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Biomedical subjects

T A Roberts

Publications and source records attributed to T A Roberts.

At least 19 recordsLinked to original sources
PubMed1992

Sequence of the gene encoding type F neurotoxin of Clostridium botulinum.

Primers designed to conserved regions of botulinum and tetanus clostridial toxins were used to amplify DNA fragments from non-proteolytic Clostridium botulinum type F (202F) DNA using polymerase chain reaction technology. The fragments were cloned and the complete nucleotide sequence of the gene encoding type F toxin determined. Analysis of the nucleotide sequence demonstrated the presence of an open frame encoding a protein of 1274 amino acids, similar to other botulinum neurotoxins. Upstream of the toxin gene is the end of an open reading frame which encodes the C-terminus of a protein with homology to non-toxic-non-hemagglutinin component of type C progenitor toxin.

Amino Acid Sequence↗
PubMed1992

Taxonomic studies on a psychrophilic Clostridium from vacuum-packed beef: description of Clostridium estertheticum sp. nov.

Taxonomic studies were performed on an anaerobic Gram-positive, spore-forming, psychrophilic bacterium originally isolated from spoiled vacuum-packed refrigerated beef. Based on the present finding it is proposed that this unknown psychrophilic bacterium be classified as a new species of the genus Clostridium, as Clostridium estertheticum sp. nov. The type strain is NCIMB 12511.

Animals↗
PubMed1991

The effects of temperature, pH, sodium chloride and sodium nitrite on the growth of Listeria monocytogenes.

An automated turbidimetric system using multiwelled plates was used to examine the effects of different combinations of NaCl (0.5-8.0% w/v), NaNO2 (0-400 micrograms/ml) pH (4.6-7.4) and temperature (5-30 degrees C) on the growth of Listeria monocytogenes in tryptone soya broth. The data presented clearly illustrate the combinations that permit visible growth of the organism. The ability of L. monocytogenes to grow at low pH levels was strongly influenced by incubation temperature as well as NaNO2 concentration. At 20 degrees C and below, no visible growth was detected, even with 50 micrograms/ml NaNO2 at pH 5.3 (or below) within 21 days. At pH 6.0 and above, NaNO2 had little effect in delaying visible growth except at higher concentrations and also at lower incubation temperatures.

Colony Count, Microbial↗
PubMed1991

Gender and the influence of evaluations on self-assessments in achievement settings.

This article reviews evidence for a gender difference in responsiveness to others' evaluations in achievement situations. Studies show that women's self-evaluations are more responsive to the valence of the evaluative feedback they receive than are men's. A number of possible explanations for this effect are then discussed, with the best evidence pointing to men's and women's differing construals of the informational value of others' evaluations in such situations. Research on the behavioral consequences of women's lower status as well as on children's experiences with evaluative feedback provides potential explanations for this effect. A more proximal explanation, however, lies in men's and women's different approaches to evaluative achievement situations. Men may be particularly likely to respond to the competitive nature of evaluative achievement and hence to adopt a self-confident approach that leads them to deny the informational value of others' evaluations. Women may be particularly likely to approach such situations as opportunities to gain information about their abilities.

Achievement↗
PubMed1990

Predicting microbial growth: graphical methods for comparing models.

Some simple computer-based graphics were used to compare different models predicting microbial growth responses of salmonellae to three factors (pH, sodium chloride concentration and incubation temperature). Simple linear regression, contour and three-dimensional surface plots all revealed gross differences between the predicted growth parameters from different growth models. Regression and contour plots were found to be more sensitive to small differences in surface topography, but three-dimensional surface plots provided a good overview.

Computer Graphics↗
PubMed1989

Predicting microbial growth: the consequences of quantity of data.

Having developed a mathematical model of the growth responses in a laboratory medium of salmonellae (mixed inoculum of Salmonella thompson, S stanley and S. infantis) as affected by pH level, NaCl concentration and storage temperature, the consequences of systematic removal of data has been examined. Three-dimensional plots of fitted response surfaces for the whole data set and the data reduced by three strategies highlighted differences between models and illustrated the consequences of using insufficient data. The risk of an erroneous model was demonstrated.

Culture Media↗
PubMed1988

Predicting microbial growth: growth responses of salmonellae in a laboratory medium as affected by pH, sodium chloride and storage temperature.

