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Biomedical subjects

R W Phillips

Publications and source records attributed to R W Phillips.

At least 19 recordsLinked to original sources
PubMed1996

Behaviour of a high-temperature-requirement A (HtrA) deletion mutant of Brucella abortus in goats.

Previous studies have shown that high-temperature-requirement A (HtrA) mutants of Brucella abortus are more sensitive to oxidative killing in vitro, are less able to survive in cultured murine macrophages and are attenuated in BALB/c mice. To measure the effect of an HtrA mutation on the virulence of B abortus in ruminants, pregnant goats in late gestation were exposed to infection by the conjunctival route with B abortus 2308 or an isogenic htrA mutant, PHE1. Infection with either 2308 or PHE1 resulted in abortion, but the serological responses to infection were consistent with 2308 but variable with PHE1. Strain 2308 was recovered post mortem both from aborted fetuses and infected dams, whereas PHE1 was recovered from neither. Nevertheless, short term studies revealed that PHE1 could be recovered from infected goats for up to two weeks after infection, suggesting that although the HtrA mutation may change the colonising ability of B abortus, the virulence of the mutant in pregnant goats is not reduced.

Abortion, Veterinary↗
PubMed1996

A three-year clinical trial using a glass ionomer cement for the bonding of orthodontic brackets.

Recent clinical studies measuring orthodontic bracket failure, when using glass ionomer cement as an adhesive, have reported a wide range of percentages of bracket failure. The present study recorded bracket failure over a 3-year period, longer than had been previously measured. Seventeen participants were randomly assigned to one of two treatment groups, either using glass ionomer cement or composite resin for bonding. In each group, brackets were bonded to incisors, canines, and premolars. Bracket failure was measured over the duration of comprehensive orthodontic treatment for all participants. Brackets bonded with the glass ionomer cement were more likely to fail (log-rank test; P < or = 0.022). This difference was clinically significant. At the present time, the disadvantage of extra bracket failures appears to outweigh potential advantages when considering glass ionomer cement for the routine bonding of orthodontic brackets.

Adhesives↗
PubMed1996

The HtrA stress response protease contributes to resistance of Brucella abortus to killing by murine phagocytes.

Compared with virulent Brucella abortus 2308, the isogenic htrA mutant PHE1 shows decreased resistance to killing by cultured murine neutrophils and macrophages and significant attenuation during the early stages of infection in the BALB/c mouse model. These findings further define the contributions of the htrA gene product to the pathogenesis of B. abortus infections.

Animals↗
PubMed1995

In vivo and in vitro stability of the broad-host-range cloning vector pBBR1MCS in six Brucella species.

Previous studies have shown that the broad-host-range plasmid pBBR1MCS can be used for genetic complementation in Brucella abortus. To extend these observations, the in vivo and in vitro stability of pBBR1MCS was evaluated in the six currently recognized species of the genus Brucella. pBBR1MCS was readily introduced into all of the strains tested by electroporation and was stably maintained in broth cultures without antibiotic selection during five serial passages over a 10-day period. Furthermore, isolates of all six Brucella strains containing pBBR1MCS obtained from the spleens of BALB/c mice 1 week postinfection maintained the plasmid. Although pBBR1MCS maintains the mobilization locus present in the parental plasmid pBBR1CM, attempts to detect transfer of pBBR1MCS between Brucella strains by conjugation were unsuccessful. These results demonstrate the in vitro and in vivo stability of pBBR1MCS in Brucella spp. and reinforce the usefulness of this cloning vector for the genetic analysis of these organisms.

Animals↗
PubMed1995

A Brucella melitensis high temperature requirement A (htrA) deletion mutant demonstrates a stress response defective phenotype in vitro and transient attenuation in the BALB/c mouse model.

