Sequence determination and comparison of the exfoliative toxin A and toxin B genes from Staphylococcus aureus

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.

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.

Distribution of Leukocidins, Exfoliative Toxins, and Selected Resistance Genes Among Methicillin-resistant and Methicillin-sensitive Staphylococcus aureus Clinical Strains in Egypt

Background:

Infection with Staphylococcus aureus (S.aureus) is an increasing health problem worldwide. This pathogen has multiple virulence factors that contribute to its pathogenesis in a wide range of diseases. The present study aimed to investigate the prevalence of leukocidins, exfoliative toxins, and common antimicrobial resistance genes among Methicillin-Resistant Staphylococcus aureus (MRSA) and Methicillin-Sensitive Staphylococcus aureus (MSSA) strains collected from various clinical sources in Egypt.

Methods:

Isolates were identified as S.aureus by the standard microbiological methods. Methicillin resistance was detected phenotypically by cefoxitin disc diffusion method and genotypically by PCR for detection of mecA gene. PCR was also used to detect the presence of leukocidin genes (LukD, LukE, LukF-PV, and LukS-PV), exfoliative toxin genes (eta and etb), and antibiotic resistance genes (tetK, tetM, ermA, ermC, msrA, and aacA-aphD).

Results:

About 50.5% of tested isolates were methicillin resistant by cefoxitin disc assay, while mecA gene was amplified in 64.6% of isolates. The highest prevalent toxin gene was lukE (93%) and the least prevalent one was eta (1%). The resistance genes tetK and tetM were detected in nearly 50% of the tested strains but lower prevalence rates were recorded for aacA-aphD, msrA, ermA, and ermC genes.

Conclusion:

Methicillin resistance was highly prevalent among tested S.aureus strains. Regarding the studied virulence and resistance genes, no significant difference was detected between MRSA and MSSA strains, except for ermA gene p<0.05 which was highly prevalent in MRSA strains. So, the variation between MRSA and MSSA strains in the response to treatment may be attributed to the resistance of MRSA strains to all β-lactams in addition to other possible acquired resistance mechanisms. Accordingly, fewer options of antimicrobial medications are available to treat MRSA infections.

Novel Tet(L) Efflux Pump Variants Conferring Resistance to Tigecycline and Eravacycline in Staphylococcus Spp

Tigecycline is regarded as one of the few important last-resort antibiotics to treat complicated skin and intra-abdominal infections. Members of the genus Staphylococcus are zoonotic pathogens and pose a serious threat to public health. Tigecycline resistance in this species appears to be a rare phenomenon, and the mechanisms underlying tigecycline resistance have not been fully elucidated. Here, we report two novel variants of the tet(L) gene in Staphylococcus spp. from swine in China, designed as tet(L)_F58L and tet(L)_A117V. The tet(L)_F58L was located within a 18,720 bp chromosomal multidrug resistance gene cluster flanked by two copies of IS257 in Staphylococcus cohnii 11-B-312, while the tet(L)_A117V was located on a 6,292 bp plasmid in S. haemolyticus 11-B-93, which could be transferred to S. aureus by electrotransformation. Cloning of each of the two tet(L) variants into S. aureus RN4220 showed 16- or 8-fold increases in the minimal inhibition concentrations (MICs), which can fully confer the resistance to tigecycline (MICs from 0.125 to 2 mg/liter) and eravacycline (MICs from 0.125 to 1 or 2 mg/liter), but no increase in the MICs of omadacycline, compared with the MICs of the recipient strain S. aureus RN4220. In the in vivo murine sepsis and in the murine pneumonia models, an increase in CFU of S. aureus 29213_pT93 carrying the tet(L)_A117V was seen despite tigecycline treatment. This observation suggests that the tet(L)_A117V and its associated gene product compromise the efficacy of tigecycline treatment in vivo and may lead to clinical treatment failure. Our finding, that novel Tet(L) efflux pump variants which confer tigecycline and eravacycline resistance have been identified in Staphylococcus spp., requires urgent attention.

IMPORTANCE Tigecycline and eravacycline are both important last-resort broad spectrum antimicrobial agents. The presence of novel Tet(L) efflux pump variants conferring the resistance to tigecycline and eravacycline in Staphylococcus spp. and its potential transmission to S. aureus will compromise the efficacy of tigecycline and eravacycline treatment for S. aureus associated infection in vivo and may lead to clinical treatment failure.

Structural insights into the role of the N-terminus in the activation and function of extracellular serine protease from Staphylococcus epidermidis

Extracellular serine protease (Esp) from Staphylococcus epidermidis is a glutamyl endopeptidase that inhibits the growth and formation of S. aureus biofilms. Previously, crystal structures of the matured and active Esp have been determined. Interestingly, many of the staphylococcal glutamyl endopeptidase zymogens, including V8 from Staphylococcus aureus and Esp from S. epidermidis, contain unusually long pro-peptide segments; however, their function is not known. With the aim of elucidating the function of these pro-peptide segments, crystal structures of the Esp zymogen (Pro-Esp) and its variants were determined. It was observed that the N-terminus of the Pro-Esp crystal structure is flexible and is not associated with the main body of the enzyme, unlike in the known active Esp structure. In addition, the loops that border the putative substrate-binding pocket of Pro-Esp are flexible and disordered; the structural components that are responsible for enzyme specificity and efficiency in serine proteases are disordered in Pro-Esp. However, the N-terminal locked Pro-Esp variants exhibit a rigid substrate-binding pocket similar to the active Esp structure and regain activity. These structural studies highlight the role of the N-terminus in stabilizing the structural components responsible for the activity and specificity of staphylococcal glutamyl endopeptidases.

