Exotoxins of Staphylococcus aureus

Chemotaxis inhibitory protein of Staphylococcus aureus, a bacterial antiinflammatory agent

Leukocyte migration is a key event both in host defense against invading pathogens as well as in inflammation. Bacteria generate chemoattractants primarily by excretion (formylated peptides), complement activation (C5a), and subsequently through activation of leukocytes (e.g., leukotriene B4, platelet-activating factor, and interleukin 8). Here we describe a new protein secreted by Staphylococcus aureus that specifically impairs the response of neutrophils and monocytes to formylated peptides and C5a. This chemotaxis inhibitory protein of S. aureus (CHIPS) is a 14.1-kD protein encoded on a bacteriophage and is found in >60% of clinical isolates. CHIPS reduces the neutrophil recruitment toward C5a in a mouse peritonitis model, even though its activity is much more potent on human than on mouse cells. These findings suggest a new immune escape mechanism of S. aureus and put forward CHIPS as a potential new antiinflammatory therapeutic compound.

Structural relationships and cellular tropism of staphylococcal superantigen-like proteins

The staphylococcal superantigen-like proteins (SSLs) are a family of polymorphic paralogs encoded in the Staphylococcus aureus genome whose function is unknown. The crystal structure of SSL7 was determined and compared to that of SSL5 and that of a classical superantigen, streptococcal pyrogenic exotoxin. Although the overall architecture of the superantigen family is retained in both SSL7 and SSL5, there are significant differences in the structures which suggest that the characteristic major histocompatibility complex binding site of superantigens has been lost. To complement these data, the abilities of SSL7 and a closely related paralog, SSL9, to interact with cells of the immune system were investigated. In populations of human white blood cells, both SSLs interacted selectively with monocytes via specific saturable but separate binding sites, which led to rapid uptake of the SSLs. In addition, SSLs were rapidly taken up by dendritic cells, but not by macrophages, into the same endosomal compartment as dextran. The ability of these secreted proteins to target antigen-presenting cells may enhance a misplaced antibody response against the proteins, which may facilitate bacterial colonization rather than contribute to host protection. Like classical superantigens, therefore, SSLs may distract the host's immune system, but they may do so via entirely different molecular mechanisms.

Staphylococcus aureus protein A induces airway epithelial inflammatory responses by activating TNFR1

Staphylococcus aureus is a major human pathogen that is associated with diverse types of local and systemic infection characterized by inflammation dominated by polymorphonuclear leukocytes. Staphylococci frequently cause pneumonia, and these clinical isolates often have increased expression of protein A, suggesting that this protein may have a role in virulence. Here we show that TNFR1, a receptor for tumor-necrosis factor-alpha (TNF-alpha) that is widely distributed on the airway epithelium, is a receptor for protein A. We also show that the protein A-TNFR1 signaling pathway has a central role in the pathogenesis of staphylococcal pneumonia.

Biological properties of staphylococcal enterotoxin-like toxin type R

We investigated the biological properties of a novel staphylococcal enterotoxin-like putative toxin, staphylococcal enterotoxin-like toxin type R (SElR). Major histocompatibility complex class II molecules were required for T-cell stimulation by SElR. SElR stimulated T cells bearing receptors Vbeta 3, 11, 12, 13.2, and 14. These results suggested that SElR acts as a superantigen.

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.

Suppression of Staphylococcal Enterotoxin B-induced Toxicity by a Nuclear Import Inhibitor

Staphylococcal enterotoxin B and related toxins that target T cells have the capacity to elicit systemic inflammation, tissue injury, and death. Genes that encode mediators of inflammation can be globally inhibited by blocking the nuclear import of stress-responsive transcription factors. Here we show that cell-permeant peptides targeting Rch1/importin alpha/karyopherin alpha 2, a nuclear import adaptor protein, are delivered to T cells where they inhibit the staphylococcal enterotoxin B-induced production of inflammatory cytokines ex vivo in cultured primary spleen cells and in vivo. The systemic production of tumor necrosis factor alpha, interferon gamma, and interleukin-6 was attenuated in mice either by a cell-permeant cyclized form of SN50 peptide or by a transgene whose product suppresses the nuclear import of transcription factor nuclear factor kappa B in T cells. The extent of liver apoptosis and hemorrhagic necrosis was also reduced, which correlated with significantly decreased mortality rates. These findings highlight nuclear import inhibitors as a potentially useful countermeasure for staphylococcal enterotoxin B and other toxins that trigger harmful systemic inflammatory responses.

