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Education ?

Medical School Score
The University of Texas at San Antonio (2000)

Awards & Distinctions ?

American Board of Surgery

Affiliations ?

Dr. Pearce is affiliated with 4 hospitals.

Hospital Affiliations

  • University Health System
  • Christus Santa Rosa
  • Audie Murphy Vamc
  • University Hospital
  • Publications & Research

    Dr. Pearce has contributed to 21 publications.
    Title Early Outcomes of Thoracic Endovascular Stent-graft Repair for Acute Complicated Type B Dissection Using the Gore Tag Endoprosthesis.
    Date January 2009
    Journal Annals of Vascular Surgery

    We assessed the technical success and early outcome of thoracic endovascular aortic repair (TEVAR) for complicated acute type B thoracic aortic dissection treated at a single institution using a commercially available device. All patients with symptomatic complicated acute type B thoracic aortic dissection treated with TEVAR since Food and Drug Administration approval of the Gore (Flagstaff, AZ) TAG endoprosthesis were identified from a prospectively maintained vascular registry. Clinical indications, operative technique, perioperative complications, follow-up imaging, and mortality were analyzed. Between March 2005 and November 2007, 127 TEVARs using the TAG endoprosthesis were performed, of which 15 (11.8%) were for complicated acute type B thoracic aortic dissection. Indications for repair were malperfusion (53%), persistent pain (27%), and primary aortic failure (33%). Technical feasibility and success with deployment proximal to the entry tear was 93.3%, requiring at least partial coverage of the left subclavian artery in seven (46.7%). Adjunctive procedures required at the time of TEVAR included renal stent (n = 2), iliac stent (n = 3), and access-artery open repair (n = 2). Twelve patients (80%) had immediate resolution of the malperfusion deficit. Major perioperative complications included paraplegia (13.3%), renal failure requiring hemodialysis (13.3%), and stroke (6.7%). Perioperative mortality was 13.3%, occurring in one patient presenting with rupture and one with profound heart failure on admission. For complicated acute type B thoracic aortic dissection, TEVAR using commercially available stent grafts showed high technical success, excellent results at resolving malperfusion, and acceptably low complications and perioperative mortality.

    Title Metachronous Giant Brachial Artery Pseudoaneurysms: a Case Report and Review of the Literature.
    Date January 2008
    Journal Vascular and Endovascular Surgery

    Brachial artery pseudoaneurysms secondary to intravenous drug abuse represent a limb-threatening problem to patients and a technical challenge to the vascular surgeon. Here information is reported about a patient with metachronous bilateral giant brachial artery pseudoaneurysms secondary to intravenous drug use that were successfully treated with excision of the aneurysm and ligation of the brachial artery. Furthermore, a review of the current literature on the treatment of brachial artery aneurysm is presented.

    Title Endovascular Solutions to Complications of Open Aortic Repair.
    Date September 2005
    Journal Vascular and Endovascular Surgery

    Open repair of abdominal aortic aneurysms (AAAs) or occlusive disease can be complicated by pseudoaneurysm formation and aneurysmal dilatation of native vessels. Reports of reoperation for these new lesions have a mortality rate of 5-17% electively, and 24-88% if ruptured. These complications are commonly several years after initial repair, and progression of other comorbidities can further complicate a repeat exploration. The authors reviewed 5 cases of late complications of open aortic bypass surgery treated with endovascular stent grafting as an alternative to reexploration in patients with increased risk for morbidity and mortality. Over a 6-year experience, 5 patients underwent endovascular stent grafting to repair paraanastomotic aneurysms. Patient records were reviewed and clinical cardiac risk evaluation was performed. Follow-up clinic notes and computed tomography (CT) scans were evaluated. Between October 1996 and February 2002, 5 patients underwent 6 endovascular procedures to repair paraanastomotic aneurysms. Mean period between interventions was 16.6 +/-6.27 years (range 10-25); mean age at endovascular procedure 74.2 +/-6.37 years (range 67-84). Cardiac clinical risk index increased in 80% of patients by Goldman Risk Index and in 40% by the Modified Cardiac Risk Index. On completion angiography, there was complete exclusion of the paraanastomotic aneurysms in all cases (100%). Length of postoperative stay was 1.5 +/-0.547 days. Mean estimated blood loss at conclusion of endovascular procedure was 577 +/-546.504 cc (range, 60 cc-1,500 cc). Mean follow-up was 24.4 +/-24.593 months (range, 5-67 months). On repeat imaging, all stent grafts remain patent without rupture or endoleak. Endovascular stent grafting to repair late complications of open AAA repair is a viable alternative to reexploration in patients with significant comorbidities. These procedures can be performed without violating the previous surgical planes of sites. The operations can be performed under local anesthesia and with reduced hospitalizations. In patients with increased risk factors, endovascular stent grafting is a less morbid alternative to open surgical techniques.

