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Biomedical subjects

D W Gregory

Publications and source records attributed to D W Gregory.

At least 19 recordsLinked to original sources
PubMed1995

Matrix damage and chondrocyte viability following a single impact load on articular cartilage.

An impact load was applied to full-depth circular samples of articular cartilage in vitro and the effects of impact energy and velocity on matrix integrity and chondrocyte viability were studied. Following a severe impact, calculated to correspond to the energy density over the cartilage surface that might be expected in a man jumping off a 1-m-high wall, the tissue was grossly disrupted. It became elliptical, fissured, and flattened. Cartilage samples remaining attached to the underlying bone showed less damage at similar drop masses and heights. Chondrocyte viability was found to decrease linearly with increasing impact energy. Cartilage biopsies maintained in culture for up to 15 days following impact gained mass over the first 3 days which they did not subsequently lose. The gain in mass increased with the severity of impact and was due to an increased hydration of the tissue. Scanning electron microscopy and light microscopy showed fissures penetrating the tissue but which were never found to pass through the full depth. They were commonly oriented at about 45 degrees to the plane of the surface and gave the appearance of being deflected parallel to the surface on reaching the transition zone. This produced a "delaminating" effect where the surface zone was separating from the deep zone.

Animals↗
PubMed1995

Intraocular deposition of metallic fragments during phacoemulsification: possible causes and effects.

We undertook a prospective slit lamp examination of 56 eyes which had undergone routine phacoemulsification, in order to determine the incidence of metallic intraocular foreign bodies. Characteristic small reflective particles were noted in 86%, with a mean of 5.1 particles per affected eye. No accompanying clinical problems were seen. The used phacoemulsification needles were examined with colour photography and scanning electron microscopy. A characteristic pattern of wear was observed, corresponding to an area under the plastic irrigating sleeve rather than at the tip. This suggests cavitation erosion rather than instrument contacts as the cause. Titanium alloy contains 6% aluminium, 4% vanadium and 0.25% iron. All its constituents may corrode and leach from the surface of the metal when in contact with body fluids and have been implicated in numerous adverse biological processes.

Aged↗
PubMed1995

Mechanism of sulphadiazine enhancement of trimethoprim activity against sulphadiazine-resistant Enterococcus faecalis.

Sulphadiazine had little or no antibacterial effect against three strains of Enterococcus faecalis (MICs of above 3600 mg/L) but it caused approximately six-fold increases in bacterial uptake of trimethoprim, increased release of bacterial ATP and produced ultrastructural damage to both the trimethoprim resistant E. faecalis 463 and the trimethoprim sensitive NCTC 5957. MICs of trimethoprim were 0.6, 0.8 and 76.8 mg/L for E. faecalis NCTC 775, NCTC 5957 and 463 respectively. When log phase E. faecalis 463 and NCTC 5957 were grown for 4 h in trimethoprim 56 and 0.6 mg/L plus sulphadiazine 320 and 100 mg/L respectively there was an approximate ten-fold and nine-fold increase in uptake of sulphadiazine and a two-fold increase in leakage of ATP. Trimethoprim caused more damage to the cell wall and cytoplasmic membrane than sulphadiazine but the combination of sulphadiazine plus trimethoprim caused the most cell damage. The increased activity observed with the combination seems very likely to have resulted from the increased uptakes of the antibacterials, which in turn had resulted from the cell wall damage and consequent increased cell permeability caused by each antibacterial. It is proposed that a markedly subinhibitory concentration of sulphadiazine enhanced the antibacterial activity of trimethoprim against all three strains of E. faecalis by this mechanism.

Adenosine Triphosphate↗
PubMed1995

A four generation hidrotic ectodermal dysplasia family: an allelic variant of Clouston syndrome?

A four generation Scottish family with hidrotic ectodermal dysplasia affecting predominantly teeth, skin and hair is described. Hypo- or oligodontia of the secondary dentition by late adolescence was characteristic and two individuals had multiple natal teeth. Flexural acanthosis nigricans during childhood and early adolescence is a feature in some of the women. All affected individuals produced sweat, but heat tolerance was variable. Hypoplasia of the pilosebaceous units was found on light microscopy in one subject. Scalp hair was thin and slow growing (but adult females described much improved quality during pregnancy) and body hair was scanty. Scanning electron microscopy of hair samples showed abnormal cuticular appearances consistent with a primary defect affecting keratin structure. The nails were normal. Relative macrocephaly due to hyperostosis of the cranial vault was variably present. Short stature (5-10th centile) present in some cases is possibly a separate familial trait. The family demonstrates overlapping features with Clouston syndrome. In Clouston syndrome, however, alopecia can be severe, palmarplantar hyperkeratosis is usually present, and hypo/oligodontia is not a prominent feature.