The growth responses of salmonellae (mixed inoculum of Salmonella thompson, S. stanley and S. infantis) as affected by NaCl concentration, pH level and storage temperature were studied in laboratory medium. Growth curves were obtained at 5 concentrations of NaCl (0.5-4.5%, w/v), 5 pH levels (5.6-6.8) and 5 storage temperatures (10-30 degrees C). Sigmoid curves (Gompertz form) were fitted to the data and the curve parameters used to produce a polynomial model from which predicted growth curves could be generated for any combination of NaCl, pH and storage temperature within the limits studied. From those growth curves values for growth rate, generation time, lag time and other values such as time to a 1000-fold increase in numbers were derived. Such a model offers a cost-effective approach to understanding the microbial growth response in foods, and forms a data-base against which other controlling factors could be evaluated. Some problems of fitting curves to microbial growth data and of modelling such data are discussed.

Animals↗
PubMed1988

Evaluation of a monoclonal antibody-based immunoassay for detecting type B Clostridium botulinum toxin produced in pure culture and an inoculated model cured meat system.

A monoclonal antibody-based amplified ELISA method for detecting Clostridium botulinum type B toxin was evaluated for its ability to detect the toxin in the supernatant fluid of pure cultures and after growth from Cl. botulinum spores inoculated into pork slurries. Slurries containing NaCl (1.5-4.5% w/v) and polyphosphate (0.3% w/v) were either unheated or heated 80 degrees C/5 min followed by 70 degrees C/2 h before incubation at 15 degrees, 20 degrees or 27 degrees C. Presence of specific toxin was confirmed by mouse bioassay and results were compared with those of the amplified ELISA method. A total of 48 strains, consisting of 38 Cl. botulinum and 10 Cl. sporogenes (putrefactive anaerobes), and 140 slurry samples were tested. Cultures of eight out of nine strains of type B Cl botulinum and 73 of 101 slurry samples containing type B toxin were positive by ELISA; the remaining 28 slurry samples contained type B toxin at levels below or close to the detection limit (20 LD50/ml) of the type B ELISA. No false-positive reactions occurred with Cl. botulinum types A, C, D, E or F, or with the 10 strains of Cl. sporogenes. Toxin produced by one strain of Cl. botulinum type B (NCTC 3807) was not detected by this single monoclonal antibody-based amplified ELISA. With a mixture of two monoclonal antibodies, however, the toxin from NCTC 3807 could be detected without reducing the sensitivity of the ELISA.

Animals↗
PubMed1987

Bacteriological status of beef carcasses at a commercial abattoir before and after slaughterline improvements.

The bacteriological status of beef carcasses was monitored at a commercial abattoir before and after two stages of modernization to the beef slaughterline which included changing from cradle dressing to dressing on an overhead rail, and the introduction of hot water spray cleaning of carcasses. Although small significant (P less than 0.05) differences in bacterial count occurred among carcass sites within modernization stages, significant visit within stage variation and stage X site interactions prevented any significant change in overall count being observed among stages and carcass sites. Principal components analysis revealed small changes in the distribution of bacterial numbers on the sites sampled.

Abattoirs↗
PubMed1987

The effect of sodium chloride and temperature on the rate and extent of growth of Clostridium botulinum type A in pasteurized pork slurry.

A selective medium was used to enumerate Clostridium botulinum growing in the presence of natural spoilage organisms in a model cured pork slurry. The growth responses of a mixed spore inoculum of six strains of Cl. botulinum type A were studied at 15 degrees, 20 degrees and 27 degrees C with 1.5, 2.5, 3.5 or 4.5% (w/v) salt added (aw range 0.961-0.990). Gompertz and logistic curves, which have a sigmoid shape, were fitted to the data and lag times, growth rates, generation times and time to maximum growth rates were derived. Variation in germination rates of the spores occasionally gave a falsely extended lag time resulting in an exceptionally high estimate for growth rate. Products containing 4.5% (w/v) NaCl would be capable of supporting growth of proteolytic strains of Cl. botulinum, even at 15 degrees C, although the lag period would be extended. In products where absence of Cl. botulinum cannot be assured additional preservative measures are essential. The information obtained provides a framework to investigate the effects of a wider range of additives or variables on the growth responses of Cl. botulinum.

Animals↗
PubMed1987

The effect of incubation time and temperature on growth of Escherichia coli on gradient plates containing sodium chloride and sodium nitrite.

Two-dimensional gradient plates are a convenient way of screening antimicrobial effects of preservative factors acting in combination across a broad range of physical and chemical conditions. We report the effects of sodium chloride, sodium nitrite and incubation temperature on the growth of Escherichia coli by staining, laser densitometry and computer graphics. Staining not only more easily distinguished the growth area but also gave an indication of the viability of cells present. 2-(p-iodophenyl)-3(p-nitrophenyl)-5-phenyl tetrazolium chloride was the more useful of the two stains used. Inhibitory concentrations of sodium chloride decreased with reduced incubation temperature. The response of E. coli to combinations of salt and nitrite on gradient plates was very similar to its response in liquid medium.

