Exotoxins of Staphylococcus aureus. Clin Microbiol Rev. 2000;13:16-34, table of contents. [PMID: 10627489 DOI: 10.1128/cmr.13.1.16-34.2000]

Distribution of newly described enterotoxin-like genes in Staphylococcus aureus from food

Extensive analysis of the Staphylococcus aureus genome has allowed the identification of new genes encoding enterotoxin-like superantigens (SEls). Some of these are thought to be involved in staphylococcal food poisoning, while others do not elicit any emetic effect. The potential impact of these members of the enterotoxin-like family on the human organism seems to rely mainly on their superantigenic activity. In this paper the distribution of the genes coding for enterotoxin-like superantigens in S. aureus isolated from food was studied. Fifty isolates of S. aureus were examined and 27 were shown to be enterotoxigenic. Only 9 of the 27 strains carried genes encoding enterotoxins SEA-SEE. In 18 SEA-SEE-negative strains the presence of newly described enterotoxin genes was detected. All SEA-SEE-positive strains simultaneously carried genes of new SEls. We show that the gene encoding SElH (staphylococcal enterotoxin-like enterotoxin H) was the most frequently detected (n=14), while genes encoding SElI together with SElG accompanied by the other genes of the egc locus were detected in three strains. We also detected the presence of three less investigated genes: sep, sel, and sek. These genes were present in eight, two, and one isolate, respectively. In one strain, sep was accompanied by genes of other SEls, while in the remaining seven it was the only enterotoxin-like gene detected. The high prevalence of newly discovered enterotoxin genes, including the genes encoding emetic toxins, was demonstrated in food-derived strains. This supports the need for additional work on its role in food poisoning and, alternatively, to monitor its presence in S. aureus isolated from food. Our results suggest that yet unknown genetic elements encoding enterotoxin genes may exist.

Bacterial cell wall-expressed protein A triggers supraclonal B-cell responses upon in vivo infection with Staphylococcus aureus

We have previously shown that staphylococcal protein A (SpA) anchored to the cell wall of Staphylococcus aureus acts as a virulence factor in septic arthritis. Apart from the ability of SpA to interact with Fcgamma, it also binds to Fab-regions with immunoglobulin heavy chains encoded by the V(H) clan III gene family. The objective of the present study was to investigate whether in vivo expression of SpA by staphylococci induces V(H)III-dependent supraclonal B-cell responses, and whether such responses may affect the ability of the host to produce anti-staphylococcal antibodies. Upon primary infection of mice, a SpA-expressing staphylococcal strain gave rise to significantly higher serum levels of V(H)III-encoded antibodies specific for SpA devoid of Fcgamma-binding ability (MSpA) than an isogeneic spa deletion mutant strain. The V(H)III-dependence of MSpA-specific antibody responses was affected by the size of the staphylococcal inoculum, and differed for IgM and IgG isotypes. Mice that had recovered from a prior mild infection from a SpA-expressing strain were protected against infection-induced weight loss upon reinfection. Although no lasting MSpA-specific IgG was induced by previous mild infection, these protected mice possessed IgG specific for clumping factor A, a conventional staphylococcal protein antigen. Our findings demonstrate that the expression of a B-cell superantigen during staphylococcal infection causes supraclonal changes to the immune system. Notably, while superantigen-triggered B-cell responses do not favor the development of SpA-specific memory B-cells, such responses do not interfere with the development of antibodies specific for a staphylococcal protein antigen associated with protective immunity.

Insights into mechanisms used by Staphylococcus aureus to avoid destruction by human neutrophils

Polymorphonuclear leukocytes (PMNs, or neutrophils) are critical for human innate immunity and kill most invading bacteria. However, pathogens such as Staphylococcus aureus avoid destruction by PMNs to survive, thereby causing human infections. The molecular mechanisms used by pathogens to circumvent killing by the immune system remain largely undefined. To that end, we studied S. aureus pathogenesis and bacteria-PMN interactions using strains originally isolated from individuals with community-acquired (CA) and hospital-acquired infections. Compared with strains from hospital infections (COL and MRSA252), strain MW2 and a methicillin-susceptible relative, MnCop, were significantly more virulent in a mouse model of S. aureus infection, and caused the greatest level of pathology in major vital organs. Although phagocytosis of each strain triggered production of reactive oxygen species and granule-phagosome fusion, those from CA infections were significantly more resistant to killing by human PMNs and caused greater host cell lysis. Microarray analysis of the strains during neutrophil phagocytosis identified genes comprising a global S. aureus response to human innate host defense. Genes involved in capsule synthesis, gene regulation, oxidative stress, and virulence, were up-regulated following ingestion of the pathogen. Notably, phagocytosis of strains from CA infections induced changes in gene expression not observed in the other strains, including up-regulation of genes encoding virulence factors and hypothetical proteins. Our studies reveal a gene transcription program in a prominent human pathogen that likely contributes to evasion of innate host defense.

Development of a multiplex PCR assay for the identification of Staphylococcus aureus enterotoxigenic strains isolated from milk and dairy products

A multiplex PCR for the simultaneous detection of Staphylococcus aureus 23S rRNA, the coagulase and thermonuclease genes as well as the enterotoxin genes sea, sec, sed, seg, seh, sei, sej, sel was developed. The method was used to determine the presence of enterotoxigenic types for 93 S. aureus strains isolated from milk and dairy products. The data obtained by mPCR resulted comparable to those obtained by immunoassay methods. In addition, the mPCR assays also amplified some se genes, whose toxins are undetectable by immunoassay. Multiplex amplification can be obtained starting from 1 pg of DNA, showing the excellent specificity and high sensitivity of the assay.

Rapid genotyping of methicillin-resistant Staphylococcus aureus (MRSA) isolates using miniaturised oligonucleotide arrays

This study evaluated a DNA oligonucleotide array that recognised 38 different Staphylococcus aureus targets, including all relevant resistance determinants and some toxins and species-specific controls. A new method for labelling sample DNA, based on a linear multiplex amplification that incorporated biotin-labelled dUTP into the amplicon, was established, and allowed detection of hybridisation of the amplicons to the array with an enzymic precipitation reaction. The whole assay was validated by hybridisations with a panel of reference strains and cloned specific PCR products of all targets. To evaluate performance under routine conditions, the assay was used to test 100 methicillin-resistant S. aureus (MRSA) isolates collected from a university hospital in Saxony, Germany. The results showed a high correlation with conventional susceptibility data. The ermA and ermC macrolide resistance genes were found in 40% and 32% of the isolates, respectively. The most prevalent aminoglycoside resistance gene was aphA3 (57% of the isolates), followed by aacA-aphD (29%) and aadD (29%); tet genes, mupR and dfrA were rare. There were no isolates with van genes or genes involved in resistance to quinupristin-dalfopristin. Enterotoxins were detected in 27% of the isolates. Genes encoding Panton-Valentine leukocidin, toxic shock syndrome toxin and exfoliative toxins were not found. The DNA array facilitated rapid and reliable detection of resistance determinants and toxins under conditions used in a routine laboratory and has the potential to be used for array-based high-throughput screening.

