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Biomedical subjects

G Johnson

Publications and source records attributed to G Johnson.

At least 37 records · Page 2Linked to original sources
PubMed2003

Detection and identification of Bartonella species pathogenic for humans by PCR amplification targeting the riboflavin synthase gene (ribC).

Several Bartonella species have now been implicated as human pathogens. The recovery of these fastidious organisms in the clinical microbiology laboratory remains difficult, and current methods are still relatively insensitive. Thus, the bartonellae are good candidates for detection by PCR. We have developed a PCR assay which uses a single primer pair targeting the riboflavin synthase gene (ribC) and detected six Bartonella species that have been implicated in human disease, B. henselae, B. quintana, B. bacilliformis, B. clarridgeiae, B. elizabethae, and B. vinsonii subsp. berkhoffii. Species identification is achieved simply by restriction enzyme digestion of the amplicon. This PCR assay appears to be specific for the Bartonella genus because it failed to amplify DNA from several other bacterial species.

Bacterial Proteins↗
PubMed2003

Incidence of visual loss in rural southwest Uganda.

BACKGROUND: Surveys have been conducted to measure prevalence of eye disease in Africa, but not of incidence, which is needed to forecast trends. The incidence of visual loss is reported in southwest Uganda. METHODS: A rural population residing in 15 neighbouring villages was followed between 1994-5 (R1) and 1997-8 (R2). Survey staff screened adult residents (13 years or older) for visual acuity using laminated Snellen's E optotype cards at each survey. Those who failed (VA >6/18) were evaluated by an ophthalmic clinical officer and an ophthalmologist. Incidence of visual loss (per 1000 person years (PY)) was calculated among those who had normal vision at R1. RESULTS: 2124 people were studied at both survey rounds (60.9% of those screened at R1); 48% were male. Participants in R1 were older (34.7 versus 31.5 years at R2, p<0.001). Visual loss in R2 occurred in 56 (2.8%) of 1997, yielding a crude incidence rate of 9.9, and an age standardised incidence rate of 13.2, per 1000 PY. Incidence of visual loss increased with age from 1.21 per 1000 PY among people aged 13-34 to 64.2 per 1000 PY in those aged 65 years or older (p for trend >0.001). The six commonest causes of visual loss were: cataract, refractive error, macular degeneration, chorioretinitis, glaucoma, and corneal opacity. If similar rates are assumed for the whole of Uganda, it is estimated that 30 348 people would develop bilateral blindness or bilateral visual impairment, per year. CONCLUSIONS: Cataract and refractive error were the major causes of incident visual loss in south west Uganda. These data are valuable for forecasting and planning eye services.

Adolescent↗
PubMed2002

Detection and characterization of mechanisms of action of aneugenic chemicals.

A comprehensive evaluation of the genotoxic potential of chemicals requires the assessment of the ability to induce gene mutations and structural chromosome (clastogenic activity) and numerical chromosome (aneugenic activity) aberrations. Aneuploidy is a major cause of human reproductive failure and an important contributor to cancer and it is therefore important that any increase in its frequency due to chemical exposures should be recognized and controlled. The in vitro binucleate cell micronucleus assay provides a powerful tool to determine the ability of a chemical to induce chromosome damage. The application of an anti-kinetochore antibody to micronuclei allows their classification into kinetochore-positive and kinetochore-negative, indicating their origin by aneugenic or clastogenic mechanisms, respectively. The availability of chromosome-specific centromere probes allows the analysis of the segregation of chromosomes into the daughter nuclei of binucleate cells to evaluate chromosome non-disjunction. Quantitative relationships between the two major causes of aneuploidy, chromosome loss and non-disjunction, can be determined. The mechanisms leading to chromosome loss and non-disjunction can be investigated by the analysis of morphological and structural changes in the cell division apparatus by the application of specific stains and antibodies for various cell division components. We illustrate such analyses by the demonstration of the interaction of the monomer bisphenol-A with the centrosome of the mitotic spindle and the folic acid antagonist pyrimethamine with the centromeres of chromosomes. Both types of modifications lead to the induction of aneuploidy in exposed cells. Our studies also implicate the products of the p53 and XPD genes in the regulation of the fidelity of chromosome segregation at mitosis.

