphylococcus aureus (MRSA) in the hospital settings of north India

BACKGROUND

The study was conducted between 2000 and 2003 on 750 human subjects, yielding 850 strains of staphylococci from clinical specimens (575), nasal cultures of hospitalized patients (100) and eye & nasal sources of hospital workers (50 & 125 respectively) in order to determine their epidemiology, acquisition and dissemination of resistance genes.

METHODS

Organisms from clinical samples were isolated, cultured and identified as per the standard routine procedures. Susceptibility was measured by the agar diffusion method, as recommended by the National Committee for Clinical Laboratory Standards (NCCLS). The modified method of Birnboin and Takahashi was used for isolation of plasmids from staphylococci. Pulsed-field gel electrophoresis (PFGE) typing of clinical and carrier Methicillin resistant Staphylococcus aureus (MRSA) strains isolated during our study was performed as described previously.

RESULTS

It was shown that 35.1% of Staphylococcus aureus and 22.5% of coagulase-negative staphylococcal isolates were resistant to methicillin. Highest percentage of MRSA (35.5%) was found in pus specimens (n = 151). The multiple drug resistance of all MRSA (n = 180) and Methicillin resistant Coagulase-negative Staphylococcus aureus (MRCNS) (n = 76) isolates was detected. In case of both methicillin-resistant as well as methicillin-sensitive Saphylococcal isolates zero resistance was found to vancomycin where as highest resistance was found to penicillin G followed by ampicillin. It was shown that the major reservoir of methicillin resistant staphylococci in hospitals are colonized/infected inpatients and colonized hospital workers, with carriers at risk for developing endogenous infection or transmitting infection to health care workers and patients. The results were confirmed by molecular typing using PFGE by SmaI-digestion. It was shown that the resistant markers G and T got transferred from clinical S. aureus (JS-105) to carrier S. aureus (JN-49) and the ciprofloxacin (Cf) and erythromycin (E) resistance seemed to be chromosomal mediated. In one of the experiments, plasmid pJMR1O from Staphylococcus aureus coding for ampicillin (A), gentamicin (G) and amikacin (Ak) resistance was transformed into Escherichia coli. The minimal inhibitory concentrations (MICs) for A and G were lower in E. coli than in S. aureus. However, the MIC for Ak was higher in E. coli transformants than in S. aureus.

CONCLUSION

There is a progressive increase in MRSA prevalence and multi-drug resistance in staphylococci. Vancomycin is still the drug of choice for MRSA infections. The major reservoir of methicillin resistant staphylococci in hospitals is colonized/infected inpatients and colonized hospital workers. Resistance transfer from staphylococci to E. coli as well as from clinical to carrier staphylococci due to antibiotic stress seemed to be an alarming threat to antimicrobial chemotherapy.

Staphylococcal scalded skin syndrome I. Purification of exfoliatin and maternal transmission of neutralizing ability against exfoliatin

Exfoliatin, an exotoxin produced by phage group 2 staphylococci, was separated and was analyzed. The toxin was separated in a single peak by Sephadex G-100 gel filtration and subsequent DEAE Sephadex chromatography. By acrylamide gel disc electrophoresis this single peak was found to contain 2 components both of which posessed exfoliative activity and the same antigenic properties. Their molecular weight, however, differed; the major component had a molecular weight of 30,000 and the minor component had 27,000. The toxin was stable when heated at 60 degrees C for 40 minutes, and labile at 100 degrees C for 20 minutes. The toxin was immunogenic to mice and produced antibody which could be transmitted to neonatal mice to neutralize exfoliative activity of the toxin. Innoculation of the bacteria caused the production of antibodies against both exfoliatin and alpha-hemolysin in mice. The antibodies were also transmitted to neonatal mice to neutralize the exfoliative activity of exfoliatin.

A Clinical and Microbiological Comparison of Staphylococcus aureus Toxic Shock and Scalded Skin Syndromes in Children

BACKGROUND

This study was designed to compare the clinical characteristics, toxin expression, virulence factors, and antimicrobial susceptibilities of staphylococci isolated from Taiwanese children with staphylococcal toxic shock syndrome (STSS) and staphylococcal scalded skin syndrome (SSSS).

METHODS

Demographic characteristics, hospital course, and outcomes of the children were analyzed. Toxin-specific and virulence genes of the staphylococci were detected by polymerase chain reaction amplification. Antimicrobial susceptibilities were determined by disk diffusion and the Etest.

RESULTS

Staphylococcus aureus was isolated from 16 children (6 in the STSS group and 10 in the SSSS group). Children with STSS tended to be older than those with SSSS, had a longer duration of hospitalization, and a much higher mortality rate. Community-associated methicillin-resistant S. aureus was isolated from 11 (68.8%) of 16 children. All of these isolates contained the ermB and mecA genes, but none had the mefA gene. All 16 isolates tested positive for the fnbA gene. The pvl and seb genes were more frequently found among S. aureus from the STSS group, compared with S. aureus from the SSSS group. We found that 67% (4 of 6) of the STSS isolates were genetically related. All of the S. aureus isolates were susceptible to vancomycin, gentamicin, doxycycline, and trimethoprim-sulfamethoxazole. Most isolates were resistant to clindamycin (63%), oxacillin (69%), and clarithromycin (81%).

CONCLUSIONS

The most distinguishing feature of these isolates is the greater frequency of pvl and seb carriage among those from the STSS group. Most of the isolates were community-associated methicillin-resistant S. aureus that were highly resistant to macrolides but susceptible to trimethoprim-sulfamethoxazole. Vancomycin remains the initial drug of choice for treatment of STSS and SSSS. More studies are needed to determine the efficacy of trimethoprim-sulfamethoxazole in children with these syndromes.

Severe bacterial infections of the skin: uncommon presentations

Although most bacterial infections of the skin prove to be minor in nature, a few such dermatologic entities are significant, to the point of even being fatal. Their course can be extremely rapid and can lead to dreadful complications. The mortality rate is usually up to 30% to 50% and depends upon the type of infection, underlying disease, and immune status. Patients suffering them usually need to be hospitalized, sometimes in intensive care or burn units. They should be treated systemically with appropriate antimicrobial therapy plus aggressive supportive care. The two life-threatening skin infections which are most commonly experienced are toxin-mediated staphylococcal and streptococcal disorders; one could overlap the other. Several other related entities will also be discussed.

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.

Epidemiology of Staphylococcal Scalded Skin Syndrome in Germany

Staphylococcal scalded skin syndrome (SSSS) is a blistering skin disorder caused by Staphylococcus aureus. The "Dokumentationszentrum schwerer Hautreaktionen", a unique population-based registry for severe skin reactions, included SSSS during a time period of 2 y in Germany. Statistical calculations indicated a low overall incidence between 0.09 and 0.13 cases per 1 million inhabitants per year with 95% confidence interval of [0-4]. The age distribution showed two clusters; one in young children and one in adults. The mortality rate was much lower in children than in adults. Young age was the main risk factor, whereas immunosuppression and consumptive infectious disease were the detected risk factors in adults.

Neonatal skin barrier: structure, function, and disorders

The development of the human skin from intrauterine to extrauterine life is a balletic interplay of maturing layers and interlocking structures. We discuss this transition and then branch out to touch on issues of premature infant as well as neonatal skin care. Disruption of the barrier function due to toxins and development errors are expounded upon. Staph scalded skin syndrome, collodion membrane, bullous congenital ichthyosiform erythroderma, autosomal recessive ichthyosis (lamellar and congenital ichthyosiform erythroderma), and harlequin fetus are used as examples of these disruptions. Discussion of therapy with the authors' experience highlights each disease.