Exfoliative toxin E, a new Staphylococcus aureus virulence factor with host-specific activity

Exfoliative toxins (ETs) are secreted virulence factors produced by staphylococci. These serine proteases specifically cleave desmoglein 1 (Dsg1) in mammals and are key elements in staphylococcal skin infections. We recently identified a new et gene in S. aureus O46, a strain isolated from ovine mastitis. In the present study, we characterized the new et gene at a genetic level and the enzymatic activity of the deduced protein. The S. aureus O46 genome was re-assembled, annotated and compared with other publicly available S. aureus genomes. The deduced amino acid sequence of the new et gene shared 40%, 53% and 59% sequence identity to those of ETA, ETB and ETD, respectively. The new et gene shared the same genetic vicinity and was similar in other S. aureus strains bearing this gene. The recombinant enzyme of the new et gene caused skin exfoliation in vivo in neonatal mice. The new et-gene was thus named ete, encoding a new type (type E) of exfoliative toxin. We showed that ETE degraded the extracellular segments of Dsg1 in murine, ovine and caprine epidermis, as well as in ovine teat canal epithelia, but not that in bovine epidermis. We further showed that it directly hydrolyzed human and swine Dsg1 as well as murine Dsg1α and Dsg1β, but not canine Dsg1 or murine Dsg1γ. Molecular modeling revealed a correlation between the preferred orientation of ETE docking on its Dsg1 cleavage site and species-specific cleavage activity, suggesting that the docking step preceding cleavage accounts for the ETE species-specificity. This new virulence factor may contribute to the bacterial colonization on the stratified epithelia in certain ruminants with mastitis.

The Role of Streptococcal and Staphylococcal Exotoxins and Proteases in Human Necrotizing Soft Tissue Infections

Necrotizing soft tissue infections (NSTIs) are critical clinical conditions characterized by extensive necrosis of any layer of the soft tissue and systemic toxicity. Group A streptococci (GAS) and Staphylococcus aureus are two major pathogens associated with monomicrobial NSTIs. In the tissue environment, both Gram-positive bacteria secrete a variety of molecules, including pore-forming exotoxins, superantigens, and proteases with cytolytic and immunomodulatory functions. The present review summarizes the current knowledge about streptococcal and staphylococcal toxins in NSTIs with a special focus on their contribution to disease progression, tissue pathology, and immune evasion strategies.

Characterization of the clonal profile of methicillin resistant Staphylococcus aureus isolated from patients with early post-operative orthopedic implant based infections

BACKGROUND

To analyze the molecular epidemiology and to compare between the major methicillin resistant Staphylococcus aureus biotypes for association with patient characteristics who had an implant for closed fracture and developed early post-operative wound infections (POWI) in a tertiary care hospital of India.

METHODS

Pulsed-field gel electrophoresis (PFGE), antimicrobial resistance, accessory gene regulator (agr) and staphylococcal cassette chromosome mec (SCCmec) types, Paton-Valentine leukocidin (PVL) gene, toxin gene profiling, biofilm formation and patient demographics were correlated with MLST clonal complexes (CC).

FINDINGS

Overall eight different sequence types (STs) were detected with a predominance of ST239 (66%), ST22 (18%) and some minor types ST772, ST30 (4% each) ST1, ST642, ST6, ST107 (2% each). All ST239 isolates belong to CC239 and SCCmec III whereas ST22 isolates belong to CC22 and SCCmec IV. The isolates varied in the distribution of various toxin genes. With 63.63% biofilm formers ST239 were all multidrug resistant with frequent resistance to erythromycin, clindamycin, gentamicin, cefuroxime, amoxyclav and ciprofloxacin indicating doxycycline, amikacin, vancomycin and linezolid can be the drug of choice.

CONCLUSION

This study shows that ST239 MRSA is still most prevalent strain with new emergence of ST642 and ST107 isolates in association with orthopedic implant based POWI. As compare to other ST types ST239 strain was associated with adverse treatment outcomes. This highlights the importance of improving nosocomial infection control measures in this unit.

Staphylococcus aureus Toxins and Their Molecular Activity in Infectious Diseases

Staphylococcus aureus is a microorganism resident in the skin and nasal membranes with a dreadful pathogenic potential to cause a variety of community and hospital-acquired infections. The frequency of these infections is increasing and their treatment is becoming more difficult. The ability of S. aureus to form biofilms and the emergence of multidrug-resistant strains are the main reasons determining the challenge in dealing with these infections. S. aureus' infectious capacity and its success as a pathogen is related to the expression of virulence factors, among which the production of a wide variety of toxins is highlighted. For this reason, a better understanding of S. aureus toxins is needed to enable the development of new strategies to reduce their production and consequently improve therapeutic approaches. This review focuses on understanding the toxin-based pathogenesis of S. aureus and their role on infectious diseases.

