Evolutionary and functional analysis of coagulase-positivity among the Staphylococci

The ability of some species of staphylococci to promote coagulation of plasma is a key pathogenic and diagnostic trait. Here, we provide a comprehensive analysis of the coagulase positivity of the staphylococci and its evolutionary genetic basis

Identification of source and sink populations for the emergence and global spread of the East-Asia clone of Community-Associated MRSA

Background: Our understanding of the factors influencing the emergence, dissemination and global distribution of epidemic clones of bacteria is limited. ST59 is a major epidemic clone of community-associated MRSA in East Asia, responsible for extensive morbidity and mortality, but has a much lower prevalence in other parts of the world. The geographic origin of ST59 and its international routes of dissemination are unclear and disputed in the literature. Results: To investigate the origin and spread of the ST59 clone, we obtained whole genome sequences of isolates from four continents, sampled over more than a decade, and carried out a time-scaled phylogeographic analysis. We discover that two distinct ST59 clades emerged concurrently, in East Asia and the USA, but underwent clonal expansion at different times. The East Asia clade was strongly enriched for gene determinants associated with antibiotic resistance, consistent with regional differences in antibiotic usage. Both clones spread independently to Australia and Europe, and we found evidence of the persistence of multi-drug resistance following export from East Asia. Direct transfer of strains between Taiwan and the USA was not observed in either direction, consistent with geographic niche exclusion. Conclusions: Our results resolve a longstanding controversy regarding the origin of the ST59 clone, revealing the major global source and sink populations and routes for the spread of multi-drug resistant clones. Additionally, our findings indicate that diversification of the accessory genome of epidemic clones partly reflects region-specific patterns of antibiotic usage, which may influence bacterial fitness after transmission to different geographic locations

The Staphylococcus aureus superantigen SElX is a bifunctional toxin that inhibits neutrophil function:SElX Inhibits Neutrophil Function

Bacterial superantigens (SAgs) cause Vβ-dependent T-cell proliferation leading to immune dysregulation associated with the pathogenesis of life-threatening infections such as toxic shock syndrome, and necrotizing pneumonia. Previously, we demonstrated that staphylococcal enterotoxin-like toxin X (SElX) from Staphylococcus aureus is a classical superantigen that exhibits T-cell activation in a Vβ-specific manner, and contributes to the pathogenesis of necrotizing pneumonia. Here, we discovered that SElX can also bind to neutrophils from human and other mammalian species and disrupt IgG-mediated phagocytosis. Site-directed mutagenesis of the conserved sialic acid-binding motif of SElX abolished neutrophil binding and phagocytic killing, and revealed multiple glycosylated neutrophil receptors for SElX binding. Furthermore, the neutrophil binding-deficient mutant of SElX retained its capacity for T-cell activation demonstrating that SElX exhibits mechanistically independent activities on distinct cell populations associated with acquired and innate immunity, respectively. Finally, we demonstrated that the neutrophil-binding activity rather than superantigenicity is responsible for the SElX-dependent virulence observed in a necrotizing pneumonia rabbit model of infection. Taken together, we report the first example of a SAg, that can manipulate both the innate and adaptive arms of the human immune system during S. aureus pathogenesis

Immunological homeostasis at the ovine placenta may reflect the degree of maternal foetal interaction

Successful mammalian pregnancies are a result of complex physiological, endocrinological and immunological processes that combine to create an environment where the mother is tolerant to the semi-allogeneic fetus. Our knowledge of the mechanisms thatcontribute to maternal tolerance is derived mainly from human and murine studies of haemochorial placentation. However, as thisis the most invasive type of placentation it cannot be assumed that identical mechanisms apply to the less invasive epitheliochorialplacentation found in other species such as ruminants. Here, we examine three features associated with reproductive immuneregulation in a transformed ovine trophoblast cell line and ex-vivo ovine reproductive tissues collected at term, namely: majorhistocompatibility complex (MHC) expression, Indoleamine 2, 3 dioxygenase-1 (IDO-1) expression and Natural Killer (NK) cellinfiltration. High levels of MHC class I protein expression were detected at the surface of the trophoblast cell line using a pan-MHCclass I specific monoclonal antibody. The majority of MHC class I transcripts isolated from the cell line clustered with classical MHCalleles. Transcriptional analysis of placental tissues identified only classical MHC class I transcripts. We found no evidence ofconstitutive transcription of IDO-1 in either the trophoblast cell line or placental tissues. Ex-vivo tissues collected from thematerno-fetal interface were negative for cells expressing NKp46/NCR1. Collectively, these observations suggest that the relatively non-invasive synepitheliochorial placentation found in sheep has a more limited requirement for local immunoregulation compared to the more invasive haemochorial placentation of primates and rodents

The Staphylococcus aureus superantigen SElX is a bifunctional toxin that inhibits neutrophil function

Bacterial superantigens (SAgs) cause Vβ-dependent T-cell proliferation leading to immune dysregulation associated with the pathogenesis of life-threatening infections such as toxic shock syndrome, and necrotizing pneumonia. Previously, we demonstrated that staphylococcal enterotoxin-like toxin X (SElX) from Staphylococcus aureus is a classical superantigen that exhibits T-cell activation in a Vβ-specific manner, and contributes to the pathogenesis of necrotizing pneumonia. Here, we discovered that SElX can also bind to neutrophils from human and other mammalian species and disrupt IgG-mediated phagocytosis. Site-directed mutagenesis of the conserved sialic acid-binding motif of SElX abolished neutrophil binding and phagocytic killing, and revealed multiple glycosylated neutrophil receptors for SElX binding. Furthermore, the neutrophil binding-deficient mutant of SElX retained its capacity for T-cell activation demonstrating that SElX exhibits mechanistically independent activities on distinct cell populations associated with acquired and innate immunity, respectively. Finally, we demonstrated that the neutrophil-binding activity rather than superantigenicity is responsible for the SElX-dependent virulence observed in a necrotizing pneumonia rabbit model of infection. Taken together, we report the first example of a SAg, that can manipulate both the innate and adaptive arms of the human immune system during S. aureus pathogenesis

Additional file 3: of Identification of source and sink populations for the emergence and global spread of the East-Asia clone of community-associated MRSA

Output from in silico antibiotic resistance testing. Genes associated with antibiotic resistance were detected using SRST2. Gene presence is denoted by the name of the gene (asterisks indicates at least one mismatched SNP or indel and a question mark indicates some low-depth bases, as described on the SRST2 website: https://github.com/katholt/srst2 ). Gene absence is denoted by a hyphen. The amino acid residue (IUPAC single letter code) is given for gyrA, grlA and grlB sites associated with fluoroquinolone resistance. Presence or absence of PVL based on mapping of short reads to lukF-PV and lukS-PV reference sequences is also reported. (XLSX 16 kb

Additional file 2: of Identification of source and sink populations for the emergence and global spread of the East-Asia clone of community-associated MRSA

List of core genome sites included in our analysis. Site numbers are relative to the published ST59 genome used as a reference for mapping short reads (GenBank accession CP003166). (TXT 20378 kb