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Biomedical subjects

P M Bennett

Publications and source records attributed to P M Bennett.

At least 19 recordsLinked to original sources
PubMed1995

Concentrated Tris solutions for the preparation, depolymerization, and assay of actin: application to erythroid actin.

High concentrations of Tris are effective in dissociating actin-containing complexes, such as the red cell membrane cytoskeleton. A preparative procedure for red cell actin is based on the dissociation of the membrane skeletal complex in a buffer containing 1 M Tris hydrochloride, followed by gel filtration chromatography in the same medium. The actin is recovered as the monomer and is fully native, as judged by its critical concentration of polymerization, inhibition of DNase I, stimulation of myosin ATPase, and the appearance in the electron microscope of filaments, both bare and decorated with heavy meromyosin, and of magnesium ion-induced paracrystals. The Tris solution causes rapid depolymerization of F-actin with no denaturation, and the solution of monomeric actin in this medium is stable for many weeks in the cold; concentrated Tris is more reliable than guanidinium chloride for the depolymerization of F-actin in the estimation of total actin concentration by the DNase I inhibition assay.

Actins↗
PubMed1995

Evaluation of freeze substitution in rabbit skeletal muscle. Comparison of electron microscopy to X-ray diffraction.

Rabbit psoas muscle fibres, relaxed and in rigor, have been freeze substituted for electron microscopy. Fourier transforms and average density maps of micrographs of transverse sections have been obtained and compared to X-ray diffraction data. The Fourier amplitudes from rigor and relaxed muscle are comparable to equatorial data from X-ray diffraction of muscle if there is more disorder in the electron micrographs which can be described by a 'temperature' factor. The phases of reflections out to the 3,2 have been determined; those reflections at the same radius and therefore not separable in the X-ray patterns, such as the 2,1 and the 1,2, are separated in the transforms of sections through the A band. In transforms from both rigor and relaxed muscle they have the same phase. In rigor muscle they have different amplitudes. All the phases are positive or negative showing that the lattice is centrosymmetric at the resolution obtained. The phases obtained generally support those suggested by model building studies using X-ray diffraction data. In rigor muscle, areas where the cross-bridges are regularly attached are clearly seen in thin transverse sections. A handedness to this structure is indicated by a lack of mirror symmetry, in both the Fourier transform of thick sections, and in the averaged density map. This correlates well with the arrangement where the myosin head is bound as in the acto-S1 structure but only to actin monomers within a limited azimuthal range.

Animals↗
PubMed1995

A clinical isolate of Aeromonas sobria with three chromosomally mediated inducible beta-lactamases: a cephalosporinase, a penicillinase and a third enzyme, displaying carbapenemase activity.

Hydrolytic profiles of Aeromonas sobria 163a, non-induced and induced, and of a derepressed mutant 163a-M, indicate that this strain has inducible beta-lactamases with activities against cephalosporins, penicillins and carbapenems. Three enzymes were identified and two of the beta-lactamase genes, ampS, encoding a penicillinase and cepS, encoding a cephalosporinase, were cloned into Escherichia coli, permitting analysis of the individual enzymes. Isoelectric focusing (IEF) analysis using inhibition profiles with EDTA and BRL 42715, confirmed AmpS (pI 7.9) and CepS (7.0) to be serine beta-lactamases. A third beta-lactamase displaying hydrolytic activity against the carbapenems was inhibited by EDTA. The carbapenemase had a pI of 9.3 and was detected on IEF gels by overlaying the gel with agarose containing imipenem and the chromogenic pH indicator, bromothymol blue. Co-inducibility and the recovery of a derepressed mutant in which all three enzymes were produced at high levels indicate that this isolate of A. sobria has three co-ordinately controlled beta-lactamase genes.

Aeromonas↗
PubMed1995

Intestinal ammonium transport by ammonium and hydrogen exchange.

BACKGROUND: Ionized ammonia (NH3) transport in the intestine has not been previously established as a mechanism of acidosis in urinary intestinal diversion or hepatic failure. STUDY DESIGN: The purpose of this study was to establish that ionized transport of ammonium (NH4) occurs in the intestine and to characterize the mechanism of its transport using the methodology of brush border membrane vesicles and acridine orange fluorescence. RESULTS: An NH4/H exchange was demonstrated and found to be the dominant mechanism causing a pH change when NH4 is transported across the lumenal membrane. Ionized NH4 transport was demonstrated to occur against an NH3 concentration gradient. The Km was 1.02 mmol and the Vmax was 247 U/sec. The Hill coefficient was 0.97, indicating a single port. Ammonium hydrogen exchange could be inhibited by amiloride but not by bumetanide. Sodium, potassium or chloride, or both, did not effect the NH4/H exchanger. CONCLUSIONS: This study establishes that ionized NH4 transport occurs across the small intestine brush border in exchange for a hydrogen ion.

Acridine Orange↗
PubMed1994

Sequence analysis of the L1 metallo-beta-lactamase from Xanthomonas maltophilia.