Transcription of the toxin genes present within the Staphylococcal phage phiSa3ms is intimately linked with the phage's life cycle

phiSa3ms, a lysogenic bacteriophage encoding the staphylococcal enterotoxins SEA, SEG, and SEK and the fibrinolytic enzyme staphylokinase (Sak), was identified in the unannotated genome sequence of the hypervirulent community-acquired Staphylococcus aureus strain 476. We found that mitomycin C induction of phiSa3ms led to increased transcription of all four virulence factors. The increase in sea and sak transcription was a result of read-through transcription from upstream latent phage promoters and an increase in phage copy number. The majority of the seg2 and sek2 transcripts were shown to initiate from the upstream phage cI promoter and hence were regulated by factors influencing cI transcription. The lysogeny module of phiSa3ms was shown to have some lambda-like features with divergent cI and cro genes. Band shift assays were used to identify binding sites for both CI and Cro within the region between these genes, suggesting a mechanism of control for the phiSa3ms lytic-lysogenic switch. Our findings suggest that the production of phage-encoded virulence factors in S. aureus may be regulated by processes that govern lysogeny.

The high-resolution functional map of bacteriophage SPP1 portal protein

An essential component in the assembly of nucleocapsids of tailed bacteriophages and of herpes viruses is the portal protein that is located at the unique vertex of the icosahedral capsid through which DNA movements occur. A library of mutations in the bacteriophage SPP1 portal protein (gp6) was generated by random mutagenesis of gene 6. Screening of the library allowed identification of 67 single amino acid substitutions that impair portal protein function. Most of the mutations cluster within stretches of a few amino acids in the gp6 carboxyl-terminus. The mutations were divided into five classes according to the step of virus assembly that they impair: (1) production of stable gp6; (2) interaction of gp6 with the minor capsid protein gp7; (3) incorporation of gp6 in the procapsid structure; (4) DNA packaging; and (5) sizing of the packaged DNA molecule. Most of the mutations fell in classes 3 and 4. This is the first high-resolution functional map of a portal protein, in which its function at different steps of viral assembly can be directly correlated with specific regions of its sequence. The work provides a framework for the understanding of central processes in the assembly of viruses that use specialized portals to govern entry and exit of DNA from the viral capsid.

Community-acquired Methicillin-resistant Staphylococcus aureus: Epidemiology and Potential Virulence Factors

Methicillin-resistant Staphylococcus aureus (MRSA) has been isolated from patients in the community. Some of these strains may have origins in the hospital, but others appear to be novel and unrelated to known hospital strains. Community MRSA strains have several distinguishing characteristics that may enable them to more readily colonize and infect otherwise healthy individuals. This article reviews recent publications addressing the epidemiology of MRSA in the community, risk factors associated with carriage, potentially associated virulence factors, and concepts of strain fitness as they pertain to MRSA. MRSA likely will be an increasingly important pathogen in the community.

Superantigens from Staphylococcus aureus induce procoagulant activity and monocyte tissue factor expression in whole blood and mononuclear cells via IL-1 beta

BACKGROUND

Staphylococcus aureus is one of the most common bacteria in human sepsis, a condition in which the activation of blood coagulation plays a critical pathophysiological role. During severe sepsis and septic shock microthrombi and multiorgan dysfunction are observed as a result of bacterial interference with the host defense and coagulation systems.

OBJECTIVES

In the present study, staphylococcal superantigens were tested for their ability to induce procoagulant activity and tissue factor (TF) expression in human whole blood and in peripheral blood mononuclear cells.

METHODS AND RESULTS

Determination of clotting time showed that enterotoxin A, B and toxic shock syndrome toxin 1 from S. aureus induce procoagulant activity in whole blood and in mononuclear cells. The procoagulant activity was dependent on the expression of TF in monocytes since antibodies to TF inhibited the effect of the toxins and TF was detected on the surface of monocytes by flow cytometry. In the supernatants from staphylococcal toxin-stimulated mononuclear cells, interleukin (IL)-1 beta was detected by ELISA. Furthermore, the increased procoagulant activity and TF expression in monocytes induced by the staphylococcal toxins were inhibited in the presence of IL-1 receptor antagonist, a natural inhibitor of IL-1 beta.

CONCLUSIONS

The present study shows that superantigens from S. aureus activate the extrinsic coagulation pathway by inducing expression of TF in monocytes, and that the expression is mainly triggered by superantigen-induced IL-1 beta release.

Identification and characterization of a new staphylococcal enterotoxin-related putative toxin encoded by two kinds of plasmids

We identified and characterized a novel staphylococcal enterotoxin-like putative toxin, which is named SER. Nucleotide sequencing analysis of the ser gene revealed that ser was most closely related to the seg gene. The ser gene product, SER, was successfully expressed as a recombinant protein in an Escherichia coli expression system, and recombinant SER (rSER) showed significant T-cell stimulation activity. The SER production in ser-harboring Staphylococcus aureus strains was confirmed by Western blot analysis using anti-rSER antibody. Moreover, ser was seen to be encoded by at least two types of plasmids. In particular, one kind of plasmid encoding the ser gene has been known as a sed- and sej-carrying pIB485-related plasmid.