    Title Modulation of Vascular Remodeling Induced by a Brief Intraluminal Exposure to the Recombinant R7020 Strain of Herpes Simplex-1.
    Date March 2005
    Journal Journal of Vascular Surgery : Official Publication, the Society for Vascular Surgery [and] International Society for Cardiovascular Surgery, North American Chapter

    OBJECTIVE: Vascular remodeling in response to injury or low shear stress (or both) is characterized by neointimal hyperplasia and luminal contraction. When profound, the response leads to restenosis after percutaneous endovascular intervention as well as to de novo stenosis in vein grafts. It has recently been reported that exposure of vein patches to neurovirulence-attenuated Herpes simplex virus-1 (HSV-1) decreases neointimal hyperplasia and increases luminal area. This experiment tested the hypothesis that R7020, a more highly attenuated mutant of HSV-1, would modulate the vascular remodeling response of experimental vein grafts chronically exposed to low shear stress. METHODS: The external jugular veins of 31 New Zealand white rabbits were clamped and intraluminally exposed to vehicle (phospate-buffered saline solution, n = 11), R7020 2.5 x 10(8) plaque forming units [PFU]/mL (n = 8), or R7020 2.5 x 10(9) PFU/mL (n = 12) for 10 or 30 minutes at an average pressure of 80 mm Hg. After exposure, an end-to-side distal external jugular-to-common carotid artery anastomosis was created, resulting in a widely patent arteriovenous fistula. The external jugular was suture-ligated just proximal to the thoracic inlet, distal to a small 10- to 50-microm venous tributary, creating a reversed vein "graft" segment immediately and abruptly exposed to arterial pressure (48 +/- 3 mm Hg) and low shear stress (0.12 +/- .02 dyne/cm(2)). In the 29 animals (N = 31) that survived to harvest, 26 grafts were found to be patent and were analyzed further. Nine grafts were harvested within the first week after operation, snap frozen in liquid nitrogen, and assayed for the presence of the Herpes viral immediate-response protein ICP0 by Western blot analysis. The 17 remaining grafts were perfusion-fixed, excised, stained, and analyzed morphometrically by digital planimetry. RESULTS: In patent grafts, the hemodynamic environment of low shear stress was maintained (shear stress at harvest, 0.26 +/- .06 dyne/cm(2)). Western blot analysis revealed the presence of ICP0 in R7020-exposed vein grafts after 2, 3, 7, and 14 days; ICP0 was not detected in unexposed vein grafts or adjacent carotid arteries. After 4 weeks, vein grafts exposed to R7020 exhibited a statistically significantly increased ratio of luminal radius to wall thickness, indicating altered remodeling (vehicle, 6.7 +/- 1.3; R7020 2.5 x 10(8), 9.1 +/- 1.3; R7020 2.5 x 10(9) ratio, 11.3 +/- 1.4; P < .05 for high dose compared with vehicle). CONCLUSION: A brief exposure of the neurovirulence-attenuated HSV-1 strain R7020 results in an increased ratio of luminal radius to wall thickness in experimental vein grafts chronically exposed to low shear stress.

