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

Transcriptome analysis reveals the inhibitory mechanism of phloretin on virulence expression of Staphylococcus aureus and its application in cooked chicken

Staphylococcus aureus (S. aureus) enterotoxins have aroused great concern to food safety owing to its increased risk of food poisoning. The current research aimed to investigate the anti-virulence mechanisms of phloretin against S. aureus in terms of toxin activity and gene expression. The results indicated that phloretin could effectively inhibit the production of hemolysins and enterotoxins, and its anti-virulence effect was exerted in a concentration-dependent manner. Transcriptome results indicated that phloretin could downregulate the transcription level of majority virulence factors related genes (68 %) of S. aureus, including the quorum sensing-related genes (agrB, agrC, agrA, sspA, splF, splD and others) and bacterial secretion system-related genes (secDF, secY2, and yidC). In addition, it was speculated that phloretin was most likely to bind to the AgrA DNA binding domain, thereby affecting the expression of downstream virulence genes (hla, seb, spa, rot, geh, etc) based on molecular docking. Finally, the application in cooked chicken indicated that phloretin could effectively decrease the content of enterotoxins and improve the storage quality of cooked chicken. These findings not only evidenced the feasible anti-virulence activity of phloretin, but also provided a new strategy to prevent S. aureus food poisoning in cooked meat preservation.

Multiplex Detection of 24 Staphylococcal Enterotoxins in Culture Supernatant Using Liquid Chromatography Coupled to High-Resolution Mass Spectrometry

Staphylococcal food poisoning outbreaks are caused by the ingestion of food contaminated with staphylococcal enterotoxins (SEs). Among the 27 SEs described in the literature to date, only a few can be detected using immuno-enzymatic-based methods that are strongly dependent on the availability of antibodies. Liquid chromatography, coupled to high-resolution mass spectrometry (LC-HRMS), has, therefore, been put forward as a relevant complementary method, but only for the detection of a limited number of enterotoxins. In this work, LC-HRMS was developed for the detection and quantification of 24 SEs. A database of 93 specific signature peptides and LC-HRMS parameters was optimized using sequences from 24 SEs, including their 162 variants. A label-free quantification protocol was established to overcome the absence of calibration standards. The LC-HRMS method showed high performance in terms of specificity, sensitivity, and accuracy when applied to 49 enterotoxin-producing strains. SE concentrations measured depended on both SE type and the coagulase-positive staphylococci (CPS) strain. This study indicates that LC-MS is a relevant alternative and complementary tool to ELISA methods. The advantages of LC-MS clearly lie in both the multiplex analysis of a large number of SEs, and the automated analysis of a high number of samples.

Analysis of Extracellular Proteome of Staphylococcus aureus: A Mass Spectrometry based Proteomics Method of Exotoxin Characterisation

Background:

Staphylococcus aureus (S. aureus), an important pathogen, causes a wide range of infections in human starting from food poisoning to septicemia. It affects the host cells with various exotoxins, known as virulence factors, which are synthesized in growth phase-dependent manner of the bacteria. S. aureus has been reported to become resistant to antibiotics rapidly. Among two common clinical isolates, Methicillin-sensitive S. aureus (MSSA) and Methicillin-resistant S. aureus (MRSA), MRSA pose major problems across hospitals around the world.

Objective:

The objective of the present study was to profile the exoproteins of Methicillin-sensitive S. aureus (ATCC 25293) and subsequently to establish a proteomics-based method of characterization of S. aureus that is crucial in treating hospital-acquired infections.

Methods:

We used two-dimensional nanoLC/ESI-MS based proteomic platform to characterize and quantify the exoproteins isolated from Methicillin-sensitive S. aureus (ATCC 25293) strain.

Results:

A total of 69 proteins were identified from extracellular proteome pool of ATCC 25293 strain that includes 18 extracellular proteins, 40 cytoplasmic proteins, 2 membrane proteins, 3 cell wall proteins and 6 uncharacterized proteins.

Conclusion:

We propose that this mass spectrometry-based proteomics method of characterization of exoproteins might be useful to identify S. aureus strains that are resistant to antibiotics.

