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

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.

Virulence Mechanisms of Staphylococcal Animal Pathogens

Staphylococci are major causes of infections in mammals. Mammals are colonized by diverse staphylococcal species, often with moderate to strong host specificity, and colonization is a common source of infection. Staphylococcal infections of animals not only are of major importance for animal well-being but have considerable economic consequences, such as in the case of staphylococcal mastitis, which costs billions of dollars annually. Furthermore, pet animals can be temporary carriers of strains infectious to humans. Moreover, antimicrobial resistance is a great concern in livestock infections, as there is considerable antibiotic overuse, and resistant strains can be transferred to humans. With the number of working antibiotics continuously becoming smaller due to the concomitant spread of resistant strains, alternative approaches, such as anti-virulence, are increasingly being investigated to treat staphylococcal infections. For this, understanding the virulence mechanisms of animal staphylococcal pathogens is crucial. While many virulence factors have similar functions in humans as animals, there are increasingly frequent reports of host-specific virulence factors and mechanisms. Furthermore, we are only beginning to understand virulence mechanisms in animal-specific staphylococcal pathogens. This review gives an overview of animal infections caused by staphylococci and our knowledge about the virulence mechanisms involved.

Identification and characterization of the causative agents of Focal Ulcerative Dermatitis in commercial laying hens

Focal Ulcerative Dermatitis (FUDS) is an emerging dermatological disease that affects cage-free laying flocks, it is characterized by the development of a lesion on the dorsum of the birds; FUDS is sporadic in nature and can result in a drop in egg production and up to 50% of cumulative mortality. A total of two cage-free flocks (flock 1: no history of FUDS; flock 2: birds affected with FUDS) from a commercial laying hen operation in the mid-west U.S. were sampled in this study. The microbial composition of skin, cloacal, cecal, and ileal samples from each bird was characterized through next generation sequencing (NGS). Results identified Staphylococcus aureus and Staphylococcus agnetis as the potential causative agents of FUDS, being the most predominant in FUDS positive birds. These results were confirmed by plating, with both staphylococci as the only pathogens isolated from lesions of FUDS positive birds. A total of 68 confirmed Staphylococcus isolates from skin and environmental samples were further analyzed by whole genome sequencing (WGS) for the presence of antimicrobial resistance (AMR) genes and virulence factors that could have contributed to the development of FUDS. Forty-four-point one-two percent of the isolates had between one and four acquired AMR genes encoding for macrolides, lincosamides, spectrogramines, and beta-lactams resistance. Six classes of virulence factors associated with adherence, enzyme, immune evasion, secretion system, toxin, and iron uptake were identified. The antimicrobial effect of 4 proprietary Bacillus Direct Fed Microbial (DFM) combinations was evaluated against the Staphylococcus aureus and Staphylococcus agnetis isolates, by agar well-diffusion (AWD) assay and competitive exclusion (CE) on broth culture. Through this antimicrobial screening, a particular two-strain combination of Bacillus pumilus was identified as the most effective inhibitor of both staphylococci. A customized Bacillus pumilus product is being used at different farms with history of FUDS resulting in the successful inhibition of both Staphylococcus aureus and Staphylococcus agnetis, decreasing FUDS mortalities, and improving harvestable eggs.

Role of Staphylococcus agnetis and Staphylococcus hyicus in the Pathogenesis of Buffalo Fly Skin Lesions in Cattle

