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C H Davis

Publications and source records attributed to C H Davis.

At least 19 recordsLinked to original sources
PubMed2002

Protein disulfide isomerase, a component of the estrogen receptor complex, is associated with Chlamydia trachomatis serovar E attached to human endometrial epithelial cells.

Chlamydia trachomatis serovar E, the leading bacterial agent responsible for sexually transmitted diseases, is required to invade genital epithelial cells for its growth and survival, yet little is known about the adhesin-receptor interactions promoting its entry. In contrast, much has been published on the heparan sulfate receptor for binding C. trachomatis L2 elementary bodies (EBs) prior to entry into HeLa cells. Using a different experimental approach in which a biotinylated apical membrane protein receptor(s) attached to EB at 4 degrees C was stripped off the surface of polarized HEC-1B cells and immunoprecipitated with polyclonal anti-EB antibodies, an approximately 55-kDa protein was reproducibly detected by enhanced chemiluminescence and two-dimensional gel electrophoresis. Matrix-assisted laser desorption ionization mass-spectrometry sequence analysis revealed the 55-kDa protein to be protein disulfide isomerase (PDI), a member of the estrogen receptor complex which carries out thiol-disulfide exchange reactions at infected host cell surfaces. Exposure of HEC-1B cells during EB attachment (1.5 to 2 h) to three different inhibitors of PDI reductive reactions--(i) the thiol-alkylating reagent DTNB (5,5'-dithiobis[2-nitrobenzoic acid]), (ii) bacitracin, and (iii) anti-PDI antibodies--resulted in reduced chlamydial infectivity. Since (i) C. trachomatis serovar E attachment to estrogen-dominant primary human endometrial epithelial cells is dramatically enhanced and (ii) productive entry into and infectivity of EB in host cells is dependent on reduction of EB cross-linked outer membrane proteins at the host cell surface, these data provide some preliminary evidence for an intriguing new potential receptor candidate for further analysis of luminal C. trachomatis serovar E entry.

Amino Acid Sequence↗
PubMed1997

The microbicidal agent C31G inhibits Chlamydia trachomatis infectivity in vitro.

Safe and effective vaginal microbicidal compounds are being sought to offer women an independent method for protection against transmission of sexually acquired pathogens. The purpose of this study was to examine the efficacy of two formulations of one such compound, C31G, against Chlamydia trachomatis serovar E alone, its host epithelial cell (HEC-1B) alone, and against chlamydiae-infected HEC-1B cells. Preexposure of isolated, purified infectious chlamydial elementary bodies (EB) to C31G, at pHs 7.2 and 5.7, for 1 h at 4 degrees C resulted in reduced infectivity of EB for HEC-1B cells. Examination of the C31G-exposed 35S-EB on sodium dodecyl sulfate-polyacrylamide gel electrophoresis autoradiographs and by Western blotting revealed a C31G concentration-dependent and pH-dependent destabilization of the chlamydial envelope, resulting in the release of chlamydial lipopolysaccharide and proteins. Interestingly, when the host human genital columnar epithelial cells were infected with chlamydiae and then exposed to dilute concentrations of C31G which did not alter epithelial cell viability, chlamydial infectivity was also markedly reduced. C31G gained access to the developing chlamydial inclusion causing damage to or destruction of metabolically active reticulate bodies as well as apparent alteration of the inclusion membrane, which resulted in premature escape of chlamydial antigen to the infected epithelial surface. These studies show that the broad-spectrum antiviral and antibacterial microbicide C31G also has antichlamydial activity.

Anti-Bacterial Agents↗
PubMed1997

Differences in the association of Chlamydia trachomatis serovar E and serovar L2 with epithelial cells in vitro may reflect biological differences in vivo.

