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David W Kennedy

Publications and source records attributed to David W Kennedy.

At least 19 recordsLinked to original sources
PubMed2006

Electrically conductive bacterial nanowires produced by Shewanella oneidensis strain MR-1 and other microorganisms.

Shewanella oneidensis MR-1 produced electrically conductive pilus-like appendages called bacterial nanowires in direct response to electron-acceptor limitation. Mutants deficient in genes for c-type decaheme cytochromes MtrC and OmcA, and those that lacked a functional Type II secretion pathway displayed nanowires that were poorly conductive. These mutants were also deficient in their ability to reduce hydrous ferric oxide and in their ability to generate current in a microbial fuel cell. Nanowires produced by the oxygenic phototrophic cyanobacterium Synechocystis PCC6803 and the thermophilic, fermentative bacterium Pelotomaculum thermopropionicum reveal that electrically conductive appendages are not exclusive to dissimilatory metal-reducing bacteria and may, in fact, represent a common bacterial strategy for efficient electron transfer and energy distribution.

Bacterial Outer Membrane Proteins↗
PubMed2006

Revision endoscopic sinus surgery.

Patients with recurrent chronic sinusitis after prior surgical intervention pose a particular challenge to the otorhinolaryngologist. Establishing a correct diagnosis is the first step and requires review of the original presurgical symptoms and imaging; review of the more recent symptoms and images;and reevaluation of environmental, general, and local host factors that may contribute to persistent disease. Although primary chronic rhinosinusitis is typically a medical disease, postsurgical persistent disease may result directly from iatrogenic causes, requiring early surgical revision. Even in this setting, however, proper preoperative medical therapy is essential. Diagnostic evaluation should include meticulous endoscopic evaluation and appropriate radiologic studies. CT typically is required in the coronal and axial planes and ideally is performed using a computer-assisted surgical navigation protocol and with reconstructions in the sagittal plane, allowing for "scrolling" through the altered anatomy and conceptualizing the surgical issues at hand. When the decision to undergo revision surgery is made, the patient and the physician need to comprehend the rigorous and prolonged schedule of postoperative care and débridements that may be required for long-term success. Appropriate surgical technique emphasizing mucosal preservation and complete dissection must be adhered to. The surgeon must be aware that bony thickening is likely to be present and to make the dissection significantly more difficult than in the primary case. Medical management and endoscopic surveillance postoperatively is continued until a stable cavity is achieved.

Chronic Disease↗
PubMed2006

Familial aggregation of sinonasal polyps correlates with severity of disease.

OBJECTIVE: Investigate familial aggregation of sinonasal polyps (NP) and correlate the severity of chronic rhinosinusitis (CRS) with a family history of NP. STUDY DESIGN AND SETTING: A questionnaire documenting NP, asthma, or aspirin intolerance was completed by 174 CRS patients. Severity of sinus disease was stratified as isolated NP, NP with concomitant asthma, and Samter's triad (polyps, asthma, and aspirin intolerance). RESULTS: Compared to controls, CRS patients had a higher incidence of a family history of NP. Additionally, patients stratified with severe CRS had a higher incidence of relatives with NPs. CONCLUSIONS: Familial aggregation of NP is demonstrated in CRS patients and correlates with disease severity. EBM RATING: B-2b.

Bias↗
PubMed2006

Metal reduction and iron biomineralization by a psychrotolerant Fe(III)-reducing bacterium, Shewanella sp. strain PV-4.

A marine psychrotolerant, dissimilatory Fe(III)-reducing bacterium, Shewanella sp. strain PV-4, from the microbial mat at a hydrothermal vent of Loihi Seamount in the Pacific Ocean has been further characterized, with emphases on metal reduction and iron biomineralization. The strain is able to reduce metals such as Fe(III), Co(III), Cr(VI), Mn(IV), and U(VI) as electron acceptors while using lactate, formate, pyruvate, or hydrogen as an electron donor. Growth during iron reduction occurred over the pH range of 7.0 to 8.9, a sodium chloride range of 0.05 to 5%, and a temperature range of 0 to 37 degrees C, with an optimum growth temperature of 18 degrees C. Unlike mesophilic dissimilatory Fe(III)-reducing bacteria, which produce mostly superparamagnetic magnetite (<35 nm), this psychrotolerant bacterium produces well-formed single-domain magnetite (>35 nm) at temperatures from 18 to 37 degrees C. The genome size of this strain is about 4.5 Mb. Strain PV-4 is sensitive to a variety of commonly used antibiotics except ampicillin and can acquire exogenous DNA (plasmid pCM157) through conjugation.

Bacterial Typing Techniques↗
PubMed2006

Isolation of a high-affinity functional protein complex between OmcA and MtrC: Two outer membrane decaheme c-type cytochromes of Shewanella oneidensis MR-1.

