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B Duke

Publications and source records attributed to B Duke.

15 recordsLinked to original sources
PubMed2000

In situ tolerance within the central nervous system as a mechanism for preventing autoimmunity.

Multiple sclerosis (MS) is believed to be an autoimmune disease in which autoreactive T cells infiltrate the central nervous system (CNS). Animal models of MS have shown that CNS-specific T cells are present in the peripheral T cell repertoire of healthy mice and cause autoimmune disease only when they are activated by immunization. T cell entry into the CNS is thought to require some form of peripheral activation because the blood-brain barrier prohibits trafficking of this tissue by naive cells. We report here that naive T cells can traffic to the CNS without prior activation. Comparable numbers of T cells are found in the CNS of both healthy recombinase activating gene (Rag)(-/)- T cell receptor (TCR) transgenic mice and nontransgenic mice even when the transgenic TCR is specific for a CNS antigen. Transgenic T cells isolated from the CNS that are specific for non-CNS antigens are phenotypically naive and proliferate robustly to antigenic stimulation in vitro. Strikingly, transgenic T cells isolated from the CNS that are specific for myelin basic protein (MBP) are also primarily phenotypically naive but are unresponsive to antigenic stimulation in vitro. Mononuclear cells from the CNS of MBP TCR transgenic but not nontransgenic mice can suppress the response of peripheral MBP-specific T cells in vitro. These results indicate that naive MBP-specific T cells can traffic to the CNS but do not trigger autoimmunity because they undergo tolerance induction in situ.

Animals↗
PubMed2000

Evaluation of serotype prediction by cpsA-cpsB gene polymorphism in Streptococcus pneumoniae.

New pneumococcal conjugate vaccines covering a limited number of serotypes are likely to come into widespread use over the next few years. It is unknown what effect this will have on the relative importance of different serotypes as causes of pneumococcal infection. Hence, it will be important to monitor serotype prevalence before, during, and after the introduction of new vaccines. We have investigated the ability of a PCR method based on polymorphisms in two genes common to the different capsule loci to predict the serotype of 93 clinical isolates of Streptococcus pneumoniae submitted to the Central Public Health Laboratory in 1997. Of 70 isolates with vaccine serotypes, 65 were predicted to belong to the correct serotype; this number was improved to 69 with the inclusion of two additional patterns to the database. Of 23 isolates with other serotypes, 19 were correctly predicted as non-vaccine serotypes, the discrepancy lying with four isolates of 6A (non-vaccine serotype) that were indistinguishable from isolates of 6B (vaccine serotype). In situations in which culture of the organism is not feasible, this method could potentially be applicable directly to clinical specimens and could be a valuable aid to the surveillance of pneumococcal serotypes.

Bacterial Capsules↗
PubMed1999

OXA-17, a further extended-spectrum variant of OXA-10 beta-lactamase, isolated from Pseudomonas aeruginosa.

Pseudomonas aeruginosa isolates 871 and 873 were isolated at Hacettepe University Hospital in Ankara and were highly resistant to ceftazidime (MIC, 128 microg/ml). Each produced three beta-lactamases, with pIs of 5.3, 6.1, and 7.9. The beta-lactamase with a pI of 5.3 was previously shown to be PER-1 enzyme. The antibiograms of the isolates were not entirely explained by production of PER-1 enzyme, insofar as ceftazidime resistance was incompletely reversed by clavulanate. The enzymes with pIs of 6.1 and 7.9 were therefore investigated. The enzyme with a pI of 6.1 proved to be a novel mutant of OXA-10, which we designated OXA-17, and had asparagine changed to serine at position 73 of the protein. When cloned into Escherichia coli XL1-blue, OXA-17 enzyme conferred greater resistance to cefotaxime, latamoxef, and cefepime than did OXA-10, but it had only a marginal (two- to fourfold) effect on the MIC of ceftazidime. This behavior contrasted with that of previous OXA-10 mutants, specifically OXA-11, -14, and -16, which predominately compromise ceftazidime. Extracted OXA-17 enzyme had relatively greater activity than OXA-10 against oxacillin, cloxacillin, and cefotaxime but, in terms of kcat/Km, it had lower catalytic efficiency against most beta-lactams. The enzyme with a pI of 7.9 was shown by gene sequencing to be OXA-2.

Anti-Bacterial Agents↗
PubMed1998

Conservation of restriction sites in isolates of Streptococcus pneumoniae with diverse restriction fragment patterns.