Comparative Secretome Analyses of Human and Zoonotic Staphylococcus aureus Isolates CC8, CC22, and CC398

The spread of methicillin-resistant Staphylococcus aureus (MRSA) in the community, hospitals and in livestock is mediated by highly diverse virulence factors that include secreted toxins, superantigens, enzymes and surface-associated adhesins allowing host adaptation and colonization. Here, we combined proteogenomics, secretome and phenotype analyses to compare the secreted virulence factors in selected S. aureus isolates of the dominant human- and livestock-associated genetic lineages CC8, CC22, and CC398. The proteogenomic comparison revealed 2181 core genes and 1306 accessory genes in 18 S. aureus isolates reflecting the high genome diversity. Using secretome analysis, we identified 869 secreted proteins with 538 commons in eight isolates of CC8, CC22, and CC398. These include 64 predicted extracellular and 37 cell surface proteins that account for 82.4% of total secretome abundance. Among the top 10 most abundantly secreted virulence factors are the major autolysins (Atl, IsaA, Sle1, SAUPAN006375000), lipases and lipoteichoic acid hydrolases (Lip, Geh, LtaS), cytolytic toxins (Hla, Hlb, PSMβ1) and proteases (SspB). The CC398 isolates showed lower secretion of cell wall proteins, but higher secretion of α- and β-hemolysins (Hla, Hlb) which correlated with an increased Agr activity and strong hemolysis. CC398 strains were further characterized by lower biofilm formation and staphyloxanthin levels because of decreased SigB activity. Overall, comparative secretome analyses revealed CC8- or CC22-specific enterotoxin and Spl protease secretion as well as Agr- and SigB-controlled differences in exotoxin and surface protein secretion between human-specific and zoonotic lineages of S. aureus.

Identification of commonly expressed exoproteins and proteolytic cleavage events by proteomic mining of clinically relevant UK isolates of Staphylococcus aureus

The range of exoproteins and core exoproteome of 14 Staphylococcus aureus isolates representing major lineages associated with asymptomatic carriage and clinical disease in the UK was identified by MS proteomics using a combined database incorporating sequences derived from 39 S. aureus genomes. In all, 632 different proteins were identified and, of these, only 52 (8 %) were found in all 14 isolates whereas 144 (23 %) were found in just a single isolate. Comparison of the observed mass of each protein (based on migration by SDS-PAGE) with its predicted mass (based on amino acid sequence) suggested that 95 % of the proteins identified were not subject to any major post-translational modification. Migration of 5 % of the proteins was not as expected: 1 % of the proteins migrated at a mass greater than predicted, while 4 % appeared to have undergone proteolytic cleavage; these included SsaA2, Aur, SspP, Ebh as well as BlaR1, MecR1, FsH, OatA and LtaS. Intriguingly, a truncated SasG was produced by a single CC8 USA300-like strain. The analysis provided evidence of the marked heterogeneity in protein expression by S. aureus in broth, while yielding a core but narrow common exoproteome.

Autolysis ofPorphyromonas gingivalisIs Accompanied by an Increase in Several Periodontal Pathogenic Factors in the Supernatant

Porphyromonas gingivalis autolyzes in the culture media. To examine in more detail the molecular components of the autolysate, two-dimensional gel electrophoresis was performed. Many protein spots varied both in number and volume. One of these spots included Arg-gingipain (Rgp) as determined by N-terminal amino acid sequencing. Corresponding to the increase in spot volume, Rgp activity also increased during autolysis. The results of this study suggested that Rgp and other proteins in the P. gingivalis autolysate may be involved with the prolongation of periodontal disease, even after the death of P. gingivalis cells.

Exploring extra-cellular proteins in methicillin susceptible and methicillin resistant Staphylococcus aureus by liquid chromatography-tandem mass spectrometry

Staphylococcus aureus (S. aureus) strains cause several diseases in humans from minor skin infections to severe lethal infections. To explore the virulence determinants of this important microorganism, two clinical isolates of methicillin susceptible S. aureus (MSSA) and methicillin resistant S. aureus (MRSA) were subjected to proteomic analysis of their extracellular products using liquid chromatography-tandem mass spectrometry. The numbers of proteins identified in MSSA and MRSA extracellular products were 168 and 261; respectively, from them 117 were shared, while 144 proteins were unique to MRSA. The shared proteins, having a higher protein score with increased number of peptide matches in MRSA over MSSA, reflect the relatively active secretory state of MRSA rather than biased analytical variances. Characteristic determinants for MRSA were identified; mostly found to play a role in the virulence. We conclude that MRSA produces distinct proteins considered as its virulence determinants and we found that the shared extracellular products are more abundant in MRSA than MSSA that supporting the high invasiveness of MRSA over MSSA in pathogenesis.