Association Between the Methicillin Resistance of Staphylococcus aureus Isolated from Slaughter Poultry, Their Toxin Gene Profiles and Prophage Patterns

In this work, 85 strains of Staphylococcus aureus were isolated from samples taken from slaughter poultry in Poland. Attempts were made to determine the prophage profile of the strains and to investigate the presence in their genome of genes responsible for the production of five classical enterotoxins (A–E), toxic shock syndrome toxin (TSST-1), exfoliative toxins (ETA and ETB) and staphylokinase (SAK). For this purpose, multiplex PCR was performed using primer-specific pairs for targeted genes. The presence of the mecA gene was found in 26 strains (30.6%). The genomes of one of the methicillin-resistant S. aureus (MRSA) strains and two methicillin-sensitive S. aureus (MSSA) strains contained the gene responsible for the production of enterotoxin A. Only one MRSA strain and two MSSA strains showed the presence of the toxic shock syndrome toxin (tst) gene. Only one of the MSSA strains had the gene (eta) responsible for the production of exfoliative toxins A. The presence of the staphylokinase gene (sak) was confirmed in 13 MRSA strains and in 5 MSSA strains. The study results indicated a high prevalence of prophages among the test isolates of Staphylococcus aureus. In all, 15 prophage patterns were observed among the isolates. The presence of 77-like prophages incorporated into bacterial genome was especially often demonstrated. Various authors emphasize the special role of these prophages in the spread of virulence factors (staphylokinase, enterotoxin A) not only within strains of the same species but also between species and even types of bacteria.

Autocatalytic activation of a thermostable glutamyl endopeptidase capable of hydrolyzing proteins at high temperatures

Glutamyl endopeptidases (GSEs) specifically hydrolyze peptide bonds formed by α-carboxyl groups of Glu and Asp residues. We cloned the gene for a thermophilic GSE (designated TS-GSE) from Thermoactinomyces sp. CDF. A proform of TS-GSE that contained a 61-amino acid N-terminal propeptide and a 218-amino acid mature domain was produced in Escherichia coli. We found that the proform possessed two processing sites and was capable of autocatalytic activation via multiple pathways. The N-terminal propeptide could be autoprocessed at the Glu^-1-Ser¹ bond to directly generate the mature enzyme. It could also be autoprocessed at the Glu^-12-Lys^-11 bond to yield an intermediate, which was then converted into the mature form after removal of the remaining part of the propeptide. The segment surrounding the two processing sites was flexible, which allowed the proform and the intermediate form to be trans-processed into the mature form by either active TS-GSE or heterogeneous proteases. Deletion analysis revealed that the N-terminal propeptide is important for the correct folding and maturation of TS-GSE. The propeptide, even its last 11-amino acid peptide segment, could inhibit the activity of its cognate mature domain. The mature TS-GSE displayed a temperature optimum of 85 °C and retained approximately 90 % of its original activity after incubation at 70 °C for 6 h, representing the most thermostable GSE reported to date. Mutational analysis suggested that the disulfide bonds Cys³²-Cys⁴⁸ and Cys¹⁸⁰-Cys¹⁸³ cumulatively contributed to the thermostability of TS-GSE.

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.

Identification of methicillin-resistant Staphylococcus aureus carrying an exfoliative toxin A gene encoding phage isolated from a hospitalized patient in Turkey

From the four known isoforms of the staphylococcal exfoliative toxins (ETs), only ETA and ETB are the major causative agents. General knowledge is that the gene for ETA is located on the chromosome, whereas that for ETB is located on a large plasmid. Yoshizawa and co-workers (2000, Microbiol. Immunol. 44(3): 189–191) isolated, for the first time, a temperate phage (φETA) that carried the structural gene for ETA from an ETA-producing strain of Staphylococcus aureus. In this study, we presented eta gene encoding temperate phages isolated from methicillin-resistant S.aureus (MRSA) isolates obtained from patients in a Turkish hospital. Molecular analysis of the phage genome revealed that the eta gene is located upstream to amidase and holin genes, the same as in the φETA genome. However, partial sequence analysis of amidase and holin genes revealed polymorphic variation. In addition to polymorphic variation, restriction fragment length polymorphism (RFLP) analysis of all of the phage genomes showed that the ETA-containing phage is different from the rest of the phage genomes. The phylogenetic dendrogram of pulsed field gel electrophoresis (PFGE) analysis showed that the ETA-carrying MRSA is quite different from the rest of the MRSA strains. This is the first report showing that a MRSA strain carries an ETA-encoding phage.

Occurrence and characteristic of methicillin-resistant Staphylococcus aureus on pig farms in the Czech Republic

In recent years, a negative trend of increasing prevalence of methicillin-resistantStaphylococcus aureus(MRSA) strains has been noted worldwide. In addition to their prevalence in humans, MRSA strains have also been detected in animals, both pets and food-producing animals, especially in pigs. At the same time, transmission of MRSA strains from animals to humans has been documented. This study brings results from the first nationwide survey on the prevalence of MRSA in herds of breeding pigs, carried out throughout the Czech Republic in accordance with the Commission Decision 2008/55/EC, including brief characteristics of isolates. In 2008, a total of 283 pooled samples (dust swabs from partitions between pens) from the holdings of breeding pigs were analyzed. In five cases, MRSA isolates were detected, with a prevalence of 1.8%. All the isolated strains belonged to a single sequence type ST398. It may be said that at present, the prevalence of MRSA on pig farms does not pose a significant general epidemiological risk for the human population.