    Title Integrating Surgery and Radiology in One Suite: a Multicenter Study.
    Date September 2004
    Journal Journal of Vascular Surgery : Official Publication, the Society for Vascular Surgery [and] International Society for Cardiovascular Surgery, North American Chapter

    PURPOSE: The study was performed to evaluate the performance of digital fixed-mounted angiographic C-arm systems in the operating room as used by surgeons, cardiologists, and interventional radiologists. METHODS: An observational study in the operating room was performed, along with a structured questionnaire and semi-structured interviews. Twenty interventions were observed at 5 sites. Workflow was analyzed. RESULTS: Integration of high-end angiographic imaging equipment in the operating room enables image-guided surgery with high-quality images, on-table quality assessment of surgical procedures, and "one-stop shopping" procedures. Integrated suites were run by surgery as well as radiology departments, and are used for a variety of procedures, including vascular, cardiothoracic, open surgical, percutaneous, and combined procedures. Operation of the angiographic system and its user interface design were not considered ideal for operating room use. Limited patient accessibility was observed, sometimes leading to uncomfortable positions for the operating physicians. Certain procedures, such as tibial artery surgery, were difficult to perform, owing to lack of accessories. Patient transfer was considered inadequate. Cleaning of the system was rated as poor. Operating room use puts an even higher demand on reliability of the system. CONCLUSION: Integration of digital angiographic systems into operating rooms has produced opportunities for new treatments and offers a superior solution for interdisciplinary work among surgeons, cardiologists, and radiologists. However, the context of use differs radically from that in the traditional radiologic examination room; the environment, users, and procedures are all different. Integration of imaging methods into the operating room can be more successful if special operating room conditions are taken into account by medical systems manufacturers.

    Title Limb Salvage After Infrainguinal Bypass Graft Failure.
    Date May 2004
    Journal Journal of Vascular Surgery : Official Publication, the Society for Vascular Surgery [and] International Society for Cardiovascular Surgery, North American Chapter

    OBJECTIVE: The purpose of this study was to examine the outcome of patients in whom an infrainguinal bypass graft failed. METHODS: This was a retrospective analysis of consecutive patients undergoing infrainguinal bypass grafting in a single institution over 8 years. RESULTS: Six hundred thirty-one infrainguinal bypass grafts were placed in 578 limbs in 503 patients during the study period. The indication for surgery was limb-threatening ischemia in 533 patients (85%); nonautologous conduits were used in 259 patients (41%), and 144 (23%) were repeat operations. After a mean follow-up of 28 +/- 1 months (median, 23 months; range, 0-99 months), 167 grafts (26%) had failed secondarily. The rate of limb salvage in patients with graft failure was poor, only 50% +/- 5% at 2 years after failure. The 2-year limb salvage rate depended on the initial indication for bypass grafting: 100% in patients with claudication (n = 16), 55% +/- 8% in patients with rest pain (n = 49), and 34% +/- 6% in patients with tissue loss (n = 73; P <.001). The prospect for limb salvage also depended on the duration that the graft remained patent. Early graft failure (<30 days; n = 25) carried a poor prognosis, with 2-year limb salvage of only 25% +/- 10%; limb salvage was 53% +/- 5% after intermediate graft failure (<2 years, n = 110) and 79% +/- 10% after late failure (>2 years, n = 15; P =.04). Multivariate analysis revealed shorter patency interval before failure (P =.006), use of warfarin sodium (Coumadin) postoperatively (P =.006), and infrapopliteal distal anastomosis (P =.01) as significant predictors for ultimate limb loss. CONCLUSION: The overall prognosis for limb salvage in patients with failed infrainguinal bypass grafts is poor, particularly in patients with grafts placed because of tissue loss and those with early graft failure.