Buffalo flies (Haematobia irritansexigua) are hematophagous ectoparasites of cattle causing production and welfare impacts in northern Australian herds. Skin lesions associated with buffalo fly infestation and Stephanofilaria nematode infection are manifested as focal dermatitis or ulcerated areas, most commonly on the medial canthus of the eye, along the lateral and ventral neck, and on the abdomen of cattle. For closely related horn flies (Haematobia irritans irritans), Staphylococcus aureus has been suggested as a contributing factor in the development of lesions. To investigate the potential role of bacterial infection in the pathogenesis of buffalo fly lesions, swabs were taken from lesions and normal skin, and bacteria were also isolated from surface washings of buffalo flies and surface-sterilized homogenized flies. Bacterial identification was conducted by matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) and strain typing by repetitive sequence-based PCR (rep-PCR) and DNA sequencing to determine species similarity and virulence factors. Of 50 bacterial isolates collected from lesions, 38 were identified as Staphylococcus agnetis and 12 as Staphylococcus hyicus, whereas four isolates from normal skin were S. hyicus and one was Mammaliicoccus sciuri. Of the Staphylococcus isolates isolated from buffalo flies, five were identified as S. agnetis and three as S. hyicus. Fifty percent of the buffalo fly isolates had rep-PCR genotypic patterns identical to those of the lesion isolates. Genome sequencing of 16 S. agnetis and four S. hyicus isolates revealed closely similar virulence factor profiles, with all isolates possessing exfoliative toxin A and C genes. The findings from this study suggest the involvement of S. agnetis and S. hyicus in buffalo fly lesion pathogenesis. This should be taken into account in the development of effective treatment and control strategies for lesions.

IMPORTANCE Skin lesions in cattle associated with feeding by Haematobia fly species are a significant welfare issue in Australia, North and South America, and Europe. The development of these lesions has been attributed to a number of causal factors, but the exact etiology and pathogenesis were unclear. This study characterized Staphylococcus agnetis and Staphylococcus hyicus strains from cattle skin lesions and in vector flies and demonstrated their role in the pathogenesis of these lesions. These findings will aid the development of targeted and more effective treatment and control strategies for lesions associated with fly infestation in cattle.

Partial reproduction of ear-tip necrosis suggests an infectious, initially bacterial aetiology

Swine ear-tip necrosis (ETN) is a disease of global presence and unclear aetiology. Little evidence is available regarding the nature of this disease. The aim of this work was to investigate if ETN is an infectious disease that could be replicated using a lesion macerate inoculum. A source farm with a history of ear-tip necrosis was identified and five weeks-old pigs (n = 12) from this farm were housed under controlled conditions and intradermally inoculated with ETN lesion macerates (right ear, n = 10) or sterile inoculum (left ear, n = 10). Two pigs were not inoculated, serving as sentinels. All animals were clinically monitored daily during 21 days, and a ETN ear score was used to follow disease progression. Anaerobic (n = 2) and aerobic (n = 2) overnight cultures, as well as raw aliquots of the lesion macerate inoculum (n = 2) and control inoculum (n = 2) were submitted for metagenomic sequencing. All inoculated ears developed lesions suggestive of early ETN, but none progressed to result in loss of the ear pinna. All completely resolved 21 days post-inoculation. Post-mortem investigation revealed areas of fibrosis, characterized by a granulomatous response in the inoculated ears (5/10) and in 1/10 control ears. Metagenomic analysis identified the presence of previously suggested bacterial etiological agents, but no relevant viral, fungal or protozoan agents in the inoculum. ETN etiology remains unclear, but an infectious cause and bacterial agents are suggested to be at least partially implicated in disease pathogenesis. Virus and fungi do not seem to significantly contribute to disease.

Exudative Epidermitis in Combination with Staphylococcal Pyoderma in Suckling Piglets

A case of generalized exudative epidermitis (EE) is described, which occurred in a very small piglet producing farm in Austria. The antimicrobial treatment prescribed by the herd veterinarian did not improve the clinical problem. Therefore, the University Clinic for Swine intervened in the case. Lab investigations were initiated in which Staphylococcus hyicus (SH) and Staphylococcus aureus (SA), both methicillin-resistant and susceptible strains, could be isolated from the skin of affected piglets. Poor hygiene and management practices were identified as predisposing factors on site. Adaptation of antimicrobial treatment according to results of the in vitro susceptibility testing and the implementation of proper hygiene measures resolved the clinical problem. Here, we describe a fatal coinfection of SH and SA in suckling piglets.