Aneuploidy↗
PubMed2001

The architecture of a collagen coating on a synthetic polymer influences epithelial adhesion.

The current study sought to identify a collagen coating methodology for application to polymer surfaces that would provide for the development of adhesive structures responsible for the sustained adhesion of corneal epithelial tissue. We compared an uncoated microporous polycarbonate surface and equivalent surfaces coated with either covalently immobilized collagen I or chemically crosslinked collagen I gel in a corneal explant outgrowth assay over 21 days. Electron microscopy was used to examine the formation of hemidesmosomes, basal lamina, and anchoring fibrils at the tissue-polymer interface. The crosslinked collagen gel preparation supported the overlying epithelial tissue across the pore openings and allowed for the formation of identifiable basal lamina, hemidesmosomes, and anchoring fibrils between the epithelial tissue and the polymer surface. Hemidesmosomal plaque, but no basal lamina or anchoring fibril formation, occurred on the uncoated surface or on that coated with covalently immobilized collagen I. We propose that the collagen matrix provided by the crosslinked collagen gel was reorganized by the epithelial tissue and that this, combined with the secretion of ECM molecules, served to limit the diffusion of basement membrane components, which permitted an increase in the local concentration of these molecules, which favored the assembly of epithelial adhesive structures.

Animals↗
PubMed2001

Acute childhood encephalitis and Mycoplasma pneumoniae.

In a prospective 5-year study of children with acute encephalitis, evidence of Mycoplasma pneumoniae infection was demonstrated in 50 (31%) of 159 children. In 11 (6.9%) of these patients, M. pneumoniae was determined to be the probable cause of encephalitis on the basis of its detection in cerebrospinal fluid (CSF) by polymerase chain reaction (PCR) or by positive results of serologic tests for M. pneumoniae and detection of the organism in the throat by PCR. CSF PCR positivity correlated with a shorter prodromal illness (P=.015) and lack of respiratory symptoms (P=.06). Long-term neurologic sequelae occurred in 64% of probable cases. Thirty children (18.9%) who were seropositive for M. pneumoniae but did not have the organism detected by culture or PCR had convincing evidence implicating other organisms as the cause of encephalitis, suggesting that current serologic assays for M. pneumoniae are not sufficiently specific to establish a diagnosis of M. pneumoniae encephalitis.

Acute Disease↗
PubMed2001

Analysis of human immunodeficiency virus type 1 drug resistance in children receiving nucleoside analogue reverse-transcriptase inhibitors plus nevirapine, nelfinavir, or ritonavir (Pediatric AIDS Clinical Trials Group 377).

In Pediatric AIDS Clinical Trials Group 377, antiretroviral therapy-experienced children were randomized to 4 treatment arms that included different combinations of stavudine, lamivudine (3TC), nevirapine (Nvp), nelfinavir (Nfv), and ritonavir (Rtv). Previous treatment with zidovudine (Zdv), didanosine (ddI), or zalcitabine (ddC) was acceptable. Drug resistance mutations were assessed before study treatment (baseline) and at virologic failure. Zdv, ddI, and ddC mutations were detected frequently at baseline but were not associated with virologic failure. Children with drug resistance mutations at baseline had greater reductions in virus load over time than did children who did not. Nvp and 3TC mutations were detected frequently at virologic failure, and Nvp mutations were more common among children receiving 3-drug versus 4-drug Nvp-containing regimens. Children who were maintained on their study regimen after virologic failure accumulated additional Nvp and 3TC mutations plus Rtv and Nfv mutations. However, Rtv and Nfv mutations were detected at unexpectedly low rates.

Adolescent↗
PubMed2001

Isolation and identification of infectious salmon anaemia virus (ISAV) from Coho salmon in Chile.