Chlamydia trachomatis serovar E is one of the most common bacterial sexually transmitted pathogens. Since it is an obligate intracellular bacterium, efficient colonization of genital mucosal epithelial cells is crucial to the infectious process. Serovar E elementary bodies (EB) metabolically radiolabeled with 35S-Cys-Met and harvested from microcarrier bead cultures, which significantly improves the infectious EB-to-particle ratio, provided a more accurate picture of the parameters of attachment of EB to human endometrial epithelial cells (HEC-1B) than did less infectious 14C-EB harvested from flask cultures. Binding of serovar E EB was (i) equivalent at 35 and 4 degrees C, (ii) decreased by preexposure of EB to heat or the topical microbicide C31G, (iii) comparable among common eukaryotic cell lines (HeLa, McCoy), and (iv) significantly increased to the apical surfaces of polarized cells versus nonpolarized cells. In parallel experiments with C. trachomatis serovar L2, serovar E attachment was not affected by heparin or heparan sulfate whereas these glucosaminoglycans dramatically reduced serovar L2 attachment. These data were confirmed by competitive inhibition of serovar E binding and infectivity by excess unlabeled live and UV-inactivated serovar E EB but not by excess serovar L2 EB. The noninvasive serovar E strains in the lumen of the genital tract enter and exit the apical domains of target columnar epithelial cells to spread canalicularly in an ascending fashion from the lower to the upper genital tract. In contrast, the invasive serovar L2 strains are primarily submucosal pathogens and likely use the glucosaminoglycans concentrated in the extracellular matrix to colonize the basolateral domains of mucosal epithelia to perpetuate the infectious process.

Bacterial Adhesion↗
PubMed1996

Spinal meningeal melanocytoma: a case report and review of the literature.

We present a case of spinal meningeal melanocytoma involving the C5 nerve root with spinal cord compression which resembled a neurinoma clinically as well as radiologically. The clinical, radiological and pathological features of this and 11 other cases reported in the literature are reviewed. The significance of correct diagnosis and aggressive surgical management of this benign neoplasm is emphasized.

Adult↗
PubMed1996

The late chlamydial inclusion membrane is not derived from the endocytic pathway and is relatively deficient in host proteins.

Chlamydiae are obligate intracellular parasites which multiply within infected cells in a membrane-bound structure termed an inclusion. Newly internalized bacteria are surrounded by host plasma membrane; however, the source of membrane for the expansion of the inclusion is unknown. To determine if the membrane for the mature inclusion was derived by fusion with cellular organelles, we stained infected cells with fluorescent or electron-dense markers specific for organelles and examined inclusions for those markers. We observed no evidence for the presence of endoplasmic reticulum, Golgi, late endosomal, or lysosomal proteins in the inclusion. These data suggest that the expansion of the inclusion membrane, beginning 24 h postinoculation, does not occur by the addition of host proteins resulting from either de novo host synthesis or by fusion with preexisting membranes. To determine the source of the expanding inclusion membrane, antibodies were produced against isolated membranes from Chlamydia-infected mouse cells. The antibodies were demonstrated to be solely against Chlamydia-specified proteins by both immunoprecipitation of [35S]methionine-labeled extracts and Western blotting (immunoblotting). Techniques were used to semipermeabilize Chlamydia-infected cells without disrupting the permeability of the inclusion, allowing antibodies access to the outer surface of the inclusion membrane. Immunofluorescent staining demonstrated a ring-like fluorescence around inclusions in semipermeabilized cells, whereas Triton X-100-permeabilized cells showed staining throughout the inclusion. These studies demonstrate that the inclusion membrane is made up, in part, of Chlamydia-specified proteins and not of existing host membrane proteins.

3T3 Cells↗
PubMed1995

Medical migration and the physician workforce. International medical graduates and American medicine.

OBJECTIVE: Because of the size and growth of the international medical graduate (IMG) contribution to graduate medical education (GME) in the United States, and subsequently to the US physician workforce, it is essential to understand the demographics and patterns of IMG training and practice as well as the routes of entry into the United States. DATA SOURCES: Published data from the American Medical Association, the American Osteopathic Association, and the Association of American Medical Colleges; tabular runs of county-level data contained on the Bureau of Health Professions' Area Resource File. RESULTS: The majority of IMGs who participate in GME in the United States ultimately enter US practices. A significant proportion of exchange visitors eventually enter into permanent practice in the United States, contrary to the intent of the J-1 visa-based GME training as an international educational exchange program. International medical graduates gravitate toward initial residency programs in internal medicine and pediatrics, many of which have unfilled positions; however, IMGs subspecialize at a disproportionately high rate, reducing their net contribution to the generalist pool. Patterns of ultimate practice location of IMGs parallel the patterns of US medical graduates (USMGs). CONCLUSIONS: In recent years, participation of IMGs in GME and practice has increased significantly. Most IMGs in GME are not exchange visitors, but are either permanent residents or US citizens. Patterns of specialization and location of IMGs ultimately mirror those of USMGs. National IMG policy must be examined in light of the projected surplus of physicians in the United States. The best option for long-term control of the number of physicians in practice, USMG or IMG, is a system of specifying the number of GME positions nationally.