Computer Graphics↗
PubMed1987

Evaluation of a monoclonal antibody-based immunoassay for detecting type A Clostridium botulinum toxin produced in pure culture and an inoculated model cured meat system.

A monoclonal antibody-based amplified enzyme-linked immunosorbent assay (ELISA) method for detecting Clostridium botulinum type A toxin was evaluated for its ability to detect the toxin in the supernatant fluid of pure cultures and after growth from Cl. botulinum spores inoculated into pork slurries. Slurries containing NaCl (1.5-4.5% w/v) and polyphosphate (0.3% w/v) were either unheated or heated, 80 degrees C/5 min + 70 degrees C/2 h, before storage at 15 degrees, 20 degrees or 27 degrees C. The presence of specific toxin was confirmed by mouse bioassay and results compared with those of the amplified ELISA method. A total of 49 strains, 39 Cl. botulinum and 10 Cl. sporogenes (putrefactive anaerobes), and 95 slurry samples were tested. Fourteen of 15 strains of type A Cl. botulinum and 34 of 36 slurry samples containing type A toxin were positive by ELISA. No false positive reactions occurred with Cl. botulinum types B, C, D, E and F, or with the 10 strains of Cl. sporogenes. However, toxin produced by one strain of Cl. botulinum type A (NCTC 2012) was not detected by the amplified ELISA.

Animals↗
PubMed1986

Microbiology of beef carcasses before and after slaughterline automation.

The bacterial status of beef carcasses at a commercial abattoir was monitored before and after slaughterline automation. Bacterial counts did not differ significantly overall (P greater than 0.05) between the original manual line and the automated line for either morning or afternoon slaughter. On the manual line counts in the morning were lower than those from carcasses slaughtered in the afternoon, but on the automated line there was no difference between morning and afternoon counts. Due to highly significant line X sample site interaction for both morning and afternoon counts, overall differences among sample sites were not found by analysis of variance. However, principal components analysis revealed a significant shift in bacterial contamination among some sites due to slaughterline changes. The incidence of Enterobacteriaceae increased marginally following automation.

Analysis of Variance↗
PubMed1985

Properties of microfilled composite resins as influenced by filler content.

Two series of composite resins were prepared with a light-cured urethane dimethacrylate matrix to which varying amounts of two types of silanated silica particles were added. One series contained volume fractions ranging from 15.8 to 28.8% silica particles of 20 nm in diameter (Type I filler) and the other series volume fractions of from 24 to 49.4% of an agglomerated silica particle of 40 nm in diameter (Type II filler). Tests were conducted to determine the effect of filler level on: depth of cure as determined by hardness measurements; color stability in both UV light and water; water sorption with time; hardness; compressive strength; strain behavior in slow compression; and resistance to toothbrush abrasion and wear by hydroxyapatite. Analysis of the data obtained for these two microfilled series indicate that increased filler levels result in trends for increased depth of cure, color stability, hardness, compressive strength, and stiffness, while water sorption and resistance to both toothbrush abrasion and wear by hydroxyapatite were reduced. These trends were more pronounced for the Type II filler series than for the Type I filler series. However, there was a greater differential in filler levels within the Type II series than within the Type I series.

Acrylates↗
PubMed1985

Effect of filler content and size on properties of composites.

Two series of dental composites, along with the unfilled resin matrix, were examined to determine the effects of filler level and size on selected properties. Both series were prepared by incorporating a silanated barium borosilicate filler into a visible-light-activated polyphenylene polymethacrylate resin matrix. One series had a filler particle size of 2 microns, with filler levels of 20, 40, 45, 50, and 53% (vol). The second series contained a 15-microns filler in amounts of 20, 40, 50, 60, and 65% (vol). Tests conducted included: depth of cure as evaluated by hardness, water sorption, compressive strength, stress-strain behavior under slow compression, toothbrush abrasion, and wear by hydroxyapatite. Analysis of the data indicated that increased filler levels resulted in increased hardness, compressive strength and stiffness, and decreased water sorption. Also, there was a slight trend toward improved depth of cure. Incorporation of the 2-microns filler decreased the abrasion resistance of the resins to toothbrushing as compared with the unfilled resin, while addition of the 15-microns filler improved resistance. All filled resins exhibited a significant improvement in resistance to wear by hydroxyapatite as compared with the unfilled resin. There was a trend for increased wear with increased filler level. The particle size of the filler appeared to have a moderate influence on the properties. When compared with 15-microns filled resins of the same filler levels, the 2-micron filled series appeared to have inferior properties in terms of depth of cure, compressive strength, water sorption, and resistance to toothbrush abrasion. Properties which were less affected by particle size were hardness, stiffness, and wear resistance to hydroxyapatite.

Chemical Phenomena↗