Contact Information

Microbiology and Immunology


Uniformed Services University of the Health Sciences
Department of Microbiology and Immunology
4301 Jones Bridge Road
Bethesda, Maryland 20814-4799
Phone: (301) 295-3419
FAX: (301) 295-1545
Email: alison.obrien@usuhs.edu

Alison D. O'Brien, Professor & Chair, Department of Microbiology and Immunology

Alison D. O'Brien

Professor & Chair
Ph.D., Ohio State University, 1976

Research: Molecular Mechanisms of Bacterial Pathogenesis

The objective of the major program in the laboratory is to define the molecular mechanisms by which enterohemorrhagic Escherichia coli (EHEC) cause hemorrhagic colitis and the hemolytic uremic syndrome. EHEC are food-borne pathogens that cause outbreaks of disease associated with ingestion of undercooked hamburgers or raw milk.  Such an outbreak occurred in 1993 in the Pacific Northwest. EHEC are characterized by the production of Shiga toxins (Stxs) and the capacity to adhere avidly to the large bowel epithelium.  Our studies on the virulence mechanisms of EHEC include: creation of molecular tools (monoclonal antibodies and DNA probes) for detecting toxin, investigation of the molecular genetics and regulation of toxin synthesis, purification and characterization of toxins, development of small animal models to further clarify pathogenic traits of EHEC, and analysis of the molecular mechanisms by which EHEC adhere to epithelial cells.

HEp-2 cells infected with EHEC O157:H7 On the left is a fluorescent image of HEp-2 cells infected with EHEC O157:H7. Polymerized actin (red), Tir (blue), and nucleolin (green) appear to be closely associated with the adherent bacteria. On the right is a phase contrast image of the same cell. (courtesy of Dr. James Sinclair).

Two related projects are also on-going in the laboratory. These include studies of: i.) the molecular mode of action of a newly described Rho-modifying toxin (cytotoxic necrotizing factor type 1) of E. coli and its role in the pathogenesis of E. coli-mediated urinary tract infections; ii.) immunoprotective monoclonal antibodies (MAbs) against Bacillus anthracis spores that confer protection against anthrax in animal models.

Selected Publications:

Smith, M.J., H.M. Carvalho, A.R. Melton-Celsa, and A.D. O'Brien. 2006. The 13C4 monoclonal antibody that neutralizes Shiga toxin Type 1 (Stx1) recognizes three regions on the Stx1 B subunit and prevents Stx1 from binding to its eukaryotic receptor globotriaosylceramide. Infect. Immun. 74:6992-6998.

Teel L.D., J.A. Daly, R.C. Jerris, D. Maul, G. Svanas, A.D. O'Brien and C.H. Park. 2007. Rapid detection of Shiga toxin-producing Escherichia coli by Optical Immunoassay. J Clin Microbiol. 45: 3377-3380.

McNichol, B.A., S.B. Rasmussen, K.C. Meysick, and A.D. O'Brien. 2007. Two domains of Cytotoxic Necrotizing Factor Type 1 bind the cellular receptor, Laminin Receptor Precursor Protein. Infect. Immun. 75: 5095-5104.

Brahmbhatt, T.N., B.K. Janes, E.S. Stibitz, S.C. Darnell, P. Sanz, S.B. Rasmussen, and A.D. O'Brien. 2007. Bacillus anthracis exosporium protein BclA affects spore germination, interaction with extracellular matrix proteins, and hydrophobicity. Infect. Immun. 75:5233-5239.

Brahmbhatt, T.N., S.C. Darnell, H.M. Carvalho, P. Sanz, T.J. Kang, R.L. Bull, S.B. Rasmussen A.S. Cross, and A.D. O'Brien. 2007. Recombinant exosporium protein BclA of Bacillus anthracis effective as a booster for mice primed with suboptimal amounts of protective antigen. Infect. Immun. 75:5240-5247.

Sanz, P., L.D. Teel, F. Alem, H.M. Carvalho, S.C. Darnell, and A.D. O'Brien. 2008. Detection of Bacillus anthracis spore germination in vivo by bioluminescence imaging. Infect Immun. 76:1036-1047.

Alcantara, C., R.V. Destura, J.E. Sevilleja; L.F. Barroso, H.M. Carvalho, L.J. Barrett, A.D. O'Brien, and R.L. Guerrant. 2008. Detection of epithelial cell injury and quantification of infection in the HCT8 organoid model of Cryptosporidiosis. J. Inf. Dis. 198:143-9.

Smith, Y.C., S.B. Rasmussen, K.K. Grande, R.M. Conran and A.D. O'Brien. 2008. Hemolysin of uropathogenic Escherichia coli evokes extensive shedding of the uroepithelium and hemorrhage in bladder tissue within the first 24 hours after intraurethral inoculation of mice. Infect Immun. 76:2978-90.

Cybulski, R.J., Jr., P. Sanz, D. McDaniel, S. Darnell, R.L. Bull, and A.D. O'Brien. 2008. Recombinant Bacillus anthracis spore proteins enhance protection of mice primed with suboptimal amounts of protective antigen. Vaccine. 26:4927-4939.