Prebiotics in infant milk formulas: new perspectives

In recent years it has become accepted that healthy human intestinal microflora may play an important part in priming the infants' systemic and mucosal immunity. Dietary modulation of the gut microbiota is a topical area of nutritional sciences and the main focus of many current functional foods such as non-digestible oligosaccharides (NDOs). Fructo-oligosaccharides (FOS) and trans-beta-galacto-oligosaccharides (TOS) have been claimed to benefit the health of the colon by selectively stimulating the growth of bifidobacteria and lactobacilli (prebiotic effect). It could be of clinical interest to manipulate colonic flora because it is supposed that specific bacteria in the gut microbial microflora could promote potentially antiallergenic processes and play a key part in atopic disease prevention. Supporting this view is the finding that analysis of the composition of the intestinal bacterial populations showed different microbial patterns between healthy and allergic individuals. Assuming that non-digestible TOS and FOS can affect the intestinal ecosystem beneficially, the opportunity for gut flora manipulation arises in bottle-fed infants. New preterm and term infant milk formulas, supplemented with a mixture of TOS and FOS as prebiotic ingredients induced a significantly higher colonization of bifidobacteria and lactobacilli. In the future, selective manipulation of the intestinal microbiota might be an approach to novel prophylactic and therapeutic intervention strategies of atopy, by redirecting allergic Th-2 responses in favour of Th-1 responses.

Epidemiologic study of intramammary infections with Staphylococcus aureus during a control program in nine commercial dairy herds

OBJECTIVE

To determine the epidemiologic pattern of intramammary infections (IMIs) with Staphylococcus aureus during implementation of a control program in 9 commercial dairy herds.

DESIGN

Cohort study.

ANIMALS

1,651 lactating cows and 53,098 quarter milk samples.

PROCEDURES

Nine herds located in different regions of Italy were enrolled. Control of S. aureus infections followed the general principles of contagious mastitis control and was based on precise diagnostic procedures and strict control and segregation of infected cows. All lactating cows in each herd were tested, and those free of S. aureus IMI were enrolled as the cohorts. Further additions to the cohort group were cows and heifers free of S. aureus IMI, as determined from aseptically collected milk samples taken approximately 7 and 14 days after calving.

RESULTS

After the ninth month of the program, incidence decreased to < 2 new IMIs/100 cow-months in 7 of the herds. At the end of the study, 8 of 9 herds had an incidence of < or = 1 new IMI/100 cow-months. Heifers were most at risk of developing an IMI.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that control of S. aureus IMIs can be achieved by use of a control program based on segregation and use of hygienic and therapeutic protocols. Analysis of incidence and identification of risk factors in a herd could avoid the possible shortcomings of the program, maximizing the probability of success.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus strains causing neonatal toxic shock syndrome-like exanthematous disease in neonatal and perinatal wards

Neonatal toxic shock syndrome-like exanthematous disease (NTED) is a new neonatal disease caused by toxic shock syndrome toxin 1 (TSST-1). We conducted a prospective surveillance study and characterized the methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from patients with NTED and compared them with the strains from patients with other MRSA infections and asymptomatic carriers. The study was performed in the neonatal intensive care unit and a general neonatal and maternal ward in the Tokyo Women's Medical University Hospital (TWMUH) from September to December 1998. Among 103 patients eligible for the study, MRSA was detected in 62 (60.2%) newborns; of these 62 newborns, 8 (12.9%) developed NTED, 1 (1.6%) had another MRSA infection, and 53 (85.5%) were asymptomatic MRSA carriers. Sixty-nine MRSA strains were obtained from the 62 newborns. DNA fingerprinting by pulsed-field gel electrophoresis showed two clusters: clone A with 8 subtypes and clone B. Sixty-seven of the 69 MRSA strains (97.1%) belonged to clone A, and type A1 was the most predominant (42 of 69 strains; 60.9%) in every neonatal and perinatal ward. All but one of the clone A strains had the TSST-1 and staphylococcal enterotoxin C genes. We also analyzed eight MRSA strains from eight NTED patients in five hospitals in Japan other than TWMUH. All the MRSA strains from NTED patients also belonged to clone A. These results suggest that a single clone that predominated in the neonatal wards of six hospitals might have caused NTED. However, the occurrence of NTED might not be dependent on the presence of an NTED-specific strain.

Genome diversification in Staphylococcus aureus: Molecular evolution of a highly variable chromosomal region encoding the Staphylococcal exotoxin-like family of proteins

Recent genomic studies have revealed extensive variation in natural populations of many pathogenic bacteria. However, the evolutionary processes which contribute to much of this variation remain unclear. A previous whole-genome DNA microarray study identified variation at a large chromosomal region (RD13) of Staphylococcus aureus which encodes a family of proteins with homology to staphylococcal and streptococcal superantigens, designated staphylococcal exotoxin-like (SET) proteins. In the present study, RD13 was found in all 63 S. aureus isolates of divergent clonal, geographic, and disease origins but contained a high level of variation in gene content in different strains. A central variable region which contained from 6 to 10 different set genes, depending on the strain, was identified, and DNA sequence analysis suggests that horizontal gene transfer and recombination have contributed to the diversification of RD13. Phylogenetic analysis based on the RD13 DNA sequence of 18 strains suggested that loss of various set genes has occurred independently several times, in separate lineages of pathogenic S. aureus, providing a model to explain the molecular variation of RD13 in extant strains. In spite of multiple episodes of set deletion, analysis of the ratio of silent substitutions in set genes to amino acid replacements in their products suggests that purifying selection (selective constraint) is acting to maintain SET function. Further, concurrent transcription in vitro of six of the seven set genes in strain COL was detected, indicating that the expression of set genes has been maintained in contemporary strains, and Western immunoblot analysis indicated that multiple SET proteins are expressed during the course of human infections. Overall, we have shown that the chromosomal region RD13 has diversified extensively through episodes of gene deletion and recombination. The coexpression of many set genes and the production of multiple SET proteins during human infection suggests an important role in host-pathogen interactions.