First Molecular Characterization of Siphoviridae-Like Bacteriophages Infecting Staphylococcus hyicus in a Case of Exudative Epidermitis

Exudative epidermitis (EE), also known as greasy pig disease, is one of the most frequent skin diseases affecting piglets. Zoonotic infections in human occur. EE is primarily caused by virulent strains of Staphylococcus (S.) hyicus. Generally, antibiotic treatment of this pathogen is prone to decreasing success, due to the incremental development of multiple resistances of bacteria against antibiotics. Once approved, bacteriophages might offer interesting alternatives for environmental sanitation or individualized treatment, subject to the absence of virulence and antimicrobial resistance genes. However, genetic characterization of bacteriophages for S. hyicus has, so far, been missing. Therefore, we investigated a piglet raising farm with a stock problem due to EE. We isolated eleven phages from the environment and wash water of piglets diagnosed with the causative agent of EE, i.e., S. hyicus. The phages were morphologically characterized by electron microscopy, where they appeared Siphoviridae-like. The genomes of two phages were sequenced on a MiSeq instrument (Illumina), resulting in the identification of a new virulent phage, PITT-1 (PMBT8), and a temperate phage, PITT-5 (PMBT9). Sequencing of three host bacteria (S. hyicus) from one single farm revealed the presence of two different strains with genes coding for two different exfoliative toxin genes, i.e., exhA (2 strains) and exhC (1 strain). The exhC-positive S. hyicus strain was only weakly lysed by most lytic phages. The occurrence of different virulent S. hyicus strains in the same outbreak limits the prospects for successful phage treatment and argues for the simultaneous use of multiple and different phages attacking the same host.

Virulence factors in coagulase-positive staphylococci of veterinary interest other than Staphylococcus aureus

Coagulase-positive Staphylococci (CoPS) can exist as commensals in humans, companion and food-producing animals, but can cause severe or even lethal diseases. Exchange of these bacteria between humans and animals has been described. Special attention has been focused on Methicillin-Resistant Staphylococcus aureus, but other CoPS can also represent an important threat. In addition to significant antimicrobial resistance, these bacteria may carry a plethora of virulence factors - molecules that allow bacteria to establish on or within a host and increase their ability to cause disease. These virulence factors have been widely described in S. aureus but information about other species of CoPS is scarce. The aim of this paper is to review the recent literature about the virulence factors of non-aureus CoPS of animal origin. Their possible effects on human health are also described. The role and prevalence of different virulence factors including leukocidins, hemolysins, adhesins, enterotoxins, exfoliative and toxic shock syndrome toxins as well as superantigen-like proteins are addressed. The effect of these virulence factors on human health is also described. The possibility of misdiagnosis of species of CoPS has been demonstrated in human clinical samples. Prevalence of zoonotic infections could be higher than thought and medical laboratories should be aware of these other staphylococcal species. In keeping with the ‘One Health’ approach to animal and human disease, medical professionals, veterinarians and health workers should be aware of the risks derived from exposure to these bacteria in people in close contact with animals, including pet owners, farmers and veterinarians themselves.

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.

Glutamyl Endopeptidases: The Puzzle of Substrate Specificity

Glutamyl endopeptidases (GEPases) are chymotrypsin-like enzymes that preferentially cleave the peptide bonds of the α-carboxyl groups of glutamic acid. Despite the many years of research, the structural determinants underlying the strong substrate specificity of GEPases still remain unclear. In this review, data concerning the molecular mechanisms that determine the substrate preference of GEPases is generalized. In addition, the biological functions of and modern trends in the research into these enzymes are outlined.

Spondylodiscitis and bacteremia due to Staphylococcus hyicus in an immunocompetent man

INTRODUCTION

Staphylococcus hyicus is a coagulase-variable Staphylococcus spp. well-known by veterinarians since it is the major agent of a severe cutaneous infection in piglets called exudative epidermitis. In other species the symptoms of infection are quite different. Human cases are uncommon but seem to occur more frequently after repeated contacts with farm animals.

CASE REPORT

We report the case of a 58-year-old man suffering from debilitating subacute lumbar pain, in whom diagnosis of infectious spondylodiscitis was based on spine MRI and positive microbiological results. A strain of S. hyicus was surprisingly isolated from blood cultures and bone biopsy. Identification was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS, Bruker, USA), and the patient was successfully cured with a six-week course of anti-staphylococcal antibiotic regimen.

CONCLUSION

The prevalence of S. hyicus in human clinical samples is very low, but may be underestimated. This pathogen may enter the bloodstream through a skin injury, and then induce various pyogenic manifestations in people working with farm animals. S. hyicus exfoliative toxins, responsible for dermatological lesions in piglets, seem unable to damage the human epidermis, explaining the absence of cutaneous blisters in the previously reported cases. Precise data about its pathogenicity in humans and the adequate therapy are lacking.

