Transferable, plasmid-mediated vanB-type glycopeptide resistance in Enterococcus faecium

An approximately 60-kb transferable, vanB-carrying plasmid has been identified in a clinical Enterococcus faecium strain. A similar plasmid has been observed in an unrelated E. faecium strain, suggesting that plasmid transfer of vanB operons occurs in nature and plays a role in the dissemination of VanB-type resistance among strains of E. faecium.     

Temperature-sensitive neuromuscular transmission in Kv1.1 null mice: role of potassium channels under the myelin sheath in young nerves

In mammalian myelinated nerves, the internodal axon that is normally concealed by the myelin sheath expresses a rich repertoire of K channel subtypes thought to be important in modulating action potential propagation. The function of myelin-covered K channels at transition zones, however, has remained unexplored. Here we show that deleting the voltage-sensitive potassium channel Kv1.1 from mice confers a marked temperature-sensitivity to neuromuscular transmission in postnatal day 14 (P14)-P21 mice. Using immunofluorescence and electrophysiology, we examined contributions of four regions of the peripheral nervous system to the mutant phenotype: the nerve trunk, the myelinated segment preceding the terminal, the presynaptic terminal membrane itself, and the muscle. We conclude that the temperature-sensitive neuromuscular transmission is accounted for solely by a deficiency in Kv1.1 normally concealed in the myelinated segments just preceding the terminal. This paper demonstrates that under certain situations of physiological stress, the functional role of myelin-covered K channels is dramatically enhanced as the transition zone at the neuromuscular junction is approached.     

Impact of chronic cough on quality of life

STUDY DESIGN: The biomechanical influence of in situ setting hydroxyapatite cement was examined for use in pedicle screw revision surgery. Pull-out testing of control and pedicle screws augmented with hydroxyapatite cement was performed in human cadaver vertebrae. OBJECTIVES: To determine the immediate effect of using hydroxyapatite cement to augment revision pedicle screws after failure of the primary pedicle screw fixation. SUMMARY OF BACKGROUND DATA: The potential problems associated with using polymethylmethacrylate to augment revision pedicular instrumentation have prompted the search for other solutions. The introduction of resorbable hydroxyapatite pastes may have provided new biocompatible solutions for pedicle screw revision. METHODS: Ten human cadaver vertebrae were instrumented with 6.0-mm pedicle screws in each pedicle. The screws were loaded to failure in axial tension (pull-out). The failed pedicles then were instrumented with 7.0-mm pedicle screws, either augmented with hydroxyapatite cement or nonaugmented, which also were loaded to failure. Finally, the nonaugmented 7.0-mm screw hole was reinstrumented with a hydroxyapatite cement-augmented, 7.0-mm pedicle screw and loaded to failure. RESULTS: The pull-out strength of the 7.0-mm, hydroxyapatite cement-augmented screws was 325% (P = 2.9 x 10(-5)) of that of the 6.0-mm control screws, whereas the strength of the 7.0-mm nonaugmented screws was only 73% (P = 2.0 x 10(-2)) of that of the 6.0-mm control screws. The 7.0-mm screws augmented with hydroxyapatite cement also were able to salvage 7.0-mm pull-out sites to 384% (P = 6.9E-5) of the pull-out strength of the 7.0-mm nonaugmented screws. CONCLUSIONS: Hydroxyapatite cement may be a mechanically viable alternative to polymethyl methacrylate for augmenting revision pedicular instrumentation and should be considered for future experimental, animal, and clinical testing.     

Screening calcaneal ultrasound and risk factors for osteoporosis among lesbians and heterosexual women

We compared calcaneal ultrasound measurements (speed of sound [SOS], broadband ultrasound attenuation [BUA], and stiffness index [SI]) of lesbian and heterosexual women to examine the medical and lifestyle risk factors for osteoporosis in each group. This was an exploratory, community-based, cross-sectional study. Subjects were mailed food frequency, health, and physical activity questionnaires. Weight, height, and calcaneal ultrasound measurements were taken at one office visit. In communities in southern and eastern Maine, 71 lesbians and 77 heterosexual women between the ages of 30 and 50 with regular menses and in good general health were the subjects. Statistical analysis used t-tests and chi-square tests to evaluate differences between study groups. Linear regression models were used to evaluate risk factors for low calcaneal ultrasound measurements. There were no differences between the lesbian and heterosexual women in age, body mass index (BMI), exercise, calcium intake, alcohol use, or calcaneal ultrasound measurements. There was a positive association between BUA and both BMI and alcohol consumption (p < 0.01). Antidepressant use significantly reduced SOS and SI (p < 0.05). There were no differences in calcaneal ultrasound measurements between lesbian and heterosexual women. BMI was strongly and positively associated with BUA. Antidepressant use in both populations was associated with a significant reduction in calcaneal bone mass. Studies are needed to define the relationship of depression and its treatment to bone mineral density and the future risk of osteoporosis.     

