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Biomedical subjects

C J Thomas

Publications and source records attributed to C J Thomas.

At least 91 records · Page 5Linked to original sources
PubMed1994

The effect of inhaled nitric oxide on the pulmonary circulation of the neonatal pig.

To study the pulmonary vasodilator selectivity of low levels of inhaled nitric oxide (NO) in a model of neonatal pulmonary hypertension, we sequentially exposed anesthetized, spontaneously breathing neonatal pigs to each of four different inspired gas mixtures: room air, room air with 25 parts per million NO, hypoxia (14% O2 in N2), and hypoxia with 25 parts per million NO. The room air, room air with NO, hypoxia, and hypoxia with NO exposures were of 15-min duration. The following measurements were made: mean systemic arterial, mean pulmonary arterial, and wedge pressures; thermodilution cardiac output; esophageal pressure; tracheal flow; and arterial PO2, PCO2, pH, hemoglobin, and methemoglobin. Inhalation of NO decreased pulmonary arterial pressure in both room air and hypoxia conditions (mean pulmonary arterial pressure 16 +/- 1 torr room air, 13 +/- 1 torr room air with NO, p < 0.005; and mean pulmonary arterial pressure 21 +/- 2 torr hypoxia, 14 +/- 1 torr hypoxia with NO, p < 0.005). NO had no significant effect on systemic arterial pressure, cardiac output, dynamic lung compliance, pulmonary resistance, or the measured blood variables during either control or hypoxic conditions. The results indicate that inhaled NO was a selective pulmonary vasodilator that could effectively reverse acute hypoxic pulmonary vasoconstriction. The normoxic vasodilation produced by NO inhalation also indicates the existence of basal vasomotor tone in the anesthetized, spontaneously breathing neonatal pig. The short-term exposures used produced no detectable manifestations of toxic side effects.

Administration, Inhalation↗
PubMed1993

Bacteriophage Lambda as a Delivery Vector for Tn10-Derived Transposons in Xenorhabdus bovienii.

Xenorhabdus bovienii wild-type strains lack a functional receptor protein (LamB) in the outer membrane and as a result are unable to adsorb coliphage lambda (lambda). Introduction of plasmids encoding lamB into X. bovienii T228 results in constitutive expression of LamB in the outer membrane of this organism. LamB-expressing strains of X. bovienii adsorb lambda bacteriophage particles and can be used as hosts for lambda::Tn constructs. A Tn10-derived transposon, element 9 (J. C. Way, D. Davis, D. Morisato, D. E. Roberts, and N. Kleckner, Gene 32:369-379, 1984) was used to construct a variety of insertion mutants of X. bovienii. Mutants that had altered expression of protease, lipase, DNase, dye-binding capability, and hemolytic activity, in addition to a series of auxotrophic mutants, were isolated.

Journal Article↗
PubMed1993

Resilient lining materials for dentures.

Modern resilient liners may be broadly classed as plasticized resins, silicone rubbers and fluoropolymers. Desirable properties would be pronounced softness and resiliency, or visco elasticity. Compression tests of Molloplast B (a silicone rubber), Kurepeet (a fluoropolymer), Visco-gel (a tissue conditioner) and Xantopren ( a silicon impression material) (as control) showed a displacement of 4% and recovery to 0.4% permanent deformation after 15s of loading for Molloplast and Xantopren, and up to 32% and 13% displacement respectively for Visco-gel and Kurepeet followed by considerable permanent deformation. Recovery of the latter showed a typical curve for visco-elasticity. The small amount of initial deformation of the elastic materials on the other hand indicated unyielding and consequently unsatisfactory properties. The deformation of Kurepeet was not as great as Visco-gel but the fact that it was visco-elastic meant that it was likely to be a suitable long-term lining material. It therefore complied with requirements that a resilient denture liner should be soft and visco-elastic.

Dental Stress Analysis↗
PubMed1992

A combined PCR and selective enrichment method for rapid detection of Listeria monocytogenes.