The amino acid sequence deduced from the L1 beta-lactamase gene of Xanthomonas maltophilia shows a significant variation from that of the CphA and Blm metallo-beta-lactamases of Aeromonas hydrophila and Bacillus cereus, respectively. Whilst the N-terminus of the L1 protein shows some similarity, particularly at the histidine residues previously suggested as a zinc-binding motif, the C-terminus of the protein demonstrates very little similarity. Such differences amongst this group of enzymes would argue for at least three subclasses within the Group 3 beta-lactamases. However, in order to predict their phylogenetic ancestry more sequence data are required from other possible metallo-beta-lactamases.

Amino Acid Sequence↗
PubMed1994

Mass mortality of common dolphins (Delphinus delphis) in south west England due to incidental capture in fishing gear.

In the first quarter of 1992, 118 dolphin carcases, of which 54 were positively identified as common dolphins (Delphinus delphis), were found stranded on the coast of Cornwall and Devon. To determine the cause, detailed post mortem examinations were carried out on 38 of the carcases, and the results were compared with those from 20 common dolphins that stranded on the coast of Cornwall and Devon in the previous 15 months. There was no evidence that the deaths were due to an infectious or parasitic disease, or acute intoxication by any of the algal toxins, trace metals or chlorinated hydrocarbons measured. However, 30 of the 38 dolphins showed signs associated with incidental capture in fishing gear. Skin lesions characteristic of capture in a small-meshed net and the predominance of recently ingested Atlantic mackerel (Scomber scombrus) and pilchard (Sardina pilchardus) in the stomachs of the dolphins suggested that they had been caught in the trawl or purse seine nets used for these fish. There is insufficient information to explain why this high mortality occurred in 1992 and not in other years.

Animal Diseases↗
PubMed1994

Guidelines for the interpretation of laboratory findings in birds and mammals with unknown reference ranges: plasma biochemistry.

The results of analyses of plasma samples from healthy and sick adult birds and mammals of a wide range of species were used to calculate reference ranges and clinical ranges for 11 biochemical variables (calcium, sodium, chloride, total protein, albumin, globulin, inorganic phosphate, potassium, bicarbonate, urea and creatinine concentrations) in six mammalian Orders (Primata, Carnivora, Pinnipedia, Proboscidea, Perissodactyla and Artiodactyla) and six avian Orders (Ciconiiformes, Gruiformes, Pelecaniformes, Psittaciformes, Falconiformes and Strigiformes). The patterns of variation between Orders for the different biochemical variables were then used to provide guidelines for the interpretation of plasma biochemistry results in the species in these Orders for which there are no reference data. The observed clinical ranges provide an indication of the potential diagnostic value of each variable.

Animal Diseases↗
PubMed1994

The occurrence and seasonal changes in the isolation of Listeria spp. in shop bought food stuffs, human faeces, sewage and soil from urban sources.

Eight hundred and twenty-two shop-bought food specimens, 136 soil and 692 faecal specimens were cultured for Listeria spp. in a regular, year round survey. 19.7% (162/822) of the foods, 93.9% (108/115) of the sewage, 14.7% (20/136) soils and 1% (7/692) of faeces yielded Listeria spp. with 10.5% foods, 60.0% sewage, 0.7% soils and 0.6% faeces containing L. monocytogenes. No seasonal variation was noted in isolates from either sewage or foods, with L. monocytogenes and L. innocua being the commonest species in both L. ivanovii when isolated from foods was strongly associated with mutton. Poultry was most likely to contain L. monocytogenes (65.6%, 21/32) and in the greatest numbers. A high percentage of beef (34.6%, 9/26), lamb (40%, 8/20), pork (28.1%, 9/32) and sausages (34.7%, 8/23) also contained L. monocytogenes. L. monocytogenes was rarely isolated from paté (1/40) or soft cheeses (1/251), both of which have been involved with foodborne listeriosis outbreak in the UK. Listeria spp. were commonest in faeces and soils in July to September but the predominant species isolated were different with L. monocytogenes and L. innocua the commonest from faeces and L. ivanovii and L. seeligeri the most common from soil.

Animals↗
PubMed1994

Heterogeneity at the beta-lactamase structural gene ampC amongst Citrobacter spp. assessed by polymerase chain reaction analysis: potential for typing at a molecular level.

