Donald R. Demuth, Ph.D.
Professor & University Scholar
Oral Health & Systemic Disease Research Group
University of Louisville
Room 209, School of Dentistry
501 S. Preston St.
Louisville, KY 40292.
Summary of Research Areas
- Microbial evasion of host immune response
- Bacterial cell-to-cell communication
- Regulation of bacterial virulence gene expression
- Molecular mechanisms of microbial biofilm development
To colonize and persist in a host, bacterial pathogens must first adhere tightly to tissue surfaces and evade or overcome the host immune response as well as various non-immune anti-microbial activities. Our studies focus on the mechanisms used by pathogens to accomplish these tasks and we utilize the complex microbial community of the human oral cavity as a model to study these processes. We are investigating the mechanism of action of several protein toxins produced by oral pathogens. These proteins target human immune cells, e.g., macrophages, neutrophils and lymphocytes, and our goal is to understand the role that these toxins play in actively avoiding the immune response during infection. Organisms may also passively avoid the immune response by growing as a biofilm. We are interested in determining how oral pathogens identify a suitable niche and colonize the complex microbial community that exists in the oral cavity. The development and growth of complex microbial communities may also require communication among the cells within the biofilm. Therefore, we are investigating mechanisms of bacterial cell-to-cell communication, focusing on quorum sensing systems that are present in oral pathogens. The goal of these studies is to determine if quorum sensing plays a role in allowing organisms to sense and respond to their local environment and the other bacteria that cohabit that environment.
1) The periodontal pathogen P. gingivalis colonizes the pre-existing oral biofilm by interacting with a surface protein (SspA) expressed by all oral streptococci. However, P. gingivalis selectively adheres to the viridans streptococci and not mutans streptococci. We have identified a discrete motif of SspA that is involved in this interaction. Using a protein engineering approach, we are investigating the specific protein structure that is recognized by P. gingivalis in order to generate peptide mimetic compounds that may block P. gingivalis colonization of the oral cavity.
2) Actinobacillus actinomycetemcomitans (Aa) expresses two toxins, a leukotoxin and a cytolethal distending toxin that target human immune cells. A small percentage of Aa strains exhibit a hyperleukotoxic and hypervirulent phenotype. These strains possess alterations within the promoter region of the leukotoxin operon. We have identified several cis-acting regulatory sequences in the promoter and are investigating the role of these sequences in the regulation of leukotoxin expression. Our goal is to determine how alteration of the promoter leads to a hypervirulent phenotype.
The cytolethal distending toxin of Aa targets human lymphocytes, causing cells to arrest in the G2 phase of the cell cycle. The toxin is composed of three subunits; two subunits function to interact with the lymphocyte cell surface and deliver the toxic subunit to the cell. We are studying how the holotoxin interacts with lymphocytes, how the toxic subunit enters the cell and the intracellular mechanism of action of the toxic subunit.
3) The gene responsible for the production of the auto-inducer 2 signal AI-2) is conserved in many bacteria, yet whether it plays a role in cell-to-cell communication in all organisms remains controversial. We are interested in determining the level of specificity in cell-to-cell communication mediated by AI-2 and in identifying the cellular components that are involved in AI-2 signal transduction in oral pathogens. The ultimate goal is to determine if quorum sensing is a viable target for therapeutic intervention of biofilm-mediated diseases.
4) Cigarette smoking often increases the severity of periodontal disease and components in smoke are known to affect aspects of the human innate immune response. However, little is known about how components in cigarette smoke affect the oral pathogens that initiate periodontitis. Our results show that P. gingivalis gene expression is dramatically altered upon exposure to smoke extracts and many of the differentially expressed genes are associated with its virulence or interaction with host tissues. Our goal is to determine if these smoke-induced changes in microbial gene expression and physiology contribute to the increased severity of disease in smokers. This may lead to novel methods to control periodontitis in these patients.
Bagaitkar, J., Williams, L.R., Renaud, D.E., Bemakanakere, M.R., Scott, D.A. and Demuth, D.R. 2009. Tobacco-induced alterations to Porphyromonas gingivalis-host interactions. Environ. Microbiol. (in press).
Rabin, S.D.P., Flitton, J.G. and Demuth, D.R. 2009. Aggregatibacter actinomycetemcomitans cytolethal distending toxin induces apoptosis in non-proliferating macrophages by a phosphatase independent mechanism. Infect. Immun. (submitted).
Bagaitkar, J., Demuth, D.R. and Scott, D.S. 2008. Tobacco use and susceptibility to bacterial infection. Tobacco Induced Diseases 4: 12-19.
Gorr, S-U., Sotsky, J.B., Shelar, A.P. and Demuth, D.R. 2008. Design of bacteria agglutinating peptides derived from parotid secretory protein, a member of the PLUNC family of BPI-like proteins. Peptides 29:2119-2127.