    Title Current Status of Intravascular Stents As Delivery Devices to Prevent Restenosis.
    Date December 2003
    Journal Vascular and Endovascular Surgery

    The acute technical success of percutaneous transluminal angioplasty (PTA) has been improved with the use of intravascular stents. However, stent placement has led to the development of an increased myointimal hyperplastic response leading to late reduction in vessel lumen. Restenosis (> or =50% reduction in reference lumen diameter) rates for coronary angioplasty and stenting are reported between 20% and 50% at 1 year. Several studies are currently evaluating novel delivery of antiproliferative agents to prevent neointimal hyperplasia. The authors review the mechanism of neointimal hyperplasia as it relates to stent placement and discuss recent and ongoing trials evaluating intravascular brachytherapy and drug-eluting stent technology in the inhibition of restenotic lesions.

    Title Construction of New Unencapsulated (rough) Strains of Streptococcus Pneumoniae.
    Date December 2002
    Journal Research in Microbiology

    To construct rough strains of Streptococcus pneumoniae in which the capsule locus was completely deleted, a genetic cassette to be used as a donor DNA in transformation was developed. The cassette contained an aphIII gene, conferring kanamycin resistance, flanked by segments of dexB and aliA. Since, in all strains of S. pneumoniae the capsule locus is between dexB and aliA, the DNA segments of these two genes allow insertion of a 1354-bp DNA fragment containing aphIII into the pneumococcal chromosome, determining the deletion of the whole capsule locus. The capsule locus was deleted from the classic type 2 and type 3 Avery's strains, from R6 (whose complete genome sequence is released) and Rx1 (the two most commonly used transformation recipients), from a type 3 clinical strain and type 19F clinical isolate G54 (whose draft genome sequence is annotated). The effect of capsule removal was tested in 4 isogenic pairs. In unencapsulated strains, growth rate increased up to 56% and transformation frequency increased up to 1075-fold. A correlation was observed between the increase in growth rate and an increase in transformation frequency.

    Title The Type 2 Capsule Locus of Streptococcus Pneumoniae.
    Date May 1999
    Journal Journal of Bacteriology

    The type 2 capsule locus of Streptococcus pneumoniae was characterized in Avery's strain D39, which is the parent strain of the standard transformation recipients currently used in pneumococcal research and is largely used as a virulent strain in studies on the pathogenesis of pneumococcal infections. The capsule locus was sequenced by using a 21.7-kb PCR fragment from the D39 genome as a template. Sequence data analysis showed the presence of 18 open reading frames, 17 of which have the same direction of transcription and all of which are potentially involved in capsule biosynthesis. It was also shown that R36A and R6, which are unencapsulated (rough) derivatives of D39, carry a 7,504-bp deletion involving nine capsule genes.

    Title Membrane Targeting of Reca During Genetic Transformation.
    Date May 1998
    Journal Molecular Microbiology

    Recombination in prokaryotes and eukaryotes is mediated by the RecA family of proteins. Although the interactions between RecA and DNA are well studied, the cellular location of these interactions is not known. Using genetic transformation of Streptococcus pneumoniae as a model system, there was increased expression of a protein, colligrin, and RecA, products of the rec locus during genetic transfer. These proteins formed a complex and were found associated with the membranes of genetically competent cells. With immunoelectron microscopy and subcellular fractionation, we showed that the induction of competence led to the translocation of RecA and colligrin to the membrane and to the formation of clusters of RecA in a colligrin-dependent step. Based on the behaviour of colligrin and RecA during genetic exchange and the numerous proteins in prokaryotes and eukaryotes with domains similar to colligrin, we suggest that there may exist a family of proteins, which gathers macromolecules at specific sites in biological membranes.