Protease-armed bacteria in the skin

The skin constitutes a formidable barrier against commensal and pathogenic bacteria, which permanently and transiently colonise the skin, respectively. Commensal and pathogenic species inhabiting skin both express proteases. Whereas proteases secreted by commensals contribute to homeostatic bacterial coexistence on skin, proteases from pathogenic bacteria are used as virulence factors, helping them colonise skin with breached integrity of the epithelial layer. From these initial sites of colonisation, pathogens can disseminate into deeper layers of skin, possibly leading to the spread of infection. Secreted bacterial proteases probably play an important role in this process and in the deterrence of innate defence mechanisms. For example, Staphylococcus aureus proteases are essential for changing the bacterial phenotype from adhesive to invasive by degrading adhesins on the bacterial cell surface. Secreted staphylococcal proteases mediate pathogen penetration by degrading collagen and elastin, essential components of connective tissue in the dermis. The activation of the contact system and kinin generation by Streptococcus pyogenes and S. aureus proteases contributes to an inflammatory reaction manifested by oedema, redness and pain. Kinin-enhanced vascular leakage might help bacteria escape into the circulation thereby causing possible systemic dissemination of the infection. The inflammatory reaction can also be fueled by the activation of protease-activated receptors on keratinocytes. Concomitantly, bacterial proteases are involved in degrading antimicrobial peptides, disarming the complement system and neutrophils and preventing the infiltration of the infected sites with immune cells by inactivation of chemoattractants. Together, this provides protection for colonising and/or invading pathogens from attack by antibacterial forces of the skin.

Development of a high-expression system for staphylococcal exfoliative toxin genes

We constructed a new expression system for staphylococcal exfoliative toxin (ET). The expression vector, pETA-exp2, was constructed based on Bacillus-Escherichia shuttle vector pHY300PLK. The pETA-exp2 vector includes the regulator of the ETA gene (eta), the promoter and Shine-Dalgarno (SD) sequences of eta, a SalI sequence at the end of the signal sequence of eta, a nucleotide sequence encoding mature ETA, an XhoI site, a 6x His sequence just before the stop codon and the end of the transcription sequence of eta. The nucleotide sequences coding for the mature proteins of ETB, ExhA, ExhB, ExhC, ExhD and SHETB were amplified by polymerase chain reaction (PCR) and inserted into pETA-exp2. These recombinant plasmids were transformed into Bacillus megaterium. The major protein in the culture supernatant of the transformant was recombinant ET (rET). The yields of all rETs were high, and all of them showed exfoliative activity in susceptible animals. The antigenicities of rETs and ETs were not distinguishable from each other.

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.

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.

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.

Molecular characterization of the copper transport system in Staphylococcus aureus

The Staphylococcus aureus copA gene codes for a putative copper-translocating P-type ATPase and the downstream copZ gene codes for a copper chaperone. Genome database analyses demonstrate that these copper transport genes are highly conserved in S. aureus. The expression of copA and copZ was inducible by copper and to some extent by ferric and lead ions. A mutant strain containing a partially deleted copA gene was more sensitive than the parent strain to copper, ferric and lead ions. The copper-sensitive phenotype was due to the accumulation of intracellular copper and thus the copA product is involved in the export of copper ions. The metal-sensitive phenotype of the mutant was complemented in trans by a 2.7 kbp DNA containing copA. We have cloned and overexpressed the metal-binding domains of CopA and CopZ and have shown by site-directed mutagenesis that the cysteine residues in the CXXC metal-binding motif in CopA are involved in copper binding and thus play an important role in copper transport in S. aureus.

Multiplex PCR for detection of three exfoliative toxin serotype genes in Staphylococcus aureus

Rapid and specific detection of exfoliative toxin (ET)-producing Staphylococcus aureus strains by multiplex polymerase chain reaction (PCR) was used for identification of exfoliative toxin genes in a diverse set of 115 clinical S. aureus strains isolated in 14 Czech cities between 1998 and 2004. Fifty-nine wild-type ET-positive isolates of which 40 strains were the causative agents of toxic epidermolysis in neonates were classified into 4 PCR types. The genes coding for ETA, ETB or ETD were not detected in any of non-ET-producing isolates. The PCR method using the multiplex and specific primer set was shown to be reliable in rapid identification of the exfoliative toxin producing S. aureus and can be used as a convenient tool for hospital epidermolytic infection control.

Microarrays reveal that each of the ten dominant lineages of Staphylococcus aureus has a unique combination of surface-associated and regulatory genes

Staphylococcus aureus is the most common cause of hospital-acquired infection. In healthy hosts outside of the health care setting, S. aureus is a frequent colonizer of the human nose but rarely causes severe invasive infection such as bacteremia, endocarditis, or osteomyelitis. To identify genes associated with community-acquired invasive isolates, regions of genomic variability, and the S. aureus population structure, we compared 61 community-acquired invasive isolates of S. aureus and 100 nasal carriage isolates from healthy donors using a microarray spotted with PCR products representing every gene from the seven S. aureus sequencing projects. The core genes common to all strains were identified, and 10 dominant lineages of S. aureus were clearly discriminated. Each lineage carried a unique combination of hundreds of "core variable" (CV) genes scattered throughout the chromosome, suggesting a common ancestor but early evolutionary divergence. Many CV genes are regulators of virulence genes or known or predicted to be expressed on the bacterial surface and to interact with the host during nasal colonization and infection. Within each lineage, isolates showed substantial variation in the carriage of mobile genetic elements and their associated virulence and resistance genes, indicating frequent horizontal transfer. However, we were unable to identify any association between lineage or gene and invasive isolates. We suggest that the S. aureus gene combinations necessary for invasive disease may also be necessary for nasal colonization and that community-acquired invasive disease is strongly dependent on host factors.

