Microbiologic characteristics of exfoliative toxin-producing Staphylococcus aureus

Genomic Epidemiology and Global Population Structure of Exfoliative Toxin A-Producing Staphylococcus aureus Strains Associated With Staphylococcal Scalded Skin Syndrome

Staphylococci producing exfoliative toxins are the causative agents of staphylococcal scalded skin syndrome (SSSS). Exfoliative toxin A (ETA) is encoded by eta, which is harbored on a temperate bacteriophage ΦETA. A recent increase in the incidence of SSSS in North America has been observed; yet it is largely unknown whether this is the result of host range expansion of ΦETA or migration and emergence of established lineages. Here, we detail an outbreak investigation of SSSS in a neonatal intensive care unit, for which we applied whole-genome sequencing (WGS) and phylogenetic analysis of Staphylococcus aureus isolates collected from cases and screening of healthcare workers. We identified the causative strain as a methicillin-susceptible S. aureus (MSSA) sequence type 582 (ST582) possessing ΦETA. To then elucidate the global distribution of ΦETA among staphylococci, we used a recently developed tool to query extant bacterial WGS data for biosamples containing eta, which yielded 436 genomes collected between 1994 and 2019 from 32 countries. Applying population genomic analysis, we resolved the global distribution of S. aureus with lysogenized ΦETA and assessed antibiotic resistance determinants as well as the diversity of ΦETA. The population is highly structured with eight dominant sequence clusters (SCs) that generally aligned with S. aureus ST clonal complexes. The most prevalent STs included ST109 (24.3%), ST15 (13.1%), ST121 (10.1%), and ST582 (7.1%). Among strains with available data, there was an even distribution of isolates from carriage and disease. Only the SC containing ST121 had significantly more isolates collected from disease (69%, n = 46) than carriage (31%, n = 21). Further, we identified 10.6% (46/436) of strains as methicillin-resistant S. aureus (MRSA) based on the presence of mecA and the SCCmec element. Assessment of ΦETA diversity based on nucleotide identity revealed 27 phylogroups, and prophage gene content further resolved 62 clusters. ΦETA was relatively stable within lineages, yet prophage variation is geographically structured. This suggests that the reported increase in incidence is associated with migration and expansion of existing lineages, not the movement of ΦETA to new genomic backgrounds. This revised global view reveals that ΦETA is diverse and is widely distributed on multiple genomic backgrounds whose distribution varies geographically.

Cutaneous infectious diseases: Kids are not just little people

The changes in immune response that occur with age play a significant role in disease presentation and patient management. Evolution of the innate and adaptive immune systems throughout life, influenced partly by hormonal changes associated with puberty, plays a role in the differences between pediatric and adult response to disease. We review a series of manifestations of dermatologic infectious diseases spanning bacterial, viral, and fungal origins that can be seen in both pediatric and adult age groups and highlight similarities and differences in presentation and disease course. Therapeutic options are also discussed for these infectious diseases, with particular attention to variations in management between these population subgroups, given differences in pharmacokinetics and side effect profiles.

Staphylococcal Scalded Skin Syndrome in Neonate

We described a case of Staphylococcal Scalded Skin Syndrome in infant age of 21 days by discussing clinical and management issues. This newborn presented large erythematous, eroded, and oozing areas covered by epidermal skin flap. The average surface of cutaneous unsticking on admission was 31.35% of body surface area corresponding to lesions of superficial second-degree burns. An important biological inflammatory syndrome including positive C-reactive protein was found. Under treatment, erythroderma decreased within 7 to 10 days and the newborn was completely healed after 3 weeks of followup, with the disappearance of the inflammatory syndrome and total body surface restored. This clinical case report showed that SSSS remains a major dermatological problem in neonates. Therefore, its diagnosis should be made without doubt and its care should start earlier in a neonate emergency unit in order to have good prognosis. And the rigorous "search and destroy" policy based on screening of staff and patients and isolation of identified patients advocated in the United Kingdom should be applied in neonate units in Côte d'Ivoire.