    Title Pyruvate Oxidase, As a Determinant of Virulence in Streptococcus Pneumoniae.
    Date December 1996
    Journal Molecular Microbiology

    Pneumococcus has been shown to bind to epithelial cells of the nasopharynx and lung, and to endothelial cells of the peripheral vasculature. To characterize bacterial elements required for attachment to these cell types, a library of genetically altered pneumococci with defects in exported proteins was screened for the loss of attachment to glycoconjugates representative of the nasopharyngeal cell receptor, type II lung cells (LC) and human endothelial cells (EC). A mutant was identified which showed a greater than 70% loss in the ability to attach to all cell types. This mutant also showed decreased adherence to the glycoconjugates containing the terminal sugar residues GalNAcbeta1-3Gal, GalNAcbeta1-4Gal and the carbohydrate GlcNAc, which are proposed components of the pneumococcal receptors specific to the surfaces of LC and EC. Analysis of the locus altered in this mutant revealed a gene, spxB, that encodes a member of the family of bacterial pyruvate oxidases which decarboxylates pyruvate to acetyl phosphate plus H2O2 and CO2. This mutant produced decreased concentrations of H2O2 and failed to grow aerobically in a chemically defined medium, unless supplemented with acetate which presumably restores acetyl phosphate levels by the action of acetate kinase, further suggesting that spxB encodes a pyruvate oxidase. The addition of acetate to the growth medium restored the adherence properties of the mutant indicating a link between the enzyme and the expression of bacterial adhesins. A defect in spxB corresponded to impaired virulence of the mutant in vivo. Compared to the parent strain, an spxB mutant showed reduced virulence in animal models for nasopharyngeal colonization, pneumonia, and sepsis. We propose that a mutation in spxB leads to down-regulation of the multiple adhesive properties of pneumococcus which, in turn, may correlate to diminished virulence in vivo.

    Title Peptide Methionine Sulfoxide Reductase Contributes to the Maintenance of Adhesins in Three Major Pathogens.
    Date October 1996
    Journal Proceedings of the National Academy of Sciences of the United States of America

    Pathogenic bacteria rely on adhesins to bind to host tissues. Therefore, the maintenance of the functional properties of these extracellular macromolecules is essential for the pathogenicity of these microorganisms. We report that peptide methionine sulfoxide reductase (MsrA), a repair enzyme, contributes to the maintenance of adhesins in Streptococcus pneumoniae, Neisseria gonorrhoeae, and Escherichia coli. A screen of a library of pneumococcal mutants for loss of adherence uncovered a MsrA mutant with 75% reduced binding to GalNAcbeta1-4Gal containing eukaryotic cell receptors that are present on type II lung cells and vascular endothelial cells. Subsequently, it was shown that an E. coli msrA mutant displayed decreased type I fimbriae-mediated, mannose-dependent, agglutination of erythrocytes. Previous work [Taha, M. K., So, M., Seifert, H. S., Billyard, E. & Marchal, C. (1988) EMBO J. 7, 4367-4378] has shown that mutants with defects in the pilA-pilB locus from N. gonorrhoeae were altered in their production of type IV pili. We show that pneumococcal MsrA and gonococcal PilB expressed in E. coli have MsrA activity. Together these data suggest that MsrA is required for the proper expression or maintenance of functional adhesins on the surfaces of these three major pathogenic bacteria.

    Title A New Genetic Strategy for the Analysis of Virulence and Transformation in Streptococcus Pneumoniae.
    Date March 1996
    Journal Developments in Biological Standardization
    Title Peptide Permeases from Streptococcus Pneumoniae Affect Adherence to Eucaryotic Cells.
    Date July 1995
    Journal Infection and Immunity

