George C. Stewart
Chairman, Department of Veterinary Pathobiology,
McKee Professor of Microbial Pathogenesis
• BS, North Texas State University, Denton, TX
• PhD, University of Texas Health Sciences Center, Dallas, TX
• Post-doc, University of North Carolina, School of Medicine, Chapel Hill, NC
Research emphasis: Regulation of virulence gene expression;
global regulation of enterotoxin gene expression in Staphylococcus aureus;
expression of sporulation-specific proteins in Bacillus; characterization
of the leukotoxin of Fusobacterium necrophorum.
Staphylococcal enterotoxin gene expression: A major emphasis
in my lab is to understand the molecular genetic mechanisms governing toxin
production in Staphylococcus aureus. This organism is an important human and
animal pathogen that is becoming increasingly resistant to antibiotic therapy.
An understanding of the networks that regulate expression of its virulence
factors may lead to novel therapeutic intervention strategies. We are studying
the gene encoding enterotoxins as a model for toxin expression and are characterizing
the regulatory proteins affecting transcription of these genes.
Spore-specific proteins of Bacillus anthracis:
Anthrax is zoonotic disease that has taken on added importance because of
concerns over bioterrorism. This bacterium survives in soil because it can
produce endospores. The surface components of the spore are important for
the environmental resistance properties of the spore, as potential regulators
of the sporulation process, and as antigens for vaccine development. My laboratory
is involved in characterization of glycoproteins produced by this bacterium.
Leukotoxin expression by Fusobacterium necrophorum: F. necrophorum
is an anaerobic bacterium responsible for calf diphtheria, foot rot in sheep
and cattle, and rumenitis-liver abscess complex in feedlot cattle. It is increasingly
recognized as a pathogen of humans, as well. The principal virulence factor
of this bacterium is a large molecular weight leukotoxin. My laboratory is
involved with the characterization of this protein, determination of its specific
mode of action against bovine polymorphonuclear leukocytes, and regulation
of its expression. The role of the toxin in human disease is also being explored.
Selected publications:
Stewart, G. C. 2005. Taking shape: Control of bacterial cell wall biosynthesis.
Mol. Microbiol. 57:1177-1181.
Oelke, A. M., T. G. Nagaraja, M. J. Wilkerson, and G. C. Stewart. 2005. The leukotoxin operon of Fusobacterium necrophorum is not present in other species of Fusobacterium. Anaerobe 11:123-129.
Nagaraja, T. G., S. K. Narayanan, G. C. Stewart, and M. M. Chengappa. 2005. Fusobacterium necrophorum infections in animals: Pathogenesis and pathogenic mechanisms. Anaerobe 11:239-246.
Zhang, F., T. G. Nagaraja, D. George, and G. C. Stewart. 2006. The two major subspecies of Fusobacterium necrophorum have distinct leukotoxin operon promoter regions. Vet. Microbiol. 112:73-78.
Shaw, L. N., I.-M. Jonnson, V. Singh, A.Tarkowski, and G. C. Stewart. 2007. Inactivation of traP has no effect on the Agr quorum sensing system or virulence of Staphylococcus aureus. Infec. Immun. 75:4519-4527.
Thompson, B. M., L.N. Waller, K. F. Fox, A. Fox, and G. C. Stewart. 2007. The BclB glycoprotein of Bacillus anthracis is involved in exosporium integrity. J. Bacteriol. 189:6704-6713.
Tadepalli, S., T. G. Nagaraja, G.C. Stewart, and S.K. Narayanan. 2008. Leukotoxin operon and differential expressions of the leukotoxin gene in bovine Fusobacterium necrophorum subspecies. Anaerobe 14:13-18.
Tadepalli, S., G. C. Stewart, T.G. Nagaraja, S. S. Jang, and S. K. Narayanan. 2008. Fusobacterium equinum possesses a leukotoxin gene and exhibits leukotoxin activity. Vet. Microbiol. 127:89-96.
Tadepalli, S., G. C. Stewart, T.G. Nagaraja, and S. K. Narayanan. 2008. Human Fusobacterium necrophorum strains have a leukotoxin gene and exhibit leukotoxin activity. J. Med. Microbiol. 57:225-231.
Hsieh, H.-Y., C. W. Tseng, and G. C. Stewart. 2008. Regulation of Rot Expression in Staphylococcus aureus. J. Bacteriol. 190:546-554.