Separation of large restriction fragments by pulsed-field gel electrophoresis is a commonly used method for epidemiological typing of Streptococcus pneumoniae and many other bacterial species. Information on the genetic changes underlying the restriction fragment polymorphisms that allow discrimination between isolates is scarce. In this study fragments adjacent to ApaI sites in a clinical isolate of S. pneumoniae were cloned and used to probe HindIII and HindIII-plus-ApaI genomic DNA digests from other isolates with very different ApaI fragment patterns. If for a given isolate the HindIII fragment detected by the probe was reduced in size on digestion with ApaI, it was deduced that the ApaI site was conserved in that isolate. The results demonstrate that of six ApaI sites in PN93/908 examined, five were retained in 11 genetically different isolates and one was retained in 2 isolates but lost in 9 others. It was concluded that point mutations at restriction sites are unlikely to account for the restriction fragment length polymorphism observed and that much of the polymorphism may be due to DNA rearrangements, possibly resulting from the insertion or deletion of mobile DNA elements.

DNA Restriction Enzymes↗
PubMed1996

Genetic relatedness within and between serotypes of Streptococcus pneumoniae from the United Kingdom: analysis of multilocus enzyme electrophoresis, pulsed-field gel electrophoresis, and antimicrobial resistance patterns.

A collection of 54 isolates of invasive Streptococcus pneumoniae of serotypes 3 and 14 and serogroups 6, 9, 19, and 23 was investigated. Multilocus enzyme electrophoresis and pulsed-field gel electrophoresis suggested that two clones were represented in the collection, one of serotype 14 isolates, most of which were resistant to erythromycin, and one of serotype 9V isolates, in which resistance to penicillin (MIC, 1 microgram/ml), cefotaxime, and co-trimoxazole was common. Among other isolates there were only a limited correlation between genetic relatedness measured by multilocus enzyme electrophoresis and expression of the same capsule type. However, isolates with highly related pulsed-field gel electrophoresis patterns always shared the same serotype and highly related allele profiles. Calculation of the index of association suggests a freely recombining population structure with epidemic spread of successful clones.

Child↗
PubMed1995

An approach to the identification of the pathogens of bacterial meningitis by the polymerase chain reaction.

A combination of universal and species-specific primers was used to detect and differentiate by nested polymerase chain reaction (PCR) the four species most commonly causing bacterial meningitis. Primers recognising conserved sequences in the 16S and 23S ribosomal RNA genes were employed to amplify the 16S-23S spacer region from Neisseria meningitidis, Haemophilus influenzae (type b), Streptococcus pneumoniae, and Streptococcus agalactiae (group B streptococcus). The sequence of the most abundant spacer product was determined in each case and used to deduce species-specific primers. A nested PCR using universal primers in the first round and a species-specific primer in the second were able to detect and distinguish between the four common pathogens, in the presence of human DNA. Streptococcus pneumoniae DNA was detected in the cerebrospinal fluid of a meningitis patient with negative culture and Gram-stain results.

Base Sequence↗
PubMed1995

Heterogeneity among 16S-23S rRNA intergenic spacers of species within the 'Streptococcus milleri group'.

The 16S-23S rRNA intergenic spacer has been suggested as a suitable region of the bacterial genome from which to derive useful taxonomic information, particularly with regard to identification at the species level. To investigate this approach as an aid to the identification of the three species comprising the 'Streptococcus milleri group' (SMG), the spacers of isolates of Streptococcus intermedius, Streptococcus anginosus and Streptococcus constellatus were amplified by PCR and length polymorphisms determined by agarose gel electrophoresis. Phenotypically atypical isolates which had been identified presumptively as belonging to these three species were also included. Spacers from two representatives of each spacer length found within the three SMG species were sequenced. 16S-23S rRNA intergenic spacer length polymorphisms allowed discrimination between S. anginosus (350 bp or 450 bp amplification product) and S. constellatus (380 bp amplification product), species that are difficult to differentiate phenotypically. S. intermedius (330 bp or 450 bp amplification product) and S. anginosus (350 bp or 450 bp amplification product) were not reliably distinguished by this method but are phenotypically distinct. Sequencing data demonstrated that the spacers had a central region of highly variable length flanked by conserved regions which included a single tRNA(Ala) gene. Polymorphism in the length of the 16S-23S spacer determined by PCR provides a rapid and useful adjunct to strain identification for S. anginosus and S. constellatus, which are not readily differentiated phenotypically.

Base Sequence↗
PubMed1992

Typing of Enterococcus species by DNA restriction fragment analysis.

Enterococci are a frequent cause of hospital-acquired infection, being associated with urinary tract infections, wound sepsis, bacteremia, and endocarditis. The source of infection is usually thought to be endogenous, but some evidence points to cross-infection between patients. A better understanding of the epidemiology of enterococci has been limited by the lack of a good discriminatory typing system. This report describes the application of two DNA-based typing methods to Enterococcus faecalis and Enterococcus faecium: comparison of restriction fragments from total DNA by conventional electrophoresis and comparison of restriction fragments hybridizing to an rRNA gene probe (ribotyping). Comparison of restriction fragments (from SstI digestion) by conventional electrophoresis was simple and highly discriminatory. The results of analysis of blood culture isolates and of repeat isolates from individual patients are reported. Ribotyping (with BscI digestion) was more applicable at the level of species discrimination.