Antibiotic sensitivity and resistance patterns in pediatric staphylococcal scalded skin syndrome

Historical resistance patterns often guide empiric antibiotic choices in staphylococcal scalded skin syndrome (SSSS), but little is known about the difference in susceptibility between SSSS and other childhood staphylococcal infections. A retrospective chart review of culture-confirmed cases of SSSS seen in the inpatient dermatology consultation service at the Children's Hospital of Philadelphia between 2005 and 2011 was performed. Most cases of SSSS at our institution are due to oxacillin-susceptible Staphylococcus aureus, and approximately half of the cases are due to clindamycin-resistant strains. Clindamycin and a penicillinase-resistant penicillin are suggested as empiric treatment for SSSS until culture susceptibility data are available to guide therapy.

The systemic and pulmonary immune response to staphylococcal enterotoxins

In response to environmental cues the human pathogen Staphylococcus aureus synthesizes and releases proteinaceous enterotoxins. These enterotoxins are natural etiologic entities of severe food poisoning, toxic shock syndrome, and acute diseases. Staphylococcal enterotoxins are currently listed as Category B Bioterrorism Agents by the Center for Disease Control and Prevention. They are associated with respiratory illnesses, and may contribute to exacerbation of pulmonary disease. This likely stems from the ability of Staphylococcal enterotoxins to elicit powerful episodes of T cell stimulation resulting in release of pro-inflammatory cytokines. Here, we discuss the role of the immune system and potential mechanisms of disease initiation and progression.

Prevalence of genes encoding extracellular virulence factors among meticillin-resistant Staphylococcus aureus isolates from the University Hospital, Olomouc, Czech Republic

A rather fast and complicated progression of an infection caused by some strains of Staphylococcus aureus could be associated with the expression and co-action of virulence factor complexes in these strains. This study screened the antibiotic susceptibility and prevalence of virulence markers in isolates of meticillin-resistant S. aureus (MRSA) obtained from patients hospitalized at the University Hospital in Olomouc, Czech Republic. A total of 100 isolates was screened for 13 genes encoding extracellular virulence determinants (tst, pvl, eta, etb, sea, seb, sec, sed, see, seg, seh, sei and sej) and for their distribution in sample types. Eighty-nine isolates were positive for at least one of the genes. Genes for etb, pvl, see and seh were not detected in any of the MRSA isolates. No statistically significant differences in the occurrence of the determinants studied among sample types were found.

Transduction of the plasmid encoding antiseptic resistance gene qacB in Staphylococcus aureus

The plasmid-borne qacA and qacB genes encode a multidrug efflux protein. The proteins encoded by qacA and qacB mediate efflux of cationic antiseptic agents such as quaternary ammonium compounds. In methicillin-resistant Staphylococcus aureus (MRSA), qacA and qacB are widely prevalent and decrease antiseptic susceptibility. However, it is difficult to find the plasmids encoding qacA or qacB in community-associated MRSA (C-MRSA) isolated from patients with impetigo. Most MRSA, the strains causative of impetigo, carry the plasmid-borne exfoliative toxin-producing gene etb. To find the reason for the paucity of qacA or qacB in MRSA isolated from patients with impetigo, we performed transfer experiments of the plasmid pTZ2162qacB encoding qacB. The pTZ2162qacB was transferred to S. aureus strain RN4220 by transduction, although no pTZ2162qacB was transferred by conjugation. Additionally, pTZ2162qacB was transduced to MRSA carrying etb, and was coexistence with the plasmid encoding etb. Our results showed that pTZ2162qacB was horizontally transferred by transduction and was compatible with the plasmid encoding etb. Consequently, there will be risk of the emergence of C-MRSA with decreased antiseptic susceptibility among patients with impetigo.

Generalized bullous impetigo in a neonate

Generalized bullous impetigo is uncommon in healthy and term neonates. It must be differentiated from staphylococcal scalded skin syndrome and other commonly encountered vesiculopustular lesions. We report generalized bullous impetigo in an otherwise healthy neonate.