Contagem de Staphylococcus sp. e detecção de enterotoxinas estafilocócicas e toxina da síndrome do choque tóxico em amostras de leite cru refrigerado

Analisaram-se 80 amostras de leite cru refrigerado a 4°C e estocado por 48 horas em tanques refrigeradores de propriedades rurais do estado de Minas Gerais quanto à contagem e identificação de Staphylococcus sp. e detecção de enterotoxinas estafilocócicas (SE) e da toxina da síndrome do choque tóxico (TSST-1). Staphylococcus sp. foi detectado em 100% das amostras de leite de tanque refrigerador em contagens que variaram de 1,0 × 10(5) a 2,5 × 10(7) UFC/ml (média = 5,60 log UFC/ml; s = 0,53 e CV = 9,5%). Isolaram-se e identificaram-se 436 estirpes como: S. aureus, S hyicus, S. epidermidis, S. intermedius, S. cohnii, S. sciuri, S. schleirferi e S. delphini. As estirpes de mesmo perfil bioquímico, oriundas da mesma amostra, foram agrupadas (pools) e induzidas a produzir SE e TSST-1. A detecção dessas enterotoxinas foi feita pelo método optimum sensitivity plate, usando-se técnica de celofane sobre ágar. Identificou-se a produção de SEA, SEB, SEC, SED e de TSST-1 em percentuais variados. Dos 138 pools preparados, 91 produziram, pelo menos, uma toxina isoladamente ou em associação a outras toxinas. Dos pools enterotoxigênicos, 24,6% eram coagulase positiva e 41,3%, coagulase negativa. A confirmação de estirpes enterotoxigênicas de Staphylococcus coagulase negativa isoladas de amostras de leite é importante em relação à saúde pública.

Microbial strategies to target, cross or disrupt epithelia

Epithelia are highly organized structures adapted to protect the underlying tissues from external aggressions, including microbial infections. Consequently, pathogens have evolved various strategies to target directly or indirectly intercellular junctions and/or components that maintain the structure of epithelia. Interestingly, some extracellular pathogens secrete enzymes that modify the extracellular part of junction components. Others produce toxins that are endocytosed and act from the inside of the cell to disrupt epithelial junctions. Other pathogens may directly inject into cells factors that are targeted to and destabilize the junctions, or that interact with signaling cascades that affect junction stability. Finally invasive bacteria or viruses may, by entering into cells, destabilize the junctions by targeting junction components directly or by inducing a series of events that lead to chemokine secretion, polymorphonuclear recruitment and inflammation.

The structure of the C5a receptor-blocking domain of chemotaxis inhibitory protein of Staphylococcus aureus is related to a group of immune evasive molecules

The chemotaxis inhibitory protein of Staphylococcus aureus (CHIPS) is a 121 residue excreted virulence factor. It acts by binding the C5a- (C5aR) and formylated peptide receptor (FPR) and thereby blocks specific phagocyte responses. Here, we report the solution structure of a CHIPS fragment consisting of residues 31-121 (CHIPS31-121). CHIPS31-121 has the same activity in blocking the C5aR compared to full-length CHIPS, but completely lacks FPR antagonism. CHIPS31-121 has a compact fold comprising an alpha-helix (residues 38-51) packed onto a four-stranded anti-parallel beta-sheet. Strands beta2 and beta3 are joined by a long loop with a relatively well-defined conformation. Comparison of CHIPS31-121 with known structures reveals striking homology with the C-terminal domain of staphylococcal superantigen-like proteins (SSLs) 5 and 7, and the staphyloccocal and streptococcal superantigens TSST-1 and SPE-C. Also, the recently reported structures of several domains of the staphylococcal extracellullar adherence protein (EAP) show a high degree of structural similarity with CHIPS. Most of the conserved residues in CHIPS and its structural homologues are present in the alpha-helix. A conserved arginine residue (R46 in CHIPS) appears to be involved in preservation of the structure. Site-directed mutagenesis of all positively charged residues in CHIPS31-121 reveals a major involvement of arginine 44 and lysine 95 in C5aR antagonism. The structure of CHIPS31-121 will be vital in the further unraveling of its precise mechanism of action. Its structural homology to S.aureus SSLs, superantigens, and EAP might help the design of future experiments towards an understanding of the relationship between structure and function of these proteins.

Comparative Prevalence of Superantigen Genes in Staphylococcus aureus Isolates Causing Sepsis With and Without Septic Shock

BACKGROUND

Staphylococcus aureus superantigens are associated with the pathogenesis of toxic shock syndrome, but their involvement in septic shock is unknown.

METHODS

We compared the distribution of 11 superantigen genes in S. aureus blood culture isolates obtained from patients with sepsis who did and did not have septic shock (19 and 61 patients, respectively), as well as from patients with suppurative infections (101 patients) and patients with colonization (25 patients).

RESULTS

The prevalence of the enterotoxin A gene (sea) increased significantly with the severity of infection (P<.001), whereas the prevalence of the enterotoxin gene cluster (egc) decreased significantly (P=.009).

CONCLUSION

Enterotoxin A (SEA) might play a key role in sea-positive S. aureus sepsis by triggering over-expression of inflammatory mediators associated with shock. Novel treatments targeting superantigens, especially the sea gene, might be beneficial in the treatment of S. aureus sepsis.

Community-acquired meticillin-resistant Staphylococcus aureus: an emerging threat

Community-acquired meticillin-resistant Staphylococcus aureus (MRSA) is becoming an important public-health problem. New strains of S aureus displaying unique combinations of virulence factors and resistance traits have been associated with high morbidity and mortality in the community. Outbreaks of epidemic furunculosis and cases of severe invasive pulmonary infections in young, otherwise healthy people have been particularly noteworthy. We review the characteristics of these new strains of community-acquired MRSA that have contributed to their pathogenicity and discuss new approaches to the diagnosis and management of suspected and confirmed community-acquired MRSA infections.

Molecular typing of Staphylococcus aureus isolated from bovine mastitic milk on the basis of toxin genes and coagulase gene polymorphisms

A total of 270 strains of Staphylococcus aureus, isolated from mastitic milk, were investigated by the polymerase chain reaction for the presence of genes encoding enterotoxins (sea to sej) and a toxic shock syndrome toxin (tst). One hundred eighty three (67.8%) bovine isolates possessed either one or more toxin genes and the most common pattern that coexisted in S. aureus was tst, sec, seg, and sei. Coagulase genotyping revealed 15 patterns, and 161 of the 270 isolates (59.6%) belonged to the coagulase genotype B1. Further, these 161 isolates possessed at least two enterotoxin genes. However, the role of these toxins in udder pathogenicity remains unclear. Moreover, the predominant isolate possessed the enterotoxin genes supporting the theory that superantigenic toxins are important for the udder pathogenesis.