Sequence Analysis of Staphylococcus hyicus ATCC 11249T, an Etiological Agent of Exudative Epidermitis in Swine, Reveals a Type VII Secretion System Locus and a Novel 116-Kilobase Genomic Island Harboring Toxin-Encoding Genes

Staphylococcus hyicus is the primary etiological agent of exudative epidermitis in swine. Analysis of the complete genome sequence of the type strain revealed a locus encoding a type VII secretion system and a large chromosomal island harboring the genes encoding exfoliative toxin ExhA and an EDIN toxin homolog.

Serological profiles in nursery piglets colonized with Staphylococcus aureus

At present, the immune response of pigs in relation to Staphylococcus aureus carriage is poorly understood. This study was aimed at investigating the dynamics of the anti-staphylococcal humoral immune response in methicillin-susceptible S. aureus (MSSA)-positive piglets and at assessing the effect of the experimental introduction of a methicillin-resistant S. aureus (MRSA) Sequence Type (ST) 398 strain. Therefore, serum samples were collected at different times from 31 weaned piglets originating from four different sows. Twenty-four out of the 31 piglets were challenged with MRSA ST398. The serum samples were analyzed for IgG antibodies to 39 S. aureus antigens, using a multiplex bead-based assay (xMAP technology, Luminex Corporation). Though antibody responses showed broad inter-individual variability, serological results appeared to be clustered by litter of origin. For most antigens, an age-related response was observed with an apparent increase in antibody titers directed against staphylococcal microbial surface components recognizing adhesive matrix molecules (MSCRAMM), which have been shown to play a role in S. aureus colonization. In most animals, antibody titers directed against staphylococcal toxins or immune-modulating proteins decreased with age, possibly reflecting the absence of bacterial invasion. The introduction of MRSA ST398 did not elicit a significant humoral immune reaction.

This study describes, for the first time, the humoral immune response in weaned pigs colonized with S. aureus.

Staphylococcus sciuri exfoliative toxin C (ExhC) is a necrosis-inducer for mammalian cells

Staphylococcus sciuri (S. sciuri) is a rare pathogen in humans, but it can cause a wide array of human infections. Recently a S. sciuri isolate (HBXX06) was reported to cause fatal exudative epidermitis (EE) in piglets and thus considered as a potential zoonotic agent. To investigate the pathogenicity of this bacterium, we cloned exfoliative toxin C (ExhC), a major toxin of the S. sciuri isolate and performed functional analysis of the recombinant ExhC-his (rExhC) protein using in vitro cell cultures and newborn mice as models. We found that rExhC could induce necrosis in multiple cell lines and peritoneal macrophages as well as skin lesions in newborn mice, and that the rExhC-induced necrosis in cells or skin lesions in newborn mice could be completely abolished if amino acids 79-128 of rExhC were deleted or blocked with a monoclonal antibody (3E4), indicating aa 79-128 portion as an essential necrosis-inducing domain. This information contributes to further understandings of the mechanisms underlying S. sciuri infection.

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.

Staphylococcus aureus seroproteomes discriminate ruminant isolates causing mild or severe mastitis

Staphylococcus aureus is a major cause of mastitis in ruminants. In ewe mastitis, symptoms range from subclinical to gangrenous mastitis. S. aureus factors or host-factors contributing to the different outcomes are not completely elucidated. In this study, experimental mastitis was induced on primiparous ewes using two S. aureus strains, isolated from gangrenous (strain O11) or subclinical (strain O46) mastitis. Strains induced drastically distinct clinical symptoms when tested in ewe and mice experimental mastitis. Notably, they reproduced mild (O46) or severe (O11) mastitis in ewes. Ewe sera were used to identify staphylococcal immunoreactive proteins commonly or differentially produced during infections of variable severity and to define core and accessory seroproteomes. Such SERological Proteome Analysis (SERPA) allowed the identification of 89 immunoreactive proteins, of which only 52 (58.4%) were previously identified as immunogenic proteins in other staphylococcal infections. Among the 89 proteins identified, 74 appear to constitute the core seroproteome. Among the 15 remaining proteins defining the accessory seroproteome, 12 were specific for strain O11, 3 were specific for O46. Distribution of one protein specific for each mastitis severity was investigated in ten other strains isolated from subclinical or clinical mastitis. We report here for the first time the identification of staphylococcal immunogenic proteins common or specific to S. aureus strains responsible for mild or severe mastitis. These findings open avenues in S. aureus mastitis studies as some of these proteins, expressed in vivo, are likely to account for the success of S. aureus as a pathogen of the ruminant mammary gland.