Two dimensional electrophoresis of the exo-proteome produced from community acquired methicillin resistant Staphylococcus aureus belonging to clonal complex 80

Two-dimensional electrophoresis (2DE) combined with mass spectrometry was used to characterize the exo-proteome secreted by two strains (ER13 and ER21) representing community acquired methicillin resistant Staphylococcus aureus (CA-MRSA) belonging to clonal complex 80 (CC80). Common spots were detected between the 2 gels using the Progenesis SameSpots software. Two hundred and fifty-one and 312 spots from the exo-proteome of ER13 and ER21 were resolved, respectively. 2DE overlap comparison showed that 59 spots were shared. LC-MS/MS analysis identified 57 proteins from these spots comprising about 21% extracellular, 48% cytoplasmic, 2% cytoplasmic membrane, 2% cell wall, and 26% with unknown localization. The identified proteins were classified with respect to their Gene Ontology (GO) annotation as ∼24% virulence determinants and toxins, ∼17% involved in carbohydrate metabolism, ∼14% involved in environmental stress, and ∼12% associated with cell division. The identification of the enterotoxin B from the exo-products of both strains used in our study, as belonging to CC80 was interesting.

Extensive proteomic profiling of the secretome of European community acquired methicillin resistant Staphylococcus aureus clone

European community acquired methicillin resistant Staphylococcus aureus (CA-MRSA) clone remains a striking pathogenic clone spreading in European and Mediterranean countries. Since analysis of the secretome produced from this clone by proteomics could provide a comprehensive picture of both core exoproteins as well as virulence factors, we applied two proteomic approaches, pre-fractionation of proteins on SDS-PAGE followed by in-gel trypsin digestion, and in-solution trypsin-digestion followed by off-line SCX fractionation, both of which were coupled with LC-MS/MS analyses. A total of 174 distinct proteins were identified with a high-confidence. Functional classification of these identified proteins resulted in16.09% of protein synthesis, 13.79% of virulence, 6.89% of toxin, and 17.24% of unknown function. Prediction of their cellular localizations revealed 18.39% in extracellular space, 36.20% in cytoplasm, 5.17% in cytoplasmic membranes, 6.89% in cell wall, 1.14% in multiple localizations, and 32.18% in unknown localization. Among them, 52% proteins were predicted to be secreted through signal peptide-independent pathways. Most notably, the expression of some proteins such as enterotoxins U and B were identified for the first time in this clone.

Type I signal peptidase and protein secretion in Staphylococcus aureus

Staphylococcus aureus is an important human pathogen whose virulence relies on the secretion of many different proteins. In general, the secretion of most proteins in S. aureus, as well as other bacteria, is dependent on the type I signal peptidase (SPase)-mediated cleavage of the N-terminal signal peptide that targets a protein to the general secretory pathway. The arylomycins are a class of natural product antibiotics that inhibit SPase, suggesting that they may be useful chemical biology tools for characterizing the secretome. While wild-type S. aureus (NCTC 8325) is naturally resistant to the arylomycins, sensitivity is conferred via a point mutation in its SPase. Here, we use a synthetic arylomycin along with a sensitized strain of S. aureus and multidimensional protein identification technology (MudPIT) mass spectrometry to identify 46 proteins whose extracellular accumulation requires SPase activity. Forty-four possess identifiable Sec-type signal peptides and thus are likely canonically secreted proteins, while four also appear to possess cell wall retention signals. We also identified the soluble C-terminal domains of two transmembrane proteins, lipoteichoic acid synthase, LtaS, and O-acyteltransferase, OatA, both of which appear to have noncanonical, internal SPase cleavage sites. Lastly, we identified three proteins, HtrA, PrsA, and SAOUHSC_01761, whose secretion is induced by arylomycin treatment. In addition to elucidating fundamental aspects of the physiology and pathology of S. aureus, the data suggest that an arylomycin-based therapeutic would reduce virulence while simultaneously eradicating an infection.

