Surface proteins that promote adherence of Staphylococcus aureus to human desquamated nasal epithelial cells

<p>Abstract</p> <p>Background</p> <p>The natural habitat of <it>Staphylococcus aureus </it>is the moist squamous epithelium in the anterior nares. About 20% of the human population carry <it>S. aureus </it>permanently in their noses and another 60% of individuals are intermittent carriers. The ability of <it>S. aureus </it>to colonize the nasal epithelium is in part due to expression of surface proteins clumping factor B (ClfB) and the iron-regulated surface determinant A (IsdA), which promote adhesion to desquamated epithelial cells present in the anterior part of the nasal vestibule. <it>S. aureus </it>strain Newman defective in IsdA and ClfB exhibited reduced but not completely defective adherence to squamous cells in indicating that other cell surface components might also contribute.</p> <p>Results</p> <p>Surface proteins IsdA, ClfB, and the serine-aspartic acid repeat proteins SdrC, SdrD and SdrE were investigated to determine their contribution to the adherence of <it>S. aureus </it>to desquamated nasal epithelial cells. This was achieved by expression of ClfB, IsdA, SdrC, SdrD and SdrE on the surface of the surrogate Gram-positive host <it>Lactococcus lactis </it>and by isolating mutants of <it>S. aureus </it>Newman defective in one or more factor. The level of adherence of strains to squamous cells isolated from the nares of volunteers was measured. Results consistently showed that ClfB, IsdA, SdrC and SdrD each contributed to the ability of <it>S. aureus </it>to adhere to squamous cells. A mutant lacking all four proteins was completely defective in adherence.</p> <p>Conclusion</p> <p>The ability of <it>S. aureus </it>Newman to adhere to desquamated nasal epithelial cells is multifactorial and involves SdrD and SdrC as well as ClfB and IsdA.</p

Identification of the Staphylococcus aureus MSCRAMM clumping factor B (ClfB) binding site in the αC-domain of human fibrinogen

Clumping factor B (ClfB) of Staphylococcus aureus binds to cytokeratin 10 and to fibrinogen. In this study the binding site in human fibrinogen was localized to a short region within the C terminus of the Aα-chain. ClfB only bound to the Aα-chain of fibrinogen in a ligand-affinity blot and in solid-phase assays with purified recombinant fibrinogen chains. A variant of fibrinogen with wild-type Bβ- and γ-chains but with a deletion that lacked the C-terminal residues from 252–610 of the Aα-chain did not support adherence of S. aureus Newman expressing ClfB. A series of truncated mutants of the recombinant Aα-chain were tested for their ability to support adherence of S. aureus Newman ClfB+, which allowed the binding site to be localized to a short segment of the unfolded flexible repeated sequence within the C terminus of the Aα-chain. This was confirmed by two amino acid substititions within repeat 5 of the recombinant Aα-chain which did not support adherence of Newman ClfB+. Lactococcus lactis expressing ClfB mutants with amino acid substitutions (N256 and Q235) located in the putative ligand-binding trench between domains N2 and N3 of the A-domain were defective in adherence to immobilized fibrinogen and cytokeratin 10, suggesting that both ligands bind to the same or overlapping regions

Staphylococcus aureus Protein A Binds to Osteoblasts and Triggers Signals That Weaken Bone in Osteomyelitis

Osteomyelitis is a debilitating infectious disease of the bone. It is predominantly caused by S. aureus and is associated with significant morbidity and mortality. It is characterised by weakened bones associated with progressive bone loss. Currently the mechanism through which either bone loss or bone destruction occurs in osteomyelitis patients is poorly understood. We describe here for the first time that the major virulence factor of S. aureus, protein A (SpA) binds directly to osteoblasts. This interaction prevents proliferation, induces apoptosis and inhibits mineralisation of cultured osteoblasts. Infected osteoblasts also increase the expression of RANKL, a key protein involved in initiating bone resorption. None of these effects was seen in a mutant of S. aureus lacking SpA. Complementing the SpA-defective mutant with a plasmid expressing spa or using purified protein A resulted in attachment to osteoblasts, inhibited proliferation and induced apoptosis to a similar extent as wildtype S. aureus. These events demonstrate mechanisms through which loss of bone formation and bone weakening may occur in osteomyelitis patients. This new information may pave the way for the development of new and improved therapeutic agents to treat this disease

Key role for clumping factor B in Staphylococcus aureus nasal colonization of humans.

Staphylococcus aureus permanently colonizes the vestibulum nasi of one-fifth of the human population, which is a risk factor for autoinfection. The precise mechanisms whereby S. aureus colonizes the nose are still unknown. The staphylococcal cell-wall protein clumping factor B (ClfB) promotes adhesion to squamous epithelial cells in vitro and might be a physiologically relevant colonization factor

Both Complement- and Fibrinogen-Dependent Mechanisms Contribute to Platelet Aggregation Mediated by Staphylococcus aureus Clumping Factor B▿

Staphylococcus aureus can stimulate activation and aggregation of platelets, which are thought to be factors in the development of infective endocarditis. Previous studies have identified clumping factor A (ClfA) and fibronectin binding proteins A and B (FnBPA and FnBPB) as potent platelet aggregators. These proteins are able to stimulate rapid platelet aggregation by either a fibrinogen- or a fibronectin-dependent process which also requires antibodies specific to each protein. Slower aggregation has been seen in other systems where specific fibrinogen binding ligands are absent and platelet aggregation is mediated by complement and specific antibodies. Bacteria expressing ClfB aggregate platelets with a longer lag time than ClfA or FnBPA and FnBPB. In order to investigate whether ClfB causes platelet aggregation in a complement- or fibrinogen-dependent manner, a non-fibrinogen-binding mutant of ClfB (ClfB Q235A) was constructed. Lactococcus lactis expressing ClfB Q235A was able to stimulate platelet aggregation in platelet-rich plasma without a significant increase in lag time. The requirements for platelet aggregation were investigated using gel-filtered platelets. Fibrinogen and specific anti-ClfB antibodies were found to be sufficient to allow platelet aggregation mediated by the wild-type ClfB protein. It seems that ClfB causes platelet aggregation by a fibrinogen-dependent mechanism. The non-fibrinogen-binding ClfB mutant was unable to stimulate platelet aggregation under these conditions. However, bacteria expressing ClfB Q235A caused platelet aggregation in a complement-dependent manner which required specific anti-ClfB antibodies

Identification of a novel sequence type of Escherichia coli as the causative agent of pyelonephritis and bloodstream infection

Introduction: Globally, extra-intestinal pathogenic Escherichia coli are one of the predominant causative agents of bacteraemia. Case presentation: This case report outlines a presentation of community-acquired pyelonephritis and secondary bloodstream infection in an 81-year-old man. Laboratory investigations revealed that the causative isolate was a multi-drug-resistant E. coli of a novel multi-locus sequence type. This sequence type (ST) was designated ST-458 and was most closely related to the globally prevalent ST-131 lineage. Conclusion: This is the first report of a novel E. coli ST, ST-458, which caused pyelonephritis and bacteraemia.Published versio