The isolation of infectious salmon anaemia virus (ISAV) from asymptomatic wild fish species including wild salmon, sea trout and eel established that wild fish can be a reservoir of ISAV for farmed Atlantic salmon. This report characterizes the biological properties of ISAV isolated from a disease outbreak in farmed Coho salmon in Chile and compares it with ISAV isolated from farmed Atlantic salmon in Canada and Europe. The virus that was isolated from Coho salmon tissues was initially detected with ISAV-specific RT-PCR (reverse transcription-polymerase chain reaction). The ability of the virus to grow in cell culture was poor, as cytopathology was not always conspicuous and isolation required passage in the presence of trypsin. Virus replication in cell culture was detected by RT-PCR and IFAT (indirect fluorescent antibody test), and the virus morphology was confirmed by positive staining electron microscopy. Further analysis of the Chilean virus revealed similarities to Canadian ISAV isolates in their ability to grow in the CHSE-214 cell line and in viral protein profile. Sequence analysis of genome segment 2, which encodes the viral RNA polymerase PB1, and segment 8, which encodes the nonstructural proteins NS1 and NS2, showed the Chilean virus to be very similar to Canadian strains of ISAV. This high sequence similarity of ISAV strains of geographically distinct origins illustrates the highly conserved nature of ISAV proteins PB1, NS1 and NS2 of ISAV. It is noteworthy that ISAV was associated with disease outbreaks in farmed Coho salmon in Chile without corresponding clinical disease in farmed Atlantic salmon. This outbreak, which produced high mortality in Coho salmon due to ISAV, is unique and may represent the introduction of the virus to a native wild fish population or a new strain of ISAV.

Animals↗
PubMed2001

White matter abnormalities in HIV-1 infection: a diffusion tensor imaging study.

Diffuse white matter pallor is the most frequent neuropathological feature of HIV-1 infection and has been found to be particularly prominent in the advanced stages of the disease. The purpose of this study was to determine whether subtle white matter abnormalities can be detected in medically stable, ambulatory HIV-1 patients, in vivo, using diffusion tensor imaging (DTI). DTI is a magnetic resonance imaging (MRI) technique that is uniquely suited for the study of subtle white matter abnormalities. DTI was performed in six HIV-1 patients and nine controls. The two groups were similar in age. Abnormal fractional anisotropy was found in the white matter of the frontal lobes and internal capsules of the HIV-1 patients, in the absence of group differences in mean diffusivity, computed proton density, and computed T2. DTI may be more sensitive than conventional MRI methods for detecting subtle white matter disruptions in HIV-1 disease.

Acquired Immunodeficiency Syndrome↗
PubMed2001

[CDT a valuable marker of overconsumption of alcohol. Guidelines for its use in connection with automobile driver examination].

According to the medical regulations for obtaining a driver's license in Sweden, alcohol abuse/dependency constitutes sufficient grounds for denial. In the case of a conviction for gross drunk driving, it is incumbent upon the offender to present a medical certificate verifying a "sober lifestyle". Biological markers are important tools for proving alcohol abuse in each of these contexts. In this connection, CDT analyses play a key role through their high marked specificity for increased alcohol consumption. The authors have agreed upon the guidelines as presented in this paper for determining sobriety as it pertains to possession of a driver's license. Special emphasis is placed on how CDT tests should be used and interpreted in such contexts, as well as their value as evidence in the case of increased CDT levels.

Alcohol Drinking↗
PubMed2001

Kabat Database and its applications: future directions.

The Kabat Database was initially started in 1970 to determine the combining site of antibodies based on the available amino acid sequences. The precise delineation of complementarity determining regions (CDR) of both light and heavy chains provides the first example of how properly aligned sequences can be used to derive structural and functional information of biological macromolecules. This knowledge has subsequently been applied to the construction of artificial antibodies with prescribed specificities, and to many other studies. The Kabat database now includes nucleotide sequences, sequences of T cell receptors for antigens (TCR), major histocompatibility complex (MHC) class I and II molecules, and other proteins of immunological interest. While new sequences are continually added into this database, we have undertaken the task of developing more analytical methods to study the information content of this collection of aligned sequences. New examples of analysis will be illustrated on a yearly basis. The Kabat Database and its applications are freely available at http://immuno.bme.nwu.edu.

Animals↗
PubMed2001

Sensitivity and performance time in MRI dephasing artifact reduction methods.