Growth-dependent release of carbohydrate metabolism-related and antioxidant enzymes from Staphylococcus aureus strain 6 as determined by proteomic analysis

Proteins released into the culture medium by Staphylococcus aureus (S. aureus) strain 6 were determined at the end of the exponential growth phase (4.5 h). Eleven proteins were identified by liquid chromatography coupled with mass spectrometry. Three proteins were predicted to have signal peptides indicating their extracellular localization. The other proteins were presumably located in the cytoplasm of the bacteria. Five out of the 11 proteins were involved in carbohydrate metabolism. Other intracellular proteins of S. aureus were not detected in the culture medium. This indicates that the release of these 11 proteins was specific and that unspecific protein release due to damaged or dying bacteria did not play a role. It is suggested that enzymes associated with carbohydrate metabolism may provide the energy necessary for the transition of bacteria from a resting to a proliferative state. Another enzyme released by S. aureus, superoxide dismutase, may catalyze redox reactions in this context. The production of other proteolytic enzymes and toxins may take place at later stages of bacterial growth. A cocktail of these 11 proteins was used for the immunization of mice. Indeed, vaccination with these proteins prolonged the survival times of mice upon infection with S. aureus strain 6. Therefore, these proteins may have implications for the development of novel strategies for the prevention and therapy of S. aureus infections.

Functional and structural characterization of soluble recombinant epsilon toxin of Clostridium perfringens D, causative agent of enterotoxaemia

Clostridium perfringens types B and D are responsible for enterotoxaemia, one of the major causes of cattle mortality and is therefore of great economic concern. The epsilon toxin produced by the organism is the major antigenic determinant and has been directly implicated for the disease causation. In the present paper, we evaluated the biological activity of the recombinant epsilon toxin (rEtx) produced as soluble protein in Escherichia coli. The rEtx was purified to near homogeneity by a one-step anion-exchange chromatography. The immunological identity of purified rEtx was confirmed by Western blotting using a monoclonal antibody against the native toxin. The rEtx formed heptamer in the Madin-Darby canine kidney (MDCK) cells and synaptosomal membrane of mouse brain and was cytotoxic to the MDCK cells with a CT(50) of 30 ng/ml. The rEtx was highly stable and its thermostability profile related well with its biological activity. The rEtx was purified in large amounts and exhibited all the properties of native toxin and therefore can be used for the development of vaccine against the pathogen.

Comprehensive characterization of methicillin-resistant Staphylococcus aureus subsp. aureus COL secretome by two-dimensional liquid chromatography and mass spectrometry

Two-dimensional LC combined with whole protein and peptide mass spectrometry is used to characterize proteins secreted by methicillin-resistant Staphylococcus aureus COL. Protein identifications were accomplished via off-line protein fractionation followed by digestion and subsequent peptide analysis by reverse phase LC-ESI-LTQ-FT-MS/MS. Peptide MS/MS analysis identified 127 proteins comprising 59 secreted proteins, seven cell wall-anchored proteins, four lipoproteins, four membrane proteins, and 53 cytoplasmic proteins. The identified secreted proteins included various virulence factors of known functions (cytotoxins, enterotoxins, proteases, lipolytic enzymes, peptidoglycan hydrolases, etc.). Accurate whole protein mass measurement (+/-1.5 Da) of the secreted proteins combined with peptide analysis enabled identification of signal peptide cleavage sites and various post-translational modifications. In addition, new observations were possible using the present approach. Although signal peptide cleavage is highly specific, signal peptide processing can occur at more than one site. Surprisingly, cleaved signal peptides and their fragments can be observed in the extracellular medium. The prediction accuracies of several signal peptide prediction programs were also evaluated.