Shewanella oneidensis MR-1 is a facultatively anaerobic bacterium capable of using soluble and insoluble forms of manganese [Mn(III/IV)] and iron [Fe(III)] as terminal electron acceptors during anaerobic respiration. To assess the structural association of two outer membrane-associated c-type decaheme cytochromes (i.e., OmcA [SO1779] and MtrC [SO1778]) and their ability to reduce soluble Fe(III)-nitrilotriacetic acid (NTA), we expressed these proteins with a C-terminal tag in wild-type S. oneidensis and a mutant deficient in these genes (i.e., Delta omcA mtrC). Endogenous MtrC copurified with tagged OmcA in wild-type Shewanella, suggesting a direct association. To further evaluate their possible interaction, both proteins were purified to near homogeneity following the independent expression of OmcA and MtrC in the Delta omcA mtrC mutant. Each purified cytochrome was confirmed to contain 10 hemes and exhibited Fe(III)-NTA reductase activity. To measure binding, MtrC was labeled with the multiuse affinity probe 4',5'-bis(1,3,2-dithioarsolan-2-yl)fluorescein (1,2-ethanedithiol)2, which specifically associates with a tetracysteine motif engineered at the C terminus of MtrC. Upon titration with OmcA, there was a marked increase in fluorescence polarization indicating the formation of a high-affinity protein complex (Kd < 500 nM) between MtrC and OmcA whose binding was sensitive to changes in ionic strength. Following association, the OmcA-MtrC complex was observed to have enhanced Fe(III)-NTA reductase specific activity relative to either protein alone, demonstrating that OmcA and MtrC can interact directly with each other to form a stable complex that is consistent with their role in the electron transport pathway of S. oneidensis MR-1.

Bacterial Outer Membrane Proteins↗
PubMed2006

Technical innovations and the evolution of endoscopic sinus surgery.

Since the introduction of endoscopic sinus surgery, a number of significant technological advances, as well as an improved understanding of disease pathogenesis and management, have enabled major evolutions in surgical techniques. Modifications to surgical instruments, imaging, the development of the microdebrider, and other newer instrumentation have all contributed to the current level of patient success associated with endoscopic intranasal techniques. At the same time, it has become evident that anatomic variations are less important in the pathogenesis of chronic rhinosinusitis than was previously thought, and that ventilation alone is insufficient to resolve well-established disease. This paper reviews the changes that have occurred in endoscopic sinus surgery over the past 20 years since the techniques were first introduced into the United States, and the technologies that have enabled these changes and the development of extended endoscopic techniques. Continuing developments of interactive computer-guided surgery, endoscopic 3-dimensional imagery, robotics, and improved adjunctive therapies will further extend the role of endoscopic transnasal approaches to an expanded number of skull base and intracranial lesions.

Debridement↗
PubMed2006

Fungus and chronic rhinosinusitis: from bench to clinical understanding.

Although fungus-related sinusitis has been described for at least 2 centuries, a more detailed pathologic description of the problem as it relates to eosinophilic disease was not detailed until 1983, when "allergic fungal sinusitis" was described histopathologically. Until then, most fungal sinus disease was perceived to occur in immunosuppressed diabetic patients with invasive fungus. It is now acknowledged that depending upon the immune status of the host, fungus-related sinus disease can take several forms. Interest in this subject matter was intensified in 1999, when it was suggested that fungi might be an important cause of most cases of chronic rhinosinusitis. This hypothesis remains controversial, and there is mounting evidence to support the multifactorial nature of chronic rhinosinusitis, which may include fungus. In fact, etiologic factors for all forms of fungus-related sinus disease are still poorly understood. The prevalence of the disease and the dominant fungal pathogen appear to vary in different geographic regions and probably are related to individual host conditions. Immunoglobulin E-mediated allergic reactions to mold appear to be associated with disease in some patients, but not in all. Although antifungal therapy is known to be lifesaving for invasive disease, its role in extramucosal disease is less well defined. Preliminary trials suggest that some systemic and topical antifungal agents are of clinical benefit in extramucosal disease. Since sinus fungi are rarely invasive in immunocompetent individuals, it is not clear whether the effects of the antifungal treatments are a result of the antifungal action itself, or due to additional properties these drugs possess. This review summarizes the available data and presents some of our clinical and experimental findings as to the role of fungus in chronic rhinosinusitis.

Adult↗
PubMed2006

c-Type cytochrome-dependent formation of U(IV) nanoparticles by Shewanella oneidensis.

Modern approaches for bioremediation of radionuclide contaminated environments are based on the ability of microorganisms to effectively catalyze changes in the oxidation states of metals that in turn influence their solubility. Although microbial metal reduction has been identified as an effective means for immobilizing highly-soluble uranium(VI) complexes in situ, the biomolecular mechanisms of U(VI) reduction are not well understood. Here, we show that c-type cytochromes of a dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1, are essential for the reduction of U(VI) and formation of extracellular UO(2) nanoparticles. In particular, the outer membrane (OM) decaheme cytochrome MtrC (metal reduction), previously implicated in Mn(IV) and Fe(III) reduction, directly transferred electrons to U(VI). Additionally, deletions of mtrC and/or omcA significantly affected the in vivo U(VI) reduction rate relative to wild-type MR-1. Similar to the wild-type, the mutants accumulated UO(2) nanoparticles extracellularly to high densities in association with an extracellular polymeric substance (EPS). In wild-type cells, this UO(2)-EPS matrix exhibited glycocalyx-like properties and contained multiple elements of the OM, polysaccharide, and heme-containing proteins. Using a novel combination of methods including synchrotron-based X-ray fluorescence microscopy and high-resolution immune-electron microscopy, we demonstrate a close association of the extracellular UO(2) nanoparticles with MtrC and OmcA (outer membrane cytochrome). This is the first study to our knowledge to directly localize the OM-associated cytochromes with EPS, which contains biogenic UO(2) nanoparticles. In the environment, such association of UO(2) nanoparticles with biopolymers may exert a strong influence on subsequent behavior including susceptibility to oxidation by O(2) or transport in soils and sediments.

Bacterial Outer Membrane Proteins↗