Biomedical subjects

T A Drake

Publications and source records attributed to T A Drake.

35 records · Page 2Linked to original sources

PubMed1989

Effects of interleukin-1, lipopolysaccharide, and streptococci on procoagulant activity of cultured human cardiac valve endothelial and stromal cells.

Fibrin is the primary constituent of the vegetation in infective endocarditis, and tissue factor expression is a major mechanism of coagulation activation on infected valves. To determine which cells may participate in coagulation activation in this setting, expression of procoagulant activity (PCA; shown to be tissue factor) was studied in cultured endothelial and stromal cells derived from human cardiac valves. Endothelial cells had negligible PCA (99 +/- 50 mU/10(5) cells, mean +/- 1 standard deviation) unless stimulated by lipopolysaccharide or interleukin-1, which increased PCA to 5,592 +/- 1,482 and 5,901 +/- 1,497 mU/10(5) cells, respectively, in 6 h. Incubation of cells with viable enterococci or viridans streptococci or with an enterococcal cell wall preparation did not induce PCA. Cultured valve stromal cells constitutively expressed high levels of PCA (14,276 +/- 8,738 mU/10(5) cells) which was not changed with exposure to interleukin-1. PCAs of stromal or stimulated endothelial cells from valves of both right and left sides of the heart were comparable. The results suggest that endothelial cells may contribute to fibrin deposition during infection if stimulated, but PCA is not directly induced by bacteria. Stromal cells could contribute PCA if exposed to blood in the course of valve injury.

Blood Coagulation Tests↗

PubMed1989

Selective cellular expression of tissue factor in human tissues. Implications for disorders of hemostasis and thrombosis.

Tissue factor (TF), the primary cellular initiator of the coagulation protease cascade, is implicated in having important roles in hemostasis, thrombogenesis, inflammation, and the cellular immune response, although the cytologic distribution of TF in tissues has yet to be described. This study used epitope-defined monoclonal antibodies to human tissue factor for immunohistochemical localization of TF in normal human tissues. TF was selectively expressed in tissues and was associated with cells rather than extracellular matrix. It was anatomically sequestered from blood, being undetectable in endothelium and peripheral blood cells. TF was present in vascular adventitia, organ capsules, epidermis, and mucosal epithelium. Most dermal and submucosal fibroblasts were negative. Except for alveolar macrophages and possibly dendritic cells of some lymphoid follicles, tissue macrophages did not express TF; (expression was demonstrable in LPS stimulated monocytes). Cerebral cortex, renal glomeruli, and cardiac myocytes were additional sites of prominent TF expression. Based on the cellular distribution of TF, it is hypothesized that intravascular initiation of coagulation requires induced expression by intravascular cells, and that the normal distribution of TF represents a hemostatic "envelope" ready to activate coagulation when vascular integrity is disrupted.

Blood Cells↗

PubMed1988

DNA probe reactivity of Mycobacterium avium complex isolates from patients without AIDS.

Mycobacterium avium complex isolates from 27 patients without AIDS and from 76 patients with AIDS were analyzed with the Gen-Probe Rapid Diagnostic System for Mycobacterium avium complex, and a retrospective chart review was performed to determine clinical significance of the isolates. While 87% of isolates from AIDS patients reacted only with the M. avium probe, only 37% from non-AIDS patients were M. avium probe positive (p less than 0.001). This pattern among non-AIDS patients was also observed among the 13 patients from whom isolates were considered to be clinically significant. Reactivity to both probes occurred with three isolates, two from non-AIDS patients that were not clinically significant and one from an AIDS patient. Results of further testing suggested that these represented dual infection with two coexisting strains. Awareness of the differences in DNA probe reactivity between isolates from AIDS and non-AIDS patients may influence testing strategies in the clinical laboratory.

Acquired Immunodeficiency Syndrome↗

PubMed1988

Staphylococcus aureus induces tissue factor expression in cultured human cardiac valve endothelium.