Development of a routine detection assay for Listeria monocytogenes in foods that uses the polymerase chain reaction (PCR) and enrichment cultures was investigated. Oligonucleotide primers were chosen to amplify a 3' region of L. monocytogenes hlyA gene spanning a conserved HindIII site. PCR detection sensitivity for L. monocytogenes in dilutions of pure enrichment cultures was between 50 and 500 colony forming units. A short enrichment period before PCR amplification allowed detection of the organisms in a range of complex foods contaminated with 10(4) cfu/g. Detection sensitivity for the assay in the presence of chicken skin and soft cheese was determined at 10-100 cfu/g. Utilization of enrichment cultures and PCR allowed identification of the organism within 24 h or 2 days.

Bacteriological Techniques↗
PubMed1992

Complete mandibular denture stability when posterior teeth are placed over a basal tissue incline.

Six patients with previous denture experience were provided with new dentures. Metal indicators were placed on either side of the mandibular denture and a cobalt-chromium alloy marker was inserted in the left bucco-posterior area of the mandible in each case. In the new dentures posterior teeth were positioned up to the retro-molar pad, over the basal tissue slope of the posterior mandibular alveolar ridge. After habituation had taken place, a cineradiographic recording was made of chewing. Prior to the second recording the mandibular teeth were removed to a point where the remaining teeth were not over inclined residual alveolar ridges. Denture movement was observed by measuring the distances between the markers on an analytical projector. The results show a significant difference between the cranial values of the two chewing experiences. Values for all denture movements were less after removal of the teeth over an incline. These results support the clinical observation that teeth placed over a basal tissue incline have a destabilizing effect during complete mandibular denture function.

Adult↗
PubMed1992

Detection of Aeromonas salmonicida from fish by using polymerase chain reaction amplification of the virulence surface array protein gene.

A DNA-based assay was developed to detect Aeromonas salmonicida from infected fish by analyzing tissues, feces, and the tank water in which the infected fish were held. This analysis was done both by direct detection from samples and after a bacterial outgrowth step. Polymerase chain reaction (PCR) amplification of a 421-bp sequence from the 3' region of the surface array protein gene (vapA) of A. salmonicida provided a specific and sensitive method for the detection and identification of this important fish pathogen. The sensitivity of PCR detection of A. salmonicida directly from tissues was less than 10 CFU/mg. Furthermore, a detection level of 5 fg, equivalent to approximately 1 cell, was obtained by using purified chromosomal DNA as the template. This highly reproducible assay, which requires 45 min to complete, is therefore sensitive enough to be used as a noninvasive method for monitoring fish populations for the presence of carrier fish. Because the surface protein array (A-layer) is a virulence factor of A. salmonicida, PCR analysis with oligonucleotide primers directed at vapA can also be used to provide information on the potential virulence of a strain.

Aeromonas↗
PubMed1992

Household products as sanitising agents in denture cleansing.

Since a large percentage of denture wearers in South Africa make use of household products as denture cleansers, it was considered desirable to find a household product which can be used as a satisfactory sanitising agent in denture cleansing routines. Six subjects, each wearing an acrylic plate with removable plugs of a standard surface area, used a different solution in rotation as a disinfectant. The following solutions were tested: a 0.04 per cent hypochlorite + 0.66 per cent NaCl (4 per cent Milton), 0.012 per cent hypochlorite + 0.19 per cent NaCl (1.2 per cent Milton), 20 per cent NaCl, undiluted vinegar and 50 per cent diluted vinegar solutions. On completion of each experimental period the plugs were removed, visually inspected and viable bacterial counts were made. All solutions resulted in a significant (p < 0.01) reduction of viable bacteria compared to the tap water control. The sodium hypochlorite solutions were more effective sanitising solutions.

Acetic Acid↗
PubMed1991

Tomato aspermy virus has an evolutionary relationship with other tripartite RNA plant viruses.

The entire RNA 3 (2214 nucleotides) of a chrysanthemum isolate of tomato aspermy virus (C-TAV) has been cloned and its sequence determined. C-TAV possesses two open reading frames which encode a 3a protein (277 amino acids) and a coat protein (229 amino acids). Computer-assisted comparisons were made between C-TAV RNA 3 and its predicted protein sequences and those of two other tripartite RNA viruses, cucumber mosaic virus (CMV) and brome mosaic virus (BMV). Results from this study suggest that a close evolutionary relationship exists between C-TAV, Q-CMV and BMV. Divergence of nucleotide and amino acid sequences between these viruses is not reflected at the level of the predicted secondary structure of the encoded proteins, where conservation is strong.