Cloning of swine desmoglein 1 and its direct proteolysis by Staphylococcus hyicus exfoliative toxins isolated from pigs with exudative epidermitis

Exudative epidermitis (EE) is an acute, often fatal skin disease of piglets caused by Staphylococcus hyicus. Clinical and histopathological manifestations of EE are similar to those of staphylococcal scalded skin syndrome (SSSS), a human blistering skin disease, in which exfoliative toxins produced by Staphylococcus aureus digest the extracellular domains of desmoglein (Dsg) 1 and cause loss of epidermal cell-cell adhesion. The aims of this study were to isolate and characterize cDNA for full length of swine Dsg1, and to determine whether the extracellular domains of swine Dsg1 produced by baculovirus (sDsg1-His) could be digested by four isoforms of exfoliative toxin produced by S. hyicus (ExhA, ExhB, ExhC and ExhD). Nucleotide sequencing revealed that swine Dsg1 cDNA consisted of an open reading frame of 3138 bp, encoding a precursor protein of 1045 amino acids. Deduced amino acid sequence of the swine Dsg1 precursor were highly homologous to corresponding bovine, canine, human and murine sequences. Immunoadsorption assay with a secreted form of sDsg1-His revealed that sDsg1-His specifically absorbs the immunoreactivity of 10 human pemphigus foliaceus sera against swine keratinocyte cell surfaces, suggesting its proper conformation. When sDsg1-His was incubated in vitro with Exhs, all four isoforms of Exh directly digested sDsg1-His into smaller peptides, whereas removal of calcium from sDsg1-His completely inhibited its proteolysis by these four Exhs. Recognition and digestion of calcium-stabilized structure on the extracellular domains of swine Dsg1 by Exhs indicated that EE shares similar molecular pathophysiological mechanisms of intra-epidermal splitting with SSSS in humans.

Characterization of a multicopper oxidase gene from Staphylococcus aureus

A multicopper oxidase gene from Staphylococcus aureus was cloned and overexpressed. Purified recombinant multicopper oxidase oxidized the substrate 3,3'-dimethoxybenzidine in the presence of copper. Disruption of mco showed copper sensitivity and H(2)O(2) resistance, suggesting roles for mco in copper homeostasis and oxidative stress response. Northern blot analysis showed copper-induced mco transcription.

Treatment of staphylococcal scalded skin syndrome

Humans are a natural reservoir for Staphylococcal aureus. Colonization begins soon after birth and predisposes to infection. S. aureus is one of the most common causes of skin infection, giving rise to folliculitis, furunculosis, carbuncles, ecthyma, impetigo, cellulitis and abscesses. In addition, S. aureus may cause a number of toxin-mediated life-threatening diseases, including staphylococcal scalded skin syndrome (SSSS). Epidermolytic toxins released by certain S. aureus strains cause SSSS by cleaving the epidermal cell adhesion molecule, desmogelin-1, resulting in superficial skin erosion. Recent experiments have revealed similarities in the pathophysiology of SSSS and pemphigus foliaceus, an autoimmune disorder that is characterized by antibodies targeting the same epidermal attachment protein. SSSS typically affects neonates and infants but may also occur in predisposed adults. It is painful and distressing for the patient and parents, although most cases respond to antibiotic treatment. Mortality is low in infants but can be as high as 67% in adults, and is dependent on the extent of skin involvement and the comorbid state. Thus, the management of adults who develop SSSS remains a major therapeutic challenge. The antibody response against the toxins neutralizes their effect and prevents recurrence or limits the effects to the area of infection, which is known as bullous impetigo.

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.

Cloning and sequence analysis of genes encoding Staphylococcus hyicus exfoliative toxin types A, B, C, and D

Exfoliative toxins produced by certain strains of Staphylococcus hyicus mediate exudative epidermitis in pigs. In this study the genes coding for four different exfoliative toxin from S. hyicus (ExhA, ExhB, ExhC, and ExhD) were cloned and sequenced. The coding sequence of the four toxin genes ranged from 816 to 834 bp. The amino acid sequences of these four toxins were homologous to the earlier described exfoliative toxins SHETB from S. hyicus and ETA, ETB, and ETD from Staphylococcus aureus. The homology between the S. hyicus toxins was at the same level as the homology to the exfoliative toxins from S. aureus. The toxins showed similarity to serine proteases, including preservation of the catalytic tract in ExhA, ExhB, and ExhC. However, in ExhD, Asp in the putative catalytic tract was replaced with Glu. The recombinant toxins could be expressed in Escherichia coli, and three of the four toxins were recognized by monoclonal antibodies raised against native exfoliative toxins.

A novel positive regulatory element for exfoliative toxin A gene expression in Staphylococcus aureus

A 1·4 kb positive regulatory element (ETAexp ) that controls staphylococcal exfoliative toxin A (sETA) transcription was cloned from Staphylococcus aureus. ETAexp is located upstream of the cloned 5·8 kb eta gene (etaJ1) obtained from the chomosomal DNA of S. aureus ZM, the standard ETA-producing strain. The cETA prepared from an Escherichia coli transformant into which the recombinant plasmid petaJ1 (5·8 kb eta/pUC9) had been introduced was expressed at high levels in the culture supernatant and the ammonium-sulfate-precipitated culture supernatant fraction as shown by immunoblotting and the single radial immunodiffusion test. However, cETA produced by the recombinant plasmid petaJ3 containing the 1·7 kb eta sequence (etaJ3) with a 1·45 kb ETAexp -deficient eta fragment (1·7 kb eta/pUC9) obtained from the 5·8 kb eta sequence by subcloning was not detected in either the culture supernatant or the ammonium-sulfate-precipitated culture supernatant fraction (167-fold concentrate of the culture supernatant) by immunoblotting or the single radial immunodiffusion test. A large amount of cETA was produced by the 1·7 kb eta sequence when it was linked to ETAexp amplified by PCR (1·7 kb eta-ETAexp /pUC9), regardless of the orientation of ETAexp insertion. Northern blot hybridization showed lower levels of the transcripts of the 1·7 kb eta sequence than of the 5·8 kb eta sequence. The rsETA prepared from an S. aureus transformant into which the recombinant plasmid 3·4 kb eta-ETAexp /pYT3 (pYT3-etaJ6) had been introduced was expressed at high levels in the culture supernatant fraction as shown by the latex agglutination test. However, the agglutination titre in the culture supernatant fraction of rsETA produced by the recombinant plasmid (1·7 kb eta/pYT3) containing the 1·7 kb eta sequence carrying the 1·4 kb ETAexp -deficient eta fragment (pYT3-etaJ3) was 2500–4000 times lower than that of pYT3-etaJ6.

