Donald R. Demuth

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The cell density-dependent control of gene expression is employed by many bacteria for regulating a variety of physiological functions, including the generation of bioluminescence, sporulation, formation of biofilms, and the expression of virulence factors. Although periodontal organisms do not appear to secrete acyl-homoserine lactone signals, several(More)
Active smokers and those exposed to secondhand smoke are at increased risk of bacterial infection. Tobacco smoke exposure increases susceptibility to respiratory tract infections, including tuberculosis, pneumonia and Legionnaires disease; bacterial vaginosis and sexually transmitted diseases, such as chlamydia and gonorrhoea; Helicobacter pylori infection;(More)
Porphyromonas gingivalis is an oral/systemic pathogen implicated in chronic conditions, although the mechanism(s) whereby it resists immune defenses and persists in the host is poorly understood. The virulence of this pathogen partially depends upon expression of fimbriae comprising polymerized fimbrillin (FimA) associated with quantitatively minor proteins(More)
The luxS gene of quorum-sensing Vibrio harveyi is required for type 2 autoinducer production. We identified a Porphyromonas gingivalis open reading frame encoding a predicted peptide of 161 aa that shares 29% identity with the amino acid sequence of the LuxS protein of V. harveyi. Conditioned medium from a late-log-phase P. gingivalis culture induced the(More)
The antigen I/II family of cell-surface-anchored polypeptides in oral streptococci are structurally complex multi-functional adhesins, with multiple ligand-binding sites. Discrete regions within these polypeptides bind human salivary glycoproteins, other microbial cells, and calcium. Sequences within the N-terminal region bind preferentially fluid-phase(More)
Actinobacillus actinomycetemcomitans is associated with early onset periodontal diseases and secretes membranous vesicles that appear to contain several virulence-associated proteins. However, the composition of these vesicles and the process leading to their secretion are not well defined. Electron micrographs of thin sectioned bacterial cells and purified(More)
Autoinducer 2 (AI-2) is required for the growth of Aggregatibacter (Actinobacillus) actinomycetemcomitans in culture under conditions of iron limitation. However, in vivo this organism thrives in a complex multispecies biofilm that forms in the human oral cavity. In this report, we show that adherent growth of A. actinomycetemcomitans on a saliva-coated(More)
The leukotoxin of Actinobacillus actinomycetemcomitans has been implicated as a virulence determinant in various human infections and is encoded by a multigene operon consisting of four known genes, designated ltxC, ltxA, ltxB, and ltxD. The ltx operon appears to be present in all A. actinomycetemcomitans strains, but levels of toxin expression vary greatly(More)
Biofilm formation by the periodontal pathogen Aggregatibacter actinomycetemcomitans is dependent upon autoinducer-2 (AI-2)-mediated quorum sensing. However, the components that link the detection of the AI-2 signal to downstream gene expression have not been determined. One potential regulator is the QseBC two-component system, which is part of the(More)
Smokers are more susceptible than non-smokers to persistent infection by Porphyromonas gingivalis, a causative agent of periodontitis. Patients who smoke exhibit increased susceptibility to periodontitis and are more likely to display severe disease and be refractory to treatment. Paradoxically, smokers demonstrate reduced clinical inflammation. We show(More)