Compartmentation of [14C]glutamate and [14C]glutamine oxidative metabolism in the rat hippocampus as determined by microdialysis

Metabolic compartmentation of amino acid metabolism in brain is exemplified by the differential synthesis of glutamate and glutamine from the identical precursor and by the localization of the enzyme glutamine synthetase in glial cells. In the current study, we determined if the oxidative metabolism of glutamate and glutamine was also compartmentalized. The relative oxidation rates of glutamate and glutamine in the hippocampus of free-moving rats was determined by using microdialysis both to infuse the radioactive substrate and to collect 14CO2 generated during their oxidation. At the end of the oxidation experiment, the radioactive substrate was replaced by artificial CSF, 2 min-fractions were collected, and the specific activities of glutamate and glutamine were determined. Extrapolation of the specific activity back to the time that artificial CSF replaced 14C-amino acids in the microdialysis probe yielded an approximation of the interstitial specific activity during the oxidation. The extrapolated interstitial specific activities for [14C]glutamate and [14C]glutamine were 59 +/- 18 and 2.1 +/- 0.5 dpm/pmol, respectively. The initial infused specific activities for [U-14C]glutamate and [U-14C]glutamine were 408 +/- 8 and 387 +/- 1 dpm/pmol, respectively. The dilution of glutamine was greater than that of glutamate, consistent with the difference in concentrations of these amino acids in the interstitial space. Based on the extrapolated interstitial specific activities, the rate of glutamine oxidation exceeds that of glutamate oxidation by a factor of 5.3. These data indicate compartmentation of either uptake and/or oxidative metabolism of these two amino acids. The presence of [14C]glutamine in the interstitial space when [14C]glutamate was perfused into the brain provided further evidence for the glutamate/glutamine cycle in brain.     

A study of chest radiography with mobile X-ray units

A survey of radiographic technique and estimated entrance surface dose has been carried out for 364 chest radiographs performed with mobile X-ray equipment in the Intensive Therapy Unit (ITU) and 30 wards at Aberdeen Royal Infirmary. Data for these two types of location were compared, as were those for two film/screen systems used on the wards. Image quality assessments were made on sets of radiographs for two patients. Entrance skin doses for chest radiographs performed in the ITU were 50% greater than on the wards with the same film/screen system. The main technique difference was the use of shorter focus-to-skin distances (FSDs) in ITU. Doses with the Kodak Insight system were 20% higher than those using Du Pont Quanta III in similar locations. No correlation was found between image quality and entrance surface dose (ESD). Results from the survey were used to recommend exposure factors for shorter FSDs. A follow-up study revealed a 35-45% reduction in ESD for Kodak Insight and a 20% reduction for Quanta III.     

A new method to estimate parameters of linear compartmental models using artificial neural networks

At present, the preferred tool for parameter estimation in compartmental analysis is an iterative procedure; weighted nonlinear regression. For a large number of applications, observed data can be fitted to sums of exponentials whose parameters are directly related to the rate constants/coefficients of the compartmental models. Since weighted nonlinear regression often has to be repeated for many different data sets, the process of fitting data from compartmental systems can be very time consuming. Furthermore the minimization routine often converges to a local (as opposed to global) minimum. In this paper, we examine the possibility of using artificial neural networks instead of weighted nonlinear regression in order to estimate model parameters. We train simple feed-forward neural networks to produce as outputs the parameter values of a given model when kinetic data are fed to the networks' input layer. The artificial neural networks produce unbiased estimates and are orders of magnitude faster than regression algorithms. At noise levels typical of many real applications, the neural networks are found to produce lower variance estimates than weighted nonlinear regression in the estimation of parameters from mono- and biexponential models. These results are primarily due to the inability of weighted nonlinear regression to converge. These results establish that artificial neural networks are powerful tools for estimating parameters for simple compartmental models.     

Mapping of specific and promiscuous HLA-DR-restricted T-cell epitopes on the Plasmodium falciparum 27-kilodalton sexual stage-specific antigen

We have characterized HLA-DR-restricted T-cell epitopes on the 27-kDa protein (Pfg27), a sexual stage-specific antigen, of the human malaria parasite Plasmodium falciparum in subjects with a history of malaria. Pfg27, expressed early in the sexual stages, is recognized by monoclonal antibodies capable of reducing the infectivity of gametocytes in mosquitoes. By using 16 Pfg27-specific CD4(+)-T-cell clones derived from three donors, seven different T-cell epitopes were identified. Among them, P11 (amino acids 191 to 210 of the Pfg27 sequence, IDVVDSYIIKPIPALPVTPD) was found to contain a previously described binding motif for multiple HLA-DR allotypes. Indeed, P11 was found to be promiscuous in that it could be recognized by T cells in the context of at least five different HLA-DR molecules. The cytokine profile of the clones was mixed. Seven of nine T-cell clones exhibited a Th0-like cytokine profile, producing high levels of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) upon stimulation with specific peptides and mitogens. The other two clones had a Th1-like cytokine profile with high expression of IFN-gamma and no IL-4. Identification of a promiscuous epitope in Pfg27 could play a significant role in the design of a subunit vaccine for suppressing malaria transmission.     

Direction determination in the minus-end-directed kinesin motor ncd

Motor proteins of the kinesin superfamily transport intracellular cargo along microtubules. Although different kinesin proteins share 30-50% amino-acid identity in their motor catalytic cores, some move to the plus end of microtubules whereas others travel in the opposite direction. Crystal structures of the catalytic cores of conventional kinesin (a plus-end-directed motor involved in organelle transport) and ncd (a minus-end-directed motor involved in chromosome segregation) are nearly identical; therefore, the structural basis for their opposite directions of movement is unknown. Here we show that the ncd 'neck' made up of 13 class-specific residues next to the superfamily-conserved catalytic core, is essential for minus-end-directed motility, as mutagenesis of these neck residues reverses the direction of ncd motion. By solving the 2.5 A structure of a functional ncd dimer, we show that the ncd neck (a coiled-coil) differs from the corresponding region in the kinesin neck (an interrupted beta-strand), although both necks interact with similar elements in the catalytic cores. The distinct neck architectures also confer different symmetries to the ncd and kinesin dimers and position these motors with appropriate directional bias on the microtubule.