Hajishengallis, G., M. Wang, S. Liang, M.A. Shakhatreh, D. James, S.-I. Nishiyama, F. Yoshimura, and D.R. Demuth. 2008. Subversion of innate immunity by periodontopathic bacteria through exploitation of complement receptor-3. In: J.D. Lambris (ed.), Current Topics of Complement II. Adv. Exp. Med. Biol. 632:203-215.
Rajendran, N., Rajnarayanan, R.V. and Demuth, D.R. 2008. Molecular phylogenetic analysis of tryptophanyl-tRNA synthetase of Actinobacillus actinomycetemcomitans. Z. Naturforsch. 63c:418-428.
Daep, C.A., Lamont, R.J. and Demuth, D.R. 2008. Interaction of Porphyromonas gingivalis with oral streptococci requires a motif that resembles the eukaryotic nuclear receptor box protein-protein interaction domain. Infect. Immun. 76:3273-3280.
Maeda, K., Tribble, G.D., Tucker, C.M., Anaya, C., Shizukuishi, S., Lewis, J.P., Demuth, D.R. and Lamont, R.J. 2008. A Porphyromonas gingivalis tyrosine phosphatase is a multifunctional regulator of virulence attributes. Mol. Microbiol.
Capestany, C.A., Tribble, G.D., Maeda, K., Demuth, D.R. and Lamont, R.J. 2008. Role of the Clp system in stress tolerance, biofilm formation and intracellular invasion in Porphyromonas gingivalis. J. Bacteriol. 190:1436-1446.
Schaeffer, L.M., Schmidt, M.L. and Demuth, D.R. 2008. Induction of Aggregatibacter actinomycetemcomitans Leukotoxin Expression by IS1301 and orfA. Microbiol. 154:528-538.
Shao, H., Lamont R.J. and Demuth, D.R. 2007. Autoinducer-2 is required for biofilm growth of Aggregatibacter (Actinobacillus) actinomycetemcomitans. Infect. Immun. 75:4211-4218.
Wang, H., Shakhatreh, M-A.K., James, D., Liang, S., Nishiyama, S., Yoshimura, F., Demuth, D.R., and Hajishengallis, G. 2007. Fimbrial proteins of Porphyromonas gingivalis mediate in vivo virulence and exploit TLR2 and complement receptor-3 to persist in macrophages. J. Immunol. 179:2349-2358.
Shao, H., James, D., Lamont, R.J. and Demuth, D.R. 2007. Differential interaction of Aggregatibacter (Actinobacillus) actinomycetemcomitans LsrB and RbsB proteins with autoinducer-2. J. Bacteriol. 189:5559-5565.
McArthur, W.P., Rhodin, N.R., Seifert, T.B., Oli, M.W., Robinette, R.A., Demuth, D.R., Brady, .LJ. 2007. Characterization of epitopes recognized by anti-Streptococcus mutans P1 monoclonal antibodies. FEMS Immunol Med Microbiol. 50:342-353.
Kinane, D.F., D.R. Demuth, S.U. Gorr, G. Hajishengallis and M. Martin. 2007. Human variability in innate immunity. Periodontol. 2000 45:1-21.
Daep, C.A., Novak, E.A., Lamont, R.J. and Demuth, D.R. 2011. Structural dissection and in vivo effectiveness of a peptide inhibitor of Porphyromonas gingivalis adherence to Streptococcus gordonii. Infect. Immun. 79:67-74.
Chawla, A., Hirano, T., Bainbridge, B.W., Demuth, D.R., Xie, H., and Lamont, R.J. 2010. Community signaling between S. gordonii and P. gingivalis is controlled by the transcriptional regulator CdhR. Mol. Microbiol. 78:1510-1522.
Daep, C.A., Novak, E.A., Lamont, R.J. and Demuth, D.R. 2010. Selective substitution of amino acids limits proteolytic cleavage and improves the bioactivity of an anti-biofilm peptide that targets the periodontal pathogen, Porphyromonas gingivalis. Peptides. 31:2173-2178.
Bagaitkar, J., Demuth, D.R., Daep, C.A., Renaud, D.E., Pierce D.L., and Scott, D.A. 2010. Tobacco Upregulates P. gingivalis Fimbrial Proteins Which Induce TLR2 Hyposensitivity. PLoS ONE 5(5): e9323. doi:10.1371/journal.pone.0009323
Novak, E.A., Shao, H., Daep, C.A. and Demuth, D.R. 2010. Autoinducer-2 and QseC control biofilm formation and in vivo virulence of A. actinomycetemcomitans. Infect. Immun. 78:2919-2926.
Shao, H. and Demuth, D.R. 2010. Quorum sensing regulation of biofilm growth and gene expression in oral bacteria and periodontal pathogens. Periodontol. 2000 52:53-67.