DNA microarray based detection of genes involved in safety and technologically relevant properties of food associated coagulase-negative staphylococci

Aim of the work was to design a polynucleotide based DNA microarray as screening tool to detect genes in food associated coagulase-negative staphylococci (CNS). A focus was laid on genes with potential health concern and technological relevance. The microarray contained 220 probes for genes encoding antibiotic resistances, hemolysins, toxins, amino acid decarboxylases (e.g. biogenic amine formation), binding proteins to extracellular matrix (ECM), lipases, proteases, stress response factors, or nitrate dissimilation. Hybridization of genomic DNA isolated from 32 phenotypically characterized CNS permitted to detect numerous genes, corresponding with the phenotype. However, numerous hybridization signals were obtained for genes without any detectable phenotype. The antibiotic resistance genes blaZ, lnuA, and tetK involved in ß-lactam, lincomycin and tetracycline resistance, respectively, were rarely identified in CNS, however, all species contained some strains with such resistance genes. Decarboxylase genes involved in biogenic amine formation were detected regularly in Staphylococcus carnosus, S. condimenti, S. piscifermentans and S. equorum, but was rarely correlated with the phenotype. The same applied for the fibrinogen (clf) and fibronectin (fbp) binding protein genes, whose phenotype (binding assay) was only correlated in S. equorum and Staphylococcus succinus. Although some CNS showed hemolytic activity and enterotoxin production (Immunoblot) the corresponding genes could not be verified. Technological relevant genes such as proteases or lipases revealed good hybridization signals. In addition, genes involved in nitrate dissimilation (nre, nar, nir), catalase (kat), or superoxide dismutase (sod) were well detected. Interestingly, genes involved in dissimilatory nitrate reduction were more prevalent in strains of S. carnosus, S. condimenti and S. piscifermentans than of S. equorum, S. succinus and S. xylosus.

Identification of a novel Staphylococcus pseudintermedius exfoliative toxin gene and its prevalence in isolates from canines with pyoderma and healthy dogs

Staphylococcal exfoliative toxins are involved in some cutaneous infections in mammals by targeting desmoglein 1 (Dsg1), a desmosomal cell-cell adhesion molecule. Recently, an exfoliative toxin gene (exi) was identified in Staphylococcus pseudintermedius isolated from canine pyoderma. The aim of this study was to identify novel exfoliative toxin genes in S. pseudintermedius. Here, we describe a novel orf in the genome of S. pseudintermedius isolated from canine impetigo, whose deduced amino acid sequence was homologous to that of the SHETB exfoliative toxin from Staphylococcus hyicus (70.4%). The ORF recombinant protein caused skin exfoliation and abolished cell surface staining of Dsg1 in canine skin. Moreover, the ORF protein degraded the recombinant extracellular domains of canine Dsg1, but not Dsg3, in vitro. PCR analysis revealed that the orf was present in 23.2% (23/99) of S. pseudintermedius isolates from dogs with superficial pyoderma exhibiting various clinical phenotypes, while the occurrence in S. pseudintermedius isolates from healthy dogs was 6.1% (3/49). In summary, this newly found orf in S. pseudintermedius encodes a novel exfoliative toxin, which targets a cell-cell adhesion molecule in canine epidermis and might be involved in a broad spectrum of canine pyoderma.

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.