Zheng, J., S. Cui, L.D. Teel, S. Zhao, R. Singh, A.D. O'Brien, and J. Meng. 2008. Identification and characterization of Shiga Toxin Type 2 variants in Escherichia coli isolated from animals, food, and humans. Appl Environ Microbiol. 74:5645-5652. PMID:18658282.

Sauter, K.A., A.R. Melton-Celsa, K. Larkin, M.L. Troxell, A.D. O'Brien, and B.E. Magun. 2008. Mouse model of hemolytic uremic syndrome by endotoxin-free Stx2 and protection by anti-Stx2 antibody. Infect Immun. 76:4469-4478. PMID:18694970.

Grande, K.K., K.C. Meysick, S.B. Rasmussen, and A.D. O'Brien. 2009. Cytotoxic Necrotizing Factor Type 1 (CNF1)- Neutralizing monoclonal antibody NG8 recognizes three amino acids in a C-terminal region of the toxin and reduces toxin binding to HEp-2 Cells. Infect Immun. 77: 170-179.

Cybulski, R.J., P. Sanz, F. Alem, S. Stibitz, R.L. Bull, and A. D. O'Brien. 2009. Four superoxide dismutases contribute to Bacillus anthracis virulence and provide spores with redundant protection from oxidative stress. Infect Immun. 77: 274-285.

Crawford, M.A., Y. Zhu, C.S. Green, M.D. Burdick, P. Sanz, F. Alem. A.D. O'Brien, B. Mehrad, R.M. Strieter, and M.A. Hughes. 2009. Antimicrobial effects of interferon-inducible CXC chemokines against Bacillus anthracis spores and bacilli. Infect Immun. 77(4):1664-78.

Smith, M.J., A.R. Melton-Celsa, J.F. Sinclair, H.M. Carvalho, C.M. Robinson, and A.D. O'Brien. 2009. The Monoclonal Antibody (MAb) 11E10 that neutralizes Shiga Toxin Type 2 (Stx2) recognizes three regions on the Stx2 A subunit, blocks the enzymatic action of the toxin in vitro, and alters the overall cellular distribution of the toxin. Infect Immun. 77(7):2730-40. PMID: 19433543.

Panda, A., I. Tatarov, A.R. Melton-Celsa, K. Kolappaswamy, E.H. Kriel, D. Petkov, T. Coksaygan, S. Livio, C.G. McLeod, J.P. Nataro, A.D. O'Brien, and L.J. DeTolla. 2010. Escherichia coli O157:H7 infection in Dutch Belted and New Zealand white rabbits. Comp. Med. 60:1-7. PMID: 20158946.

Mohawk, K.L., A.R. Melton-Celsa, T. Zangari, E.E. Carroll, and A.D. O'Brien. 2010. Pathogenesis of Escherichia coli O157:H7 strain 86-24 following oral infection of BALB/c mice with an intact commensal flora. Microb. Pathog. 48:131-42. PMID: 20096770.

Mohawk, K.L., A.R. Melton-Celsa, C.M. Robinson, and A.D. O'Brien. 2010. Neutralizing antibodies to Shiga Toxin Type 2 (Stx2) reduce colonization of mice by Stx2-expressing Escherichia coli O157:H7. Vaccine. 28:4777-85. PMID: 2897901.

Zumbrun, S.D., L. Hanson, J.F. Sinclair, J. Freedy, A.R. Melton-Celsa, J. Rodriguez-Canales, J.C. Hanson, and A.D. O'Brien. 2010. Human intestinal tissue and cultured colonic cells contain globotriaosylceramide synthase mRNA and the alternate Shiga Toxin receptor, globotetraosylceramide. Infect Immun. 78:4488-99. PMID: 20732996.

Wilson, M.W., J.M. Vergis, F. Alem, J.R. Palmer, A.M. Keane-Myers, T.N. Brahmbhatt, C.L. Ventura, and A.D. O'Brien. 2011. Bacillus cereus G9241 makes anthrax toxin and capsule like highly virulent B. anthracis Ames but behaves like attenuated toxigenic nonencapsulated B. anthracis Sterne in rabbits and mice. Infect Immun. 79:3012-3019.

Flemming S., L.D. Teel, L. Beutin, D. PiƩrard, G. Buvens, H. Karch, A. Melmann, A. Caprioli, R. Tozzoli, , A.R. Melton-Celsa, M. Sanchez, S. Persson, N.A. Strockbine and A.D. O'Brien. 2012. A multi-center evaluation of a sequence-based protocol to subtype Shiga toxins and standardize Stx nomenclature. J. Clin. Microbiol. In press.

Cote, C.K., L. Kaatz, J. Reinhardt, J. Bozue, S.A. Tobery, A.D. Bassett, P. Sanz, S.C. Darnell, F. Alem, A.D. O'Brien, and S.L. Welkos. 2012. Characterization of a multi-component anthrax vaccine designed to target the initial stages of infection as well as toxemia. J. Med. Microbiol. In press.