Bacterial stress response proteins of the high temperature requirement A (HtrA) family are serine proteases which appear to play an important role in scavenging oxidatively damaged proteins from the cell before they reach toxic levels. An isogenic htrA deletion mutant, designated RWP5, was constructed from virulent Brucella melitensis 16M via gene replacement to determine whether the B. melitensis HtrA protein functions as a stress response protein, and to evaluate the contribution of this protein to virulence. Unlike the parental strain, RWP5 would not form isolated colonies on solid media at 40 degrees C or grow on Schaedler agar without blood supplementation. RWP5 also grew poorly in broth culture in contrast to 16M. The B. melitensis htrA mutant was significantly more sensitive (P < 0.001) to killing by H2O2 and puromycin than the parental strain, and a significant reduction (P < 0.001) in the number of RWP5 recovered from the spleens and livers of experimentally infected BALB/c mice was observed at one week post infection compared to 16M. However, by 3 weeks post-infection and continuing thereafter through to 20 weeks post-infection, the levels of RWP5 and 16M recovered from the spleens and livers of experimentally infected mice were similar. In vitro and in vivo evaluation of RWP5 reisolates obtained from the spleens of mice at 4 and 16 weeks post-infection demonstrated that mouse passage did not significantly alter these characteristic in vitro and in vivo properties of RWP5. These results support a stress response function for the B. melitensis HtrA protein and suggest that this protein contributes to the pathogenesis of B. melitensis early in infection. The basis for the recovery of RWP5 at later timepoints in infected mice is presently unknown; however, the results presented here suggest that it is not caused by a stable genetic change resulting from mouse passage.

Animals↗
PubMed1994

Practical and clinical nutritional concerns during spaceflight.

Experience with space exploration to date has raised more questions regarding nutritional requirements for astronauts than it has answered. As mission lengths continue to increase, nutrient imbalances due to alterations in intake, dietary requirements, bioavailability, or excretion, may become more important. Factors adversely affecting intake include those as straightforward as stress and as complex as space-adaptation syndrome. Metabolic alterations induced by shifts in fluid and electrolyte balance, neuroendocrine function, and changes in hepatic protein synthesis and skeletal muscle type that result in nutrient partitioning to different biochemical pathways may also affect dietary requirements. Food processing effects on nutrient stability and digestibility, which apply to limited quantities of our usual diet on Earth, may become more important for diets that contain little fresh food during extended-length missions. Whereas nutrient and water recycling through ecosystems is taken for granted on Earth, specific effects of trace contaminant accumulation will require greater attention for prolonged space flights. Human factors, esthetics, and user-friendly operations will be necessary to facilitate the psychological as well as physiological health of the astronauts.

Adaptation, Physiological↗
PubMed1994

Characterization and genetic complementation of a Brucella abortus high-temperature-requirement A (htrA) deletion mutant.

In order to evaluate the biological function of the Brucella abortus high-temperature-requirement A (HtrA) stress response protein homolog, the majority of the htrA gene was deleted from the chromosome of B. abortus 2308 via gene replacement. In contrast to the parental strain, the resulting htrA deletion mutant, designated PHE1, failed to grow on solid medium at 40 degrees C and demonstrated increased sensitivity to killing by H2O2 and O2- in disk sensitivity assays. BALB/c mice were infected with strains 2308 and PHE1 to assess the effect of the htrA mutation on virulence, and significantly fewer brucellae were recovered from the spleens of mice infected with PHE1 than from those of mice infected with 2308 at 1 week postinfection. Genetic complementation studies were performed to confirm the relationship between the htrA mutation and the phenotype observed for PHE1. Plasmid pRIE1 was constructed by inserting a 1.9-kb EcoRI fragment encoding the B. abortus htrA gene into the broad-host-range plasmid pBBR1MCS. Introduction of pRIE1 into PHE1 relieved the temperature- and H2O2-sensitive phenotypes of this mutant in vitro, and PHE1(pRIE1) colonized the spleens of BALB/c mice at levels equivalent to those of the parental 2308 strain at 1 week postinfection. These results support our previous proposal that the B. abortus htrA gene product functions as a stress response protein and further suggest that this protein contributes to virulence. These studies also demonstrate the utility of the broad-host-range plasmid pBBR1MCS for genetic complementation studies in Brucella spp., establishing a key reagent for more detailed genetic analysis of this important zoonotic pathogen.

Animals↗
PubMed1993

beta-Carotene inhibits rectal mucosal ornithine decarboxylase activity in colon cancer patients.

Colonic adenocarcinoma affects approximately 6% of adults in many Western countries. beta-Carotene (BC), a safe, inexpensive, and widely available compound, has been proposed as a cancer chemopreventive agent. To evaluate whether BC shows promise as an inhibitor of colonic carcinogenesis, we studied 20 male subjects who had previously undergone resection of colonic adenocarcinoma. Each subject received beta-carotene, 30 mg orally, daily for 6 months. Rectal mucosa was sampled at multiple intervals prior to, during, and following BC administration. Mucosal ornithine decarboxylase (ODC) activity and serum and mucosal BC concentrations were determined at each interval. ODC activity was inhibited by 44% (P < 0.05) and 57% (P < 0.01) after 2 and 9 weeks, respectively, of BC administration and remained low compared with baseline even 6 months following discontinuation of BC. Serum and mucosal BC concentrations increased as expected during BC administration and remained elevated for 6 months following BC discontinuation. The demonstrated inhibition of rectal mucosal ODC activity in these patients with resected colon cancer suggests that BC may prove useful as a cancer chemopreventive agent.