Characterization of Staphylococcus aureus enterotoxin L

Staphylococcus aureus causes a wide variety of diseases. Major virulence factors of this organism include enterotoxins (SEs) that cause both food poisoning and toxic shock syndrome. Recently, a novel SE, tentatively designated SEL, was identified in a pathogenicity island from a bovine mastitis isolate. The toxin had a molecular weight of 26,000 and an isoelectric point of 8.5. Recombinant SEL shared many biological activities with SEs, including superantigenicity, pyrogenicity, enhancement of endotoxin shock, and lethality in rabbits when administered in subcutaneous miniosmotic pumps, but the protein lacked emetic activity. T cells bearing the T-cell receptor beta chain variable regions 5.1, 5.2, 6.7, 16, and 22 were significantly stimulated by recombinant SEL.

Prevalence of genes encoding pyrogenic toxin superantigens and exfoliative toxins among strains of Staphylococcus aureus isolated from blood and nasal specimens

A total of 429 different Staphylococcus aureus isolates encompassing 219 blood isolates and 210 isolates taken from anterior nares were systematically searched by two multiplex PCR-DNA enzyme immunoassays (PCR-DEIA) for exfoliative toxin (ET) genes eta and etb, as well as for the classical members of the pyrogenic toxin superantigen (PTSAg) gene family comprising the staphylococcal enterotoxin (SE) genes sea-see and the toxic shock syndrome toxin 1 gene tst. In addition, a third PCR-DEIA was established to investigate the possession of four recently described SE genes, viz. seg-sej. The most frequent PTSAg/ET genes amplified were seg and sei, which were found strictly in combination in 55.0% of the S. aureus isolates tested. Other frequently detected toxin genes were tst (20.3%), sea (15.9%), and sec (11.2%). Only five isolates harbored ET genes. Regarding the origin of the S. aureus isolates, a significant difference (P = 0.037) was found for the possession of the sed/sej gene combination (10.5% of blood isolates versus 3.3% of nasal strains). Overall, about half of S. aureus isolates tested harbored genes of the classical members of the PTSAg family and ETs (50.8%), whereas 73.0% of S. aureus isolates were toxin gene positive if the recently described SE genes were included. This notable higher prevalence indicates that the possession of PTSAg genes in particular seems to be a habitual feature of S. aureus. Moreover, mainly due to the fixed combinations of seg plus sei, as well as sed plus sej, the possession of multiple PTSAg genes (62.9%) is more frequent than assumed so far.

Toxic shock syndrome in a horse with Staphylococcus aureus pneumonia

A 3-year-old Thoroughbred gelding was examined because of clinical signs of pneumonia and shock. Mucous membrane petechiation and ventral edema were observed and considered to be a result of vasculitis. Epidermal necrosis developed on the distal portions of the limbs. The horse had a persistent high fever that was unresponsive to nonsteroidal anti-inflammatory treatment, and Staphylococcus aureus was isolated from a nasal swab specimen and 2 transtracheal wash fluid samples. Antimicrobial, anti-inflammatory, and supportive treatment resulted in clinical improvement. However, resolution of the pulmonary infection required long-term (42 days) antimicrobial administration. Staphylococcus aureus strains isolated from this horse were positive for the toxic shock syndrome toxin-1 gene and were shown to produce toxic shock syndrome toxin-1, the causative factor in toxic shock syndrome in humans. The horse's clinical signs were attributed to toxic shock syndrome secondary to pulmonary S. aureus infection.

Role of staphylococcal enterotoxin A in a fatal case of endocarditis

A young female with no identifiable risk factors developed rapid, overwhelming Staphylococcus aureus endocarditis. Despite rapid sterilization of the blood and the mitral valve with optimal antimicrobials, she had persistent septic shock. In order to investigate this, the toxin-producing capacity of the infecting strain and the patient's ability to produce antibodies were determined. The strain produced high levels of both alpha-toxin and staphylococcal enterotoxin A (SEA), whilst the patient responded with modestly high levels of antibodies to alpha-toxin and low-normal levels to SEA. The patient was most probably susceptible to the actions of SEA and developed a toxic-shock-syndrome-like disease that further aggravated her valvular dysfunction. This case illustrates that optimal antimicrobial therapy alone is not sufficient treatment in patients with persistent toxic shock and that there is a need to evaluate immunomodulatory strategies in such patients.

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.