Nationwide epidemiological study revealed the dissemination of meticillin-resistant Staphylococcus aureus carrying a specific set of virulence-associated genes in Japanese hospitals

To study comprehensive toxin profiles and the chromosomal diversity of current Japanese hospital-associated meticillin-resistant Staphylococcus aureus (HA-MRSA) strains, we conducted PCR-based identification of 28 toxin genes, and staphylococcal cassette chromosome mec (SCCmec) typing and PFGE analysis of 208 MRSA strains isolated from 100 hospitals throughout Japan. Of the tested HA-MRSA strains, 80.3 % were tst-positive. The most frequent toxin gene profile was characterized by the carriage of 13 genes, tst, sec, seg, sei, sel, sem, sen, seo, lukED, hla, hlb, hld and hlg-2. Ninety of the 208 strains had this profile, which was named pattern A. Among the 118 non-pattern A strains, 100 had similar toxin gene profiles, the concordance rates to pattern A of which were more than 80 %. Consequently, 91.3 % of the examined HA-MRSA strains carried similar toxin profiles, although PFGE patterns showed a wide variation. These strains belonged to SCCmec type II, agr II and coagulase type II. We concluded that, unlike MRSA from many other countries, most of the Japanese HA-MRSA strains belonged to, or were related to, a specific group carrying the set of 13 toxin genes, irrespective of chromosomal diversity. In addition, among the 13 toxin genes, the coexistence rates of tst, sec and sel, and those of seg, sei, sem, sen and seo, were higher than for the other toxin genes. High coexistence rates of tst, sec and sel genes suggested the presence of the pathogenicity island SaPIn1 in these strains.

Variations in amount of TSST-1 produced by clinical methicillin resistant Staphylococcus aureus (MRSA) isolates and allelic variation in accessory gene regulator (agr) locus

Background

Staphylococcus aureus (S. aureus) is an important pathogen associated with both nosocomial and community-acquired infections and its pathogenicity is attributed to its potential to produce virulence factors. Since the amount of toxin produced is related to virulence, evaluating toxin production should be useful for controlling S. aureus infection. We previously found that some strains produce relatively large amounts of TSST-1; however, no reports have described the amount of TSST-1 produced by clinical isolates.

Methods

Amounts of TSST-1 produced by clinical methicillin resistant S. aureus (MRSA) isolates were measured by Western blotting. We determined their accessory gene regulator (agr) class by PCR and investigated whether TSST-1 production correlates with variations in the class and structure of the agr.

Results

We found that 75% of surveyed MRSA isolates (n = 152) possessed the tst gene and that 96.7% belonged to agr class 2. The concentrations of TSST-1 secreted into culture supernatants by 34 strains measured by Western blotting differed 170-fold. Sequencing the entire agr locus (n = 9) revealed that some had allelic variations regardless of the amount of TSST-1 produced whereas sequencing the sar, sigma factor B and the tst promoter region revealed no significant changes.

Conclusion

The amounts of TSST-1 produced by clinical MRSA isolates varied. The present results suggest that TSST-1 production is not directly associated with the agr structure, but is instead controlled by unknown transcriptional/translational regulatory systems, or synthesized by multiple regulatory mechanisms that are interlinked in a complex manner.

Coupling immunomagnetic separation on magnetic beads with matrix-assisted laser desorption ionization-time of flight mass spectrometry for detection of staphylococcal enterotoxin B

The growing importance of mass spectrometry for the identification and characterization of bacterial protein toxins is a consequence of the improved sensitivity and specificity of mass spectrometry-based techniques, especially when these techniques are combined with affinity methods. Here we describe a novel method based on the use of immunoaffinity capture and matrix-assisted laser desorption ionization-time of flight mass spectrometry for selective purification and detection of staphylococcal enterotoxin B (SEB). SEB is a potent bacterial protein toxin responsible for food poisoning, as well as a potential biological warfare agent. Unambiguous detection of SEB at low-nanogram levels in complex matrices is thus an important objective. In this work, an affinity molecular probe was prepared by immobilizing anti-SEB antibody on the surface of para-toluene-sulfonyl-functionalized monodisperse magnetic particles and used to selectively isolate SEB. Immobilization and affinity capture procedures were optimized to maximize the density of anti-SEB immunoglobulin G and the amount of captured SEB, respectively, on the surface of magnetic beads. SEB could be detected directly "on beads" by placing the molecular probe on the matrix-assisted laser desorption ionization target plate or, alternatively, "off beads" after its acidic elution. Application of this method to complex biological matrices was demonstrated by selective detection of SEB present in different matrices, such as cultivation media of Staphylococcus aureus strains and raw milk samples.