Phage conversion of exfoliative toxin A in Staphylococcus aureus isolated from cows with mastitis

An exfoliative toxin produced by Staphylococcus aureus is the causative agent of staphylococcal scalded-skin syndrome (SSSS) in young children. Recently, we reported that only few isolates of S. aureus from bovine mastitis contained the eta gene encoding exfoliative toxin A (ETA) and produced ETA in vitro. In this study, we isolated temperate phages from two ETA-positive bovine isolates of S. aureus by treatment with mitomycin C. Polymerase chain reaction (PCR) assay of the phage genomes suggested that the temperate phages carried the structural gene for ETA. Moreover, the nucleotide sequence analysis of the PCR products revealed that the eta gene was located very close to an amidase gene on the phage genomes. The nucleotide sequence for the amidase gene of the bovine phage (bovine phi ETA) differed at nine positions from that of the amidase gene of phi ETA from a human isolate reported by Yamaguchi et al. [Mol. Microbiol. 38 (2000) 694], suggesting that eta-converting phages are heterogeneous. Bovine phi ETA had a head with a hexagonal outline and a non-contractile and flexible tail. Bovine phi ETA was able to lysogenize ETA-negative bovine isolates of S. aureus, and the lysogenized S. aureus isolates had the ability to produce ETA. These results suggest the possibility of horizontal transmission of the eta gene by temperate bacteriophages among bovine isolates of S. aureus.

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.

NaCl-sensitive mutant of Staphylococcus aureus has a Tn917-lacZ insertion in its ars operon

Staphylococcus aureus is a Gram-positive bacterium that is extremely halotolerant. To investigate the molecular mechanisms by which S. aureus can cope with osmotic stress, Tn917-lacZ-induced NaCl-sensitive mutants were isolated. An NaCl-sensitive mutant showed a longer lag period, slower growth rate, and lower final culture turbidity than the parent strain in liquid medium containing 1.5 M NaCl. Electron microscopic observation of the NaCl-sensitive mutant under NaCl stress conditions revealed large, pseudo-multicellular cells. Addition of exogenous osmoprotectants, such as glycine betaine, choline, L-proline, and proline betaine, did not relieve the NaCl sensitivity of the mutant. The region flanking the transposon insertion site in the NaCl-sensitive S. aureus chromosome was sequenced. The mutated gene was 99% identical to arsR, the arsenic operon regulatory protein present on the pI258 plasmid of S. aureus. The ars operon from pI258 was subcloned into the shuttle vector pLI50 and transferred into the NaCl-sensitive mutant. The ars operon in trans restored NaCl tolerance in the mutant, suggesting that NaCl sensitivity is due to the mutation in arsR.

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.

Desmoglein as a target in autoimmunity and infection

Clinical phenotypes of most diseases are complex. However, once the mechanism behind the scene is clarified, the nature shows amazing beauty. There is a simple logic behind a complex disease. The exact molecular mechanism of the blister formation in staphylococcal scalded skin syndrome (SSSS) remained to be elucidated for 3 decades since exfoliative toxin was discovered by Melish and Glasgow in 1970. A knowledge accumulated to understand the pathogenesis of pemphigus and cell-cell adhesion of keratinocytes led us to solve this question. Desmoglein 1, which is a cadherin type cell-cell adhesion molecule in desmosomes, is targeted in two different skin diseases, pemphigus foliaceus, and SSSS. In pemphigus foliaceus IgG autoantibodies are developed against desmoglein 1 and inhibit its adhesive function with resultant blister formation in the superficial epidermis. In SSSS, exfoliative toxin produced by Staphylococcus aureus specifically binds and cleaves desmoglein 1 with resultant blister formation at the identical site.

Two-dimensional analysis of exoproteins of methicillin-resistant Staphylococcus aureus (MRSA) for possible epidemiological applications

We applied two-dimensional gel electrophoresis (2-DE) to the total exoproteins secreted from pathogenic MRSA strains and identified major protein spots by N-terminal amino acid sequence analysis. In approximately 300 to 500 spots visualized on each gel, various exoproteins and cell-associated proteins were identified and their sites on the gels confirmed for construction of a reference map. Major exotoxins such as enterotoxins SEA, SEB, and SEC,, toxic shock syndrome toxin-1 (TSST-1), and hemolysins were distributed in the region of pI 6.8 to 8.1 and MW 21 to 35 kDa. Although the differences between calculated and observed values of pI and MW were relatively small in each exoprotein, those of several proteins including alpha-hemolysin and SEB were considerably deviated from the positions of the expected values. Some exoproteins were detected as multiple spots. These included beta-hemolysin, enterotoxins SEA, SEB, and SEC3, glutamic acid-specific endopeptidase, glycerophosphoryl diester phosphodiesterase and triacylglycerol lipase. The multiple spots of these exoproteins may be generated by the action of own proteases. Certain similarities of 2-DE patterns among strains belonging to the same coagulase types were observed. On the basis of 2-DE image analysis, coagulase type II strains secreted somewhat larger amounts of SEB and SEC3 as well as TSST-1 than the strains belonging to other coagulase types. Taken together, 2-DE analysis of exoproteins is applicable to epidemiological studies for MRSA, as compared with pulsed field gel electrophoresis of restricted chromosomal DNA.