Induction of emetic response to staphylococcal enterotoxins in the house musk shrew (Suncus murinus)

The emetic responses induced by staphylococcal enterotoxin A (SEA), SEB, SEC2, SED, SEE, SEG, SEH, and SEI in the house musk shrew (Suncus murinus) were investigated. SEA, SEE, and SEI showed higher emetic activity in the house musk shrew than the other SEs. SEB, SEC2, SED, SEG, and SEH also induced emetic responses in this animal model but relatively high doses were required. The house musk shrew appears to be a valuable model for studying the mechanisms of emetic reactions caused by SEs.

Comparative molecular analysis of community- or hospital-acquired methicillin-resistant Staphylococcus aureus

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a growing public health concern that has been associated with pediatric fatalities. It is hypothesized that the evolution of CA-MRSA is a recent event due to the acquisition of mec DNA by previously methicillin-susceptible strains that circulated in the community. This study investigated the genetic relatedness between CA-MRSA, hospital-associated MRSA (HA-MRSA), and nonmenstrual toxic shock syndrome (nmTSS) isolates. Thirty-one of 32 CA-MRSA isolates were highly related as determined by pulsed-field gel electrophoresis and spa typing yet were distinguishable from 32 HA-MRSA strains. The 31 related CA-MRSA isolates produced either staphylococcal enterotoxin B (n = 5) or C (n = 26), and none made TSS toxin 1. All CA-MRSA isolates tested contained a type IV staphylococcal cassette chromosome mec (SCCmec) element. In comparison, none of the HA-MRSA isolates (n = 32) expressed the three superantigens. Antibiotic susceptibility patterns were different between the CA-MRSA and HA-MRSA isolates; CA-MRSA was typically resistant only to beta-lactam antibiotics. Six of twenty-one nmTSS isolates were indistinguishable or highly related to the CA-MRSA isolates. MnCop, an nmTSS isolate obtained in Alabama in 1986, was highly related to the CA-MRSA isolates except that it did not contain an SCCmec element. These data suggest that CA-MRSA strains may represent a new acquisition of SCCmec DNA in a previously susceptible genetic background that was capable of causing nmTSS. CA-MRSA poses a serious health risk not only because it is resistant to the antibiotics of choice for community-acquired staphylococcal infections but also because of its ability to cause nmTSS via superantigen production.

Characterization of a novel staphylococcal enterotoxin-like superantigen, a member of the group V subfamily of pyrogenic toxins

Staphylococcus aureus is an important human pathogen, causing a variety of diseases. Major virulence factors of this organism include staphylococcal enterotoxins (SEs) that cause food poisoning and toxic shock syndrome. Our study identified a novel enterotoxin-like protein that is a member of the new subfamily (group V) of pyrogenic toxin superantigens (PTSAgs) and examined its biochemical and immunobiological properties. The gene encoding the SE-like protein is directly 5' of another recently identified PTSAg, SEK. The SE-like protein had a molecular weight of 26000 and an experimentally determined isoelectric point between 7.5 and 8.0. We demonstrated that the PTSAg had many of the biological activities associated with SEs, including superantigenicity, pyrogenicity, and ability to enhance endotoxin shock, but lacked both lethality in rabbits when administered in subcutaneous miniosmotic pumps and emetic activity in monkeys. Recombinant protein stimulated human CD4 and CD8 T cells in a T cell receptor variable region, beta chain (TCRVbeta) specific manner. T cells bearing TCRVbeta 2, 5.1, and 21.3 were significantly stimulated.

Mycobacterium bovis BCG-infected mice are more susceptible to staphylococcal enterotoxin B-mediated toxic shock than uninfected mice despite reduced in vitro splenocyte responses to superantigens

Type 1 T-cell responses against intracellular pathogens play a crucial role in mediating protection. We examined whether the induction of a strong type 1 T-cell response during a chronic bacterial infection influences responses to superantigens capable of inducing acute shock. Intravenous infection of mice with Mycobacterium bovis BCG appeared to induce a progressive anergy towards staphylococcal enterotoxin B (SEB) and towards antigen preparation of BCG (BCG-Ag) itself, based on diminished gamma interferon (IFN-gamma) production by SEB- and BCG-Ag-stimulated splenocytes from infected mice. In contrast to these in vitro results, injection of SEB into BCG-infected mice led to a dramatic increase in the serum IFN-gamma levels and the death of infected but not of control mice. In vitro hyporesponsiveness towards SEB and BCG-Ag occurred only with unfractionated splenocyte cultures, as purified T cells from infected mice produced higher levels of IFN-gamma. Hyporesponsiveness towards SEB and BCG-Ag in unfractionated splenocyte cultures was not due to suppressive antigen-presenting cells (APCs), as APCs from infected mice stimulated higher levels of IFN-gamma from purified T cells. The diminished IFN-gamma levels observed with bulk splenocytes appear to be due to changes in the T-cell-to-APC ratio that result in a decreased proportion of T cells, coupled to reduced proliferative responses and an increased susceptibility of effector T cells to activation-induced cell death in vitro. Our results indicate that the reported phenomena of T-cell anergy during mycobacterial infection may be an in vitro consequence of the development of a strong type 1 response in vivo.