Education, Medical, Graduate↗
PubMed1995

Spinal cord compression caused by ossification of the transverse ligament of the atlas.

Although ossification of the posterior longitudinal ligament and ligamentum flavum are well known, ossification of the transverse ligament of the atlas is extremely rare. We present the case of a 79-year-old man who developed a gradually progressive spastic quadriparesis caused by upper cervical canal stenosis due to ossification of the transverse ligament of the atlas together with ligamentum flavum hypertrophy.

Aged↗
PubMed1994

Chlamydia trachomatis does not bind to alpha beta 1 integrins to colonize a human endometrial epithelial cell line cultured in vitro.

Chlamydia trachomatis is the leading cause of bacterially acquired sexually transmitted diseases in the United States and Europe. As an obligate intracellular pathogen, this bacterium must invade epithelial cells in order to survive and grow. Thus, multiple strategies probably exist for initial binding of chlamydiae to their target cells. Since a variety of bacteria have exploited integrins to colonize tissues, and a precedent existed for the involvement of extracellular matrix components in chlamydial attachment, this study first analyzed, by flow cytometry, integrins expressed by the human endometrial epithelial cell line HEC-1B. The genital cells were then exposed to monoclonal antibodies directed against those integrins and assayed for chlamydial attachment and inclusion development. Monoclonal antibodies bound to the alpha and/or beta 1 subunit of classic integrin receptors displayed by HEC-1B cells were not able to prevent colonization and infection of the epithelial cells by a genital isolate of C. trachomatis.

Antibodies, Monoclonal↗
PubMed1994

Effect of clinically relevant culture conditions on antimicrobial susceptibility of Chlamydia trachomatis.

Infection of polarized human endometrial-gland epithelial cells obtained at hysterectomy with Chlamydia trachomatis serovar E may provide a relevant in vitro model for studies of pharmacokinetics in genital chlamydial infections. The minimal bactericidal concentration of azithromycin against C. trachomatis was lower in this model than in studies with nonpolarized cells (0.125 and 0.5 mg/L, respectively). Polarized cells also internalized more azithromycin over 24 hours. The results indicate that the eradication of chlamydial infections may be difficult to prove by antigen detection methods: the persistence of chlamydial envelope material within the intracellular vacuoles of azithromycin-treated cells may lead to a false-positive diagnosis of persisting chlamydial infection.

Anti-Bacterial Agents↗
PubMed1994

Expression of recombinant DNA introduced into Chlamydia trachomatis by electroporation.

Electroporation was used to introduce DNA into the elementary bodies of the obligate parasitic bacterium Chlamydia trachomatis. The source of DNA for these experiments was the chimeric plasmid pPBW100, which was constructed from the well-characterized 7.5-kb plasmid of C. trachomatis and the Escherichia coli plasmid pBGS9. To select directly for C. trachomatis carrying pPBW100, an in-frame gene fusion between the chlamydial promoter P7248 and a promoterless chloramphenicol acetyltransferase (cat) cassette was incorporated into the plasmid. After infection of McCoy cells with electroporated elementary bodies containing pPBW100, the following were observed: (i) the plasmid DNA was detected inside the chloramphenicol-resistant chlamydial inclusions by in situ and Southern hybridization analyses; (ii) both physical and biochemical evidence showed that chloramphenicol acetyltransferase was synthesized by the electroporated C. trachomatis; (iii) expression of P7248::cat was developmentally regulated and occurred during the early stages of chlamydial reticulate body development; and (iv) although the expression from P7248::cat was mainly transient, there were rare instances where chloramphenicol-resistant C. trachomatis were observed after four passages.