    To gain access to tissues within the human host, Streptococcus pneumoniae initially colonizes the nasopharynx and then interacts with glycoconjugates on the surfaces of target cells at various sites of infection. Although pneumococcal adhesins are currently unknown, exported proteins on the bacterial surface are potential candidates. To identify bacterial elements involved in this process, mutants of S. pneumoniae with defects in exported proteins were screened for the inability to adhere to cells representative of three in vivo niches: (i) agglutination of bovine erythrocytes, which reflects adherence to cells which reside in the nasopharynx; (ii) human type II pneumocytes (lung cells [LC]), representing the alveolar site of infection; and (iii) human vascular endothelial cells (EC), representing the endovascular site. The capacity of the mutants to adhere during the course of pneumococcal disease was also assessed by using cytokine-activated LC and EC. All of the 30 mutants analyzed produced hemagglutination values comparable with those of the parent strain. Four independent mutants demonstrated a greater than 50% decrease in adherence to both LC and EC. Sequence analysis of the altered alleles from these strains showed that mutations had occurred in two previously identified loci, plpA and ami, which belong to the family of genes encoding protein-dependent peptide permeases. Mutations in the ami locus resulted in an inability to recognize the GalNAc beta 1-4Gal glycoconjugate receptor present on resting LC and EC, whereas mutations in plpA resulted in a failure to recognize a GalNAc beta 1-3Gal glycoconjugate receptor also present on resting cells. Mutations in neither allele affected recognition of GlcNAc receptors present on cytokine-activated LC and EC. These results suggest that peptide permeases modulate pneumococcal adherence to epithelial and endothelial cells either by acting directly as adhesins or by modulating the expression of adhesins on the pneumococcal surface during the initial stages of colonization of the lung or the vascular endothelium.

    Title The Rec Locus, a Competence-induced Operon in Streptococcus Pneumoniae.
    Date January 1995
    Journal Journal of Bacteriology

    To study competence and the process of transformation (TFN) in pneumococci, we developed a method for isolating TFN- mutants using insertional inactivation coupled with fusions to the gene for alkaline phosphatase (phoA). One TFN- mutant transformed 2 log units less efficiently than the parent strain. Reconstitution of the mutated region revealed a locus, rec, that contains two polycistronic genes, exp10 and the previously identified recA (B. Martin, J. M. Ruellan, J. F. Angulo, R. Devoret, and J. P. Claverys, Nucleic Acids Res. 20:6412, 1992). Exp10 is likely to be a membrane-associated protein, as it has a prokaryotic signal sequence and an Exp10-PhoA fusion localized with cell membranes. On the basis of sequence similarity, pneumococcal RecA is a member of bacterial RecA proteins responsible for homologous recombination of DNA. DNA-RNA hybridization analysis showed that this locus is transcribed as a polycistronic message, with increased transcription occurring during competence. With an Exp10-PhoA chimera used as a reporter, there was a 10-fold increase in the expression of the rec locus during competence while there was only minimal expression under growth conditions that repressed competence. The TFN- mutant containing the exp10-phoA fusion produced activator, a small extracellular polypeptide that induces competence, and the expression of rec was induced in response to activator. Therefore, the rec locus is directly required for genetic transformation and is regulated by the cell signaling mechanism that induces competence.

    Title Genetic Identification of Exported Proteins in Streptococcus Pneumoniae.
    Date November 1994
    Journal Molecular Microbiology

    A strategy was developed to mutate and genetically identify exported proteins in Streptococcus pneumoniae. Vectors were created and used to screen pneumococcal DNA in Escherichia coli and S. pneumoniae for translational gene fusions to alkaline phosphatase (PhoA). Twenty five PhoA+ pneumococcal mutants were isolated and the loci from eight of these mutants showed similarity to known exported or membrane-associated proteins. Homologues were found to: (i) protein-dependent peptide permeases, (ii) penicillin-binding proteins, (iii) Clp proteases, (iv) two-component sensor regulators, (v) the phosphoenolpyruvate: carbohydrate phosphotransferases permeases, (vi) membrane-associated dehydrogenases, (vii) P-type (E1E2-type) cation transport ATPases, (viii) ABC transporters responsible for the translocation of the RTX class of bacterial toxins. Unexpectedly one PhoA+ mutant contained a fusion to a member of the DEAD protein family of ATP-dependent RNA helicases suggesting export of these proteins.