Although shimming can improve static field inhomogeneity, local field imperfections induced by tissue susceptibility differences cannot be completely corrected and can cause substantial signal loss in gradient echo images through intravoxel dephasing. Dephasing increases with voxel size so that one simple method of reducing the effect is to use thin slices. Signal-to-noise ratio (SNR) can then be increased by averaging over the subslices to form the final, thick slice. We call this method subslice averaging or SSAVE. Alternatively, a range of different amplitude slice select rephase gradients can be used to compensate for different susceptibility induced gradient offsets. The final image can then be formed by combining individual images in a variety of ways: summation, summation of the squares of the images, forming the maximum intensity projection of the image set, and Fourier transformation followed by summation. We show here that, contrary to previous claims, the theoretical sensitivity (i.e., SNR divided by the square root of the imaging time) of all these alternative methods is very similar. However, performance time (i.e., minimum-imaging time) of the simplest method, SSAVE, is much shorter than that of alternatives. This is confirmed experimentally on phantoms and anesthetized mice. Magn Reson Med 45:470-476, 2001.

Animals↗
PubMed2001

Optimal dose of Gd-DTPA in dynamic MR studies.

The relationship between the administered dose d of Gd-DTPA and the accuracy of measurements of the glomerular filtration rate G and the cardiac output O was investigated. For a wide range of values the concentration of Gd-DTPA can be uniquely derived from MR signals and precontrast longitudinal relaxation time. Fixed and random errors in these measured variables were analyzed. Depending on noise level and the level of renal function, errors in G reach a minimum for d = 1.4-2.8 mmol. Random errors in G are relatively insensitive to d as long as d > 1.5 mmol. These results establish the feasibility of dynamic MR measurements using doses of Gd-DTPA that are several times lower than current standards.

Cardiac Output↗
PubMed2001

Analysis of FIGO Stage IIIc endometrial cancer patients.

OBJECTIVE: The aim of this study was to analyze FIGO Stage IIIc endometrial cancer (EC) patients to better define clinicopathologic associations, patterns of failure, and survival. METHODS: Charts were abstracted from EC patients with lymph node metastasis from 1989 to 1998. Data on clinicopathologic variables, adjuvant treatment, site of first recurrence, and survival were collected. Associations between variables were tested by chi(2) and Wilcoxon rank sums. Survival analyses were performed by the Kaplan-Meier method, and multiple regression analysis was done by the Cox proportional hazards model. RESULTS: From 607 EC patients evaluated, 47 (8%) were identified with FIGO Stage IIIc disease. All 47 underwent hysterectomy and pelvic lymph node (PLN) sampling, and 42/47 had para-aortic lymph node (PALN) sampling. Stage IIIc disease was defined by positive PLN alone in 38%, positive PLN and PALN in 41%, and positive PALN alone in 17%. Twelve of 47 also had positive peritoneal cytology and/or adnexal metastases. Grade III tumors were present in 56% and >50% myometrial invasion in 61%. No association between depth of invasion (DOI) and grade was seen, however. Nearly 1/3 of cases had papillary serous or clear cell histology. Postoperative adjuvant treatment included whole abdominal radiation (36%), pelvic radiation with (19%) and without (17%) extended field, chemotherapy (17%), and oral progestins (11%). The 3-year and 5-year survival estimates for all patients were 77 and 65%, respectively. At a median follow-up of 37 months, 5 patients are alive with disease, and 10 are dead of disease. A distant site of first recurrence was most common (21%), followed by pelvic failure (9%). Only 1 patient has had an abdominal recurrence. Univariate predictors of survival included age, DOI, and extranodal disease, but not grade, histology, or PALN involvement. For the 12 patients with nodal disease and positive cytology and/or adnexa, 3-year survival was 39% versus 93% for those patients without evidence of extranodal disease. In a multivariate analysis only DOI was an independent predictor of survival (P = 0.03). CONCLUSIONS: Once lymph node involvement occurs, the importance of additional extranodal disease increases. Consideration of substaging Stage IIIc patients based on positive adnexa or cytology is supported by the data. The extent which adjuvant treatments contributed to the 77% 3-year survival remains to be defined. The patterns of failure suggest a possible role for combined modalities in future treatments.