Enterotoxins and toxic shock syndrome toxin in Staphylococcus aureus recovered from human nasal carriers and manually handled foods: epidemiological and genetic findings

A set of 269 Staphylococcus aureus isolates recovered from nasal carriers and manually handled foods in a region of Spain was analyzed for pyrogenic toxin production and toxin genes. Fifty-seven isolates producing at least one of four enterotoxins (SEA, SEB, SEC, SED), 10 isolates producing only toxic shock syndrome toxin (TSST-1), and 10 isolates producing both toxin types were found. The 77 toxigenic isolates were discriminated into 36 SmaI genomic and 13 EcoRI plasmid profiles. A strong relationship between toxin profiles with both SmaI genomic and EcoRI plasmid profiles was revealed. SmaI genomic profiles showing six or less mismatching fragments and similarity coefficient > or =0.7 were included in a lineage. Eight lineages were differentiated; six of them grouped both human and food isolates and two of these also included outbreak-implicated isolates. Two lineages, represented by TSST-SEA and TSST-1, on the one hand, and SEC and SEC-SED isolates, on the other hand, were the most frequent, but only the second was outbreak-related. When SmaI genomic and EcoRI plasmid profiles were hybridized with tst, sea, seb, and sec toxin probes, it was observed that each probe mapped on a different SmaI fragment from isolates falling into the same lineage. All of the probes only mapped on genomic fragments, but sed also mapped on three plasmid fragments. When sej and ser probes were included, they mapped together with sed on the chromosome and on the plasmids. Two plasmids (ca. 33 and 36 kb) carried the expected sed-sej-ser genes, while the other (ca. 53.5 kb) carried sed-sej and ser-like genes. The latter plasmid and the chromosomal location of sed-sej-ser are new findings from this study.

Laboratory exposures to staphylococcal enterotoxin B

First report of symptoms after ocular exposure to staphylococcal enteroxin B in the laboratory is detailed.

Staphylococcal enterotoxins are 23- to 29-kDa polypeptides in the bacterial superantigen protein family. Clinical symptoms from intoxication with staphylococcal enterotoxins vary by exposure route. Ingestion results in gastrointestinal symptoms, and inhalation results in fever as well as pulmonary and gastrointestinal symptoms. Review of occupational exposures at the U.S. Army Medical Research Institute of Infectious Diseases from 1989 to 2002 showed that three laboratory workers had symptoms after ocular exposure to staphylococcal enterotoxin B (SEB). Conjunctivitis with localized cutaneous swelling occurred in three persons within 1 to 6 hours after exposure to SEB; two of these persons also had gastrointestinal symptoms, which suggests that such symptoms occurred as a result of exposure by an indirect cutaneous or ocular route. Ocular exposures from SEB resulting in conjunctivitis and localized swelling have not previously been reported. Symptoms from these patients and review of clinical symptoms of 16 laboratory-acquired inhalational SEB intoxications may help healthcare workers evaluate and identify SEB exposures in laboratory personnel at risk.

Detection of Panton-Valentine leukocidin gene in Staphylococcus aureus by LightCycler PCR: clinical and epidemiological aspects

The prevalence of the Panton-Valentine leukocidin (PVL) gene in Staphylococcus aureus was investigated with a simple, reproducible and rapid real-time LightCycler SYBR Green I PCR assay. The PVL gene was detected in one isolate from 65 patients with S. aureus bacteraemia, in four isolates from 55 patients with respiratory tract infections, and in two isolates from 91 patients with cutaneous infections. In contrast, 15 of 25 cutaneous isolates of methicillin-resistant S. aureus (MRSA) were positive. All PVL-positive cutaneous MRSA isolates were community-acquired and comprised three different clones as determined by pulsed-field gel electrophoresis. The PVL gene was detected in isolates from patients with recurrent primary skin infections and S. aureus bacteraemia, but PVL did not seem to be an important virulence factor in the pathogenesis of staphylococcal bacteraemia.

Detection of Staphylococcus aureus enterotoxin A and B genes with PCR-EIA and a hand-held electrochemical sensor

Two electrochemical assays for detecting Staphylococcus aureus enterotoxin A and B genes were developed. The assays are based on PCR amplification with biotinylated primers, hybridization to a fluorescein-labeled probe, and detection with horseradish peroxidase-conjugated anti-fluorescein antibody using a hand-held electrochemical detector. The limit of detection (LOD) for both assays was approximately 16 copies of the sea and seb genes. The assays were evaluated in blinded studies, each with 81 samples that included genomic and cloned S. aureus DNA, and genomic DNA from Alcaligens, Bacillus, Bacteroides, Bordetella, Borkholderia, Clostridium, Comanonas, Enterobacter, Enterococcus, Escherichia, Francisella, Haemophilus, Klebsiella, Listeria, Moraxella, Neisseria, Proteus, Pseudomonas, Salmonella, Serratia, Shigella, Streptococcus, Vibrio and Yersinia species. Both assays showed 100% sensitivity. The specificity was 96% for the SEA assay and 98% for the SEB assay. These results demonstrate the feasibility of performing probe-based detection of PCR products with a low-cost, hand-held, electrochemical detection device as a viable alternative to colorimetric enzyme-linked assays of PCR products.

Body temperature, behavior, and plasma cortisol changes induced by chronic infusion of Staphylococcus aureus in goats

Most experimentally induced fevers are acute, usually lasting ∼6–12 h, and thus do not mimic chronic natural fevers, which can extend over several days or more. To produce a model of chronic natural fever, we infused eight goats ( Capra hircus) intravenously with 2 ml of 2 × 1011 cell walls of Staphylococcus aureus ( S. aureus) for 6 days using osmotic infusion pumps (10 μl/h) while measuring changes in body temperature, behavior, and plasma cortisol concentration. Seven control animals were infused with sterile saline. Abdominal temperature-sensitive data loggers and osmotic infusion pumps were implanted under halothane anesthesia. To compare our new model with existing models of experimental fever, we also administered 2-ml bolus intravenous injections of 2 × 1011 S. aureus cell walls, 0.1 μg/kg lipopolysaccharide ( Escherichia coli, serotype 0111:B4), and sterile saline in random order to six other goats. Bolus injection of lipopolysaccharide and S. aureus induced typical acute phase responses, characterized by fevers lasting ∼6 h, sickness behavior, and increased plasma cortisol concentration. Infusion of S. aureus evoked prolonged fevers, which lasted for ∼3 days, starting on day 4 of infusion (ANOVA, P < 0.05), and did not disrupt the normal circadian rhythm of body temperature. However, pyrogen infusion did not cause plasma cortisol concentration to rise (ANOVA, P > 0.05) or the expression of sickness behavior. In conclusion, infusion of S. aureus produced a fever response resembling that of sustained natural fevers but did not elicit the cortisol and behavioral responses that often are described clinically and during short-term experimental fevers.

