Producibility of exfoliative toxin and staphylococcal coagulase types of Staphylococcus aureus strains isolated from skin infections and atopic dermatitis

Dissemination of multiple MRSA clones among community-associated methicillin-resistant Staphylococcus aureus infections from Japanese children with impetigo

The proportion of MRSA strains that cause skin and soft infections has recently increased. In 3 months we have characterized 17 MRSA strains isolated from children with impetigo at a Japanese hospital. Seventeen MRSA strains belonged to 7 clones defined by clonal complex (CC) in MLST genotype and type of SCCmec, which were rarely identified among healthcare-associated MRSA: CC 91-SCCmecIIb (4 strains); CC91-SCCmecIIn (2 strains); CC91-SCCmecIVa (2 strains); CC91-SCCmecV (4 strains); CC88-SCCmecIVg (3 strains); CC1-SCCmecIVc (1 strain); and CC5-SCCmecIVn (1 strain). Although one strain belonged to CC5, which has been commonly identified in healthcare-associated MRSA, it did not carry type II SCCmec, but carried type IV SCCmec. Fourteen of the 17 strains carried exfoliative toxin a or b gene, and none carried Panton-Valentine leukocidine gene. Furthermore, we determined the entire nucleotide sequences of two type V SCCmec elements carried by strains JCSC5952, a CC91 strain, and TSGH17, a Taiwanese CC59 strain. The structure of SCCmecJCSC5952 was more than 99% homologous in nucleotide identity with those of Taiwanese PVL-positive ST59 MRSA strains TSGH17 and PM1, which were designated as type V (5C2&5). Identification of multiple MRSA clones distinct from those disseminating at the hospital suggests that MRSA strains might be emerging in the community from MSSA strains by acquiring SCCmec elements on various occasions. Carriage of the similar type V(5C2&5) SCCmec element by strains of distinct genetic backgrounds, CC91 and CC59, suggested horizontal transfer of the SCCmec element.

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.

Association of recurrent furunculosis with Panton-Valentine leukocidin and the genetic background of Staphylococcus aureus

Staphylococcus aureus is a major cause of skin and soft tissue infections, such as furuncles, carbuncles, and abscesses, but it also frequently colonizes the human skin and mucosa without causing clinical symptoms. Panton-Valentine leukocidin (PVL) is a pore-forming toxin that has been associated with soft tissue infections and necrotizing pneumonia. We have compared the genotypes, virulence gene repertoires, and phage patterns of 74 furunculosis isolates with those of 108 control strains from healthy nasal carriers. The large majority of furunculosis strains were methicillin sensitive. Clonal cluster (CC) 121 (CC121) and CC22 accounted for 70% of the furunculosis strains but for only 8% of the nasal isolates. The PVL-encoding genes luk-PV were detected in 85% of furunculosis strains, while their prevalence among colonizing S. aureus strains was below 1%. luk-PV genes were distributed over several lineages (CCs 5, 8, 22, 30, and 121 and sequence type 59). Even within the same lineages, luk-PV-positive phages characterized furunculosis strains, while their luk-PV-negative variants were frequent among nasal strains. The very tight epidemiological linkage between luk-PV and furunculosis, which could be separated from the genetic background of the S. aureus strain as well as from the gene makeup of the luk-PV-transducing phage, lends support to the notion of an important role for PVL in human furunculosis. These results make a case for the determination of luk-PV in recurrent soft tissue infections with methicillin-sensitive as well as methicillin-resistant S. aureus.

Increased susceptibility to Staphylococcus aureus colonization of the skin of the NOA mouse: a potentially useful animal model for evaluating antiseptic effects

Isolation of bacteria from wet skin lesions was attempted using Naruto Research Institute Otsuka Atrichia (NOA) mice, which develop such lesions spontaneously at a high rate. As a result, Staphylococcus aureus was demonstrated to have colonized the wet skin lesions at high density. In addition, the isolated S. aureus was found to be similar to the strain of S. aureus thought to colonize the eczematous lesions seen in humans with atopic dermatitis. Furthermore, a survey of the S. aureus colonization status of NOA mice with no wet skin lesions confirmed colonization at higher density than in HR-1 mice as control, indicating that the skin of the NOA mouse has the novel characteristic of increased susceptibility to S. aureus colonization. Thus, by using changes in S. aureus counts as an index, the NOA mouse can be expected to serve as a useful animal model for evaluating the effects of topical antiseptics. The antiseptic effects of an ointment and a lotion containing chlorhexidine gluconate were confirmed using this animal model.

Presence of staphylococcal exfoliative toxin A in sera of patients with atopic dermatitis

BACKGROUND

It has been reported that the toxins that Staphylococcus aureus produces are associated with the exacerbation of atopic dermatitis (AD). It has been shown in many studies that staphylococcal enterotoxin (SE) A and SEB contribute to AD by humoral immunity through IgE production as a superantigen. On the other hand, little attention has been paid to the relationship between AD and exfoliative toxin x (ETx).