Molecular mechanisms of blister formation in bullous impetigo and staphylococcal scalded skin syndrome

Bullous impetigo due to Staphylococcus aureus is one of the most common bacterial infections of man, and its generalized form, staphylococcal scalded skin syndrome (SSSS), is a frequent manifestation of staphylococcal epidemics in neonatal nurseries. Both diseases are mediated by exfoliative toxins (ETs), which show exquisite pathologic specificity in blistering only the superficial epidermis. We show that these toxins act as serine proteases with extremely focused molecular specificity to cleave mouse and human desmoglein 1 (Dsg1) once after glutamic acid residue 381 between extracellular domains 3 and 4. Mutation of the predicted catalytically active serine to alanine completely inhibits cleavage. The mutated ETs bind specifically to Dsg1 by immunofluorescence colocalization and by coimmunoprecipitation. Thus, ETs, through specific recognition and proteolytic cleavage of one structurally critical peptide bond in an adhesion molecule, cause its dysfunction and allow S. aureus to spread under the stratum corneum, the main barrier of the skin, explaining how, although they circulate through the entire body in SSSS, they cause pathology only in the superficial epidermis.

Extracellular proteases of Staphylococcus spp

Bacterial proteases secreted into an infected host may exhibit a wide range of pathogenic potentials. Staphylococci, in particular Staphylococcus aureus, are known to produce several extracellular proteases, including serine-, cysteine- and metalloenzymes. Their insensitivity to most human plasma protease inhibitors and, even more, the ability to inactivate some of these make the proteases potentially harmful. Indeed, several recent studies have shown that staphylococcal proteases are able to interact with the host defense mechanisms and tissue components as well as to modify other pathogen-derived virulence factors. A tight, cell density-dependent control of proteolytic activity expression, similar to that of the well-defined virulence determinants, further suggests the role of staphylococcal proteases in the infection process. Consistently, alterations in coordinated expression of extracellular proteins markedly diminished the virulence. However, despite these data and the fact that a strain deficient in sspABC operon coding for serine (sspA) and cysteine (sspB) proteases was highly attenuated in virulence in the animal infection model, it was impossible to unambiguously demonstrate the importance of any particular protease as a virulence factor. Therefore, it can be assumed that the orchestrated expression and interaction of a variety of extracellular and cell surface proteins rather than any particular one is responsible for the staphylococcal pathogenicity and that the proteases apparently play an important role in this complex process. Such redundant mechanism is very well suited for promoting the survival of staphylococci under diverse environmental conditions encountered in the infected host.

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.

EmtA, a rRNA methyltransferase conferring high-level evernimicin resistance

Enterococcus faecium strain 9631355 was isolated from animal sources on the basis of its resistance to the growth promotant avilamycin. The strain also exhibited high-level resistance to evernimicin, a drug undergoing evaluation as a therapeutic agent in humans. Ribosomes from strain 9631355 exhibited a dramatic reduction in evernimicin binding, shown by both cell-free translation assays and direct-binding assays. The resistance determinant was cloned from strain 9631355; sequence alignments suggested it was a methyltransferase and therefore it was designated emtA for evernimicin methyltransferase. Evernimicin resistance was transmissible and emtA was localized to a plasmid-borne insertion element. Purified EmtA methylated 50S subunits from an evernimicin-sensitive strain 30-fold more efficiently than those from a resistant strain. Reverse transcription identified a pause site that was unique to the 23S rRNA extracted from resistant ribosomes. The pause corresponded to methylation of residue G2470 (Escherichia coli numbering). RNA footprinting revealed that G2470 is located within the evernimicin-binding site on the ribosome, thus providing an explanation for the reduced binding of the drug to methylated ribosomes.

Toxin genes and other characteristics of Staphylococcus aureus isolates from milk of cows with mastitis

In the present study, 103 Staphylococcus aureus strains isolated from milk samples from 60 cows with mastitis from eight different farms in seven different locations in one region of Germany were compared pheno- and genotypically and by identification of various toxins. On the basis of culture and hemolytic properties and by determination of the tube coagulase reaction, all of the isolates could be identified as S. aureus. This could be confirmed by PCR amplification of species-specific parts of the gene encoding the 23S rRNA. In addition, all of the S. aureus isolates harbored the genes encoding staphylococcal coagulase and clumping factor and the genes encoding the X region and the immunoglobulin G binding region of protein A. These four genes displayed size polymorphisms. By PCR amplification, the genes for the toxins staphylococcal enterotoxin A (SEA), SEC, SED, SEG, SEI, SEJ, and TSST-1 but not those for SEB, SEE, SEH, and the exfoliative toxins ETA and ETB could be detected. To analyze the epidemiological relationships, the isolates were subjected to DNA fingerprinting by macrorestriction analysis of their chromosomal DNAs. According to the observed gene polymorphisms, the toxin patterns, and the information given by macrorestriction analysis of the isolates by pulsed-field gel electrophoresis, a limited number of clones seemed to be responsible for the cases of bovine mastitis on the various farms.