PCR detection of staphylococcal enterotoxin genes in Staphylococcus spp. strains isolated from meat and dairy products. Evidence for new variants of seG and seI in S. aureus AB-8802

AIMS

Evaluation of the occurrence of most known staphylococcal enterotoxin (SE) genes, egc (enterotoxin gene cluster) and TSST1 (toxic shock syndrome toxin 1) gene in both coagulase-positive (CPS) and coagulase-negative (CNS) staphylococcal strains isolated from meat and dairy products.

METHODS AND RESULTS

Specificity and reliability of the PCR detection methods used were ascertained by using nine reference strains of Staphylococcus (S. aureus) harbouring SE genes (seA to seE; seG, seH, seI, seM, seJ, seN and seO) and egc (containing the following sequence of genes: seO, seM, seI, phient1, phient2, seN and seG). Of 109 wild Staphylococcus spp. strains analysed, only 11 S. aureus strains were SE and/or TSST1 PCR-positive. The last 11 strains also appeared to harbour the egc. Restriction endonuclease analysis of part of the egc of both reference and wild strains showed that different variants of the egc exist. Moreover, nucleotide sequences of seG and seI indicate that the egc of the strain AB-8802 is characterized by the presence of variants of these enterotoxins (seGv and seIv).

CONCLUSIONS

The occurrence of SE genes in CNS and other non-S. aureus species isolated from Napoli-type salami, raw water buffalo milk and natural whey cultures used for mozzarella cheese manufacturing is very rare.

SIGNIFICANCE AND IMPACT OF THE STUDY

During this study it was shown that at least five different egc may exist in S. aureus. A thorough study of egc polymorphism should provide further insight into the phylogenetics of the egc.

Cloning, expression and interaction of human T-cell receptors with the bacterial superantigen SSA

Superantigens (SAgs) are a class of disease-causing and immunostimulatory proteins of bacterial or viral origin that activate a large number of T-cells through interaction with the Vbeta domain of T-cell receptors (TCRs). In this study, recombinant TCR beta chains were constructed with human variable domains Vbeta5.2, Vbeta1 and Vbeta2.1, expressed as inclusion bodies, refolded and purified. The Streptococcus pyogenes SAg SSA-1 was cloned and expressed as a soluble periplasmic protein. SSA-1 was obtained both as a monomer and a dimer that has an intermolecular disulfide bond. We analyzed the biological activity of the recombinant SAgs by proliferation assays. The results suggest that SSA dimerization occludes the TCR interaction site. Naturally occurring SSA dimerization was also observed in supernatants of S. pyogenes isolates. An SSA mutant [SSA(C26S)] was produced to eliminate the Cys responsible for dimerization. Affinity assays using a resonant biosensor showed that both the mutant and monomeric wild type SSA have affinity for human Vbeta5.2 and Vbeta1 with Kd of 9-11 microm with a fast kass and a moderately fast kdiss. In spite of the reported stimulation of Vbeta2.1 bearing T-cells by SSA, we observed no measurable interaction.

Natural history of community-acquired methicillin-resistant Staphylococcus aureus colonization and infection in soldiers

BACKGROUND

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is an emerging pathogen for which the prevalence, risk factors, and natural history are incompletely understood.

METHODS

In this prospective observational study, we evaluated 812 US Army soldiers to determine the prevalence of and risk factors for CA-MRSA colonization and the changes in colonization rate over time, as well as to determine the clinical significance of CA-MRSA colonization. Demographic data and swab samples from the nares for S. aureus cultures were obtained from participants at the start of their training and 8-10 weeks later. Over this time period, participants were observed prospectively to monitor for soft-tissue infections. S. aureus isolates were characterized by in vitro examination of antibiotic susceptibilities, mecA confirmation, pulsed-field gel electrophoresis, and Panton-Valentine leukocidin (PVL) gene testing.

RESULTS

At the initial sampling, 24 of the participants (3%) were colonized with CA-MRSA, 9 of whom (38%) developed soft-tissue infections during the study period. In contrast, 229 participants (28%) were colonized with methicillin-susceptible S. aureus (MSSA), 8 (3%) of whom developed clinical infections during the same period (relative risk, 10.7; 95% confidence interval, 4.6-25.2; P<.001). At follow-up culture, the CA-MRSA colonization rate dropped to 1.6% without eradication efforts. Previous antibiotic use was a risk factor for CA-MRSA colonization at the initial sampling (P=.03). PVL genes were detected in 66% of 45 recovered CA-MRSA isolates, including all 9 clinical isolates available for analysis. Of subjects hospitalized, 5 of 6 had PVL-positive CA-MRSA infections.

CONCLUSIONS

CA-MRSA colonization with PVL-positive strains was associated with a significant risk of soft-tissue infection, suggesting that CA-MRSA may be more virulent than MSSA. Previous antibiotic use may play a role in CA-MRSA colonization.

Genetic procedures for identification of enterotoxigenic strains of Staphylococcus aureus from three food poisoning outbreaks

Three food poisoning restaurant outbreaks due to Staphylococcus aureus, occurring during June-October 2002 in the Principality of Asturias (PA), Spain, provided the basis for investigating some aspects of the molecular epidemiology of this organism. The methods applied to identify strains and lineages included multiplex-polymerase chain reaction (PCR) to detect nine enterotoxin (se) genes, and three DNA fingerprinting procedures: pulsed-field gel electrophoresis (PFGE) with SmaI, randomly amplified polymorphic DNA (RAPD) with two selected primers, and plasmid restriction analysis with HindIII. Thirty-two isolates were differentiated into three non-se and 12 se strains, which were outbreak-specific, except for one that was represented in two of the outbreaks. In outbreak 1, the 16 food isolates analyzed had sec, seg and sei genes and generated a distinctive DNA fingerprint, being assigned to a single strain. This strain could be categorized as endemic in the PA and associated to manually handled dairy products and nasal carriers. In outbreak 2, the four food isolates analyzed fell into three strains, each one displaying a different se-gene profile (sea, sec and seg-seh-sei) and a distinctive DNA fingerprint. In outbreak 3, the five food isolates tested fell into four seg-sei strains generating identical RAPD but different PFGE and plasmid profiles, and one sea strain also collected from two nasal carriers. This last strain had also been found in manually handled vegetables in outbreak 2, and it belongs to a not very frequently found sea lineage in the PA. Multiplex-PCR to detect se genes together with the three applied DNA fingerprint typing procedures proved therefore to be useful tools in subclassifying S. aureus for epidemiological purposes.

A toroid model for in vitro investigations of toxic shock syndrome toxin-1 production

Human behaviours and consumer products may affect vaginal microbial ecology, thereby influencing women's health. Relevant experimentation systems are needed to understand such possible links. Here, we describe the development of a practical semi-solid in vitro model to assess the effects of interactions between vaginal environment and the presence of tampons, on bacterial communities, including the production of toxic shock syndrome toxin-1 (TSST-1) by Staphylococcus aureus.

