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Biomedical subjects

H J Spencer

Publications and source records attributed to H J Spencer.

At least 19 recordsLinked to original sources
PubMed1989

Evaluation of four newer antimicrobial agents in the Avantage susceptibility test system.

Antimicrobial elution disks containing amoxicillin-clavulanic acid (Augmentin), cefotetan, ciprofloxacin, or norfloxacin were tested in the Avantage automated susceptibility test system. Performance was compared against an agar diffusion procedure in a three-site collaborative study. Results of 1,500 comparison with amoxicillin-clavulanic acid showed a full accord (agreement of both systems) of 93.6% and an essential accord (agreement excluding minor discrepancies) of 97.6%. Results for cefotetan showed a full accord of 95.1% and an essential accord of 98.3% by the two methods. Results for both ciprofloxacin and norfloxacin were in full accord for more than 98% of tests with gram-negative bacilli and staphylococci, but tests with enterococci gave 38 and 26.1% minor discrepancies (the result of one method was resistant or susceptible and the result of the other method was intermediate), respectively. The results indicated that the Avantage test system is accurate and reliable and provides appropriate determination of bacterial susceptibility with the four antibiotics tested.

Amoxicillin↗
PubMed1982

A microvolume molecular filter.

A microvolume polymer membrane filter based on Amicon hollow fibers in described which permits separation of low molecular weight compounds from proteins, and can be used for desalting volumes of 100 microliter or less, or to separate cellular protein debris from perfusates during release studies. The filter has the advantage of being reusable and having almost no void volume.

Animals↗
PubMed1981

Mass spectographic analysis of stimulated release of endogenous amino acids from rat hippocampal slices.

Amino acids released from in vitro rat hippocampal slices following stimulation of the Schaffer's collateral pathway, were collected by micro-perfusion and analysed by chemical ionization mass spectrometry, with isotope ratiodetermination as the quantitative technique, through the use of stable, isotopically labeled internal standards. Stimulation at 10 pulses/sec resulted in a doubling of the release of aspartic acid over the resting level and about a 60% increase in glutamate release, which is in essential agreement with studies utilizing K+ depolarization-evoked release from slices.

Amino Acids↗
PubMed1981

An automatic, optically isolated, biphasic constant current stimulator adapter for artefact suppression.

A stimulator adapter is described that automatically generates true biphasic constant current pulses from the single pulse output of a standard stimulator. Variations in the width or amplitude of the driving pulse are automatically duplicated in the biphasic pulses generated, permitting great ease of control of stimulating parameters. The device is simple, small in size and has a low current drain, permitting battery operation.

Electric Stimulation↗
PubMed1980

Clinical laboratory evaluation of the Abbott MS-2 automated antimicrobial susceptibility testing system: report of a collaborative study.

The MS-2 system (Abbott Diagnostics, Division of Abbott Laboratories, Dallas, Tex.) was evaluated for its efficacy in determining the susceptibilities of both clinical and selected challenge (nonfastidious, facultative, and aerobic) isolates. The MS-2 results were compared with standard Kirby-Bauer disk diffusion and microdilution results by using fresh clinical isolates. For gram-positive isolates other than enterococci, overall agreement between MS-2 and reference results was 93 to 98%. With enterococci, MS-2 agreement with disk diffusion was 68% but with microdilution was 86% (agreement between disk diffusion and microdilution was 73%). The main discrepancies with enterococci were with cephalothin, penicillin, gentamicin, and kanamycin. With clinical gram-negative isolates, the overall agreement was 91 to 93%, with most discrepancies occurring with Enterobacter spp. and beta-lactam antibiotics (MS-2 versus disk diffusion, 84%; MS-2 versus microdilution, 84%; disk diffusion versus microdilution, 87%) and with Serratia spp. and colistin (false-susceptible results). The agreement of MS-2 results with established reference antibiograms of a special collection of challenge strains was 91 to 97% for the gram-positive cocci and 86 to 98% for the gram-negative strains. (With Enterobacter spp., agreement was 86%, but was greater than 90% for all other organism groups.) Of the 98 finite MS-2 minimum inhibitory concentrations (MICs) that could be directly compared with microdilution MICs, 77 (79%) were within +/- 1 well of the geometric mean microdilution MIC. MS-2 analysis time ranged from 2.8 to 6.5 h (mean, 4.2 h). On the basis of these results, we conclude that the MS-2 can be expected to yield rapid and accurate results with most nonfastidious, facultative, and aerobic pathogens.

Anti-Bacterial Agents↗
PubMed1976

GDEE antagonism of iontophoretic amino acid excitations in the intact hippocampus and in the hippocampal slice preparation.

Glutamic acid diethylester (GDEE) reversibly antagonized excitations produced by glutamate and aspartate but not those produced by acetylcholine when applied iontophoretically to rat CA1 hippocampal neurons in penthrane (methoxyfluorane) anesthetized rats and to CA1 neurons in in vitro slice preparations. GDEE did not appear to differentiate between the excitations produced by glutamate aspartate and appeared to be a more potent antagonist than has previously been reported. CA1 cells were remarkably sensitive to acetylcholine; 5-50 nA being sufficient to produce marked amino acid-like excitations, which were unrelated to the pH of the acetylcholine. The nature of the responses to applied substances was virtually identical between the intact animal and the in vitro slice preparation. A description of the in vitro technique is given as an Appendix.

Acetylcholine↗
PubMed1976

Antagonism of cortical excitation of striatal neurons by glutamic acid diethyl ester: evidence for glutamic acid as an excitatory transmitter in the rat striatum.

Rat striatal cells that were excited by cortical stimulation were found to respond to cortical stimulation with an average latency of 12 msec. Each response consisted of a variable number of spikes with, on the average, a less than 1:1 relationship between the stimulus and the number of spikes generated. Iontophoretic application of glutamic acid diethyl ester (GDEE), a substance reported to be a glutamate antagonist, at currents of +50 to +125 nA in the vicinity of neurons exicted by cortical stimulation, almost totally suppressed the excitation in 90% of the cells, and this suppression was fully reversible. All cells were excited by glutamate. GDEE also suppressed neuronal excitation produced by iontophoretic aspartate, glutamate and DL-homocysteic acid. It is concluded from this study that an excitatory amino acid, either aspartic or glutamic, may function as the transmitter in the corticostriate projection.

Animals↗
PubMed1975

Enhancement of immunity against murine syngeneic tumors by a fraction extracted from non-pathogenic mycobacteria.

The data reported here demonstrate that a preparation extracted from nonpathogenic mycobacteria such as Mycobacterium smegmatis and hereafter referred to as interphase material protected mice against Ehrlich ascitic carcinoma, L-1210 leukemia, and another syngeneic lymphoid leukemia. Furthermore, mice treated by this preparation were much less susceptible to endotoxins than when stimulated by BCG (bacillus Calmette-Guerin) or M. smegmatis cells. Moreover, guinea pigs treated by interphase material administered in Freund's incomplete adjuvant showed an increased immune response, yet their sensitivity to tuberculin was much weaker than that of controls sensitized with Freund's complete adjuvant. Finally, resistance to Columbia SK virus infection could be demonstrated when interphase material was administered to mice prior to virus challenge.

Adjuvants, Immunologic↗