OBJECTIVE

We investigated the toxins that are frequently detected from the skin of patients and how these toxins affect AD.

METHODS

S. aureus, isolated from the skin of 100 patients with mild to severe AD, were examined for the producibility of toxins by polymerase chain reaction. Serum samples were obtained from 21 patients with mild and moderate AD. The levels of SEB, ETA, total IgE, specific IgE, and specific IgG in sera were measured by ELISA.

RESULTS

SEB was most frequently detected from S. aureus on the skin of these patients as previously reported. And ETx, to which little attention has been paid so far, was frequently detected next to SEB. Furthermore, ETA was detected from the sera of almost all the AD patients. SEB was not detected at all. Although the level of ETA in the AD group was significantly higher than that of controls, ETA-specific IgE was not detected from their sera. High levels of ETA tended to be detected from infantile patients. Although there were no significant differences in the levels of ETA-IgG between AD and the controls, its prevalence was more than twice as high as the controls in AD.

CONCLUSION

These results suggest that many AD patients were exposed to ETx. We conclude that ETx may contribute to exacerbation of AD, particularly in infants, by a mechanism that is not through specific IgE production, unlike SEB.

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

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

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).

Adherence characteristics and susceptibility to antimicrobial agents of Staphylococcus aureus strains isolated from skin infections and atopic dermatitis

We examined the adherence characteristics and susceptibility to various antimicrobial agents of 130 strains of Staphylococcus aureus isolated from infective skin lesions and 135 strains of S. aureus isolated from non-infective eczematous lesions of atopic dermatitis (AD) patients. The isolation rate of methicillin-resistant S. aureus (MRSA) was 27.7% in strains from clinical sources excluding AD and 31.1% in those from AD. Coagulase type II strains were most frequently observed in MRSA strains isolated from all sources excluding AD, and coagulase type III strains were most frequently observed in those isolated from AD. We proposed that antimicrobial treatment for AD patients should be carefully designed to prevent MRSA infection. Plasma coagulation ability was lowest in S. aureus strains isolated from abscesses, suggesting that the lower production of fibrin observed in abscesses may assist the infiltration of neutrophils into skin tissues and that a decrease in plasma coagulation ability may enable abscess formation. Adherence to polypropylene tubes with slime production was most evident in S. aureus strains isolated from felon and least evident in those isolated from cellulitis and lymphangitis. Tube adherence was characteristic of the S. aureus strains attached to superficial skin tissues, but not necessarily for strains that had infiltrated the deep skin tissues. Fusidic acid demonstrated significant antimicrobial activity against the MRSA strains, but rifampicin was the strongest antimicrobial agent.

Adherence characteristics of Staphylococcus aureus and coagulase-negative staphylococci isolated from various skin lesions

We investigated the adherence characteristics of Staphylococcus aureus and coagulase-negative staphylococci (CNS) isolated from various skin lesions by examining hydrophobicity, negative charge, tube adherence, slime production, and promotion of adherence to coverslips by blood proteins. Our results in the present study indicate that high hydrophobicity and high capacity for adhesion to tubes with slime production are much more detected in CNS from infective origin than in those from colonization origin. The results also indicate that host plasma tends to enhance adherence of S. aureus to coverslips, but it does not enhance adherence of most coagulase-negative staphylococci to coverslips.

Effects of zinc oxide on the attachment of Staphylococcus aureus strains

We examined the attachment of Staphylococcus aureus to plastic tissue-culture coverslips after incubation for 24 h. The attachment to coverslips was weaker in rabbit plasma with 5% zinc oxide (ZnO) than in the control rabbit plasma without ZnO (P < 0.01). Plasma coagulation by S. aureus strains was not detected in plasma with 5% ZnO after incubation for 24 h. The membranous structure (an immature biofilm) was formed on the coverslips by S. aureus cells in plasma after incubation for 24 h. The colony counts of S. aureus cells on the membranous structures were lower in plasma with 5% ZnO, plasma with 0.2% hinokitiol, plasma with 5% ZnO + 0.2% hinokitiol, plasma with cefdinir at 4 minimum inhibitory concentration (MIC) and plasma with levofloxacin at 4 MIC, than in the control plasma after incubation for 24 h (P < 0.01). The colonies on the membranous structures completely disappeared in the case of plasma with 5% ZnO and 0.2% hinokitiol. The colony counts on membranous structures were lower in plasma with cefdinir at 4 MIC or levofloxacin at 4 MIC containing 5% ZnO than in plasma with cefdinir at 4 MIC or levofloxacin at 4 MIC only, (P < 0.05). The MICs of hinokitiol against S. aureus strains peaked at an MIC distribution of 16-32 micrograms/ml. The peak shifted to below 1 microgram/ml by adding 5% ZnO in agar plate method. The results suggest that the attachment of S. aureus cells to the coverslips is suppressed in the presence of 5% ZnO and that antistaphylococcal activities of cefdinir, levofloxacin and hinokitiol increase in the presence of 5% ZnO.