A strategy based on 5' nuclease multiplex PCR to detect enterotoxin genes sea to sej of Staphylococcus aureus

We describe the development of a strategy based on 5' nuclease multiplex PCR for the rapid detection of nine enterotoxin genes (sea, seb, sec, sed, see, seg, seh, sei, sej) of Staphylococcus aureus. The genotyping scheme consists in identifying these nine enterotoxin genes by three 5' nuclease Triplex-PCR assays. The strategy was evaluated using a collection of S. aureus reference strains previously examined with conventional PCR assays, and by testing previously characterized food S. aureus field strains. The 5' nuclease Triplex-PCR assays correctly detected the se genes in all the reference strains. In tests with field strains there was generally excellent agreement with the results obtained by conventional PCR, except for some strains harbouring variant se genes. The detection limits of the Triplex-PCR assays evaluated using fivefold dilution of recombinant plasmids for each se gene ranged from 16 to 2000 copies of target se genes in the PCR tube. The 5' nuclease Triplex-PCR assays developed are fast and specific, and provide a useful diagnostic tool for the detection and genotyping of se genes. The development of this method is an improvement that should facilitate epidemiological investigations of staphylococcal food poisoning outbreaks.

Panton-valentine leukocidin and staphyloccoccal skin infections in schoolchildren

The Panton-Valentine leukocidin is associated with staphylococcal skin and pulmonary infections. We describe a school outbreak of skin infections and the public health response to it. Nasal carriage of a Panton-Valentine leukocidin-positive Staphylococcus aureus clone was detected only in previously ill classmates and their family members.

Interplay Between Superantigens and Immunoreceptors

Superantigens (SAGs) cause a massive T-cell proliferation by simultaneously binding to major histocompatibility complex (MHC) class II on antigen-presenting cells and T-cell receptors (TCRs) on T cells. These T-cell mitogens can cause disease in host, such as food poisoning or toxic shock. The best characterized groups of SAGs are the bacterial SAGs secreted by Staphylococcus aureus and Streptococcus pyogenes. Despite a common overall three-dimensional fold of these SAGs, they have been shown to bind to MHC class II in different ways. Recently, it has also been shown that SAGs have individual preferences in their binding to the TCRs. They can interact with various regions of the variable beta-chain of TCRs and at least one SAG seems to bind to the alpha-chain of TCRs. In this review, different subclasses of SAGs are classified based upon their binding mode to MHC class II, and models of trimolecular complexes of MHC-SAG-TCR molecules are described in order to reveal and understand the complexity of SAG-mediated T-cell activation.

Behavioural endocrine immune-conditioned response is induced by taste and superantigen pairing

Administration of bacterial superantigen, such as staphylococcal enterotoxin B (SEB), induces in vivo stimulation of T cell proliferation and cytokine production such as interleukin-2 (IL-2). It has been previously reported that SEB administration induces fever, c-Fos expression in the brain, and hypothalamus-pituitary-adrenal axis activation, demonstrating that the brain is able to sense and respond to SEB. Previously it had been shown that immune functions can be behaviourally conditioned pairing a novel gustatory stimulus together with an immunomodulatory drug or an antigen. We designed an experimental protocol using Dark Agouti rats in which saccharin taste, as conditioned stimulus, was paired with an i.p. injection of SEB (2 mg/kg), as unconditioned stimulus. Six days later, when conditioned animals were re-exposed to the conditioned stimulus they displayed strong conditioned taste avoidance to the saccharin. More importantly, re-exposure to the conditioned stimulus significantly increased IL-2, interferon-gamma and corticosterone plasma levels, in comparison with conditioned animals which had not been re-exposed to saccharin taste. These results demonstrate a behavioural-immune-endocrine conditioned response using a superantigen as unconditioned stimulus. In addition, they illustrate the brain abilities to mimic the unconditioned effects of a superantigen by yet unknown mechanisms.

Intravitreal human immune globulin in a rabbit model of Staphylococcus aureus toxin-mediated endophthalmitis: a potential adjunct in the treatment of endophthalmitis

OBJECTIVES

To test the feasibility of human immune globulin (IG, Gamimune N, 10%) as a new treatment for endophthalmitis, the ocular tolerance, distribution, and ability of intravitreal IG to attenuate the toxic effects of Staphylococcus aureus culture supernatant were evaluated in a rabbit model.

METHODS

Effects of intravitreally injected IG were assessed histologically and with Western blot analysis performed 1 to 5 days after injection. IG reactivity to products of S. aureus strain RN4220 was tested by Western blotting, using known toxins (beta hemolysin and toxic shock syndrome toxin-1) and a concentrated culture supernatant containing S. aureus exotoxins (pooled toxin, PT). Endophthalmitis was induced by intravitreal PT injection. For treatment, IG and PT were mixed and injected simultaneously, or IG was injected immediately after, or 6 hours after, PT injection. PT toxicity was graded clinically and histologically over 9 days.

RESULTS

IG persisted intravitreally at least 5 days, inducing no clinical inflammation and minimal mononuclear cell infiltration. In the endophthalmitis model, toxicity from PT was significantly reduced when IG was mixed with PT and injected simultaneously, or when IG was delivered immediately after PT. Only minimal clinically detectable reductions were observed when IG delivery was delayed 6 hours.

CONCLUSIONS

Intravitreal IG is well tolerated in the rabbit eye and attenuates the toxicity of culture supernatant containing S. aureus exotoxins. Because toxin elaboration likely occurs gradually in true infection, reduced effects observed with delayed treatment in this toxin-injected model do not preclude clinical application. IG may represent a novel adjunct in endophthalmitis treatment.

Structural, energetic, and functional analysis of a protein-protein interface at distinct stages of affinity maturation

Due to a paucity of studies that synthesize structural, energetic, and functional analyses of a series of protein complexes representing distinct stages in an affinity maturation pathway, the biophysical basis for the molecular evolution of protein-protein interactions is poorly understood. Here, we combine crystal structures and binding-free energies of a series of variant superantigen (SAG)-major histocompatibility complex (MHC) class II complexes exhibiting increasingly higher affinity to reveal that this affinity maturation pathway is controlled largely by two biophysical factors: shape complementarity and buried hydrophobic surface. These factors, however, do not contribute equivalently to the affinity maturation of the interface, as the former dominates the early steps of the maturation process while the latter is responsible for improved binding in later steps. Functional assays reveal how affinity maturation of the SAG-MHC interface corresponds to T cell activation by SAGs.

Detection and genotyping by real-time PCR of the staphylococcal enterotoxin genes sea to sej

This paper describes real-time fluorescence PCR assays for detecting and toxinotyping nine enterotoxin genes from Staphylococcus aureus. A universal set of primers allowed sea, seb, sec, sed, see, seg, seh, sei, sej enterotoxin genes from S. aureus to be detected in a single real-time PCR assay with the LightCycler (LC) instrument. Using the universal forward primer and a type-specific reverse primer, real-time PCR assays allowed the S. aureus enterotoxin genes to be specifically genotyped. A collection of S. aureus isolates (n=83) was detected and further characterised for sea, seb, sec, sed, see, seg, seh, sei, sej, using real-time PCR assays, and data were compared with those obtained by conventional block cycler PCR. Isolates were also tested for their ability to produce staphylococcal enterotoxins A, B, C and D by a commercial reversed passive latex agglutination (RPLA) test. Real-time PCR assays developed on the LightCycler system (LC-PCR) are a powerful tool for rapid detection and toxinotyping of the enterotoxin genes sea to sej from S. aureus. The work offers a very quick, reliable and specific alternative to conventional block cycler PCR assays to identify the enterotoxin profile of toxigenic S. aureus.