Adult↗
PubMed1995

An investigation into sound attenuation by earmould tubing.

A major problem in high-gain post-aural hearing aids is acoustic feedback. One of the sources of feedback is the plastic tubing that guides the sound from the hearing aid hook to the ear canal. The objectives of this study were to determine the effects of increases in tubing wall thickness on the amount of acoustic feedback in the hearing aid system and to characterize earmould tubing. Five different samples of Tygon tubing were tested, of which four had different wall thicknesses; the study also compared Tygon tubing with medical grade PVC tubing. Measurement of the wall thickness, taken from scanning electron micrographs, showed that the wall thickness differed from the National Association of Earmould Laboratories standard by less than 6% and was well within the manufacturer's tolerances. Measurement of sound attenuation showed that an increase in the tubing wall thickness of 0.330 mm (Tygon 13 Standard to Tygon 13 Double Wall) caused an increase in sound attenuation of 2 dB, across the frequency range measured (0.5-4 kHz). It was also found that the medical grade PVC had a 5 dB greater sound attenuation than the equivalent Tygon tubing. While these differences are quite small, they could contribute to a reduction in acoustic feedback when used in conjunction with other hearing aid or earmould improvements.

Acoustics↗
PubMed1994

Helical growth of hyphae of Candida albicans.

When grown on a range of surfaces in conditions favouring hyphal growth, hyphae of Candida albicans grew in a right-handed helical fashion. This phenomenon was observed with eight strains and with two nutrient media. It is suggested that this is a result of rotation of the hyphal apex as it extends, which on some surfaces results in a helical hyphal wall, but which in a liquid results in a straight hypha. The consequence is that on a surface, a helically growing hypha will be exposed to a more diverse environment than a straight hypha. This phenomenon may have significance in the colonization of tissue by C. albicans.

Anti-Bacterial Agents↗
PubMed1994

Investigation of touch-sensitive responses by hyphae of the human pathogenic fungus Candida albicans.

Candida albicans is a fungus that commonly infects the mucosal surface of humans. The hyphal growth form of this fungus may initiate the primary invasion of the host. Here we show that hyphae respond thigmotropically and morphologically to cues such as the presence of a surface, pores, grooves and ridges. Growth on some firm surfaces elicits a helical growth response. Hyphae follow grooves and ridges of inert substrates and penetrate pores of filtration membranes. Our in vitro experiments suggest that thigmotropism may enhance the ability of a hypha to invade epithelia of a host at sites of weakened integrity.

Candida albicans↗
PubMed1994

Syndromes associated with trichothiodystrophy.

Sparse, brittle, sulphur-deficient hair is an excellent marker for several autosomal recessive neurocutaneous syndromes. The term 'trichothiodystrophy' is commonly used in publications on such syndromes and the best characterized trichothiodystrophy syndrome is associated with skin photosensitivity and intellectual impairment. Patients with these three cardinal signs usually have an underlying DNA repair defect. Here we describe clinical and laboratory findings in two patients with trichothiodystrophy and defective DNA repair alongside findings in three other cases who have different trichothiodystrophy syndromes without defective DNA repair. These patients' features are discussed in the light of a practical classification scheme which is based upon a check-list of clinical abnormalities associated with trichothiodystrophy syndromes (Van Neste, 1991).

Adolescent↗
PubMed1993

Investigation of cell envelope damage to Pseudomonas aeruginosa and Enterobacter cloacae by dibromopropamidine isethionate.

Electron micrographs of log-phase Pseudomonas aeruginosa and Enterobacter cloacae cultured for 4 h in the presence of subinhibitory concentrations of dibromopropamidine isethionate indicate that this antibacterial agent can cause marked damage to the cell envelope structures of both species. This result provides an explanation of how dibromopropamidine can enhance the uptake and thus the activity of a second antibacterial agent used in combination with it.

Anti-Bacterial Agents↗
PubMed1993

An electronmicroscope study of the effect of sulphadiazine and trimethoprim on Enterobacter cloacae.