Base Sequence↗
PubMed1993

Molecular characterization and outer membrane association of a Chlamydia trachomatis protein related to the hsp70 family of proteins.

One route by which Chlamydia trachomatis is internalized into host endometrial epithelial cells is receptor-mediated endocytosis. Although this implies an adhesin-receptor interaction exists, specific chlamydial surface molecules have not been identified. We are investigating potential adhesin molecules using an in vitro functional assay to select for chlamydial recombinant Escherichia coli expressing an adherent phenotype. We have previously shown that E. coli JM109(pPBW58) attaches to epithelial cells by a specific process paralleling C. trachomatis and expresses at least three plasmid-encoded proteins (18, 28, and 82 kDa; Schmiel, D. H., Knight, S. T., Raulston, J. E., Choong, J., Davis, C. H., and Wyrick, P. B. (1991) Infect. Immun. 59, 4001-4012). In this report, we demonstrate that (i) the 82-kDa protein is associated with the outer membrane of both E. coli JM109-(pPBW58) and C. trachomatis serovar E elementary bodies; (ii) the plasmid-encoded protein is identical to the native chlamydial protein by mass, charge, antigenicity, and partial proteolytic peptide profiles; (iii) a highly homologous protein is present in C. trachomatis biovariant lymphogranuloma venereum; (iv) the 82-kDa protein is not covalently linked by disulfide bonds to other protein species in either E. coli JM109(pPBW58) or C. trachomatis; (v) sequence analysis of the open reading frame indicates this protein is a relative of the heat shock 70 family of proteins; and (vi) the inferred amino acid sequence contains a contiguous 73-amino acid region having 51% identity with the extracellular sperm receptor binding domain in Strongylocentrosus purpuratus (Foltz, K. R., Partin, J. S., and Lennarz, W. J. (1993) Science 259, 1421-1425). The potential involvement of an hsp70 protein in attachment may provide new insight on adherence mechanisms by obligate intracellular pathogens.

Amino Acid Sequence↗
PubMed1993

In-vitro activity of azithromycin on Chlamydia trachomatis infected, polarized human endometrial epithelial cells.

The in-vitro activity of azithromycin on Chlamydia trachomatis infected human endometrial epithelial cells, both primary and transformed cells growing in a polarized and non-polarized orientation, was analyzed. Addition of azithromycin two hours after adsorption inoculation with continued exposure until 72 h gave an MIC90 and MBC90 of 0.063 and 0.5 mg/L, respectively. In addition, the MBC results were more pronounced in infected cells growing in a polarized orientation. Numerous small fluorescent 'spots' (presumed small abnormal inclusions) were visible in the infected cells exposed to MIC concentrations of azithromycin. Immuno-transmission electron microscopy examination revealed intracellular inclusions filled with chlamydial envelope ghosts. Since standard diagnostic antigen detection methods use anti-envelope antibodies, the aberrant envelope-filled inclusions might be interpreted as viable inclusions by fluorescent microscopy and result in high false positive readings. To simulate treatment of an infected patient, azithromycin was added at 18 h to infected cells containing many reticulate bodies and exposure continued for 54 h after which killing of chlamydiae was seen. The use of polarized human cells may offer a more relevant in-vitro model system for examining the efficacy of antimicrobial action.

Azithromycin↗
PubMed1992

Location of the origin of replication for the 7.5-kb Chlamydia trachomatis plasmid.

The hypothetical origin of replication for the 7.5-kb plasmid common to Chlamydia trachomatis is believed to be in a region of the plasmid that contains four 22-bp tandem repeats preceded by an A-T-rich region. To test this hypothesis, replication of plasmid DNA in metabolically active reticulate bodies of the Lymphogranuloma venereum biovar of C. trachomatis was examined by electron microscopy. The results presented show that the origin of replication appears to be near the tandem repeats of pCHL2. In addition, replication of the 7.5-kb plasmid is unidirectional, and the copy number during replication is 7-10. The evidence presented suggests that C. trachomatis has a homologue to the Escherichia coli dnaA gene and that this homologue might be involved in replication of the C. trachomatis 7.5-kb plasmid.

Base Sequence↗