Managing the risk of staphylococcal food poisoning from cream-filled baked goods to meet a food safety objective

The International Commission on Microbiological Specifications for Foods (ICMSF) has recently proposed a scheme for the management of microbial hazards for foods that involves the concept of food safety objectives (FSOs). FSOs are intended to specify the maximum levels of hazardous agents required to meet a given public health goal. This scheme offers flexibility for the food industry in terms of allowing the use of alternative but equivalent means for achieving a given FSO. This paper illustrates the application of the ICMSF model via the analysis of the microbiological hazard of Staphylococcus aureus in cream-filled baked goods. Cream-filled baked goods have a notorious history as vehicles for foodborne illness, particularly staphylococcal food poisoning. Although the numbers of cases reported in the United States and Europe have declined in recent years, staphylococcal food poisoning may be much more common than is recognized, particularly in other countries. The ICMSF principles for setting FSOs and the use of performance criteria, process criteria, and validation in relation to hazard analysis critical control point and good hygiene practice plans for managing S. aureus in cream-filled baked goods are described.

Generation of protective immunity by inactivated recombinant staphylococcal enterotoxin B vaccine in nonhuman primates and identification of correlates of immunity

At this time there are no vaccines or therapeutics to protect against staphylococcal enterotoxin B (SEB) exposure. Here, we report vaccine efficacy of an attenuated SEB in a nonhuman primate model following lethal aerosol challenge and identify several biomarkers of protective immunity. Initial in vitro results indicated that the mutation of key amino acid residues in the major histocompatibility complex (MHC) class II binding sites of SEB produced a nontoxic form of SEB, which had little to no detectable binding to MHC class II molecules, and lacked T-cell stimulatory activities. When examined in a mouse model, we found that the attenuated SEB retained antigenic structures and elicited protective immune responses against wild-type SEB challenge. Subsequently, a vaccine regimen against SEB in a nonhuman primate model was partially optimized, and investigations of immune biomarkers as indicators of protection were performed. SEB-naïve rhesus monkeys were vaccinated two or three times with 5 or 20 microg of the attenuated SEB and challenged by aerosol with wild-type SEB toxin. Unlike exposure to the native toxin, the vaccine did not trigger the release of inflammatory cytokines (TNF alpha, IL6, or IFN gamma). All rhesus monkeys that developed anti-SEB serum titers > or = 10(4) and elicited high levels of neutralizing antibody survived the aerosol challenge. These findings suggest that the attenuated SEB is fully protective against aerosolized toxin when administered to unprimed subjects. Moreover, experiments presented in this study identified various biomarkers that showed substantial promise as correlates of immunity and surrogate endpoints for assessing in vivo biological responses in primates, and possibly in humans, to vaccines against SEs.

Correlation of body temperature with protection against staphylococcal enterotoxin B exposure and use in determining vaccine dose-schedule

The immunoprotective potential of a recombinant vaccine against the incapacitating effect of aerosolized staphylococcal enterotoxin B (SEB) in nonhuman primates is reported. SEB belongs to a family of structurally related superantigens responsible for serious, life threatening pathologies. Injecting the recombinant SEB vaccine did not induce temperature elevation in rhesus monkeys, a classical symptom of toxic-shock syndrome. No temperature elevation was noted following injection with control tetanus toxoid. In addition to 100% survival, we observed a clear correlation between vaccine dose and mitigation of temperature elevation after a lethal SEB aerosol challenge. We conclude that the recombinant SEB vaccine is non-pyrogenic and that monitoring changes in body temperature is an important biomarker of toxic shock in a primate animal model.

Community-acquired methicillin-resistant Staphylococcus aureus: an emerging pathogen

The prevalence of MRSA in the nosocomial setting has been well studied, and its control remains a challenge for infection control professionals. Complicating this problem is the increasing number of reports on the spread of community-acquired MRSA (CA-MRSA). CA-MRSA strains differ from hospital-acquired MRSA (HA-MRSA) strains in that they are generally susceptible to most antibiotics. These strains share the presence of staphylococcal cassette chromosome mec (SCCmec) type IV in their genomes, are frequently virulent, and predominantly cause skin and soft tissue infections. The genome sequence of the prototypic CA-MRSA strain, MW2, revealed the presence of additional virulence factors not commonly present in other S. aureus strains. We determined the genetic relatedness of 30 geographically diverse CA-MRSA isolates clustered based on SCCmec type IV by sequence analysis of the polymorphic repeat region of the protein A gene (spa typing). These results indicated that most strains shared a common spa type (131), identical to MW2. Because this group tends to infect healthy individuals with no known risk factors for nosocomial acquisition of MRSA, we refer to it as CA-MRSA without risk factors. A second group, CA-MRSA with risk factors, consists of two related genotypes, spa types 1 and 7, which differ by one nucleotide change. These strains have caused severe infections in HIV-positive patients in Los Angeles and New York. Although CA-MRSA strains share genetic determinants, they are not clonal but rather are derived from different genetic backgrounds. The genetic characteristics and the epidemiology of CA-MRSA with and without risk factors are discussed.

Targeting bacterial virulence: the role of protein synthesis inhibitors in severe infections. Insights from the Society of Infectious Diseases Pharmacists

Morbidity and mortality due to certain bacterial pathogens have not declined despite the availability of effective antimicrobial treatments. Staphylococcus aureus and Streptococcus pyogenes cause a number of serious infections, such as necrotizing fasciitis and toxic shock syndrome, which are associated with the release of bacterial toxins. Animal studies have demonstrated clindamycin, a protein synthesis inhibitor, to be more effective in treating these severe infections than other more susceptible antimicrobial treatments. Linezolid, another protein synthesis inhibitor, also has shown efficacy in in vitro studies. Human trials to validate the effects of antibiotic therapies on bacterial virulence have not been performed. Future animal and human studies are needed to help elucidate the immunomodulatory mechanisms of protein synthesis inhibitors in order to optimize antimicrobial treatment and decrease the morbidity and mortality associated with severe bacterial infections.