Electronmicroscopy of thin sections of log phase cells of Enterobacter cloacae NCTC 10005 grown for 4 h in the presence of sulphadiazine 250 micrograms/ml, trimethoprim 12.5 microliters/ml or the combination of sulphadiazine 250 micrograms/ml plus trimethoprim 12.5 micrograms/ml indicated that both agents caused marked morphological damage even though the MIC of sulphadiazine for the E. cloacae strain was > 3000 micrograms/ml. The damage took the form of electron-transparent areas devoid of ribosomes in the cytoplasm and detachment of the outer membrane. The latter was most marked with trimethoprim, which also caused damage to the cytoplasmic membrane. It is postulated that the synthesis of the peptidoglycan layer was affected by the antimetabolites since the morphological effects were strikingly similar to those caused by treatment of E. cloacae with disodium edetate plus lysozyme. Viable counts of cultures undergoing the same treatments as those prepared for electronmicroscopy indicated that although sulphadiazine merely partially inhibited growth it nevertheless enhanced the bactericidal action of trimethoprim over a 5-h period.

Cell Membrane↗
PubMed1993

Viruses accumulate spontaneously near droplet surfaces: a method to concentrate viruses for electron microscopy.

Virus particles suspended in a drop of water tend to concentrate at or near its surface with the air. The concentrated, and probably more purified, particles may then be collected on a film-coated grid for negative staining and electron microscopy. This is a useful method, simpler than others (e.g. high-speed centrifugation, Lyphogel, or precipitation by (NH4)2SO4) which are used to process clinical specimens for diagnosis where virus particles may be too dilute in the original sample. It is shown, by freeze-fracturing for electron microscopy, that Orf virus particles do accumulate at and just below the surfaces of drops. Various physical effects which may cause the particles to accumulate are considered. Results from a computer model suggest that Brownian motion alone could be adequate to transport a useful quantity of the particles in the body of a 2-mm-diameter hemispherical drop to its surface if the particles do not clump and if they remain trapped at the surface when they reach it. In practice, transport by Brownian motion is likely to be augmented by swirling, convection and other effects within drops.

Bacitracin↗
PubMed1993

Scanning electron microscopy of scales from pityriasis amiantacea.

The scanning electron microscope has been used to examine scales taken from the scalp of 3 patients with pityriasis amiantacea alone, 3 psoriatic patients with pityriasis amiantacea and one patient with both atopic dermatitis and pityriasis amiantacea. Samples from 2 patients were additionally studied by different fixation techniques and in the frozen hydrated state, but no cementing of the scales could be observed. There was no evidence of an infective agent.

Humans↗
PubMed1992

Contact sensing in Candida albicans: a possible aid to epithelial penetration.

Hyphal development in the dimorphic pathogenic fungus Candida albicans is thought to facilitate the primary invasion of surface epithelia during superficial infections. When mycelia were grown on Nuclepore membrane filters that were placed over serum-containing agar, the hyphae grew over the membrane surface and through the pores thereby crossing to the other side of the membrane. Hyphae that did not contact the lip of a pore did not enter it. The response was likely to be due to contact guidance (thigmotropism) and not chemotropism towards the nutrients since hyphae growing on the underside of the membrane also entered the pores then grew away from the underlying nutrient agar. The response therefore seems to be due to sensation of the substrate topography, and tropic movement in relation to changes in contour. This behaviour may enable the hyphae to penetrate epithelia at microscopic wound sites, membrane invaginations and other foci where the integrity of the epithelium is weak.

Candida albicans↗
PubMed1990

Some of the factors involved in the Sarvazyan method for recording ultrasound field distributions with special reference to the application of ultrasound in physiotherapy.

The mapping of ultrasound fields using the dye paper method is described. The mode of action by which the dye concentration is increased has been investigated. Microbubbles on the paper surface and microstreaming of dye solution seem to be essential features of the mapping method. The streaming is thought to inhibit the formation of a dye depletion layer near the paper to an extent dependent on local sound intensity A linear relation between streaming velocity and intensity is derived.

Coloring Agents↗
PubMed1989

Ultrasound-induced damage of veins in pig ears, as revealed by scanning electron microscopy.

Pig ear veins have been treated in situ with ultrasound at a frequency of 750 kHz and intensity of 1.5 W cm-2 (spatial average) during which the temperature in the surrounding tissues rose to 52-54 degrees C. The veins were examined by scanning electron microscopy. Gaps developed between the endothelial cells, which showed many fine perforations in their membranes. Extensive blood clots were observed in which erythrocytes had become more spherical and showed damaged membranes. Effects on membranes were also found with HeLa cells heated to 50 degrees C, and have been previously described by others in heat-treated blood vessels.

Animals↗