Cecilia Rydén

Binding of fibronectin to the surface of group A, C, and G streptococci isolated from human infections

Sixty-nine haemolytic and non-haemolytic streptococcal strains were isolated from various human infections and serogrouped with the coagglutination test. The amount of125I-fibronectin bound to bacterial cells in a standard assay was determined. Most of the group A, C, and G strains were able to bind fibronectin. None of the group B or D strains bound significant amounts of fibronectin. Group A, C, and G streptococci appear to preferentially bind the N-terminal region of the fibronectin molecule because the 25K N-terminal fragment of the protein could effectively inhibit the binding of125I-fibronectin to cells. Furthermore, the ability of representative strains of group A, C, and G to bind fibronectin was markedly reduced after trypsin treatment of the cells. Fibronectin binding components released from one strain by trypsin treatment inhibited the binding of125I-fibronectin to all group A, C, and G streptococci strains. These findings indicate similarities among fibronectin binding proteins of the three groups of streptococci tested. However, the relative susceptibility to trypsin of fibronectin receptors of the three strains differed as did the relative potency of the inhibitory activity of receptors solubilized from different strains. Binding of fibronectin to the cell surface of group A, C, and G streptococci may contribute to virulence, for instance by promoting specific attachment to exposed fibronectin in open wounds and tissue lesions.

Virulence of a hemB mutant displaying the phenotype of a Staphylococcus aureus small colony variant in a murine model of septic arthritis

Persistence of Staphylococcus aureus during invasive infections has been associated with a small-colony variant (SCV) phenotype. SCVs are frequently auxotrophic for menadione or hemin, two compounds involved in the biosynthesis of the electron transport chain. SCVs have been shown to be more resistant to antibiotics such as aminoglycosides, grow slowly and persist intracellularly. The aim of this study was to assess the virulence of an hemB mutant, which has been shown to display the typical characteristics of clinical SCVs, in a murine model of septic arthritis. NMRI mice were inoculated intravenously with either the wild type strain Newman or with its mutant displaying the SCV phenotype. The clinical, bacteriological, and histopathological progression of the disease was studied. Mice inoculated with the hemB mutant displayed a higher frequency and a significantly higher severity of arthritis than mice inoculated with the wild type Newman strain. Despite that, the mutant inoculated mice displayed significantly lower bacterial burden in their kidneys and joints compared with mice exposed to the wild parental strain. Notably, the hemB mutant produced almost 20 times more protease in vitro than the parental strain. We conclude that the small colony variants of S. aureus are more virulent on a per organism basis than its isogenic parental strain in the model of septic arthritis. This can at least in part be explained by the ability of SCV to produce high amounts of destructive proteases.

Binding of Microbial Pathogens to Connective Tissue Fibronectin: An Early Step in Localized and Invasive Infections

Fibronectin (fn) is a major protein of plasma and connective tissue which binds to Staphylococcus aureus and strains of other staphylococcal species often isolated from pyogenic infections. Strains of pyogenic streptococci (group A, C, and G strains) also bind fn in a similar time-dependent, saturable, and functionally irreversible way. Fibronectin-binding components released from staphylococcal and streptococcal cells after treatment with bacteriolytic or proteolytic enzymes are sensitive to protease degradation. Cross-absorption experiments with fn peptides show that the major binding for both organisms occurs to the NH2 terminal (29 kdalton) fragment while enterotoxigenic E. coli strains of the 06 serogroup show binding to one or two fn fragments outside the NH2 terminal domain. S. aureus cells bind to fn immobilized on plastic surfaces, suggesting that binding to biomaterials is an important portal of entry for pyogenic cocci to invade subepithelial tissues. Recent observations that other pathogens such as Treponema pallidum, tissue invasive parasites, and Candida albicans also bind fn indicate that many microbial pathogens may invade tissues by first binding to fn, or other connective tissue matrix proteins such as collagens or laminin. We recently defined uropathogenic E. coli and S. pyogenes strains binding to laminin or collagen. Finally, one protein A mutant of S. aureus (SA113-spA26) which is low in fn binding has a low virulence in experimental infections, indicating that fn binding is an important step in colonization of tissues and development of localized tissue infections.

Integrin-associated protein (IAP)-deficient mice are less susceptible to developing Staphylococcus aureus-induced arthritis.

The integrin-associated protein (IAP) has been shown to function in a signaling complex with beta3 integrins, influencing the migration of phagocytic cells into inflamed tissues. We have previously shown that gene-targeted mice deficient for IAP succumbed to peritonitis when inoculated with gram-negative bacteria. The aim of this study was to assess the role of IAP in our recently established model of haematogenously induced Staphylococcus aureus septicaemia and arthritis. In this model, neutrophils play a crucial role in the early phase of the infection. Mice lacking IAP and congenic controls were intravenously inoculated with S. aureus LS-1. The IAP-/- mice were resistant to developing clinical signs of arthritis compared with their IAP-expressing littermates. The clinical findings were corroborated by histopathological evaluation indicating that the IAP-/- mice had less cartilage and bone destruction in the joints. We believe that a delayed migration of leukocytes into the joints of mice lacking IAP expression leads to decreased susceptibility to develop S. aureus-induced arthritis.

Antibodies to Staphylococcus aureus Bone Sialoprotein-Binding Protein Indicate Infectious Osteomyelitis

ABSTRACT Discrimination of soft tissue infection from osteomyelitis in diabetic foot infections is a common clinical problem. Staphylococcus aureus isolates from patients with osteomyelitis express bone sialoprotein-binding protein (Bbp) that binds the bone matrix protein bone sialoprotein. The serological assay with Bbp discriminated cases of osteomyelitis from soft tissue infections in patients with diabetic foot ulcers.