In vitro infection of cultured human cardiac valve endothelium (HCVE) with Staphylococcus aureus was used as a model to study potential mechanisms of vegetation formation in infective endocarditis. S. aureus was observed to adhere to and be ingested by HCVE. Infection for 8 h resulted in increased levels of procoagulant activity in HCVE, shown to be tissue factor by a specific assay. Mean activity in infected HCVE was 662 +/- 149 (mU/10(5) HCVE +/- 1 SD) versus 221 +/- 78 in control HCVE; surface-expressed activity was 57 +/- 25 in infected monolayers and undetectable (less than or equal to 10) in controls. Bacteria alone had no activity. These results suggest that endothelium may have a functional role in the pathogenesis of S. aureus endocarditis and may provide one potential mechanism for activating coagulation to initiate vegetation formation on a colonized cardiac valve.

Cell Survival↗

PubMed1987

Rapid identification of Mycobacterium avium complex in culture using DNA probes.

A commercial DNA probe procedure for identification of Mycobacterium avium complex isolates was evaluated for accuracy and applicability for use in the clinical laboratory. The test (Gen-Probe Rapid Diagnostic System for Mycobacterium Avium Complex; Gen-Probe Corp., San Diego, Calif.) uses hybridization in solution of two 125I-labeled cDNA probes. One probe is complementary to rRNA from M. avium, and the other is complementary to rRNA from M. intracellulare. Results are expressed as absolute percent hybridization, with values greater than or equal to 10% considered positive. The procedure accurately identified all 134 M. avium complex isolates and concomitantly identified them to species level. There were no false-positives with 66 other mycobacteria, including 22 M. tuberculosis and 18 M. kansasii isolates, or with 8 Nocardia isolates. The mean percent hybridization (+/- the standard deviation) of M. avium probe-positive isolates (94 isolates) was 48.0 +/- 9.9 (range, 11.5 to 72.7); for M. intracellulare (40 isolates), it was 45.7 +/- 8.8 (range, 22.7 to 60.7). Among the 74 non-M. avium complex isolates, the percent hybridization range was 1.0 to 4.2, except for a single value of 9.7 which was less than 5 when the test was repeated. Four M. avium complex isolates reacted positively with both probes on initial testing, and three were confirmed. On repeat testing of subcultures, each reacted with only one probe, suggesting the presence of a mixed culture. The procedure can be completed in as little as 2 h and could easily be performed in most clinical laboratories.

Culture Media↗

PubMed1985

Pathogenesis of endocarditis.

The pathophysiology of infective endocarditis comprises at least three critical elements: preparation of the cardiac valve for bacterial adherence, adhesion of circulating bacteria to the prepared valvular surface, and survival of the adherent bacteria on the surface, with propagation of the infected vegetation. It appears that circulating bacteria do not readily adhere to normal endothelial surfaces. Trauma to the valve, however, produces an alteration in the endothelial cells, leading to either disruption of the surface and deposition of platelets and fibrin, or other phenomena that render the surface susceptible to colonization by circulating bacteria. Once the surface is prepared, some bacterial strains appear to adhere to the fibrin-platelet matrix more avidly than others. The bacterial virulence factors that promote adherence are complex, but at least one, an extracellular polysaccharide (dextran), has been identified. Adherence can be blocked by antibodies directed against various surface structures. The survival of bacteria adherent to the surface of the vegetation appears to be complex as well, requiring resistance in situ to the bactericidal properties of complement and phagocytosis by white cells. In addition, vegetation propagation involves activation of the clotting cascade. For at least some streptococci, this occurs partly through perturbation of the valvular cells to produce tissue factor (tissue thromboplastin), which results in the deposition and growth of a fibrin-platelet clot over the rapidly growing bacterial colonies.

Animals↗

PubMed1985

Effects of sub-bactericidal concentrations of antibiotics in experimental models of endocarditis.

