Disruption of the defense barriers between the host and its indigenous microflora can lead to opportunistic infections which have a serious impact on human health. Intra-abdominal abscesses are formed following perforation of the bowel often due to appendicitis, diverticulitis, carcinoma, or surgery. These infections are composed of mixed intestinal flora with the indigenous intestinal anaerobe, Bacteroides fragilis as the predominant component. 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. In the current funding period we have documented that there is an acute oxidative stress response which is designed to minimize the immediate affects of oxygen radicals. This is mediated by the regulator OxyR which is necessary for optimal abscess formation in mice. We also have shown that there is a novel, widespread induction of genes associated with metabolism, which occurs when there is extended exposure to oxidative stress. For the current application, we hypothesize that this extended phase and the accompanying expansive induction of metabolic genes is critical for prolonged resistance to oxidative stress and for in vivo survival in extra-intestinal sites. We will learn how this Prolonged Oxidative STress (POST) response promotes adaptation to extended oxidative stress, determine if it is necessary to maintain the organism in a resistant state and elucidate some of the mechanisms that control it. Ultimately we will discover if it enhances persistence in the abscess milieu of necrotic cell debris, viable PMNs, and host serum factors.
Three aims will address this central hypothesis.
Three specific aims will address this central hypothesis.
In specific aim1 we will elucidate the mechanisms that regulate the POST response, determine how it is controlled by stress stimuli, and if it leads to multiple stress resistance.
In specific aim 2 we will show that a robust thiol metabolism is an integral component of the POST response and determine if it is needed to survive in vivo. Finally in specific Aim 3 we will examine mechanisms of iron storage and how they help prevent oxidative damage during POST. We will determine if the iron storage proteins can contribute to the repair of iron sulfur proteins and the in vivo expression of their cognate genes will be measured to gain insight into their role during infection.

Public Health Relevance

Every mucosal surface of the human body is inhabited by bacteria that have developed a commensal relationship with their host. Bacteroides fragilis is part of this indigenous, "normal", flora in the colon and the primary goal of this research is learn how it causes intra-abdominal infections after being translocated from the colon due to disease or trauma. The successful completion of this research could lead to the discovery innovative new treatment strategies based on intervention in the pathogenic process or unique properties of the organism.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Bacterial Pathogenesis Study Section (BACP)
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Baqar, Shahida
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East Carolina University
Schools of Medicine
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Nicholson, Samantha A; Smalley, Darren; Smith, C Jeffrey et al. (2014) The recA operon: A novel stress response gene cluster in Bacteroides fragilis. Res Microbiol 165:290-9
Ndamukong, Ivan C; Gee, Jason; Smith, C Jeffrey (2013) The extracytoplasmic function sigma factor EcfO protects Bacteroides fragilis against oxidative stress. J Bacteriol 195:145-55
Gauss, George H; Reott, Michael A; Rocha, Edson R et al. (2012) Characterization of the Bacteroides fragilis bfr gene product identifies a bacterial DPS-like protein and suggests evolutionary links in the ferritin superfamily. J Bacteriol 194:15-27
Lobo, Leandro A; Smith, Charles J; Rocha, Edson R (2011) Flavin mononucleotide (FMN)-based fluorescent protein (FbFP) as reporter for gene expression in the anaerobe Bacteroides fragilis. FEMS Microbiol Lett 317:67-74
Reott, Michael A; Parker, Anita C; Rocha, Edson R et al. (2009) Thioredoxins in redox maintenance and survival during oxidative stress of Bacteroides fragilis. J Bacteriol 191:3384-91
Bacic, Melissa K; Smith, C Jeffrey (2008) Laboratory maintenance and cultivation of bacteroides species. Curr Protoc Microbiol Chapter 13:Unit 13C.1
Rocha, Edson R; Tzianabos, Arthur O; Smith, C Jeffrey (2007) Thioredoxin reductase is essential for thiol/disulfide redox control and oxidative stress survival of the anaerobe Bacteroides fragilis. J Bacteriol 189:8015-23
Sund, Christian J; Greg Wells, William; Jeffrey Smith, C (2006) The Bacteroides fragilis P20 scavengase homolog is important in the oxidative stress response but is not controlled by OxyR. FEMS Microbiol Lett 261:211-7
Robertson, Kirstin P; Smith, C Jeffrey; Gough, Andrea M et al. (2006) Characterization of Bacteroides fragilis hemolysins and regulation and synergistic interactions of HlyA and HlyB. Infect Immun 74:2304-16
Spence, Cheryl; Wells, W Greg; Smith, C Jeffrey (2006) Characterization of the primary starch utilization operon in the obligate anaerobe Bacteroides fragilis: Regulation by carbon source and oxygen. J Bacteriol 188:4663-72

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