Staphylococcal enterotoxin H contrasts closely related enterotoxins in species reactivity

Staphylococcus aureus enterotoxin H (SEH) belongs to the staphylococcal enterotoxin (SE) family of superantigens (SAgs). SEH has structural similarities to other SE; however, its biological properties are less well characterized. SEH binds with high affinity to human major histocompatibility complex (MHC) class II and exhibits strong mitogenic activity in human T cells, although it was found to be less potent than the related SEA. Surprisingly and in sharp contrast to related SEs, SEH did not possess superantigen activity in murine T cells and T cells from three investigated rat strains. However, SEH bound to a high extent to murine MHC class II expressing cells and when presented by these cells SEH stimulated human T cells to proliferate. Thus, SEH interacts with the murine MHC class II molecule in a functional manner. Notably, SEH had an inhibitory effect on murine SEA response, demonstrating that SEH interferes with the SEA interactions with murine cells. Despite this, murine T cells did not proliferate regardless of whether SEH was presented on human or murine MHC class II expressing cells. Consequently, SEH differs in species reactivity as compared to related SEs and lacks critical properties for T-cell activation in mice. We propose that unlike other SEs, SEH does not interact with murine T cells since it is not recognized by murine T-cell receptors.

Microcin E492, a channel-forming bacteriocin from Klebsiella pneumoniae, induces apoptosis in some human cell lines

The cytotoxic effect of microcin E492, a low-molecular-mass channel-forming bacteriocin (7,887 Da) produced by a strain of Klebsiella pneumoniae, was characterized in HeLa cells. At low (5 microg/ml) and intermediate (10 microg/ml) concentrations, microcin E492 induced biochemical and morphological changes typical of apoptosis, such as cell shrinkage, DNA fragmentation, extracellular exposure of phosphatidylserine, caspase activation, and loss of mitochondrial membrane potential. Treatment with zVAD-fmk, a general caspase inhibitor, completely blocked the cytotoxic effect of this bacteriocin. At higher microcin concentrations (>20 microg/ml) a necrotic phenotype was observed. Induction of apoptosis by microcin E492 was associated with the release of calcium from intracellular stores, probably after microcin-triggered ion channel formation. Microcin E492 also presented a cytotoxic effect on Jurkat and RJ2.25 cells, but had no effect on KG-1 cells nor on a primary culture of human tonsil endothelial cells, suggesting that there is a specific interaction of the bacteriocin with components of the target cell surface. This report describes a bacteriocin that has the capacity to induce apoptosis in human cell lines.

Detection of seg, seh, and sei genes in Staphylococcus aureus isolates and determination of the enterotoxin productivities of S. aureus isolates Harboring seg, seh, or sei genes

To investigate the distribution of staphylococcal enterotoxin (SE) A to I (SEA to SEI) genes (sea to sei) in Staphylococcus aureus, 146 isolates obtained in Japan from humans involved in and samples from food poisoning outbreaks, healthy humans, cows with mastitis, and bovine raw milk were analyzed by multiplex PCR. One hundred thirteen (77.4%) S. aureus isolates were found to be positive for one or more se genes. The se genotype was classified into 14 genotypes. seg and sei coexisted in the same S. aureus strain. The newly developed sandwich enzyme-linked immunosorbent assay showed that most seh-harboring S. aureus isolates were able to produce a significant amount of SEH. However, most of the S. aureus isolates harboring seg and about 60% of the isolates harboring sei did not produce a detectable level of SEG or SEI, while reverse transcription-PCR analysis proved that the mRNAs of SEG and SEI were transcribed in S. aureus strains harboring seg and sei genes. These results suggest the importance of quantitative assessment of SEG and SEI production in foods in order to clarify the relationship between these new SEs and food poisoning.

Repression of the Staphylococcus aureus accessory gene regulator in serum and in vivo

Subgenomic DNA microarrays were employed to evaluate the expression of the accessory gene regulator (agr locus) as well as multiple virulence-associated genes in Staphylococcus aureus. Gene expression was examined during growth of S. aureus in vitro in standard laboratory medium and rabbit serum and in vivo in subcutaneous chambers implanted in either nonimmune rabbits or rabbits immunized with staphylococcal enterotoxin B. Expression of RNAIII, the effector molecule of the agr locus, was dramatically repressed in serum and in vivo, despite the increased expression of secreted virulence factors sufficient to cause toxic shock syndrome (TSS) in the animals. Statistical analysis and clustering of virulence genes based on their expression profiles in the various experimental conditions demonstrated no positive correlation between the expression of agr and any staphylococcal virulence factors examined. Disruption of the agr locus had only a minimal effect on the expression in vivo of the virulence factors examined. An effect of immunization on the expression of agr and virulence factors was also observed. These results suggest that agr activation is not necessary for development of staphylococcal TSS and that regulatory circuits responding to the in vivo environment override agr activity.