Subinhibitory and sub-bactericidal concentrations of antibiotics significantly influence host-bacterial interactions. This paper reviews the pathogenesis of endocarditis and examines how subinhibitory concentrations of antibiotics may influence the course of the disease. At present significant effects have been documented only for the stage of bacterial adherence to the damaged valve.

Adhesiveness↗

PubMed1985

Influence of the developmental state of valvular lesions on the antimicrobial activity of cefotaxime in experimental enterococcal infections.

Cefotaxime has little antimicrobial activity in vitro against most strains of enterococci, as measured by conventional MICs and MBCs. However, the MICs of cefotaxime against many enterococci are markedly reduced by the addition of serum to the test medium. To assess the relevance of this observation in vivo, we examined the efficacy of cefotaxime in experimental Streptococcus faecalis endocarditis. Since response to antimicrobial agents may vary with the degree of vegetation development, therapeutic efficacy was assessed both in rabbits with newly formed vegetations and in rabbits with well-developed endocardial lesions. Peak serum levels of cefotaxime (50.1 +/- 20.0 micrograms/ml) exceeded the MIC in medium supplemented with serum (4 micrograms/ml), but not in Mueller-Hinton broth alone (greater than 64 micrograms/ml). After 4 days of therapy, animals with newly formed lesions (therapy initiated 1 h after infection, transvalvular catheters removed) had lower mean vegetation bacterial titers than did untreated controls. Among animals with mature vegetations (therapy initiated 12 h after infection, catheters indwelling), the rate of mortality was significantly reduced by cefotaxime therapy. However, no difference in vegetation titers was observed. Thus, cefotaxime demonstrated antienterococcal activity within newly formed vegetations, but did not inhibit bacterial proliferation within well-established vegetations.

Animals↗

PubMed1985

Effect of fibronectin on adherence of Staphylococcus aureus to fibrin thrombi in vitro.

Staphylococcus aureus binds to purified fibronectin in solution and may bind to fibronectin present in wound tissue. When incorporated into a solid fibrin thrombus, however, plasma fibronectin may fail to bind S. aureus, because the S. aureus-binding sites on fibronectin may be occupied by fibrin. Both S. aureus and fibrin bind to the same 27-kilodalton amino-terminal fragment of fibronectin. To determine whether fibronectin incorporated into fibrin still promotes the adherence of S. aureus, we clotted citrated normal plasma and fibronectin-depleted plasma onto petri dishes. We then measured bacterial adherence to these in vitro fibrin thrombi. We found that the adherence of five of seven S. aureus strains decreased significantly (by 26 to 58%) when fibronectin had been depleted from the fibrin thrombi. Adding fibronectin back reversed this decrease in adherence. The reversal was dose dependent; the increase was in proportion to the amount of fibronectin added back to the plasma. Bacteria known not to bind to fibronectin (Escherichia coli and Staphylococcus epidermidis) adhered 100-fold less than S. aureus, and their adherence was unaffected by the absence of fibronectin in the fibrin thrombus. We conclude that fibronectin incorporated into solid fibrin thrombi does mediate the adherence of most S. aureus strains to fibrin thrombi. Fibronectin may be an important molecule that mediates the adherence of S. aureus to fibrin in wounds.

Adhesiveness↗

PubMed1984

Antibacterial activity of beta-lactam antibiotics in experimental meningitis due to Streptococcus pneumoniae.

In order to define the characteristics of the antibacterial activity of beta-lactam antibiotics in the treatment of bacterial meningitis, the relationship between cerebrospinal fluid (CSF) drug concentrations and the rate of bacterial killing was investigated for penicillin G and four new cephalosporins in an animal model of meningitis due to Streptococcus pneumoniae. All five drugs showed a significant correlation between increasing drug concentrations in CSF and increasing bactericidal rates. Minimal activity was observed in CSF at drug concentrations of approximately the broth minimal bactericidal concentration (MBC). Maximal activity occurred with CSF concentrations 10-30 times higher. In vitro tests did not reproduce the unique correlation of increasing drug concentrations and killing activity found in vivo. When evaluating new beta-lactam antibiotics for the treatment of bacterial meningitis, it is reasonable to establish a minimum standard of CSF drug concentrations of greater than or equal to 30 times the MBC against the infecting organism.