Augmentation of staphylococcal alpha-toxin signaling by the epidermal platelet-activating factor receptor

Staphylococcal alpha-toxin is a cytolytic toxin secreted by many strains of Staphylococcus aureus that has proinflammatory and cytotoxic effects on human keratinocytes. alpha-toxin exerts its effects by forming a transmembrane pore that behaves like an ionophore for ions such as calcium. Because cellular membrane disruption with resultant intracellular calcium mobilization is a potent stimulus for the synthesis for the lipid mediator platelet-activating factor, the ability of alpha-toxin to induce platelet-activating factor production was assessed, and whether the epidermal platelet-activating factor receptor could augment toxin-induced signaling in epithelial cells examined. Treatment of the human keratinocyte-derived cell line HaCaT with alpha-toxin resulted in significant levels of platelet-activating factor, which were approximately 50% of the levels induced by calcium ionophore A23187. alpha-toxin also stimulated arachidonic acid release in HaCaT keratinocytes. Pretreatment of HaCaT cells with platelet-activating factor receptor antagonists, or overexpression of the platelet-activating factor metabolizing enzyme acetylhydrolase II blunted alpha-toxin-induced arachidonic acid release by approximately one-third, suggesting a role for toxin-produced platelet-activating factor in this process. Finally, retroviral-mediated expression of the platelet-activating factor receptor into the platelet-activating factor receptor-negative epithelial cell line KB resulted in an augmentation of alpha-toxin-mediated intracellular calcium mobilization and arachidonic acid release. These studies suggest that alpha-toxin-mediated signaling can be augmented via the epidermal platelet-activating factor receptor.

An outbreak of neonatal toxic shock syndrome-like exanthematous disease (NTED) caused by methicillin-resistant Staphylococcus aureus (MRSA) in a neonatal intensive care unit

Neonatal toxic shock syndrome-like exanthematous disease (NTED) is a new entity of methicillin-resistant Staphylococcus aureus (MRSA) infection. Most of NTED cases reported previously in the literature were sporadic ones. In the present report, we describe an outbreak of NTED that occurred in a neonatal intensive care unit (NICU) between April, 1999 and April, 2000 in Japan. All MRSA strains isolated from 14 patients (6 NTED, 2 infections and 6 colonizations) in this outbreak belonged to the group of coagulase II and produced toxic shock syndrome toxin 1 (TSST-1). Of these, 14 strains produced staphylococcal enterotoxin C (SEC). No other superantigenic toxins were produced by these strains. The pulsed field gel electrophoresis (PFGE) patterns of genomic DNA digested with SmaI were indistinguishable each other due to no band shifting in all of the 13 strains except for strain O-21 and M56. Strain M56 was different from the dominant type in the positions of only 2 bands, whereas the pattern of strain O-21 had no similarity with the other pattern, suggesting that this outbreak was associated with the spread of a unique MRSA strain in the NICU. Two-dimensional electrophoresis (2-DE) analysis of exoproteins revealed that the patterns of these 14 strains were very indistinguishable to each other, and that these strains produced very large amounts of TSST-1 and SEC3 subtype superantigens, as measured with computer-assisted image analysis of the intensity of 2-DE spots. The 2-DE gel of O-21 showed the different pattern from the others. These results as well as the profiles of toxin production also supported the conclusion drawn from PFGE analysis. Based on these results, the involvement of TSST-1 and SEC3 in the pathogenesis of NTED is discussed.

Genetic basis of neonatal methicillin-resistant Staphylococcus aureus in Japan

Methicillin-resistant Staphylococcus aureus (MRSA) is still one of major problems of drug-resistant microorganisms and healthcare-acquired infections. Methicillin-resistant Staphylococcus aureus is highly prevalent in patients in neonatal intensive care units (NICU) in Japan. The most predominant MRSA in NICU is multidrug resistant and produces superantigenic exotoxin, toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin C (SEC). These predominant MRSA strains belong to coagulase type II, SCCmec type II, mecA-Tn554 polymorph type I-A and show closely related pulse field gel electrophoresis types. The dissemination of MRSA is wide, and there is a pandemic distribution of a single MRSA clone in the NICU of Japan. Since 1992, the nationwide spread of this clone has also led to the development of a new neonatal disease known as neonatal toxic shock-like exanthematous disease (NTED), which is caused by overactivation of vbeta2+ T cells induced by TSST-1. The spread of MRSA in NICU in Japan has been attributed to overcrowding, high rates of extremely low birthweight babies, understaffing, low control measures of infection and overuse of antibiotics. The environment of NICU and infection control intervention should be improved and a new strategy for control like vaccination or probiotics is required.

Chronic Staphylococcal enterotoxin B and lipopolysaccharide induce a bimodal pattern of hepatic dysfunction and injury

OBJECTIVE

To determine the effect of chronic exposure to endotoxin (lipopolysaccharide) and Staphylococcal enterotoxin B on hepatic injury and function.

DESIGN

Prospective, controlled trial.

SETTING

Research laboratory in a university hospital.

SUBJECTS

Male Sprague-Dawley rats weighing 325-350 g with chronic vascular and bile catheters.

INTERVENTIONS

Chronically catheterized rats were treated daily with saline, 50 microg/kg Staphylococcal enterotoxin B alone, 1000 microg/kg lipopolysaccharide alone, 1000 microg/kg lipopolysaccharide with 50 microg/kg Staphylococcal enterotoxin B, or 100 microg/kg lipopolysaccharide with 50 microg/kg Staphylococcal enterotoxin B for 10 days. Serum and biliary measures of hepatic injury and dysfunction were measured before and then 6 hrs and 1, 2, 3, 7, and 10 days after the start of treatment. The animals were killed at 10 days and the livers examined histologically.

MEASUREMENTS AND MAIN RESULTS

Mean rates of bile flow, biliary indocyanine green excretion, and bile acid flux were significantly decreased immediately after treatment (6 hr, 1 and 2 days) and then at 10 days. Increases in biliary and serum gamma-glutamyltransferase and serum bile acids also occurred in a similar bimodal pattern. Animals treated with lipopolysaccharide or Staphylococcal enterotoxin B alone became tolerant and did not develop the bimodal pattern of hepatic dysfunction. Histologic examination of the liver at 10 days revealed periportal inflammation and fibrosis.

CONCLUSIONS

The combination of lipopolysaccharide and Staphylococcal enterotoxin B leads to late liver injury, whereas either toxin alone does not. These data may explain the frequent development of liver dysfunction in patients exposed to multiple bacterial toxins such as in sepsis, multiple-system organ failure, and other diseases with altered intestinal permeability.

Induction of cytokine production by different Staphylococcal strains

In light of the important role of cytokines in the pathogenesis of bacterial infections, we analyzed the cytokine production induced by different Staphylococcus aureus (S. aureus), S. epidermidis and S. saprophyticus strains in human mononuclear cells (MNCs). MNCs secreted high amounts of interleukin-1beta (IL-1beta) and IL-6 proteins in responses to stimulation with all three species of Staphylococci. Interestingly, a large majority of the S. aureus strains induced significantly higher IL-12 and interferon (IFN) titers than did the S. epidermidis and S. saprophyticus strains. The RNase protection assay revealed high increases in IL-1alpha, IL-1 beta, IL-1 receptor antagonist, IL-6 and IL-12 p40 transcript levels in MNCs stimulated with Staphylococci. All of the tested Staphylococcal strains proved highly efficient in mediating the induction of these genes. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis indicated considerable increases in IFNA transcript levels in MNCs stimulated with S. aureus strains, while only a very weak expression was stimulated by S. epidermidis and S. saprophyticus. These results confirm that heat-killed Staphylococci exert strong immunomodulatory effects, and suggest that the contribution of T-helper 1 (Th(1)) cells to the immune response may be much extensive in infections caused by S. aureus strains, due to their high IL-12p70 and IFN-alpha-inducing activities.