Antimicrobial susceptibilities of exfoliative toxigenic and non-toxigenic Staphylococcus hyicus strains in Japan

Staphylococcus hyicus isolates (n=207), including 150 exfolitative toxigenic and 57 non-toxigenic strains, were examined for their susceptibility to 13 antimicrobial agents by using the dehydrated 96-well MIC panel system. The frequency of their resistance to penicillin and ampicillin was 76.8% (159/207), followed by erythromycin (56%, 116/207), trimethoprim-sulfamethoxazole (28.5%, 59/207), chloramphenicol (24.2%, 50/207), kanamycin (19.8%, 41/207), and doxycycline (1.4%, 3/207). Resistance to chloramphenicol and trimethoprim-sulfamethoxazole was significantly higher in toxigenic strains than non-toxigenic strains (p<0.01), whereas kanamycin and erythromycin resistance was significantly higher in non-toxigenic strains (p<0.01 and <0.05, respectively). Resistance to two or more antimicrobials was observed in 85.5% (177/207) of total strains, with a significantly higher occurrence in toxigenic strains (89.3%, 134/150 vs. 75.4%, 43/57; p<0.05).

Distribution of the putative virulence factor encoding gene sheta in Staphylococcus hyicus strains of various origins

In the present study, Staphylococcus (S.) hyicus strains isolated in Russia (n = 23) and Germany (n = 17) were investigated for the prevalence of the previously described genes sheta and shetb. Sheta was detected in 16 S. hyicus strains. Sheta-positive strains were mainly found among strains isolated from exudative epidermitis, and frequently together with the exfoliative toxin-encoding genes exhD and exhC. Partial sequencing of sheta in a single S. hyicus strain revealed an almost complete match with the sheta sequence obtained from GenBank. None of the S. hyicus strains displayed a positive reaction with the shetb-specific oligonucleotide primer used in the present study. According to the present results, the exotoxin encoding gene sheta seems to be distributed among S. hyicus strains in Russia and Germany. The toxigenic potential of this exotoxin, which does not have the classical structure of a staphylococcal exfoliative toxin, remains to be elucidated.

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.

Distribution of the exfoliative toxin D gene in clinical Staphylococcus aureus isolates in France

Exfoliative toxin D (ETD) was identified recently as a new exfoliative toxin serotype. Like other exfoliative toxins, ETD induces intra-epidermal cleavage through the granular layer of the epidermis of neonatal mice. The distribution of ETD production was investigated in Staphylococcus aureus isolates from infected and colonised patients in France. The etd gene was found in 55 (10.5%) of 522 isolates tested. Isolates responsible for bullous impetigo and generalised staphylococcal scalded skin syndrome did not harbour etd, but etd was significantly more frequent in isolates causing cutaneous abscesses and furuncles. Most etd- and Panton-Valentine leukocidin-positive strains belonged to the clone of community-acquired methicillin-resistant S. aureus spreading currently throughout France.

Nationwide molecular surveillance of exfoliative toxigenic Staphylococcus hyicus on pig farms across Japan

We investigated the carriage of Staphylococcus hyicus and their exfoliative toxin genes (exhA, exhB, exhC, exhD, and shetb) among 424 pigs from 38 Japanese pig farms by PCR and characterized the isolates by 16S-23S intergenic spacer region polymorphism analysis. S. hyicus (n=207) were isolated from 17.9% of pigs and 72.5% of them were toxigenic. The isolation rate of toxigenic S. hyicus was four times higher in the pigs with exudative epidermitis than the healthy pigs (87.6% versus 19.6%; p<0.01). Among the toxins, exhA was the most prevalent, being detectable in 49.3% of toxin gene-positive strains. S. hyicus isolates were distributed into nine ITS-PCR types (a-i), with ITS-PCR types d, h, and e being predominant accounting for 70% (145/207) of total isolates or 76% (114/150) of toxin gene-positive strains. This study denotes high prevalence of toxigenic strains among S. hyicus circulating on pig farms in Japan.

Prevalence of genes encoding exfoliative toxins among Staphylococcus hyicus isolated in Russia and Germany

