Impedance microbiology--a rapid change for microbiologists.
Explore the source record for details and available documents.
Electric Impedance↗
Biomedical subjects
P Silley
Publications and source records attributed to P Silley.
Harmonic generation in "non-linear" biological systems.
We describe a high performance, low frequency Fourier Transform based spectrum analyser, with design features particularly suited to the harmonic analysis of the non-linear amplitude transfer functions of various biological systems. A previous published method, using general purpose systems to produce reference and signal plus reference "power" spectra, was susceptible to ambiguous interpretation of results. Unlike that design, the present spectrometer derives quantitative complex voltage (amplitude and phase) harmonics of sampled voltage data, maintaining potentially important information. Based on the use of a basic IBM or compatible PC, it features high sensitivity, high speed data processing and large dynamic range, is compact, easy to use, flexible in operation and low in cost. Its precision current signal source eliminates harmonics generated at the drive electrodes from the measurement. Use of the instrument leads us to conclude that, contrary to previous assertions, no repeatable dielectric or conductive non-linearity is exhibited in the bulk cell suspensions tested under the field and frequency conditions reported.
Electric Impedance↗
Harmonic 'signatures' of microorganisms.
The frequency/amplitude effect of various microorganisms exposed to periodic (time varying) electric fields, when proximate to immersed electrodes, has been studied using a novel analytical instrument. The harmonic distribution, in complex signals caused by cells exposed to harmonic free waveforms and occupying part of the electrode/suspension interface volume, was shown to be almost entirely due to the change in the standing interfacial transfer function by the (dielectrically nonlinear) presence of cells. Thus, the characteristic interfacial non-linearity is viewed as variable, being uniquely modulated by the presence of particular cells in the interfacial region. Little can be attributed to bulk (far field) effects. The tendency for subtle (characteristic) signal distortion to occur as a function of particulate (cell or molecular) occupancy of the near electrode interfacial region under controlled current conditions leads to the method of sample characterisation by harmonic (Fourier) analysis. We report here, as a sequel to our original studies (Hutchings et al., 1993; Hutchings and Blake-Coleman, 1993), preliminary results of the harmonic analysis of microbial suspensions under controlled signal conditions using a three-electrode configuration. These data provide three-dimensional graphical representations producing harmonic 'surfaces' for various microorganisms. Thus, cell type differences are characterised by their 'harmonic signature'. The visual distinction provided by these 'surface' forming three-dimensional plots is striking and gives a convincing impression of the ability to identify and enumerate specific microorganisms by acquisition of cell-modulated electrode interfacial Fourier spectra.
Candida↗
Susceptibility testing methods: why use the MIC?
Explore the source record for details and available documents.
Anti-Bacterial Agents↗
Cephalexin in ponies: a preliminary investigation.
The administration of a single dose of the antibacterial agent cephalexin intramuscularly to six ponies at a dose rate of 7 mg/kg was well tolerated. No reactions at the injection site were apparent. It was absorbed rapidly and reached a mean peak plasma concentration of 6.77 micrograms/ml after a mean of 1.41 hours; plasma concentrations above 2.0 and 0.5 micrograms/ml were maintained for 3.8 and 9.8 hours, respectively.
Absorption↗
Model simulation of a single oral dose of cefuroxime axetil and the related in-vitro kill kinetics against four bacterial species.
An in-vitro model was shown to be capable of simulating a cefuroxime serum profile equivalent to that observed in human volunteer studies, following a single dose of 250 mg cefuroxime axetil. The model was used to carry out kill kinetic studies and showed cefuroxime to lyse the four bacterial test strains, time of onset of lysis being related to the sensitivity of the respective organisms. The more sensitive Staphylococcus aureus and Haemophilus influenzae strains were subject to a higher absolute kill and showed no regrowth over the duration of the simulated serum profile. In contrast, Proteus mirabilis and Escherichia coli showed regrowth after 4 and 5 h respectively. The kill kinetic profiles of the respective organisms are discussed in relation to the pharmacokinetic analysis of the cefuroxime serum profile.
Administration, Oral↗
Mode of action of GR69153, a novel catechol-substituted cephalosporin, and its interaction with the tonB-dependent iron transport system.
GR69153 is a novel cephalosporin incorporating a catechol-substituted 7-aminothiazolyl-oxime. The antibiotic is actively transported into gram-negative cells via iron-regulated outer membrane proteins regulated by the tonB product. This transport enhances bactericidal activity most significantly at low concentrations, essentially removing the permeability barrier for antibiotic uptake.
Biological Transport↗
Kill kinetics of the cephalosporin antibiotics cephalexin and cefuroxime against bacteria of veterinary importance.
Kill kinetic studies for two cephalosporin antibiotics, cephalexin and cefuroxime were carried out against veterinary strains of Escherichia coli, Pasteurella multocida, Streptococcus suis, Erysipelothrix rhusiopathiae and a laboratory culture of Staphylococcus aureus. In more than 90 per cent of cases a kill of more than 99 per cent was achieved within four hours of antibiotic treatment at concentrations of 2 or 4 micrograms/ml. Although cefuroxime was effective at lower concentrations than cephalexin the rates of kill of the two antibiotics were comparable. The results are discussed in relation to in vivo dosage regimens.
Cefuroxime↗
Pharmacokinetics of cephalexin in dogs and cats after oral, subcutaneous and intramuscular administration.
A three-way crossover study was carried out in 10 dogs and nine cats to establish the pharmacokinetic parameters of the semi-synthetic cephalosporin antibiotic, cephalexin sodium, when administered orally, subcutaneously or intramuscularly. Ten dogs received a subcutaneous or intramuscular injection of 10 mg/kg bodyweight cephalexin or an oral dose of three 50 mg cephalexin tablets; the peak serum concentrations achieved were 24.9, 31.9 and 18.6 micrograms/ml, respectively, and the times taken to reach these peak levels were 1.2, 0.9 and 1.8 hours. Nine cats received either a subcutaneous or intramuscular dose of 0.25 ml cephalexin suspension (approximately 20 mg/kg bodyweight) or an oral dose of one 50 mg tablet; the peak serum concentrations achieved were 54.0, 61.8 and 18.7 micrograms/ml for the subcutaneous, intramuscular and oral administrations respectively, with times to peak concentrations of 1.1, 0.7 and 2.6 hours.
Administration, Oral↗
Changes in metabolism and cell size of the anaerobic bacterium Selenomonas ruminantium 0078A at the onset of growth in continuous culture.
Initial metabolism of Selenomonas ruminantium 0078A in continuous culture was characterized by a high lactate and low volatile fatty acid production; this was associated with poor growth as determined by bacterial dry weight production, yet individual cells were considerably larger than those of the inoculum. Biomass production increased, cell size decreased and the fermentation pattern reverted to the characteristic low lactate and high volatile fatty acid production after approximately 90 h growth.
Animals↗
Changes in metabolism of the rumen bacterium Streptococcus bovis H13/1 resulting from alteration in dilution rate and glucose supply per unit time.
Streptococcus bovis H13/1 was grown in a glucose-limited chemostat. A concomitant increase in dilution rate and glucose supply per unit time caused both an increase in lactate production per mole of glucose fermented and a linear increase in growth yield over the dilution rate range 0.052 to 0.141/h. When the dilution rate was increased with no change in glucose supply per unit time there was a reduction in lactate production and an increase in that of acetate and ethanol coinciding with a non-linear increase in growth yield. YMaxglu = 38.6 and a maintenance coefficient, ms = 0.290 mmol/l glucose/g cells/h were calculated. The results also suggested an interaction between the formate and CO2 pools.
Acetates↗