Amino Acid Sequence↗
PubMed1991

The influence of exercise-induced temperature elevations on the auditory brain-stem response (ABR).

The influence of exercise on the auditory brain-stem response (ABR) was examined in 16 healthy volunteers (8 female and 8 male). Ipsilateral ABR recordings were obtained before and after exercise on a bicycle ergonometer. The rise of body temperature so generated was 0.5-2.1 degrees C (mean, 1.3 degrees C) as measured in the contralateral external auditory meatus. Latencies of waves III and V (but not wave I) were found to be significantly lower immediately post-exercise (P less than 0.01). The temperature relations of the latency of wave V are described by the regression equation: Latency (ms) = 11.06-0.146 x temp. (degrees C). (The effects on amplitude were not significant, nor were male/female differences.) It is suggested that exercise hyperthermia could be an appropriate model for the evaluation of the ABR in fever.

Adult↗
PubMed1991

The early development of palatal rugae in the rat.

The palatal rugae in rats are contained in two of three zones of morpho-differentiation and develop around the time of palatal closure. Previous studies in humans and pigs have been based on crown-rump lengths but now controlled breeding in rats has allowed exact timing to be established. Twenty-nine female DB IX rats were fertilized and sacrificed in a controlled procedure and foetuses processed for light microscopy and SEM. Serial sagittal sections were made and stained with haematoxylin and eosin and Verhoef's stains. At day 13 the palate was open and no rugae were visible. At day 14 the palatal shelves had started to migrate medially and the ante-molar rugae appeared. At day 15 the palatal shelves were touching and the inter-molar rugae became visible, and at day 16 fusion was all but complete and the definitive rugal pattern established. The development and differentiation is more advanced than in humans and it is concluded that the rugae probably have a role to play in the oral function of animals whereas in humans they are becoming attenuated and the development timetable is retarded because of redundancy.

Animals↗
PubMed1990

A new fimbrial type (PCFO9) on enterotoxigenic Escherichia coli 09:H- LT+ isolated from a case of infant diarrhea in central Australia.

The genes determining the biosynthesis of a new putative colonization factor, designated PCF09 have been cloned from an LT+ enterotoxigenic Escherichia coli 09:H- isolated during an outbreak of infant diarrhea in Central Australia. Electron microscopy has shown it to be of the fibrillar type. Purification of the major pilin subunit showed it to have a size of approximately 27 kDa. NH2-terminal analysis of the major subunit has shown the PCFO9 determinant to be distinct from other fimbriae although there is some conservation of certain residues. A synthetic oligodeoxynucleotide probe based on the NH2-terminal amino acid sequence of the purified protein has been used in Southern hybridization analyses to define the region on pPM1320 encoding the structural gene for the major pilin subunit.

Amino Acid Sequence↗
PubMed1990

Impression material consistency and peripheral tissues.

The behaviour of three alginate impression materials was tested in vivo by sectioning the peripheries of a series of impressions in a standard manner and measuring the extension in three directions: buccal, lingual and into the depth of the sulcus. The three materials used reacted in accordance with their various consistencies. There were statistically significant differences between all the materials in the inferior measurement, but very few differences in the buccal dimension. Lingually however, one extended significantly further than the other two. It is concluded that the facial tissues, probably muscles, play a restraining role in buccal impression material extension but that the inferior and lingual extensions are more susceptible to the consistency of the material rather than the tissues. This should be carefully considered before selecting a suitable material for impressions.

Adult↗
PubMed1990

Role of the P plasmid in attenuation of Vibrio cholerae O1.