In the present study, previously characterized Staphylococcus hyicus isolated in Russia (n=23) and Germany (n=17) were investigated for the prevalence of the exfoliative toxin encoding genes exhA, exhB, exhC and exhD by multiplex PCR resulting in the detection of exhD positive strains among the S. hyicus isolated from pigs with exudative epidermitis in Russia and the detection of exhC and exhD for one and two strains isolated from exudative epidermitis in Germany respectively. The toxin gene negative strains were generally isolated from apparently healthy pigs, from other animals and from specimens where the relation between the isolation of S. hyicus and the clinical symptoms remained unclear. Partial sequencing of the toxin genes of selected exhC and exhD positive strains and comparing the sequencing results with sequences of exhC and exhD reference strains revealed an almost complete identity. The results of the present study were in agreement with the findings of Andresen and Ahrens (J. Appl. Microbiol., 96, 2004, 1265) and Andresen (J. Vet. Rec., 157, 2005, 376) that the presented multiplex PCR could be used to investigate S. hyicus for toxinogenic potential and that there is an association between the presence of toxin genes in S. hyicus strains from exudative epidermitis. However, comparable with the S. hyicus strains isolated in Germany which were investigated previously by Andresen (J. Vet. Rec., 157, 2005, 376), exhD seems to predominate in S. hyicus strains from Russia.

Dissemination of the gene encoding exfoliative toxin of Staphylococcus intermedius among strains isolated from dogs during routine microbiological diagnostics

Phenotypic properties and species-specific PCR tests based on the nuc gene of Staphylococcus intermedius and S. aureus, and a conserved region of 16S rDNA were used to identify 45 S. intermedius and four S. aureus isolated from samples of dogs during routine diagnostics. Four S. pseudintermedius strains used for control purposes reacted positively with the S. intermedius nuc PCR showing the close relationship between both species. Investigating the 45 S. intermedius and four S. pseudintermedius strains for the prevalence of the exfoliative toxin SIET encoding gene yielded the presence of the gene for 21 of the S. intermedius and two of the S. pseudintermedius strains. Partial sequencing of the toxin gene of a single S. intermedius strain and comparing this sequence with that obtained from GenBank revealed an almost complete identity. The presence of the exfoliative toxin gene could mainly be found among S. intermedius isolated from skin and wound infections and from otitis externa possibly indicating a role of this toxin for the clinical symptoms.

A highly pathogenic strain of Staphylococcus sciuri caused fatal exudative epidermitis in piglets

Staphylococcus sciuri are important human pathogens responsible for endocarditis, peritonitis, septic shock, urinary tract infection, pelvic inflammatory disease and wound infections. However, little information is known regarding the pathogenicity of S. sciuri to animals. From the pericardial fluid of a diseased piglet with exudative epidermitis (EE), we isolated a strain of Staphylococcus in pure culture. Surprisingly, this isolate was a member of S. sciuri rather than S. hyicus as identified by its biochemical traits and also by analysis of 23S ribosomal DNA using Internal Transcribed Spacer PCR. In addition, inoculation of newborn piglets with 1x10(10) CFU of the isolate by oral feeding or intra-muscular injection successfully reproduced EE in piglets, which suggested that the oral intake of the pathogen by the animals is one of the major routes of exposure. These unexpected findings prioritized S. sciuri as important zoonotic agents, which may have ramifications for human medicine.

Identification of Staphylococcus hyicus by polymerase chain reaction mediated amplification of species specific sequences of superoxide dismutase A encoding gene sodA

A species specific PCR test, based on manganese-dependent superoxide dismutase A encoding gene sodA, was developed for the identification of Staphylococcus hyicus, an important bacterial pathogen in pigs. The designed primers allowed a rapid and reliable identification of phenotypically characterized S. hyicus, isolated in Russia, Germany and Denmark. No cross reactivities could be observed investigating staphylococcal reference strains representing 18 different species and subspecies. The use of the described primers might improve a future diagnosis of this bacterial pathogen.

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.