Staphylococcal scalded skin syndrome: diagnosis and management

Staphylococcal scalded skin syndrome (SSSS) is a common disorder that is usually seen in infants and children and rarely seen in adults. SSSS usually presents with a prodrome of sore throat or conjunctivitis. Extremely tender flaccid bullae, which are Nikolsky sign-positive, develop within 48 hours and commonly affect the flexures; occasionally, large areas of the skin may be involved. The bullae enlarge and rupture easily to reveal a moist erythematous base, which gives rise to the scalded appearance. SSSS in adults is a rare disorder, though there are now over 50 documented cases. Usually SSSS occurs in predisposed individuals, but not all adults have an underlying illness. Whereas mortality in childhood SSSS is approximately 4%, the mortality rate in adults is reported to be greater than 60%. SSSS is caused by an infection with a particular strain of Staphylococcus aureus, which leads to blistering of the upper layer of the skin, by the release of a circulating exotoxin. It has recently been demonstrated that the exfoliative exotoxin responsible for SSSS leads to the cleavage of desmoglein 1 complex, an important desmosomal protein. The same toxins that are responsible for causing SSSS also cause bullous impetigo. There appears to be a relationship between the disease extent, the amount of toxin produced and whether the toxin is released locally or systemically. As a result there is likely to be a spectrum of disease and there are likely to be a number of milder cases of adult SSSS that go undiagnosed. Social improvements and hygiene have led to a dramatic fall in the number of cases of SSSS. Treatment is usually straightforward, when there is no coexistent morbidity and the presentation is mild, but can be demanding if the patient is particularly ill. SSSS is still associated with mortality, particularly when it occurs in adults.

Staphylococcal exfoliative toxin B specifically cleaves desmoglein 1

Staphylococcal scalded skin syndrome and its localized form, bullous impetigo, show superficial epidermal blister formation caused by exfoliative toxin A or B produced by Staphylococcus aureus. Recently we have demonstrated that exfoliative toxin A specifically cleaves desmoglein 1, a desmosomal adhesion molecule, that when inactivated results in blisters. In this study we determine the target molecule for exfoliative toxin B. Exfoliative toxin B injected in neonatal mice caused superficial epidermal blisters, abolished cell surface staining of desmoglein 1, and degraded desmoglein 1 without affecting desmoglein 3 or E-cadherin. When adenovirus-transduced cultured keratinocytes expressing exogenous mouse desmoglein 1 or desmoglein 3 were incubated with exfoliative toxin B, desmoglein 1, but not desmoglein 3, was cleaved. Furthermore, cell surface staining of desmoglein 1, but not that of desmoglein 3, was abolished when cryosections of normal human skin were incubated with exfoliative toxin B, suggesting that living cells were not necessary for exfoliative toxin B cleavage of desmoglein 1. Finally, in vitro incubation of the recombinant extracellular domains of desmoglein 1 and desmoglein 3 with exfoliative toxin B demonstrated that both mouse and human desmoglein 1, but not desmoglein 3, were directly cleaved by exfoliative toxin B in a dose-dependent fashion. These findings demonstrate that exfoliative toxin A and exfoliative toxin B cause blister formation in staphylococcal scalded skin syndrome and bullous impetigo by identical molecular pathophysiologic mechanisms.

egc, a highly prevalent operon of enterotoxin gene, forms a putative nursery of superantigens in Staphylococcus aureus

The recently described staphylococcal enterotoxins (SE) G and I were originally identified in two separate strains of Staphylococcus aureus. We have previously shown that the corresponding genes seg and sei are present in S. aureus in tandem orientation, on a 3.2-kb DNA fragment (Jarraud, J. et al. 1999. J. Clin. Microbiol. 37:2446-2449). Sequence analysis of seg-sei intergenic DNA and flanking regions revealed three enterotoxin-like open reading frames related to seg and sei, designated sek, sel, and sem, and two pseudogenes, psi ent1 and psi ent2. RT-PCR analysis showed that all these genes, including seg and sei, belong to an operon, designated the enterotoxin gene cluster (egc). Recombinant SEG, SEI, SEK, SEL, and SEM showed superantigen activity, each with a specific V beta pattern. Distribution studies of genes encoding superantigens in clinical S. aureus isolates showed that most strains harbored such genes and in particular the enterotoxin gene cluster, whatever the disease they caused. Phylogenetic analysis of enterotoxin genes indicated that they all potentially derived from this cluster, identifying egc as a putative nursery of enterotoxin genes.

