Grace Tang-Siegel, Ph.D.

Research Assistant Professor

Tang-Siegel, Grace


Dr. Tang-Siegel obtained her professional training as a dental surgeon (MDS), and her PhD in microbiology and Genetics, working on understanding pathogenesis of human oral microbiome, from the University of Hong Kong. She continued her postdoctoral training in microbiology and molecular genetics in the University of Vermont and the University of Southern California, before she became a faculty member in the Department of Molecular Physiology and Biophysics, College of Medicine.


Given C249

Given C249


Research Description

Dr. Tang-Siegel and her laboratory are interested at understanding pathogenesis of orally originated microorganisms and, bacteriophage manipulation of human microbiome. The Gram-negative, capnophilic, facultative anaerobe, Aggregatibacter actinomycetemcomitans is a causative agent of periodontitis, mostly notable for its association with aggressive forms of the disease and its resilient survival in two important serum-rich habitats, i.e., inflammatory periodontal pockets and blood circulations, due to its naturally developed resistance to complement-mediated phagocytosis. A. actinomycetemcomitans can be found from the oral cavity of approximately 20% of the population and potentially causes systemic infections, e.g., infective endocarditis, as well as morbidities, including autoimmune diseases and neurodegenerative disorders driven by stimulation and release of proinflammatory cytokines. Importantly, this microorganism has been identified with acquired antibiotic resistance mechanisms, including mobile rRNA methylase genes and the multidrug efflux pump system. The rising antimicrobial resistance and the emergent resistance mechanisms, including from human oral microbiome, as well as the unique in vivo resilience and the highly genomic diversity of this microorganism with seven known serotypes lead to the investigation of bacteriophages and A actinomycetemcomitans. The increased application of using phages as alternative anti-microbial agents requires understanding phage infection and replication in vivo. A. actinomycetemcomitans can be developed as a platform to provide insights into phage behaviors in a mimic, in vivo physiological condition. 

Faculty Highlighted Publications

1. Tang-Siegel G.G. (2023). Human serum mediated bacteriophage life cycle switch in Aggregatibacter actinomycetemcomitans is linked to pyruvate dehydrogenase complex. Life. DOI: 13(2):436. DOI:

2. Tang-Siegel G.G., Chen C., Mintz K.P. (2022). Increased sensitivity of Aggregatibacter actinomycetemcomitans to human serum is mediated by induction of a bacteriophage. Mol Oral Microbiol. DOI: 

3. Tang-Siegel G.G., Radermacher M., Mintz K.P., Ruiz T. (2022). Serotype specific sugars impact structure but not functions of the trimeric autotransporter adhesin EmaA of Aggregatibacter actinomycetemcomitans. J Bacteriol. 204(12):e0021522. DOI:

4. Tang-Siegel G.G., Danforth D.R., Tristano J., Ruiz T., Mintz K.P. (2022). The serotype a-EmaA adhesin of Aggregatibacter actinomycetemcomitans does not require O-PS synthesis for collagen binding activity. Microbiology 168(5). DOI:

5. Danforth D.R., Tang-Siegel G.G., Ruiz T. & Mintz KP. (2018). A non-fimbrial adhesin of Aggregatibacter actinomycetemcomitans mediates biofilm biogenesis. Infect Immun 87(1):e00704-18. DOI:

6. Tang-Siegel G.G., Bumgarner R., Ruiz T., Kittichotirat W., Chen W. & Chen. C. (2016). Human-serum specific activation of alternative sigma factors, the stress responders in Aggregatibacter actinomycetemcomitans PLoS One 11(8):e0160018. DOI:

Selected Awards

National Institutes of Health-National Institute of Dental and Craniofacial Research (NIH-NIDCR R03DE029275).

National Institute of Health (NIH) training grant R90 DE22528-3 in Bacteriology, University of Southern California, Los Angeles, CA. 2013-2015