The conjugative plasmid P of Vibrio cholerae has been shown to have a suppressive effect on the virulence of hypertoxigenic strains like 569B. In this study, we have sought to analyze this phenomenon. Utilizing the infant mouse cholera model, we have demonstrated that the presence of P increases the 50% lethal dose of V. cholerae classical Inaba 569B by more than 300-fold. No effect of P on cholera toxin (CT) production, whether measured by GM1 enzyme-linked immunosorbent assay, by CT activity in ligated rabbit ileal loops, or by transcription from the CT promoter, could be discerned. Colonization of the intestine by P+ derivatives was dramatically reduced although only a minor effect could also be demonstrated on in vitro attachment to intestinal strips. Electron microscopic examination suggested that the P plasmid was affecting the production of the TCP pilus. Another conjugative plasmid, V, has also been examined, but it had no effect on virulence.

Animals↗
PubMed1990

Clinical study of the modified Equipoise clasp.

The modified Equipoise clasp has been developed to overcome the negative aesthetics of anterior clasping. Fifteen patients involving twenty-two Equipoise clasps were followed up for retention, aesthetics and oral health. Examiners found that 36.4% of the clasps gave poor retention, 18.1% were reasonable and 45.5% were good. Aesthetics were 23.6% poor, 36.4% reasonable and 50% good. Oral health was 9.1% poor, 50% reasonable and 40.9% good. The patients reported that retention was 13.3% reasonable and 86.7% good. Twenty percent of the patients felt aesthetics were reasonable and 80% felt it was good. The clasps were reasonably comfortable in 13.3% and most comfortable in 86.7%. The Equipoise clasp can be used with success for, among others, the Kennedy Class IV case if the correct clinical and laboratory procedures are followed. However, it is unsuitable in, for example, a Class I dentition where posterior stability is poor. Its lingual window can adversely affect oral hygiene and careful patient selection is necessary.

Consumer Behavior↗
PubMed1989

An indirect in vivo method for quantification of wear of denture teeth.

A method using a reflex microscope to undertake direct and highly precise three-dimensional measurements of denture casts for the purpose of mapping and determining the volumetric loss of material over a period of time has been developed. The wear that occurred in tooth 46 after clinical use for one year was measured and found to be 7.2 mm3. This technique has proved to be an accurate and objective quantification of what has previously often been a subjective impression.

Denture, Complete↗
PubMed1989

The toxin-coregulated pilus (TCP) of Vibrio cholerae: molecular cloning of genes involved in pilus biosynthesis and evaluation of TCP as a protective antigen in the infant mouse model.

A serum containing antibodies to non-lipopolysaccharide (non-LPS) protective antigens of Vibrio cholerae has been used, after extensive absorption, to facilitate the cloning of genes involved in the synthesis of toxin-coregulated pili (TCP). A gene bank was constructed from V. cholerae Z17561 DNA using a mobilizable cosmid vector in Escherichia coli, and subsequently transferred by conjugation into V. cholerae O17. This strain does not produce TCP in vitro and lacks non-LPS protective antigens. Eight positive clones were isolated, and of these, four produced TCP as determined by electron microscopic and immunoblotting analyses. TCP-positive O17 clones were 70-fold more virulent than TCP-negative clones or O17 in the infant mouse cholera model. Only the former could remove protective antibodies from the clone-probing serum by absorption. As a corollary, serum containing antibodies to TCP protected mice from challenge with TCP-positive clones, but not with TCP-negative clones or O17. Our data indicate that TCP can function as both a virulence determinant and a protective antigen in the infant mouse model.

Animals↗
PubMed1989

Genes for biosynthesis and assembly of CS3 pili of CFA/II enterotoxigenic Escherichia coli: novel regulation of pilus production by bypassing an amber codon.

The complete nucleotide sequence of the 4746bp HindIII fragment encoding the genes for the biosynthesis and assembly of CS3 pili has been determined. By site-directed mutagenesis in conjunction with analysis of the plasmid-encoded proteins in minicells, the actual reading frames for the various products have been determined. This demonstrated that the genes for four of the proteins (63 kD, 48 kD, 33 kD, and 20 kD in size) are encoded entirely within the same open reading frame as a fifth protein (104 kD). However, for synthesis of this latter protein, suppression or readthrough of an internal amber codon is required. Termination at this codon is also necessary for synthesis of the former proteins. Two further proteins are also encoded within the HindIII fragment: a 27 kD precursor of a periplasmic protein and the 17.5kD precursor of the major CS3 fimbrial subunit.

Amino Acid Sequence↗