Staphylococcus hyicus exfoliative toxins selectively digest porcine desmoglein 1

Virulent strains of Staphylococcus hyicus can cause exudative epidermitis in pigs. The major symptom of this disease is exfoliation of the skin in the upper stratum spinosum. Exfoliation of the skin is strongly associated with exfoliative toxin including ExhA, ExhB, ExhC, ExhD, SHETA, and SHETB. Recently, genes for ExhA, ExhB, ExhC and ExhD were cloned. Exfoliative toxins produced by S. aureus have been shown to selectively cleave human or mouse desmoglein 1, a desmosomal adhesion molecule, that when inactivated results in blisters. In this study, we attempted to identify the molecular target of Exhs in porcine skin. Each of recombinant Exhs injected in the skin of pigs caused superficial epidermal blisters or crust formation. Cell surface staining of desmoglein 1, but not that of desmoglein 3, was abolished when cryosections of normal porcine skin were incubated with one of Exhs suggesting that Exh selectively degrade porcine desmoglein 1. In vitro incubation of the recombinant extracellular domains of desmoglein 1 and desmoglein 3 of human, mouse or canine origin demonstrated that only mouse desmogleins 1alpha and 1beta were cleaved by ExhA and ExhC at high concentration. Furthermore, injection of ExhA and ExhC at high concentration caused superficial blisters in neonatal mice. These findings strongly suggest that Exhs cause blister formation of porcine skin by digesting porcine desmoglein 1 in a similar fashion to exfoliative toxins from S. aureus.

Survey of genes encoding staphylococcal enterotoxins, toxic shock syndrome toxin 1, and exfoliative toxins in members of the Staphylococcus sciuri group

Genes encoding staphylococcal enterotoxins (sea to see, seg, and seh), toxic shock syndrome toxin 1 (tst), and exfoliative toxins (eta and etb) were not detected in a large panel of 48 Staphylococcus sciuri group isolates tested. This strongly suggests that production of the staphylococcal exotoxins by these bacteria is highly unlikely.

Exudative epidermitis in pigs caused by toxigenic Staphylococcus chromogenes

Staphylococcus chromogenes is closely related to Staphylococcus hyicus, which is recognised as the causative agent of exudative epidermitis (EE) in pigs. S. chromogenes is part of the normal skin flora of pigs, cattle and poultry and has so far been considered non-pathogenic to pigs. A strain of S. chromogenes producing exfoliative toxin type B, ExhB, was identified by the use of a multiplex PCR specific for the exfoliative toxins from S. hyicus. The exfoliative toxin from S. chromogenes reacted in immunoblot analysis with polyclonal and monoclonal antibodies specific to ExhB from S. hyicus and had an apparent molecular weight of 30 kDa. Sequencing the gene encoding the exfoliative toxin from S. chromogenes revealed that the molecular weight of the toxin with the signal peptide and the mature toxin was 30,553 and 26,694 Da, respectively. Comparison of the exhB genes from S. chromogenes strain VA654 and S. hyicus strain 1289D-88 showed differences in seven base pairs of the DNA sequences and in two amino acid residues in the deduced amino acid sequences. Pigs were experimentally inoculated with S. chromogenes strain VA654. By clinical observations and histopathological evaluation of the skin alterations, all pigs revealed development of generalized exudative epidermitis. No toxin producing S. hyicus was isolated from the pigs and all ExhB-positive bacterial isolates were identified as S. chromogenes. This confirmed that the disease-causing agent was the inoculated S. chromogenes strain VA654. The results of this study show that S. chromogenes may cause exudative epidermitis in pigs.

A multiplex PCR for detection of genes encoding exfoliative toxins from Staphylococcus hyicus

AIMS

To develop a multiplex PCR for detection of genes encoding the exfoliative toxins ExhA, ExhB, ExhC and ExhD from Staphylococcus hyicus and to estimate the prevalence of exfoliative toxins among Staph. hyicus isolates from Danish pig herds with exudative epidermitis (EE).

METHODS AND RESULTS

A multiplex PCR employing specific primers for each of the genes encoding four different exfoliative toxins was developed and evaluated using a collection of Staph. hyicus with known toxin type and a number of other staphylococcal species. A total of 314 Staph. hyicus isolates from pigs with EE were screened by multiplex PCR and the combined results of the present and previous investigations showed that ExhA, ExhB, ExhC and ExhD was found in 20, 33, 18 and 22%, respectively, of 60 cases of EE investigated.

CONCLUSIONS

This study has provided a new tool for detection of toxigenic Staph. hyicus and a more comprehensive picture of the prevalence of the Staph. hyicus exfoliative toxins in Danish pig herds.

SIGNIFICANCE AND IMPACT OF THE STUDY

The multiplex PCR can be used in studies on the prevalence of toxigenic Staph. hyicus elucidating the epidemiology of EE in pigs. The multiplex PCR is currently being used for selection of Staph. hyicus isolates for production of autogenous vaccine.