Double mutant and formaldehyde inactivated TSST-1 as vaccine candidates for TSST-1-induced toxic shock syndrome

Up to now there is no treatment for staphylococcal toxic shock syndrome, a disease mainly induced by toxic shock syndrome toxin-1(TSST-1). There is great demand in finding means to control the disease, one of them is the development of an effective and safe vaccine against TSST-1. In this study we constructed a series of vaccine candidates and investigated their biological activity, toxicity, and potential to invoke an immune response. TSST-1 was isolated from Stahylococcus aureus supernatants and recombinantly expressed as a N-terminal 6x histidine-tagged protein in Escherichia coli. In order to obtain molecules with minimal toxicity we constructed single mutants (G31R and H135A) and one double mutant (G31R/H135A) with both residues exchanged. We also detoxified native TSST-1 isolated from S. aureus, and recombinantly expressed TSST-1 by treatment with formaldehyde. Functional activity of native and recombinant TSST-1 and grade of inocuity of mutants and toxoids was determined by investigating mitogenity, T-cell activation, and cytokine release upon stimulation of human mononuclear cells with the vaccine candidates. All substances were tested in a rabbit immunization study. After primary immunization and three additional boosts all vaccinated animals developed antibody titers against TSST-1 and were protected against challenge with a lethal doses of superantigen potentiated with lipopolysaccharide.

Enterotoxigenic potential of Staphylococcus intermedius

Staphylococcal food poisoning (SFP) caused by enterotoxigenic staphylococci is one of the main food-borne diseases. In contrast to Staphylococcus aureus, a systematic screening for the enterotoxins has not yet been performed on the genomic level for the coagulase-positive species S. intermedius. Therefore, the enterotoxigenic potential of 281 different veterinary (canine, n = 247; equine, n = 23; feline, n = 9; other, n = 2) and 11 human isolates of S. intermedius was tested by using a multiplex PCR DNA-enzyme immunoassay system targeting the staphylococcal enterotoxin genes sea, seb, sec, sed, and see. Molecular results were compared by in vitro testing of enterotoxin production by two immunoassays. A total of 33 (11.3%) S. intermedius isolates, including 31 (12.6%) canine isolates, 1 equine isolate, and 1 human isolate, tested positive for the sec gene. In vitro production of the respective enterotoxins was detected in 30 (90.9%) of these isolates by using immunological tests. In contrast, none of 65 veterinary specimen-derived isolates additionally tested and comprising 13 (sub)species of coagulase-negative staphylococci were found to be enterotoxigenic. This study shows on both molecular and immunological levels that a substantial number of S. intermedius isolates harbor the potential for enterotoxin production. Since evidence for noninvasive zoonotic transmission of S. intermedius from animal hosts to humans has been documented, an enterotoxigenic role of this microorganism in SFP via contamination of food products may be assumed.

Staphylococcus aureus isolated in cases of impetigo produces both epidermolysin A or B and LukE-LukD in 78% of 131 retrospective and prospective cases

Clinical symptoms of impetigo and staphylococcal scalded skin syndrome may not only be expressed as the splitting of cell layers within the epidermis but are often accompanied by some localized inflammation. Toxin patterns of Staphylococcus aureus isolates originating from patients with impetigo and also from those with other primary and secondary skin infections in a retrospective isolate collection in France and a prospective isolate collection in French Guiana revealed a significant association (75% of the cases studied) of impetigo with production of at least one of the epidermolysins A and B and the bicomponent leucotoxin LukE-LukD (P < 0.001). However, most of the isolates were able to produce one of the nonubiquitous enterotoxins. Pulsed-field gel electrophoresis (PFGE) of genomic DNA hydrolyzed with SmaI showed a polymorphism of the two groups of isolates despite the fact that endemic clones were suspected in French Guiana and France. The combination of toxin patterns with PFGE fingerprinting may provide further discrimination among isolates defined in a given cluster or a given pulsotype and account for a specific virulence. The new association of toxins with a clinical syndrome may reveal principles of the pathological process.

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

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

Possible virulence factors of Staphylococcus sciuri

Staphylococcus sciuri is an opportunistic pathogen of controversial clinical significance. The factors that contribute to colonization and/or infection caused by this bacterium have not been studied intensively so far. The present research was carried out in order to study the presence of potential virulence factors in 121 human and animal isolates of this bacterium. Isolates were examined for biofilm formation, hemagglutination, presence of clumping factor, production of spreading factors and exotoxins, cytotoxicity and capacity to stimulate nitric oxide production. The results showed that S. sciuri is highly capable of biofilm production, that it displays strong proteolytic and DNase activities, produces hemolysins and stimulates nitric oxide production by rat macrophages. Although the present study showed existence of a wide spectrum of possible virulence determinants of S. sciuri, their exact contribution to virulence of this bacterium in vivo remains to be determined.