Bacteremia↗
PubMed1992

Epidemiology of Enterococcus faecalis urinary tract infection in a teaching hospital in London, United Kingdom.

Enterococcus faecalis is a frequent cause of urinary tract infection in hospitalized patients. Recent reports have suggested that the organism may frequently be acquired by cross-infection from other patients. In this study, we used total DNA restriction patterns to type 135 urine isolates of E. faecalis from four sets of patients. Isolates were placed into types (all bands identical) and into groups (most bands identical). Most isolates were discriminated by the typing method, and the results suggested that direct cross-infection occurred rarely if at all. However, two groups of clonally related isolates occurred frequently in the urine specimens and also in feces from hospital-associated patients and were often associated with antibiotic resistance. Isolates from these two groups were found less frequently in feces from people not associated with the hospital.

Cluster Analysis↗
PubMed1982

Effects of systemic hypertension on ischemic and nonischemic regional left ventricular function in awake, unsedated dogs after experimental coronary occlusion.

Hypertension and atherosclerotic coronary arterial obstruction frequently coexist in patients. However, the effect of increased aortic pressure on ischemic segmental dysfunction is not well understood. We studied the effects of aortic pressure increases on segmental left ventricular function during myocardial ischemia. Eighty-two dogs instrumented with three to six pairs of pulse-transit piezoelectric crystals were studied in an awake, unsedated state to measure segmental wall thickness. A pneumatic balloon occluder was positioned around the proximal left anterior descending artery (LAD). Thirty-three dogs underwent LAD occlusion and served as normotensive controls (group A). Group B dogs (n = 23) received a 6-hour infusion of phenylephrine (PE) beginning 5 minutes after LAD occlusion to increase aortic diastolic arterial pressure to 120-130 mm Hg; aortic pressure was then allowed to return to normal for the subsequent 18 hours. The eight dogs in group C received a 6-hour infusion of PE, but no coronary arterial occlusion was produced. In group D (n = 12), distal constriction of the thoracic aorta was maintained for 24 hours after LAD occlusion. Regional myocardial blood flow (RMBF) was measured with radioactive microspheres in six conscious dogs and both RMBF and intramyocardial PCO2 were measured in seven open-chest dogs to assess alterations in regional myocardial oxygen supply and demand. Segments of myocardium were arbitrarily grouped according to the amount of net systolic thickening (NET) present 5 minutes after LAD occlusion and before increasing aortic pressure: group 1 retained 67-100+% of control NET, group 2 0-67%, and group 3 less than 0% (paradoxic motion). In dogs receiving PE plus LAD occlusion and in dogs with aortic constriction and LAD occlusion, NET was transiently depressed in groups 1 and 2 compared with the normotensive cohort; 24 hours after occlusion, NET in groups 1, 2 and 3 did not differ significantly from that in the normotensive dogs. Systemic hypertension resulted in a significant increase in endocardial and midwall RMBF and, in seven open-chest dogs, decreased the intramyocardial accumulation of carbon dioxide after LAD occlusion. Increased aortic pressure in dogs without coronary occlusion produced reversible decreases in end-diastolic wall thickness, NET and LV dP/dt. Thus, the production of systemic hypertension with diastolic pressures of 110-120 mm Hg acutely or for 6 hours during evolving canine myocardial infarction does not appear to exert an important deleterious effect on myocardial oxygen supply and demand. However, 24 hours of mildly increased aortic pressure accentuates end-diastolic wall thinning in segments with paradoxic systolic motion and results in a failure of their return to control values at this period.

Animals↗
PubMedDate not supplied

Analysis of locus heterogeneity in Waardenburg syndrome types 1 and 2 using highly informative microsatellite markers.

We performed linkage and locus heterogeneity analyses of Waardenburg syndrome (WS) types 1 and 2 using 9 DNA markers from 2q35-q37, including two highly polymorphic microsatellites very closely linked to the PAX3 candidate gene. None of 5 WS type 2 (WS2) families showed linkage to the PAX3 candidate region. We localized the marker D2S102 to less than 1 cM from PAX3 (lod = 33.7, theta = 0), but a complete absence of crossovers prevented determining whether it maps distal or proximal to PAX3. Study of 14 WS type 1 (WS1) families yielded a maximum lod score of 27.81 at PAX3, theta f = 0.010, theta = 0.007 assuming homogeneity. However, we found significant evidence of locus heterogeneity, with one family initially classified as WS1 unlinked to the PAX3 region. Reevaluation of the clinical features of this family revealed atypical morphology of inner canthi. This produced the appearance of dystopia canthorum and high W-index scores. While our one unlinked WS1 family exhibits atypical canthal morphology, our type 1 families with classic dystopia appear to be homogeneously linked to PAX3. These and other findings identify precautions that need to be addressed before using PAX3-linked markers for diagnostic purposes.

Chromosome Mapping↗