Adult↗
PubMed2001

Endoscopic prosthesis augmentation of the lower esophageal sphincter in swine.

HYPOTHESIS: Endoscopically delivered prostheses are safe, durable, and may augment a defective lower esophageal sphincter (LES). METHODS: Pigs were studied as normal-LES or LES-weakened animals. A novel endoscopic delivery system was developed in order to place multiple hydrogel prostheses into the LES submucosa. Histopathology sections evaluated ultimate durability and the relationship of the prostheses to esophageal anatomy. RESULTS: Overall, 97% of 179 prosthesis delivery attempts were successful. LES-weakened animals had LES pressures return to normal or supranormal values at 2 weeks and 2 months after prosthesis augmentation. Weakened gastric yield pressures improved to normal values at 2 weeks after prosthesis augmentation. The thickness of the muscular layers and the mucosal integrity of the esophagus was unaffected by the retained prostheses. CONCLUSIONS: Endoscopically delivered hydrogel prostheses are safe and durable. These prostheses can successfully augment a defective sphincter without recognizable damage to the esophagus.

Animals↗
PubMed2001

Association of the HNK-1 epitope with the detergent-soluble G4 isoform of acetylcholinesterase from human neuroblastoma cells.

The HNK-1 carbohydrate epitope is expressed in neural and natural killer cells and is a mediator of cell adhesion. It is well documented that acetylcholinesterase has a secondary function in cell adhesion and differentiation. The presence of HNK-1 on isoforms of Torpedo and Electrophorus acetylcholinesterase, as well as isoforms from the bovine central nervous system has been described. In this paper, we have investigated the association of the epitope with acetylcholinesterase from human neuroblastoma cells. Acetylcholinesterase was extracted, with or without detergent, purified on immunoaffinity columns and the isoforms separated by sucrose density gradient sedimentation. Secreted acetylcholinesterase, from spent serum-free culture medium, was similarly treated. The presence of the HNK-1 epitope was determined by ELISA using the anti-HNK-1 and Elec 39 monoclonal antibodies. The epitope was found to be associated with the detergent-soluble G4 isoform, but not with the hydrophilic G1 nor the secreted hydrophilic G4 isoforms. Likewise, no HNK-1 was observed associated with human erythrocyte acetylcholinesterase. These results indicate that acetylcholinesterase-G4, anchored in the extracellular membrane, is capable of mediating cell-substrate adhesion through HNK-1.

Acetylcholinesterase↗
PubMed2001

Establishing an employee baseline purified protein derivative status in the division of immigration health Service Processing Centers.

While the incidence of reportable tuberculosis in United States born persons declined, the number of cases among foreign-born persons increased by 6 percent in 1998. The Immigration and Naturalization Service (INS) processes about 95,000 undocumented aliens annually from countries with a high prevalence of tuberculosis. An effort was made to establish a baseline Purified Protein Derivative (PPD) status of employees of the Division of Immigration Health (DIH) and INS, Services Processing Centers (SPC). This was achieved through a special operation (project) of a one time, two-step, mass PPD testing of all SPC employees on all eleven sites in the United States and Puerto Rico. A reading of > 10mm was considered positive. The operation was optional and open to all SPC employees. Exclusion criteria for the study included a history of PPD skin testing within six months of the operation, past history of positive PPD test and past history of tuberculosis. Preliminary results from El Paso SPC, Texas, which is the largest SPC, showed that of the 148 employees which were tested (67 percent of all employees), 17 (11 percent) were PPD positive. Security officers constituted 100 percent of all positive cases. Eighty-one percent of the employees at El Paso are security officers, eighty-seven percent of whom participated in the study. Only 20 (23 percent) of administrative staff participated in the study. Results from El Paso are suggestive of differences in the pattern PPD positivity among SPC employees. The complete results of the study should provide sound evidence for formulating appropriate policies for establishing an effective employee tuberculosis prevention and surveillance program in the Service Processing Centers.

Emigration and Immigration↗