    Title Peptide Permeases Modulate Transformation in Streptococcus Pneumoniae.
    Date November 1994
    Journal Molecular Microbiology

    To identify elements participating in the process of transformation, a bank of genetically altered mutants of Streptococcus pneumoniae with defects in exported proteins was assessed for a decrease in transformation efficiency. One mutant consistently transformed 10-fold less than the parent strain. Sequence analysis and reconstitution of the altered locus revealed a gene, plpA (permease-like protein), which encodes a putative substrate-binding protein belonging to the family of bacterial permeases responsible for peptide transport. The derived amino acid sequence for this gene was 80% similar to AmiA, a peptide-binding protein homologue from pneumococcus, and 50% similar over 230 amino acids to Spo0KA which is a regulatory element in the process of transformation and sporulation in Bacillus subtilis. PlpA fusions to alkaline phosphatase (PhoA) were shown to be membrane associated and labelled with [3H]-palmitic acid, which probably serves as a membrane anchor. Experiments designed to define the roles of the plpA and ami determinants in the process of transformation showed that: (i) mutants with defects in plpA were > 90% transformation deficient while ami mutants exhibited up to a fourfold increase in transformation efficiency; (ii) compared to the parental strain, the onset of competence in an ami mutant occurred earlier in logarithmic growth, whereas the onset was delayed in a plpA mutant; and (iii) the plpA mutation decreases the expression of a competence-regulated locus. Since the permease mutants would fail to bind specific ligands, it seems likely that the substrate-permease interaction modulates the process of transformation.

    Title Some Properties of an Endodextranase Inhibitor from Continuous Cultures of Streptococcus Sobrinus.
    Date January 1994
    Journal Journal of Enzyme Inhibition

    Cell-free filtrates of Streptococcus sobrinus, cultured at low growth rate in the chemostat, contain a dextranase inhibitor that can completely inhibit the activity of S. sobrinus endodextranase. The range of conditions under which inhibition occurs, and the situations in which enzyme activity can reappear, have been examined in continuous cultures of strain 6715-13WT and the dextranase-deficient mutant 6715-13-201. A purified preparation of the inhibitor was specific for S. sobrinus dextranase, having no action on dextranases from other oral streptococci. The percentage inhibition of S. sobrinus dextranase varied with the enzyme concentration, and the complete inhibition of low amounts of enzyme indicated a very tight bond between the inhibitor and the enzyme.

    Title A Chlamydial Plasmid is Differentially Transcribed During the Life Cycle of Chlamydia Trachomatis.
    Date January 1992
    Journal Plasmid

    A 7.5-kb cryptic plasmid is found in all serotypes of the obligate intracellular parasite, Chlamydia trachomatis. Although at least nine open reading frames are apparent from sequence analysis of plasmid DNA, only a small region of approximately 500 bp has been consistently shown to be transcriptionally active by Northern blot analysis. In this study, transcription was analyzed using a host-free system in which RNA synthesized by chlamydiae isolated from host cells was hybridized to different regions of the plasmid. The results suggest that fragments corresponding to all open reading frames are transcribed, but at varied relative levels depending upon the stage of the life cycle. The hybridization patterns also suggested a net chemical degradation of plasmid-specified RNA in a 3' to 5' direction.

    Title Effect of Variation in Growth Conditions on the Activity of Dextranase Inhibitor in Continuous Cultures of Streptococcus Sobrinus.
    Date June 1991
    Journal Microbios

    The activity of free extracellular dextranase inhibitor was determined in strains of Streptococcus sobrinus which were grown in a chemostat under a variety of defined conditions. Maximum release of dextranase inhibitor occurred at low growth rate in glucose-limited medium at pH 6.5. Free inhibitor could not be detected when the strains were grown at high growth rate or in batch culture.

    Title Mapping of Transcripts Encoded by the Plasmid in Chlamydia Trachomatis.
    Date February 1991
    Journal Fems Microbiology Letters

    Mapping of the plasmid-encoded RNA of the intracellular parasite, Chlamydia trachomatis revealed that the upstream control elements are different from those of other Gram-negative bacteria. A tetranucleotide, AYAA was found near the -10 position, in 5 out of 8 upstream sequences described so far. The plasmid also has a developmentally regulated promoter. The chlamydial upstream elements do not function as promoters in E. coli and vice versa. An E. coli promoter-like sequence has been found to occur fortuitously upstream from the plasmid-encoded dnaB gene. Such sequences may be evolutionary relics.

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