Analysis of Twin-Arginine Translocation Pathway Homologue in Staphylococcus aureus

Staphylococcus aureus releases a large number of exoproteins, including membrane-active proteins and toxins with superantigenic activity involved in pathogenicity. However, the export pathways of exoproteins in S. aureus have not been reported. We analyzed the function of the staphylococcal twin-arginine translocation (Tat) pathway homologue, the presence of which was recently discovered according to the genome database. The amino-acid sequences of the Tat homologues of S. aureus do not have a high similarity with those of Escherichia coli and other bacteria. Constructed tatC-deficient mutants from distinct parent strains showed the same patterns of exoproteins compared with those of parent strains on two-dementional gel electrophoresis, and the amounts of secreted staphylococcal enterotoxins and toxic shock syndrome toxin-1, of which signal peptides have some features often seen in signal sequences of Tat-dependent proteins, did not change with Western blotting analyses. Therefore, it seems that the Tat pathway does not play a major role in the secretion system of S. aureus, but other export pathways may play an important role in toxin secretion. This is the first experimental report showing the influence of the Tat pathway on the secretion of S. aureus.

Identification of immunoreactive antigens in membrane proteins enriched fraction from Francisella tularensis LVS

Francisella tularensis is a Gram-negative, facultative intracellular bacterium causing disease in many mammalian species. The low infectious dose of F. tularensis and the ease of air-borne transmission are the main features responsible for the classification of this bacterium as a potential biological weapon. The live attenuated strain of F. tularensis live vaccine strain (LVS) is currently only effective vaccine against tularemia, however, this type of vaccine has not been approved for human use. In the presented study, sub-immunoproteome analysis was performed to search for new immunogenic proteins of Francisella tularensis LVS grown under different conditions. By this approach 35 immunoreactive antigens were identified, 19 of them showed to be novel immunogens. In conclusion, sub-immunoproteome analysis resulted in successful identification of novel immunoreactive proteins.

Global analysis of community-associated methicillin-resistant Staphylococcus aureus exoproteins reveals molecules produced in vitro and during infection

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is a threat to human health worldwide. Although progress has been made, mechanisms of CA-MRSA pathogenesis are poorly understood and a comprehensive analysis of CA-MRSA exoproteins has not been conducted. To address that deficiency, we used proteomics to identify exoproteins made by MW2 (USA400) and LAC (USA300) during growth in vitro. Two hundred and fifty unique exoproteins were identified by 2-dimensional gel electrophoresis coupled with automated direct infusion-tandem mass spectrometry (ADI-MS/MS) analysis. Eleven known virulence-related exoproteins differed in abundance between the strains, including alpha-haemolysin (Hla), collagen adhesin (Cna), staphylokinase (Sak), coagulase (Coa), lipase (Lip), enterotoxin C3 (Sec3), enterotoxin Q (Seq), V8 protease (SspA) and cysteine protease (SspB). Mice infected with MW2 or LAC produced antibodies specific for known or putative virulence factors, such as autolysin (Atl), Cna, Ear, ferritin (Ftn), Lip, 1-phosphatidylinositol phosphodiesterase (Plc), Sak, Sec3 and SspB, indicating the exoproteins are made during infection in vivo. We used confocal microscopy to demonstrate aureolysin (Aur), Hla, SspA and SspB are produced following phagocytosis by human neutrophils, thereby linking exoprotein production in vitro with that during host-pathogen interaction. We conclude that the exoproteins identified herein likely account in part for the success of CA-MRSA as a human pathogen.

Rot repression of enterotoxin B expression in Staphylococcus aureus

The accessory gene regulator (Agr) system is a quorum-sensing system of Staphylococcus aureus responsible for upregulation of certain exoprotein genes and downregulation of certain cell-wall associated proteins during the post-exponential phase of growth. The enterotoxin B (seb) determinant is upregulated by the Agr system. Agr-regulated cis elements within the seb promoter region were examined by deletion analyses of the seb promoter by a hybrid promoter approach utilizing the staphylococcal lac operon promoter. To identify the regulatory pathway for enterotoxin B expression, the seb promoter fused to the chloramphenicol acetyltransferase reporter gene was introduced into mutants of S. aureus lacking agr or different members of the Sar family of transcriptional regulators. Agr control of seb promoter activity was found to be dependent upon the presence of a functional Rot protein, and Rot was shown to be able to bind to the seb promoter. Therefore, the Agr-mediated post-exponential-phase increase in seb transcription results from the Agr system's inactivation of Rot repressor activity.

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.