The spread of antibiotic resistance among bacterial pathogens poses a significant problem to the successful treatment of infectious diseases worldwide.  Resistance to all classes of antibiotics is known to occur and antibiotic resistant variants of all major bacterial pathogens have been described.  One of our research projects centers on the genetic characterization of antibiotic resistance genes and the mechanisms that control their dissemination among our indigenous microflora.  Through the use of molecular genetic techniques the regulation and structure of antibiotic resistance genes are analyzed in order to understand the evolutionary origins and widespread dissemination of these genes among bacterial species.  Further studies focus on the genetic elements responsible for the transmission of these resistance genes and on the novel molecular mechanisms of the gene transfer process. 

            The human microbiome or indigenous microflora outnumbers the human host cells by more than 10 to 1.  This normal microflora has a commensal association with the host which influences many of the host’s physiological, nutritional, and immunological activities.  The commensal relationship is maintained by physical barriers and immunological processes that keep the microbial populations in check.  However, disruption of these defense mechanisms leads to opportunistic infections which can have a serious impact on human health. So just how does our indigenous microflora cause disease?  In order to address this question my laboratory studies intra-abdominal abscesses which are formed in response to contamination of the peritoneal cavity with indigenous intestinal bacteria following perforation of the bowel (appendicitis, diverticulitis, carcinoma, surgery).  These are polymicrobic infections that result in a multifactorial host response designed to wall off and contain the invading microbes.  Bacteroides fragilis is the predominant anaerobe associated with intra-abdominal infections and we hypothesized that resistance to oxidative stress is an important factor in the development of these infections.  This is because relative to the colon, the peritoneal cavity is an oxygenated environment, and the recruitment of PMNs to the site of infection will result in exposure of B. fragilis to reactive oxygen species. Our work has documented that B. fragilis induces an acute oxidative stress response which is designed to minimize the immediate effects of oxygen radicals and that this rapid response, mediated by the regulator OxyR, is necessary for abscess formation in mice.  We also have shown that following the acute phase there is a novel, widespread induction of genes associated with metabolism which occurs when there is prolonged exposure to oxidative stress.  Our long range goals for this work are to understand the genetic mechanisms that regulate this global response to oxidative stress and determine how these anaerobic bacteria evade host defense mechanisms in the peritoneal cavity.  We ultimately wish to learn how these virulence factors enhance persistence in the abscess milieu of necrotic cell debris, viable PMNs, and host serum factors.

Rocha, E.R., and C.J. Smith, 1997. Regulation of Bacteroides fragilis katB mRNA by oxidative stress and carbon limitation. J. Bacteriol. 179:7033-7039

Smith, C.J. and A.C. Parker. 1998. The transfer origin for Bacteroides mobilizable transposon Tn4555 is related to a plasmid family from gram-positive bacteria. J. Bacteriol. 180:435-439.

Smith, C.J., G.B. Tribble, and D. Bayley. 1998. Genetic elements of the Bacteroides: a moving story. Plasmid 40:12-29.

Rocha, E.R. and C.J. Smith. 1998. Characterization of a peroxide resistant mutant of the anaerobic bacterium Bacteroides fragilis. J. Bacteriol. 180:5906-5912.

Tribble, G. D., A. C. Parker, and C. J. Smith. 1999. Genetic structure and transcriptional analysis of a mobilizable, antibiotic resistance transposon from Bacteroides. Plasmid 42:1-12.

Tribble, G.D., A.C. Parker, and C.J. Smith. 1999. Identification of the genes required for transposition of the Bacteroides fragilis mobilizable transposon Tn4555:role of a novel targeting gene. Mol. Microbiol. 34:385-394.

Rocha, E. R., and C. J. Smith. 2000. The redox-sensitive transcriptional activator OxyR regulates the peroxide respons regulon in the obligate anaerobe Bacteroides fragilis. J. Bacteriol. 182:5059-5069.

Bayley, D.P., E.R. Rocha, and C.J. Smith. 2000. Analysis of cepA and other Bacteroides fragilis genes reveals a unique promoter structure. FEMS Microbiol. Lett. 193:149-154.

Smith, C.J., A.C. Parker, and M. Bacic. 2001. Analysis of a Bacteroides Conjugative Transposon Using a Novel "Targeted Capture" Model System. Plasmid 46:47-56.

Smalley, D., E.R. Rocha, and C.J. Smith. 2002. An Aerobic-Type Ribonucleotide Reductase in the Anaerobe Bacteroides fragilis. J. Bacteriol. 184:895-903.

Herren, C., E.R. Rocha, and C.J. Smith. 2003. Regulation of an Important Oxidative Stress Locus in the Anaerobic Pathogen Bacteroides fragilis. Gene 316:167-175.

Rocha, E.R., C.D. Herren, D. J. Smalley, and C.J. Smith. 2003. The Complex Oxidative Stress Response of Bacteroides fragilis:the role of OxyR in Control of Gene Expression. Anaerobe 9:165-173.

Parker, A.C. and C.J. Smith. 2004. A Multicomponent System Is Required for Tetracycline-Induced Excision of Tn4555. J. Bacteriol. 186:438-444.

Rocha, E.R. and C.J. Smith 2004. Transcriptional regulation of the Bacteroides fragilis ferritin gene (ftnA) by redox stress. Microbiology 150:2125-2134.

Dinez, C.G., L.M. Farias, M.A.R. Carvalho, E.R. Rocha, and C.J. Smith. 2004. Differential gene expression in a Bacteroides fragilis metronidazole resistant mutant. J. Antimicrob. Chemother. 54:100-108.

Bacic, M., A.C. Parker, J. Stagg, H.P. Whitley, W.G. Wells, L.A. Jacob and C.J. Smith. 2005. Genetic and Structural Analysis of the Bacteroides Conjugative Transposon CTn341. J. Bacteriol. 187:2858-2869.

Bacic, M., and C.J. Smith. 2005. Analysis of chromosomal insertion sites for Bacteroides Tn4555 and the role of TnpA. Gene 353:80-88.

Robertson, K.P., C. J. Smith, A.M. Gough, and E.R. Rocha. 2006. Characterization of Bacteroides fragilis Hemolysins and Regulation and Synergistic Interactions of HlyA and HlyB. Infect. Immun. 74:2304-2316.

Spence, C., W.G. Wells, and C.J. Smith. 2006. Characterization of the primary starch utilization operon in the obligate anaerobe Bacteroides fragilis: regulation by carbon source and oxygen. J. Bacteriol. 188:4663-4672.

Sund, C.J., W.G. Wells, and C.J. Smith. 2006. The Bacteroides fragilis P20 scavengase homolog is important in the oxidative stress response but is not controlled by OxyR. FEMS Microbiol. Lett. 261:211-217.

Bacic, M., J.C. Jain, A.C. Parker, and C.J. Smith 2007. Analysis of the Zinc Finger Domain of TnpA, a DNA Targeting Protein Encoded by Mobilizable Transposon Tn4555. Plasmid 58:23-30.

Rocha, E.R., A.O. Tzianabos, and C.J. Smith. 2007.  Thioredoxin reductase is essential for the thiol/disulfide redox control and oxidative stress survival in the anaerobe Bacteroides fragilis.  J. Bacteriol. 189:8015-8023.

Sund, C.J., E.R. Rocha, A.O. Tzianabos, W.G. Wells, J.M. Gee, M.A. Reott, D.P. O’Rourke and C.J. Smith.  2008.  The Bacteroides fragilis Transcriptome Response To Oxygen and H2O2: The Role Of OxyR And Its Effect On Survival And Virulence.  Mol. Microbiol. 67:129-142.