Mucosal vaccination with recombinantly attenuated staphylococcal enterotoxin B and protection in a murine model

Previous work in our laboratory revealed that mice parenterally vaccinated with recombinantly attenuated staphylococcal enterotoxin (SE) or toxic shock syndrome toxin 1 develop protective antibodies against a lethal intraperitoneal (i.p.) toxin challenge. This study investigated the efficacy of nasal and oral immunizations with an SEB vaccine (SEBv) toward an i.p. or mucosal (via an aerosol) toxin challenge. Both vaccination routes, with the immunoadjuvant cholera toxin (CT), elicited comparable SEB-specific immunoglobulin A (IgA) and IgG levels in saliva. Nasal or oral inoculations also generated SEB-specific IgA, IgG, and IgM in the serum, but the nasal route yielded higher specific IgG titers. SEBv alone, when given nasally or orally, did not induce any detectable SEB-specific antibody. Mice vaccinated mucosally were protected against a 50% lethal dose of wild-type SEB given i.p. or mucosally, thus demonstrating that nasal or oral administration of this SEBv, with CT, elicits systemic and mucosal antibodies to SEB that protect against SEB-induced lethal shock.

Role of T cells and gamma interferon during induction of hypersensitivity to lipopolysaccharide by toxic shock syndrome toxin 1 in mice

The superantigenic function of toxic shock syndrome toxin 1 (TSST-1) is generally regarded as an important determinant of its lethal effects in humans or experimental animals. This study examined the role of superantigenicity in a BALB/c mouse model of lethal TSST-1-induced hypersensitivity to lipopolysaccharide (LPS). In this model, TSST-1 greatly potentiated both LPS-induced lethality, as well as LPS-induced serum tumor necrosis factor alpha (TNF-alpha) activity. Although BALB/c-SCID mice were resistant to these LPS enhancement effects of TSST-1, BALB/c-SCID mice reconstituted with T cells were completely susceptible to the enhancement effect of TSST-1 on LPS-induced serum TNF-alpha. Mice pretreated with cyclosporine (Cs) or neutralizing antibodies against gamma interferon (IFN-gamma) did not develop lethal LPS hypersensitivity when injected with TSST-1, and these agents reduced the enhancement effect of TSST-1 on LPS-induced serum TNF-alpha by 99 and 85%, respectively. Cs pretreatment also completely inhibited the known capacity of TSST-1 to amplify LPS-induced levels of IFN-gamma in serum. In contrast, mice given Cs after a priming injection of TSST-1, but before LPS, still exhibited lethal hypersensitivity to LPS. Cs given after TSST-1 also did not inhibit enhancement of LPS-induced serum TNF-alpha by TSST-1 but inhibited the enhancement effect of TSST-1 on LPS-induced serum IFN-gamma by 50%. These experiments support the theory that TSST-1-induced hypersensitivity to LPS is mediated primarily by IFN-gamma derived from superantigen-activated T cells.

Biochemical and biological properties of Staphylococcal enterotoxin K

Staphylococcus aureus is an important human pathogen which is implicated in a wide variety of diseases. Major determinants of the virulence of this organism include extracellular virulence factors. Staphylococcal enterotoxins (SEs) are important causative agents in staphylococcal toxic shock syndrome and food poisoning. Our study identified a novel enterotoxin, SEK, and examined its biochemical and biological properties. SEK had a molecular weight of 26,000 and an experimentally determined pI of between 7.0 and 7.5. SEK was secreted by clinical isolates of S. aureus. We demonstrated that SEK had many of the biological activities associated with the SEs, including superantigenicity, pyrogenicity, the ability to enhance the lethal effect of endotoxin, and lethality in a rabbit model when administered by subcutaneous miniosmotic pump. Recombinant SEK was shown to stimulate human CD4(+) and CD8(+) T cells in a Vbeta-specific manner; T-cells bearing Vbeta 5.1, 5.2, and 6.7 were significantly stimulated to proliferate.

Rapid isolation and identification of staphylococcal exoproteins by reverse phase capillary high performance liquid chromatography-electrospray ionization mass spectrometry

The isolation of staphylococcal extracellular toxins and enzymes (exoproteins) usually requires time-consuming purification steps such as repeated chromatographic separations and isoelectric focusing. We performed rapid isolation, quantification and identification of staphylococcal exoproteins by reverse phase capillary high performance liquid chromatography-electrospray ionization mass spectrometry (LC-ESI/MS) followed by the determination of N-terminal amino acid sequences of separated peaks. We identified two novel exoproteins as well as previously reported antigens ORF-1 and ORF-2, glutamyl endopeptidase in Staphylococcus aureus NCTC8325 and protein A, staphylococcal enterotoxin C3 (SEC3), toxic shock syndrome toxin-1 (TSST-1) and alpha-toxin in a clinical isolate methicillin-resistant S. aureus (MRSA) 3543. MRSA3543 secreted 5.33 and 1.45 microg of SEC3 and TSST-1 per 20 microg total exoproteins ml(-1), respectively. The capillary LC treatment of the exoprotein fraction separated at least 12 peaks, indicating its high-resolution power. We found that when a protein was once determined by its N-terminal sequence, its mass spectrum and the obtained molecular mass was applicable for the assignment of the protein.