Colonization of the cardiovascular endothelium by viridans group streptococci can result in infective endocarditis and possibly atherosclerosis; however, the mechanisms of pathogenesis are poorly understood. We investigated the ability of selected oral streptococci to infect monolayers of human umbilical vein endothelial cells (HUVEC) in 50% human plasma and to produce cytotoxicity. Planktonic Streptococcus gordonii CH1 killed HUVEC over a 5-h period by peroxidogenesis (alpha-hemolysin) and by acidogenesis but not by production of protein exotoxins. HUVEC were protected fully by addition of supplemental buffers and bovine liver catalase to the culture medium. Streptococci were also found to invade HUVEC by an endocytic mechanism that was dependent on polymerization of actin microfilaments and on a functional cytoskeleton, as indicated by inhibition with cytochalasin D and nocodazole. Electron microscopy revealed streptococci attached to HUVEC surfaces via numerous fibrillar structures and bacteria in membrane-encased cytoplasmic vacuoles. Following invasion by S. gordonii CH1, HUVEC monolayers showed 63% cell lysis over 4 h, releasing 64% of the total intracellular bacteria into the culture medium; however, the bacteria did not multiply during this time. The ability to invade HUVEC was exhibited by selected strains of S. gordonii, S. sanguis, S. mutans, S. mitis, and S. oralis but only weakly by S. salivarius. Comparison of isogenic pairs of S. gordonii revealed a requirement for several surface proteins for maximum host cell invasion: glucosyltransferase, the sialic acid-binding protein Hsa, and the hydrophobicity/coaggregation proteins CshA and CshB. Deletion of genes for the antigen I/II adhesins, SspA and SspB, did not affect invasion. We hypothesize that peroxidogenesis and invasion of the cardiovascular endothelium by viridans group streptococci are integral events in the pathogenesis of infective endocarditis and atherosclerosis.Viridans group streptococci comprise a large proportion of the commensal bacteria that colonize oral surfaces (20,24,25). These bacteria frequently enter the bloodstream following trauma to oral tissues (12,17,41,58) and can then adhere to surfaces of abnormal or previously damaged heart valves (15,21,29,47) or become implanted in arterial atherosclerotic plaques (11). Streptococci growing on heart valve surfaces (causing infective endocarditis) become encased in a matrix of fibrin and platelets, which form macroscopic verrucous lesions and can lead to valve perforation, abnormalities in cardiac conduction, valve ring abscesses, pericarditis, aneurysm of the sinus of Valsalva, and release of peripheral emboli (21, 56). Viridans group streptococci are the most common cause of native valve endocarditis in humans, accounting for 45 to 80% of cases (5, 55). A variety of virulence factors have been implicated in the initial colonization of bacteria to cardiac valve surfaces (1, 32, 49, 50, 54), but those responsible for the ultimate destruction of underlying tissues are not well unders...
SUMMARYStaphylococcus aureus (n = 75) isolated from mammary secretions of cows with subclinical and clinical mastitis from several geographic locations in the USA were examined using polymerase chain reaction-based DNA fingerprinting. DNA fingerprints were produced using a synthetic oligonucleotide primer (5'GTAACGCC3') to produce a distinct spectrum of amplified DNA
Summary Adherence of an encapsulated (UT 101) and a non‐encapsulated (UT 102) strain of Streptococcus uberis to a bovine mammary epithelial cell line (MAC‐T) and to extracellular matrix proteins (ECMP) including fibronectin, collagen and laminin was investigated. S. uberis was co‐cultured at 4 °C with MAC‐T cell monolayers. Both strains of S. uberis adhered to MAC‐T cells. However, the non‐encapsulated strain of S. uberis adhered better to MAC‐T cells than the encapsulated strain. Preincubation of MAC‐T cells with lipoteichoic acid (LTA) and/or treatment of S. uberis with antibodies directed against the carboxyl‐terminal half of type 24 M protein reduced adherence of both strains of S. uberis to MAC‐T cells. Adherence to ECMP was measured by incubating bis‐carboxyethyl‐carboxyfluorescein acetomethyl ester (BCECF‐AM) labelled S. uberis in 96‐well plates coated with fibronectin, collagen or laminin. Both strains adhered to ECMP, however, the encapsulated strain adhered better to ECMP than the non‐encapsulated strain. Results of this investigation demonstrated that both strains of S. uberis evaluated were capable of adhering to bovine mammary epithelial cells and to ECMP. Adherence of S. uberis to mammary epithelium may be an extremely important mechanism in the establishment and progression of bovine intramammary infections.
The purpose of this study is to evaluate the primary mechanism through which interferon (IFN)- exhibits target-mediated drug disposition (TMDD) and whether the theoretical assumptions of TMDD models are consistent with experimental pharmacokinetic (PK) data. Recombinant murine IFN- was administered as an intravenous injection at two dose levels (0.5 and 1 million IU/kg) to male wild-type (WT) and type-I IFN-␣/ receptor subunit (IFNAR-1) knockout (KO) mice (A129S7/SvEvBrd strain). Sampling was conducted at various times (n ϭ 3/time point), and plasma was analyzed for IFN- concentrations using a validated enzymelinked immunosorbent assay. The pharmacodynamic (PD) biomarker was IP-10 mRNA that was isolated from the distal femur bone and quantified using reverse transcription-polymerase chain reaction. An integrated model that includes rapid-binding TMDD and an indirect mechanism of drug action was used to characterize the PK/PD profiles. For an experimental control, PK profiles of recombinant murine erythropoietin (muEPO), another drug that exhibits TMDD, were determined after a single intravenous dose (0.5 g/kg) in WT and KO animals. The concentration-time profiles for IFN- differed substantially at initial times for the WT and KO mice at the same dose levels. These differences are characteristic of ligands exhibiting receptor-mediated disposition and were well described by a rapid-binding TMDD model. No differences in muEPO PK were observed in the control study. In summary, the intact IFNAR receptor is a primary regulator of in vivo IFN- exposure. An integrated PK/PD model was successfully used to assess the receptor-mediated disposition and dynamics of IFN-.
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