Clinical, microbial, and biochemical aspects of the exfoliative toxins causing staphylococcal scalded-skin syndrome

The exfoliative (epidermolytic) toxins of Staphylococcus aureus are the causative agents of the staphylococcal scalded-skin syndrome (SSSS), a blistering skin disorder that predominantly affects children. Clinical features of SSSS vary along a spectrum, ranging from a few localized blisters to generalized exfoliation covering almost the entire body. The toxins act specifically at the zona granulosa of the epidermis to produce the characteristic exfoliation, although the mechanism by which this is achieved is still poorly understood. Despite the availability of antibiotics, SSSS carries a significant mortality rate, particularly among neonates with secondary complications of epidermal loss and among adults with underlying diseases. The aim of this article is to provide a comprehensive review of the literature spanning more than a century and to cover all aspects of the disease. The epidemiology, clinical features, potential complications, risk factors, susceptibility, diagnosis, differential diagnoses, investigations currently available, treatment options, and preventive measures are all discussed in detail. Recent crystallographic data on the toxins has provided us with a clearer and more defined approach to studying the disease. Understanding their mode of action has important implications in future treatment and prevention of SSSS and other diseases, and knowledge of their specific site of action may provide a useful tool for physiologists, dermatologists, and pharmacologists.

Exfoliative toxin detection using reversed passive latex agglutination: clinical and epidemiologic applications

A rapid and simple method for detecting exfoliative toxin serotypes A and B from clinical isolates has been developed as a test kit (EXT-RPLA; Denka Seiken Co. Ltd., Niigata, Japan). This method is based on reversed passive latex agglutination. The detection limit of the EXT-RPLA observed for purified exfoliative toxin serotypes A and B was 1 ng/ml. We evaluated the clinical and epidemiologic uses of the EXT-RPLA. A total of 381 isolates of Staphylococcus aureus, 292 from various clinical specimens and 89 from the skin of dermatologic patients, were studied. The EXT-RPLA detected 19 exfoliative toxin producers, including 16 serotype A producers and 3 serotype B producers, but no double producers. The sensitivity and specificity of the EXT-RPLA were confirmed by the newborn mouse bioassay and a PCR assay for the structural genes for exfoliative toxin serotypes A and B (eta and etb, respectively). The overall positivity rate of exfoliative toxin producers was 5.0% (19 of 381), including 16 serotype A isolates and 3 serotype B isolates. Of the 89 isolates from the skin of dermatologic patients, 12 (13.5%) were positive for exfoliative toxin production. Only 2 (1.3%) of the 153 methicillin-resistant S. aureus isolates produced exfoliative toxin, while 17 (7.5%) of the 228 methicillin-sensitive isolates produced exfoliative toxin. The EXT-RPLA assay is a simple and reliable method for detecting exfoliative toxin, and we recommend its use for the rapid diagnosis of staphylococcal scalded skin syndrome. We also recommend its use for detection of this syndrome so that effective control measures can be taken against the spread of this syndrome.

Staphylococcal scalded skin syndrome in adults. A clinical review illustrated with a new case

Staphylococcal scalded skin syndrome is rarely observed in adults; only 32 cases have been reported. In contrast to infant cases, the mortality rate is high. Two major risk factors have been identified: kidney failure and immunosuppression. In adults, clinical features are similar to those of the typical pediatric disease, but blood cultures are often positive for Staphylococcus aureus. Detection of the exfoliative toxin is required for diagnosis; the newborn mouse bioassay is, therefore, usually performed. New immunologic methods allow precise characterization of the toxins and oligonucleotide probes can be used for rapid detection of toxigenic strains. We report a case of staphylococcal scalded skin syndrome in an immunocompetent adult in whom blood cultures were positive; this is the first case in which both exfoliative toxins A and B have been identified in an adult.