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J G O'Neill

Publications and source records attributed to J G O'Neill.

16 recordsLinked to original sources
PubMed1999

Evaluation of a dielectrophoretic bacterial counting technique.

Dielectrophoresis, an electrokinetic migration of particles, can occur in non-uniform alternating electric fields and is dependent upon the dielectric nature of the cells and their suspending medium. An enumeration system utilising this phenomenon is described, which has the potential to count particles selectively, including different bacterial or eukaryotic cell species and even sub-populations of different cell viability states or sizes. Relationships were observed between suspension concentrations and the extent of dielectrophoretic (DEP) collection for polystyrene latex beads, pure bacterial samples and mixtures of bacterial species including Escherichia coli, Serratia marcescens, Pseudomonas aeruginosa and Bacillus subtilis. A similar relationship was utilised for polystyrene latex as a calibration line to enable the concentration of particles in a suspension to be determined according to the level of DEP collection. The particle concentration of an unknown test sample was found to lie within the predicted concentration range determined on the basis of DEP collection. In addition, the predicted limits were found only to deviate between -6.2 and +6.9% from the mean particle concentration.

Colony Count, Microbial↗
PubMed1998

Bacterial loss from biofilms exposed to free chlorine.

Previous studies have demonstrated the increased resistance of biofilm bacteria to biocides when compared with freely suspended planktonic cells, but there have been few investigations of sloughing and losses from biofilms in response to biocide activity. A model biofilm system was used to demonstrate that the loss of sloughed bacteria (including Escherichia coli as a pathogen indicator organism) from actively growing biofilm reached levels of 10(6)-10(7) CFU ml-1 of eluted medium. The sloughing response was examined in response to a range of free chlorine concentrations from 0.6 to 5.0 mg l-1. While chlorine treatment greatly reduced bacterial sloughing, significant bacterial loss into the planktonic phase still occurred with free chlorine concentrations below 3.0 mg l-1, indicating active growth and sloughing of biofilm organisms. Exposure of the biofilm to higher levels of free chlorine resulted in inhibition of bacterial loss, though biocide removal was accompanied by a rapid, almost immediate, recovery of sloughing ability. This work demonstrates the endurance and speed of biofilm recovery upon quenching of chlorine residuals, highlighting a potentially significant public health risk from biofilm recovery and the sloughing of pathogenic organisms associated with the biofilm.

Actinomycetaceae↗
PubMed1997

Measurement of the dielectrophoretic enrichment of yeast on grid electrodes using image analysis.

Dielectrophoresis using grid electrode structures offers many advantages for the abstraction and enrichment of cells in analytical microbiology. Modifications to the quantification method of a grid-based dielectrophoresis system are described, utilizing a more rapid and efficient image analysis technique. The grid electrode arrangement enabled dielectrophoretic enrichment of Saccharomyces cerevisiae, resulting in between 36.2 and 46.1% concentration of cells (by a single pass), relative to an identical control sample suspension analysed without an applied electric field. These enrichment factors compare favourably with previously obtained data using alternative measurement techniques. In addition, the image analysis technique is considerably less labour intensive and enables the continuous detection of cellular concentration and dielectrophoretic behaviour. Utilizing differences in frequency dependent cell responses, the system described could be suitable for highly selective pre-enrichment or cell separation on a large scale. Dielectrophoretic techniques, including enrichment, viable cell analysis and assessment of low microbial concentrations, could enhance or replace many existing methods for the analysis of micro-organisms and other cells.

Electrodes↗
PubMed1996

Dose-dependent dielectrophoretic response of Cryptosporidium oocysts treated with ozone.

Dielectrophoresis, the motion of particles in non-uniform electric field, was investigated as a technology with the potential for rapid analysis of ozonated Cryptosporidium parvum oocysts. The ratio of dielectrophoretic collection at two key frequencies (100 kHz and 10 MHz) was determined to compare the effect of ozonation at various dosages. A relationship was found between this ratio and the in vitro excystation value obtained at the end of the experiments. The magnitude of the ratio changed in a non-linear manner with increasing ozone dose. The results are consistent with a decrease in oocyst internal conductivity as supported by the predictions of a mathematical model for the dielectrophoresis of two-shell spherical particles.

Animals↗
PubMed1989

Ontogeny of the lymphoid organs in an Antarctic teleost, Harpagifer antarcticus (Notothenioidei: Perciformes).

The effect of an evolutionary adaptation to low environmental temperature on the development of lymphoid organs was examined in Harpagifer antarcticus from Signy Island (South Orkney Islands; 60 degrees 43'S, 45 degrees 38'W). Thymus, pronephric kidney and spleen were typical, both in position and structural development, of those observed in warmer-water teleosts. The pronephric kidney was the first organ to be infiltrated by leucocytes, at 1 h post-hatch, though the infiltration of the thymic epithelia and the development of the splenic anlage were not observed until 4 weeks post-hatch. Full development of the lymphoid organs was not achieved until the juvenile stage. Although an increased infiltration of the thymus, by subepithelial connective tissues and epithelial mucous cells, occurred in the juvenile and adult stages, there was no evidence of an advanced stage of thymic regression or involution in the adult Harpagifer. Thus, a suppressive influence of the low temperature environment, on the onset and degree of lymphoid organ development and thymic involution, was indicated in this species.