Aged↗
PubMed1993

Effect of crosslinking agent content, monomer functionality, and repeat unit chemistry on properties of unfilled resins.

Seven mechanical/physical properties were used to evaluate 10 unfilled resins: eight aromatic dimethacrylates and two urethane dimethacrylates. Physical property tests included compressive strength, Young's modulus in compression, uniaxial tensile strength, intrinsic yield point, toothbrush abrasion, Knoop hardness, and water sorption. Controlled changes were made in the following four material parameters: amount of crosslinking diluent present in the uncured monomer, functionality of the monomer, repeat unit chemistry of the monomer (urethane vs. aromatic structure) and mode of activation (chemical vs. visible light). Polymers containing a high concentration of crosslinking agent (50 wt%) were found to be tougher and to possess lower hardness than materials containing lesser amounts of crosslinking agent. This was attributed to the flexible nature of the triethylene glycol dimethacrylate crosslinking molecule. Exposure to water plasticized the highly crosslinked materials to the degree that the yield point and elastic modulus were effectively lowered. Most of the tested properties were unaffected by differences in functionality except resistance to toothbrush abrasion, which was enhanced for polymers derived from high functionality monomers. The urethane-based polymers sorbed substantially more water than the aromatic-based materials, which presumably resulted in lower values for surface hardness. However, the urethane resins were very tough, and excellent resistance to toothbrush abrasion was observed. Property differences caused by differences in activation mode were small, although the visible light materials did sorb more water.

Absorption↗
PubMed1992

Proliferation of jejunal mucosal cells in rats flown in space.

To examine the effects of spaceflight on the proliferation and turnover of jejunal mucosal cells, we compared the percentages of mitotic cells present in the crypts of Lieberkühn in the proximal, middle, and distal jejunum in each of five rats flown on the COSMOS 2044 mission and in rats included in the vivarium, synchronous, and caudal-elevated groups. On the basis of the data obtained, there was no difference in mitotic indexes between animals in the flight and vivarium (ground control) groups. Thus it appears that the ability of jejunal mucosal cells to proliferate is not affected by microgravity conditions associated with spaceflight. Although the length of villi and depth of crypts were reduced in flight animals compared with those in the vivarium group, the observed reduction is probably attributable to changes in the connective tissue core of villi and is not likely due to an impairment of the proliferation and migration of jejunal mucosal cells.

Animals↗
PubMed1991

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry.

Subjects of the past decade in the dental literature are reflected in this year's Committee report. We note the decrease in the prevalence of caries, the influence of dental implants, the advancements in dental materials, and the continued efforts to control adhesive events in the oral cavity. This year we included comments from and about many significant review articles published this past year. The Committee continues to be concerned about the quality of some of the work reported and the quality of the reporting. We have attempted to select the distinguished work, that which provides new information to our profession. The subjects covered include pulp biology, caries prevention, periodontics, implants, craniomandibular function and dysfunction, occlusion, and dental materials.

Dental Bonding↗
PubMed1991

Barrett's esophagus. Natural history, incidence, etiology, and complications.

This article reviews the natural history of Barrett's esophagus. The pathology and etiopathogenesis are considered in detail, as are the symptoms and complications of this condition. The indication and efficacy of medical and surgical therapy are reviewed, and the question "Does regression of Barrett's metaplasia occur?" is posed.

Barrett Esophagus↗
PubMed1990

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry.

The growth in the dental literature continues to escalate, as evidenced by the publication of at least 326 new books in 1988 and 1989 and more than 20 new journals in 1989. There still appears to be undue emphasis on quantity instead of quality of research. This proliferation in the literature poses ever increasing difficulties to this Committee in filtering out the articles that are of particular interest to the members of the Academy and identifying those that are most likely to have a major impact on dental practice and service. The subjects covered include periodontics, caries and preventive dentistry, craniomandibular disorders, occlusion, pulp biology, ceramics, and restorative dental materials.

Dental Caries↗