Animals↗

PubMed1984

Endocarditis due to methicillin-resistant Staphylococcus aureus in rabbits: expression of resistance to beta-lactam antibiotics in vivo and in vitro.

Whether a strain of methicillin-resistant Staphylococcus aureus susceptible to cephalothin by the disk-diffusion method was also susceptible to cephalothin in vivo was evaluated in the rabbit model of endocarditis. Rabbits with aortic-valve endocarditis due to methicillin-resistant S. aureus that were treated for four days with cephalothin had the same numbers of organisms in vegetations as did untreated rabbits. Treatment with cephalothin caused emergence of a highly resistant subpopulation in aortic-valve vegetations. Organisms highly resistant to cephalothin were also highly resistant to nafcillin. Thus broth-dilution and disk-diffusion tests may not predict therapeutic failure for cephalothin against strains of methicillin-resistant S. aureus. Because of cross-resistances among beta-lactam drugs, these strains should be considered uniformly resistant to this general class of antimicrobial agents, regardless of results from these tests.

Animals↗

PubMed1984

Single versus combination antibiotic therapy for pneumonia due to Pseudomonas aeruginosa in neutropenic guinea pigs.

Studies of therapy for experimental pneumonia due to Pseudomonas aeruginosa have failed to document beta-lactam-aminoglycoside synergy for most antibiotics examined, in contrast to results usually observed with pseudomonas infections at other sites. The neutropenic guinea-pig model of pseudomonas pneumonia was modified to resemble more closely therapy for clinical infections. Animals were treated 16 hr after infection with ticarcillin, azlocillin, ceftazidime, tobramycin, and netilmicin, alone and in combination. As predicted by in vitro synergy testing, in all cases combination drug therapy was more effective than the corresponding drugs given alone (P less than .05), as assessed by quantitative lung culture. Among single-drug regimens, those in which peak antibiotic levels did not exceed the minimal bactericidal concentration for the organism were significantly less effective. Resistance to aminoglycosides did not develop during therapy, and therefore, in this study does not explain the mechanism of synergy observed with beta-lactam antibiotics.

Agranulocytosis↗

PubMed1984

Tissue factor is a major stimulus for vegetation formation in enterococcal endocarditis in rabbits.

We examined the possible mechanisms of local initiation of coagulation in vegetation formation in enterococcal endocarditis by using a rabbit model. Contact activation and tissue factor expression by freshly excised aortic valves were assessed using assays developed for use with cultured cells. Bacteria alone lacked procoagulant activity and contact activation of plasma by excised valves did not occur. 4-d infected but not control valves expressed significant tissue factor activity (231 +/- 17 mU vs. 51 +/- 7 SE), which did not correlate with numbers of bacteria in vegetations. Tissue factor activity was also present in valves from rabbits infected for 1 and 2 d, as well as those from granulocytopenic and monocytopenic animals. Our findings suggest that tissue factor, expressed by host cells in response to infection, is a major stimulus for fibrin deposition in vegetation development.

Animals↗

PubMed1983

Value of serum tests in combined drug therapy of endocarditis.

Two in vitro tests, the serum killing level and the serum bactericidal rate assays, were evaluated for correlation with therapeutic efficacy in the rabbit model of Staphylococcus aureus endocarditis. Animals were treated with nafcillin alone and in combination with tobramycin or gentamicin. Both were effective therapies, but rapidity of vegetation sterilization by the single and combined regimens was shown by the serum bactericidal rate assay but not the serum killing level assay. As a direct measure of bactericidal activity in serum during therapy, the serum bactericidal rate assay may be a clinically useful supplemental test for providing information that the serum killing level assay cannot.

Animals↗

PubMedDate not supplied

Failure of a once-daily regimen of cefonicid for treatment of endocarditis due to Staphylococcus aureus.