Acclimatization↗
PubMed1981

Morphology of the veins draining the coronary sinus of the dog.

The morphology of the superficial cardiac veins draining the coronary sinus was investigated in 47 normal adult dogs, using the injection-corrosion-fluorescence technique. The veins pertaining to the left coronary territory all drain directly to the coronary sinus and include the following vessels: the great coronary vein and its tributaries, the left posterior atrial and ventricular veins. The veins pertaining to the right coronary territory include the posterior interventricular vein and the small cardiac vein. A comparison with the human pattern was made, particularly regarding the number of interventricular septal branches and it was suggested that such a reduction in number in the dog could be due to a take-over from the Thebesian veins in the venous drainage of the interventricular septum.

Animals↗
PubMed1980

Blood clearance of MS2 bacteriophage in Salmo trutta: a paradoxon.

A primary challenge of MS2 bacteriophage was cleared from the blood of the teleost Salmo trutta within 2.5 days. In contrast the clearance of a 2nd challenge required an extra 3.5 days and the induction of the secondary antibody response was delayed, though immune memory was observed later.

Animals↗
PubMed1976

Acetone production by methylobacteria.

An accumulation of acetone was observed during the metabolism of ethane and products of ethane oxidation by washed suspensions of Methylosinus trichosporium OB3B. This strain possessed an acetoacetate decarboxylase and 3-hydroxybutyrate dehydrogenase, and a decline in poly-beta-hydroxybutyric acid occurred under the same conditions as acetone formation. A pathway of acetone production from poly-beta-hydroxybutyric acid via 3-hydroxybutyrate and acetoacetate was suggested.

Acetoacetates↗
PubMed1976

Substrate specificity of the L-serine O-sulphate degrading activities of Pseudomonas FR.

1. Two enzyme systems obtained from Pseudomonas FR capable of catalysing the alphabeta-elimination of L-serine O-sulphate exhibit a wide range of substrate specificity. Greatest activity was exhibited towards beta-substituted serine and cysteine derivatives. Enzyme A shows a marked preference for the L-isomeric form and enzyme B shows a preference for D-isomers. 2. The alternative activities were shown to be properties of the same enzyme by inhibition properties and heat denaturation experiments. 3. The assay of enzyme A by a number of alternative substrates at various stages during its purification confirmed the multi-substrate specificity of the system. 4. Growth of Pseudomonas FR on S-methyl-L-cysteine as the sole carbon source also resulted in the induction of enzyme B. Growth patterns and levels of induced enzyme were similar to those obtained when L-serine O-sulphate was employed in comparable circumstances.

Isoenzymes↗
PubMed1976

An electrolytic method for determining oxygen dissociation curves using small blood samples: the effect of temperature on trout and human blood.

1. A detailed account is given of an electrolytic method for determining the oxygen dissociation curve of fish blood using a single sample of 50-100 mul for the whole curve. The accuracy and some of the problems arising from its uses are discussed. 2. Oxygen dissociation curves have been determined for trout blood and human blood at temperatures of 15 and 37 degrees C. The relationship between P50 and temperature is similar to that obtained using other methods. Absolute values of P50 are generally lower than those obtained by other methods, especially in the case of fish blood. 3. The effect of PCO2 and pH on the oxygen dissociation curve of trout blood is tested and it is shown that PCO2 has a more marked effect than pH when the other factor is maintained at a constant level. The Bohr factor (delta log P50/delta pH) appears to be approximately the same and independent of the PCO2. 4. The P50 of ray blood determined from fish during and after an operation showed an increased Bohr factor.

Animals↗
PubMed1975

Morphological study on the thebesian veins of the right cavities of the heart in the dog.

The authors studied 48 dog hearts, using the injection-corrosion-fluorescence method to study the topography of thebesian veins in all the walls of the cardiac cavities. The thebesian veins are small, situated deep in the myocardium, opening after a short course into the cardiac cavities, by small openings with diameters in general not exceeding 1 mm, known 'foraminula'. They have a centripetal course, while every other vein in the heart has a centrifugal one, to reach the subepicardial zone. In the heart of the dog five types of thebesian veins were served: arboriform, sinuous, brush-like, canaliculated and stellate. The thebesian veins are almost regularly found in every wall of the cardiac cavities. The authors also observed that they predominated in the right ventricle (81.24%) and in the right atrium (77.43%).

Animals↗
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Community-Institutional Relations↗