Genetic variation among hospital isolates of methicillin-sensitive Staphylococcus aureus: evidence for horizontal transfer of virulence genes

Staphylococcus aureus strains often carry in their genomes virulence genes that are not found in all strains and that may be carried on discrete genetic elements. Strains also differ in that they carry one of four classes of an accessory gene regulator (agr) locus, an operon that regulates virulence factor expression and that has been proposed to be a therapeutic target. To look at their distribution among hospital strains, we investigated 38 methicillin-sensitive S. aureus isolates, classifying the isolates by agr class and screening them for the presence and restriction fragment length polymorphisms (RFLPs) of 12 core and 14 accessory virulence genes. Twenty-three (61%) were agr class I, 10 (26%) were agr class II, and 5 (13%) were agr class III. None were agr class IV. The S. aureus strains had distinguishable RFLP profiles, although clusters of isolates with clearly related core gene profiles were found among our strains, including all five agr class III strains, two sets of six strains within agr class I, and six strains within agr class II. Within these clusters there was evidence of horizontal acquisition and/or loss of multiple accessory virulence genes. Furthermore, two isolates from the same patient were identical except for the presence of the sea gene, indicating that movement of mobile elements may occur in vivo. Several strong correlations with the carriage of virulence genes between strains were seen, including a positive correlation between tst and agr class III and negative correlations between tst and lukE-splB and between lukE-splB and seg-sei. This suggests that the core genome or the presence of accessory genetic elements within a strain may influence acquisition and loss of other elements encoding virulence genes.

A simple and rapid method for purifying staphylococcal exfoliative toxin A

A rapid and efficient method of purification of staphylococcal exfoliative toxin A, the causative agent of staphylococcal scalded skin syndrome (SSSS), has been developed. It is based on ammonium sulfate precipitation of the culture supernatant and hydrophobic interaction chromatography on Phenyl-Sepharose CL-4B. This procedure results in 87-fold purification of this toxin, which appears as a single band in sodium dodecyl sulfate-polyacrylamide gels.

Genotypic and phenotypic characterization of Staphylococcus aureus strains isolated in subjects with atopic dermatitis. Higher prevalence of exfoliative B toxin production in lesional strains and correlation between the markers of disease intensity and colonization density

Staphylococcus aureus strains generally colonize eczematous lesions of subjects with atopic dermatitis much more frequently than in the skin of normal individuals. The aim of this study was to provide a detailed genotypic and phenotypic analysis of S. aureus strains colonizing four different sites (lesional and non-lesional skin areas, nasal and pharyngeal mucosas) of 49 patients with atopic dermatitis. The 88 isolates were analyzed in duplicate by pulsed field gel electrophoresis and in their exfoliative toxin A or B production by latex test. The patients were characterized by age, sex, severity scoring of atopic dermatitis and serum eosinophil cationic protein. Fourteen (28.6%) of the patients were completely negative for S. aureus while 35 (71.4%) were positive in at least one site. The severity scores and eosinophil cationic protein levels were significantly correlated variables (P<0.001), linked to the colonization intensity (P ranging between 0.05 and <0.001 depending on the site) and to the number of colonized sites (P at least <0.01). The genotypic patterns, widely heterogeneous, showed no restriction to peculiar patterns. Only eight strains produced exfoliative toxin B which was significantly restricted to the lesional isolates (P=0.012).

Genetic analysis of exfoliative toxin A-producing Staphylococcus aureus isolated from mastitic cow's milk

Exfoliative toxin A (ETA), produced by Staphylococcus aureus, is the causative agent of staphylococcal scalded-skin syndrome (SSSS) in children. Recently, we reported that ETA was detected by reverse passive latex agglutination in three isolates of S. aureus from cow's milk, but that these ETA-positive isolates did not cause the so-called Nikolsky sign in neonatal mice. In this study, therefore, the eta gene encoding ETA and regulatory genes of these bovine isolates were analyzed by the polymerase chain reaction (PCR) and sequencing. The eta gene was amplified from three bovine isolates by PCR and their resulting nucleotide sequences found to correspond to the eta gene from the human isolate, except for three nucleotides in the upstream region of the eta open reading frame (ORF). An accessory gene regulator (agr), which is a global regulatory locus, was detected in these bovine isolates by PCR amplification. In addition, the ORF (J-4), located 120 bp upstream from the eta ORF of the human isolate, was also amplified from these bovine isolates, with their nucleotide sequences differing at 32 positions from the human isolate. Bovine and human ORF J-4 equally enhanced production of ETA in the recombinants of the eta gene, suggesting that the variation in bovine ORF J-4 may be not be the cause of the difference in amount of ETA produced by bovine and human isolates.

Purification of protease from a mixture of exfoliative toxin and newborn-mouse epidermis

Although the role of exfoliative toxin in staphylococcal scalded-skin syndrome has been suggested to be that of a serine protease, it has not been demonstrated to show proteolytic activity. Our purpose was to purify a proteolytic enzyme from a mixture of exfoliative toxin and newborn-mouse epidermis. We used gel filtration and ion-exchange and hydroxyapatite chromatography with a high-pressure liquid chromatography system. A casein-hydrolyzing enzyme was isolated from the mixture. The molecular mass of the enzyme was confirmed to be 20 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Subcutaneous injection of the purified enzyme into newborn mice reproduced the epidermal splitting that is seen in staphylococcal scalded-skin syndrome. These results suggest that exfoliative toxin does not work as a protease itself but that some reaction between exfoliative toxin and an epidermal component(s) first produces a protease, after which epidermal splitting occurs.