Detection and recovery of sublethally-injured enterotoxigenic Staphylococcus aureus

AIMS

To determine whether sublethally-injured (acid- or heat-shocked) Staphylococcus aureus cells are recoverable using selective agar overlays.

METHODS AND RESULTS

Brain Heart Infusion (BHI) Agar overlaid with either Baird-Parker Agar (BPA) or Gram-Positive Agar (GPA) was compared in the ability to resuscitate heat- and acid-shocked enterotoxigenic Staph. aureus. BHI/BPA overlays allowed for greater recovery of both heat- and acid-shocked cells than BHI/GPA, although the former was not selective and allowed growth of bacteria other than Staph. aureus. No significant difference existed in percent recovery of heat- and acid-shocked cells between the two overlay approaches. Significant differences were noted in counts on BHI/GPA plates and straight selective GPA/GPA plates, however. Viability of heat- and acid-shocked Staph. aureus was also examined using fluorescence microscopy, the relative counts of which correlated well to the calculated percent recovery on selective agar overlays.

CONCLUSIONS

This work has shown that an improved agar overlay technique increases the sensitivity of the standard plate count while enumerating sublethally-injured enterotoxigenic Staph. aureus compared with direct plating onto selective media.

SIGNIFICANCE AND IMPACT OF THE STUDY

These data emphasize the need to develop practical and cost-effective methods that reliably detect and enumerate sublethally-injured pathogens such as Staph. aureus.

Staphylococcal and streptococcal superantigens: molecular, biological and clinical aspects

Superantigens (SAgs) include a class of certain bacterial and viral proteins exhibiting highly potent lymphocyte-transforming (mitogenic) activity towards human and or other mammalian T lymphocytes. Unlike conventional antigens, SAgs bind to certain regions of major histocompatibility complex (MHC) class II molecules of antigen-presenting cells (APCs) outside the classical antigen-binding groove and concomitantly bind in their native form to T cells at specific motifs of the variable region of the beta chain (Vbeta) of the T cell receptor (TcR). This interaction triggers the activation (proliferation) of the targeted T lymphocytes and leads to the in vivo or in vitro release of high amounts of various cytokines and other effectors by immune cells. Each SAg interacts specifically with a characteristic set of Vbeta motifs. The review summarizes our current knowledge on S. aureus and S. pyogenes superantigen proteins. The repertoire of the staphylococcal and streptococcal SAgs comprises 24 and 8 proteins, respectively. The staphylococcal SAgs include (i) the classical enterotoxins A, B, C (and antigenic variants), D, E, and the recently discovered enterotoxins G to Q, (ii) toxic shock syndrome toxin-1, (iii) exfoliatins A and B. The streptococcal SAgs include the classical pyrogenic exotoxins A and C and the newly identified pyrogenic toxins, G, H, I, J, SMEZ, and SSA. The structural and genomic aspects of these toxins and their molecular relatedness are described as well as the available 3-D crystal structure of some of them and that of certain of their complexes with MHC class II molecules and the TcR, respectively. The pathophysiological properties and clinical disorders related to these SAgs are reviewed.

Protein A is a virulence factor in Staphylococcus aureus arthritis and septic death

Staphylococcal protein A (SpA), a cell wall anchored protein of Staphylococcus aureus, has the ability to interact with several host components, possibly indicating a role as a virulence factor in S. aureus infections. In this study, the contribution of SpA to bacterial virulence was investigated in a murine model of S. aureus arthritis. Intravenous inoculation of S. aureus wild-type strain Newman gave rise to more severe arthritis and higher mortality than the isogenic spa mutant strain DU5873. The wild-type strain caused more in vitro spleen cell proliferation than the SpA-deficient strain. However, IL-6 and TNF-alpha levels were higher after stimulation with thespa mutant strain compared to the wild-type strain. To conclude, our results clearly indicate that SpA is a virulence factor of S. aureus in murine septic arthritis.

A superantigen bioassay to detect staphylococcal enterotoxin A

Current detection methods for enterotoxins of Staphylococcus aureus are labor intensive and limited in sensitivity. Furthermore, these immunochemical protocols fail to adequately detect heat-treated enterotoxins. Staphylococcal enterotoxins cause severe gastrointestinal illness at relatively low concentrations and retain toxigenicity even after heat treatment. Presented here is a novel method to detect staphylococcal enterotoxin A (SEA). This method is a bioassay that exploits SEA's activity as a superantigen in that it induces in cytotoxic T lymphocytes a cytotoxic response against SEA-bound Raji cells. Target cell death is assayed colorimetrically with the CytoTox 96 cell lysis detection kit. In the experiments presented here, this bioassay was also able to detect heat-treated SEA, albeit with a slight compromise in sensitivity. This system detected SEA at picomolar concentrations. Because of the sensitivity of this assay, it is conceivable that it could be incorporated into current detection methods as a confirmatory test.

Molecular epidemiological studies of Staphylococcus aureus in urinary tract infection

In recent years, the increasing incidence of urinary tract infection (UTIs) caused by Staphylococcus aureus has been noted at the urology ward, Okayama University Hospital. We investigated the molecular epidemiological characteristics of 139 UTI isolates, including 45 methicillin-sensitive S. aureus (MSSA) and 94 methicillin-resistant S. aureus (MRSA), collected over a 10-year period from 1990 to 1999. The antibiotic resistance genes ( mecA, aph(3')-III, aac(6')-aph(2"), ant(4')-I) and the toxin genes (tst, sea, seb, and sec) were detected by using multiplex polymerase chain reaction (PCR). Since 1996, the prevalence of the ant(4')-I, tstand secgenes has increased markedly in coagulase type II S. aureus possessing the mecA gene (MRSA). The presence of toxin genes in MRSA was higher than that in MSSA; 66.0% and 26.7% for tst, 7.4% and 4.4% for sea, 24.5% and 8.9% for seb, and 66.0% and 28.9% for sec, respectively. In the review of medical records, it was found that febrile episodes occurred in 12 of 72 patients with monomicrobial UTI caused by S. aureus. For the febrile patients, S. aureus isolates with both the tst and sec genes were found significantly more often (11 of 12; 91.7%) than those without the tst and sec genes ( P = 0.0484). Molecular typing of MRSA isolates, by using random amplified polymorphic DNA analysis and pulsed-field gel electrophoresis analysis, revealed no apparent clonality of these isolates over the 10 years, suggesting that most of the recent MRSA infections are not due to cross-infection in the urology ward.