Considerable biochemical diversity and polynucleotide sequence variation have been reported amongst strains of Citrobacter spp. However, sequence heterogeneity has not been investigated at gene loci of clinical relevance. In this study, sequence heterogeneity in the beta-lactamase structural gene, ampC, amongst 91 clinical isolates of Citrobacter spp. that showed resistance to various third-generation cephalosporins was investigated. Variation was examined by high-stringency polymerase chain reactions (PCR) with primers homologous to the known ampC sequences of C. freundii strains OS60 and I113, and C. diversus NF85. If an isolate contained an ampC gene homologous to one of these three characterised ampC genes, a single PCR band of a predictable size was generated with the appropriate primer set; 50 (60%) of isolates gave a PCR product of the expected size with the OS60 primer set and nine (10%) gave a product with the I113 primer set. All these 59 isolates were identified as C. freundii by API-20E strips. Six isolates (7%) gave a product with the C. diversus NF85 primer set but only four of these were identified as C. diversus in API-20E tests; the other two isolates were identified as C. freundii. Of the 91 isolates, 28 (31%), were identified as either C. freundii or C. diversus, but gave no PCR product with any primer set tested. Five of these showed no homology to any of the reference strain ampC PCR products in hybridisation tests. Nevertheless, all showed beta-lactamase activity. Overall, this method allowed the identification of novel ampC gene loci, which may serve as a basis for the identification of Citrobacter spp. rapidly at a molecular level.

Base Sequence↗
PubMed1993

The survival of bacteria exposed to desiccation on surfaces associated with farm buildings.

The survival of 11 species of Gram-negative and Gram-positive bacteria was examined on different surfaces exposed to desiccation. There were large variations between species; Pseudomonas spp. and Rhizobium leguminosarum biovars survived for less than 2 d, whilst Enterococcus spp. survived for more than 11 weeks. The type of surface on to which the bacteria were deposited affected survival, but with different effects between species. In addition the survival of spontaneous nalidixic acid-resistant (Nal-r) mutants of a natural Escherichia coli isolate were compared. Overall the differences were slight, but of seven resistant mutants, five survived better than the parent whilst one survived less well. Nine transposon insertion derivatives of one of the Nal-r mutants (ECO80) which survived better than the parent were compared; all survived similarly to the parent except ECO883 which survived less well. The growth characteristics of ECO883 and ECO80 were compared; at high osmotic pressures (> 0.4 mol 1-1 NaCl) ECO883 grew more slowly and showed a longer lag time than the parent. Of the osmoregulatory functions studied, ECO883 appeared to be altered with respect to K+ transport or accumulation, although the transposon insertion had occurred in a gene distant from known K+ transport genes.

Agriculture↗
PubMed1993

The effect of soft X-radiation on myofibrils.

Myofibrils, the contractile organelles from striated muscles, have been examined in the X-ray microscope to determine the effect of radiation on their function and structure. Using X-rays of energy 350-385 eV in the water window we find that after an exposure to 7.5 x 10(5) photons/micron2 (calculated to give an absorbed dose of 20,000 Gy) the myofibrils will no longer contract. The use of the free radical scavenging agent, DMSO, gives some protection to the fibrils. It has also been found that after this much irradiation the fibrils lose up to 20% of their mass. Further substantial mass loss occurs on subsequent irradiation. After 25 times the loss-of-function exposure only 30% of the mass remains. Analysis of a series of images of the same myofibril covering this range of exposures shows that the mass is preferentially lost in some areas of the structure and consequently significant structural changes occur.

Animals↗
PubMed1991

Development of LYNX: a computer application for disease diagnosis and health monitoring in wild mammals, birds and reptiles.

IBM-compatible software has been developed so that quantitative and qualitative haematological and biochemical reference data for over 500 species of mammals, birds and reptiles can be made readily accessible to veterinary surgeons. The LYNX software makes it possible to retrieve these data at different taxonomic levels (species, genera, families, orders and classes) and to select data by age and sex. The data for each variable may be presented in the form of a reference range or as a frequency histogram. Notes describing the variations in blood cell morphology observed in healthy individuals of each species are included in the database. The user's own haematological and biochemical data can also be entered, stored and used.

Animals↗
PubMed1991

The future contribution of transposition to antimicrobial resistance.

Antibiotic resistance is commonplace in clinical bacterial isolates. Many of the resistance genes are transposon-borne and have the potential for rapid dispersal throughout the bacterial kingdom. Resistance genes are constantly subject to mutation and reassortment. Given appropriate selection pressure, the new resistance determinants can emerge rapidly to pose significant treatment problems. It seems likely that in the future bacterial resistance will continue to be a problem, both with respect to current antibiotics and to new ones and that transposon-borne resistance genes will continue to figure prominently.

DNA Transposable Elements↗
PubMed1991

Inhibition of K88ab-mediated haemagglutination by polymyxin B nonapeptide.

The ability of the cyclic peptide polymyxin B nonapeptide (PMBN) to inhibit haemagglutination of erythrocytes by Escherichia coli bearing K88ab, K99 or F41 fimbriae was examined. The agent strongly inhibited K88ab-mediated haemagglutination, but had little or no effect on haemagglutination mediated by K99 or F41 fimbriae. Inhibition of K88ab-mediated haemagglutination did not result from release of fimbrial adhesins from the bacterial cell surface, nor from solubilization of K88ab receptors in erythrocytes. Since PMBN also prevented haemagglutination mediated by partially-purified K88ab fimbriae, the agent may directly obstruct access of fimbriae to their mammalian receptor binding sites.

Adhesins, Escherichia coli↗