Cefonicid, a new long-acting cephalosporin, was evaluated for treatment of endocarditis due to Staphylococcus aureus. Four patients, all with infection of the tricuspid valve, were treated with a single daily injection. By the fifth day of therapy, three of the four patients continued to have spiking fevers and positive blood cultures, and treatment with cefonicid was discontinued. Even though peak concentrations of antibiotic in serum were greater than 20-40 times the minimum inhibitory concentration of the antibiotic for the infecting organism, serum bactericidal titers were less than 1:8 in three patients. Susceptibility testing of 52 clinical isolates in broth confirmed a marked difference between inhibitory and bactericidal concentrations for 40% of these strains. In addition, susceptibility testing performed in serum rather than broth resulted in a sixfold increase in the minimum inhibitory concentration, a result suggesting that protein binding may be in part responsible for these failures of treatment. Cefonicid administered as a single daily dose is inadequate for treatment of endocarditis due to S. aureus and should not be used for treatment of bacteremia or life-threatening infections known or suspected to be caused by this organism.

Adult↗

PubMedDate not supplied

Expression of major histocompatibility antigens and vascular adhesion molecules on human cardiac allografts preserved in University of Wisconsin solution.

The impact of cold storage of cardiac allografts on expression of major histocompatibility complex antigens and vascular adhesion molecules is not known. We obtained serial endomyocardial biopsy specimens at harvest, on implantation, and approximately 15 minutes after reperfusion from six consecutive human cardiac allografts stored in University of Wisconsin solution. Cold ischemia time was 187 +/- 45 minutes. A fourth endomyocardial biopsy specimen was obtained from the recipients of cardiac allografts 1 week after operation. Expression of major histocompatibility complex antigens and vascular adhesion molecules was studied by immunohistochemistry. The intensity was scored blindly by a semiquantitative method. On vascular endothelial cells, the expression of major histocompatibility complex class I and II antigens was strong; ICAM-1 expression was moderate, and expression of VCAM-1 and ELAM-1 was weak to absent. The expression of these antigens on vascular endothelial cells did not change in sequential biopsy specimens. The expression of major histocompatibility complex class I antigens on myocardial cells was weak and remained unchanged. Myocardial cells did not express major histocompatibility complex class II antigens, ICAM-1, VCAM-1, or ELAM-1 on serial examinations. During cold storage of cardiac allografts in University of Wisconsin solution, the expression of major histocompatibility complex antigens and vascular adhesion molecules on endothelial cells and myocardial cells remains unchanged.

Adenosine↗

PubMedDate not supplied

Experimental cardiac allograft vasculopathy in mice.

Cardiac allograft vasculopathy is the most common cause of death in heart transplant recipients after the first postoperative year. The pathogenesis of cardiac allograft vasculopathy is not clearly defined. To better study this disease, a genetically well-defined and reproducible animal model such as the mouse is needed. We performed heterotopic, intraabdominal heart transplantation between two inbred strains of mice. The B10.A strain served as donors, and the B10.BR strain served as recipients. No immunosuppressive therapy was administered. The allografts in groups I (n = 6) and II (n = 6) were harvested at 30 and 50 days after operation, respectively. All allografts had palpable contractions at the time of harvest. The cardiac allografts from both groups showed mild to moderate acute cellular rejection. In groups I and II, 55% +/- 26% and 60% +/- 18% of arteries showed intimal thickening, respectively. Pathologically, the vascular lesions were characterized with varying degrees of intimal thickening, subendothelial mononuclear cell infiltration and fibrosis, frequent disruption of the internal elastic lamina, and perivascular inflammation. These findings are characteristic of cardiac allograft vasculopathy seen clinically. Isografts (n = 6) showed no vascular lesions. The heterotopic transplantation of B10.A-strain hearts into B10.BR recipients provides a useful murine model for future studies in the pathogenesis and treatment of cardiac allograft vasculopathy.

Animals↗