Richard E. Cowart

Learn More
Iron is tightly controlled in mammalian tissues and regulates virulence factors in various pathogenic organisms. The influence of Fe availability upon production of cryptococcal capsular polysaccharide was studied. Polysaccharide, measured as cell-bound glucuronyl residues, increased more than threefold as available Fe in the culture medium was varied from(More)
The differential effects of iron on the growth of virulent and avirulent Listeria monocytogenes were examined. We found that virulent strains exhibited faster rates of growth as a function of iron than did the avirulent strains. We also noted that serum was microbiostatic, but this microbiostasis was overcome either by saturating the serum transferrin with(More)
 We studied the potential of multidimensional flow cytometry to evaluate the frequency and maturation/activation status of dendritic cells in minimally manipulated peripheral blood mononuclear cell preparations (i.e., only separated on Ficoll-Hypaque) of normal donors and cancer patients. A rare subset of HLA-DR+ leukocytes (less than 1% mononuclear cells)(More)
The uptake of iron by Listeria monocytogenes was studied. The microorganism was found to bind both 59Fe(II) and [59Fe3+]citrate. In contrast, L. monocytogenes was unable to acquire iron from [59Fe3+]ferroxamine or [59Fe3+]EDTA or as 59FeCl3. The data suggest that iron is acquired principally as iron(II) and that a citrate-inducible iron uptake system is(More)
The extracellular enzymatic reduction of iron by microorganisms has not been appropriately considered. In this study the reduction and release of iron from ferrioxamine were examined using extracellular microbial iron reductases and compared to iron mobilization by chemical reductants, and to chelation by EDTA and desferrioxamine. A flavin semiquinone was(More)
Regulation of iron homeostasis in many pathogens is principally mediated by the ferric uptake regulator, Fur. Since acquisition of iron from the host is essential for the intracellular pathogen Listeria monocytogenes, we predicted the existence of Fur-regulated systems that support infection. We examined the contribution of nine Fur-regulated loci to the(More)
Little is known about how pathogenic microorganisms that do not produce low-molecular-weight iron-chelating agents, termed siderophores, acquire iron from their environment. We have identified an extracellular enzyme produced by Listeria monocytogenes that can mobilize iron from a variety of iron-chelate complexes via reduction of the metal. The iron(More)
The response of human peripheral blood mononuclear cells (MNC) to Aspergillus fumigatus in vitro was evaluated. In studies of the proliferative response of MNC from 18 healthy donors to heat-killed A. fumigatus conidia, 15 displayed a significant response, with a stimulation index (SI) between 4 and 193. In contrast, all donors displayed a positive response(More)
Iron is an essential element for the growth and metabolism of microbial cells. Most pathogenic microbes elaborate powerful iron chelating agents (siderophores) to mobilize iron from ferric ligands. The pathogenic yeast, Cryptococcus neoformans has not been found to produce siderophores and its mechanism of iron acquisition is unknown. This investigation(More)
This study identifies extracellular iron reductases in culture supernatant fluids of the siderophore-producing microorganisms Escherichia coli and Pseudomonas aeruginosa. These enzymes were constitutively produced and reduced and released iron from a variety of ferric chelators. Dialyzable cofactors, necessary for the transfer of electrons in the enzymatic(More)