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Biomedical subjects

D G White

Publications and source records attributed to D G White.

At least 109 records · Page 6Linked to original sources
PubMed1989

Isolation and identification of coagulase-negative Staphylococcus species from bovine body sites and streak canals of nulliparous heifers.

Heifers (n = 103) ranging in age from 1d to 2 yr were sampled to determine the coagulase-negative staphylococcal flora of haircoat, nares, vagina, teat skin, and streak canal. A total of 2706 staphylococal strains were identified from 3612 bacterial isolates. Other genera or groups identified included Bacillus, Micrococcus, Corynebacterium, and coliforms. Staphylococci were identified utilizing a simplified biochemical scheme. Staphylococcus xylosus, S. chromogenes, and S. warneri were the predominant species recovered from anatomic sites and streak canal. Staphylococcal strains identified from specific body sites (expressed as percentage of heifers harboring these species) were: nares 74% S. xylosus and 48% S. warneri; haircoat, 70% S. xylosus and 57% S. chromogenes; vagina, 60% S. chromogenes and 54% S. xylosus; teat skin 62% S. chromogenes and 61% S. warneri; streak canal 53% S. chromogenes, and 43% S. warneri. The prevalent staphylococcal strains identified differed from heifers in confined housing compared with heifers on pasture. Differences observed in distribution of Staphylococcus species among body sites, particularly those between teat skin and streak canal, suggest that establishment of staphylococcal microflora depends on the ability of a species to adapt to and colonize anatomic sites as well as on environmental conditions present.

Aging↗
PubMed1988

Role of infected food handler in hotel outbreak of Norwalk-like viral gastroenteritis: implications for control.

Investigation of an outbreak of viral (Norwalk-like) gastroenteritis amongst staff (40 cases), resident guests (over 70 cases), and persons attending functions (54 cases) at one hotel over 8 days suggested that the main vehicle of infection was cold foods prepared by a food handler during and after a mild gastrointestinal illness. He was excreting Norwalk-like virus particles 48 hours after the illness. In addition, ill kitchen staff vomited in the kitchen area and may have contaminated surfaces and stored foods. It is recommended that food handlers should be regarded as potentially infectious until at least 48 hours after clinical recovery from viral gastroenteritis. Stored foods that may have been contaminated should be immediately discarded and areas of the work place which may have been affected should be identified and decontaminated.

Food Handling↗
PubMed1988

Relationship of calf antibody status to disease and performance.

Three tests were used to measure the circulating immunoglobulin in 381 purchased calves as they entered a commercial calf-rearing unit. A correlation of 0.64 was found between the zinc sulphate turbidity (ZST) test and a quantitative latex agglutination test (LAT) measuring IgG1 (P less than 0.001). A qualitative version of the LAT related poorly to the quantitative version. The proportion of plasma samples identified by the quantitative LAT as having an IgG1 concentration of less than 5 g/litre which were incorrectly identified as positives (greater than or equal to 5 g/litre) by the qualitative LAT was 0.65. The proportion of plasma samples identified by the quantitative LAT as having a IgG1 concentration of greater than or equal to 5 g/litre which were incorrectly identified as negative (less than 5 g/litre) was 0.11. There was no statistically significant relationship between plasma IgG1 concentration and initial liveweight, subsequent overall daily liveweight gain or disease incidence (P greater than 0.05). Calves treated for infectious disease, particularly respiratory disease after weaning, had statistically significantly lower liveweight gains than healthy calves (P less than 0.001).

Analysis of Variance↗
PubMed1988

Endothelium-derived relaxing factor and atriopeptin II elevate cyclic GMP levels in pig aortic endothelial cells.

1. Two directly-acting stimulants of soluble guanylate cyclase, glyceryl trinitrate (0.1 microM) and sodium azide (10 microM), and a receptor-mediated stimulant of particulate guanylate cyclase, atriopeptin II (10 nM), each elevated the cyclic GMP content of primary cultures of pig aortic endothelial cells without affecting the cyclic AMP content. 2. Two receptor-mediated stimulants of adenylate cyclase, glucagon (1 microM) and isoprenaline (10 microM), had no effect on the cyclic AMP or cyclic GMP content of these cells, but the directly acting stimulant, forskolin (30 microM), induced a small increase in cyclic AMP content. 3. Three agents that release endothelium-derived relaxing factor (EDRF); bradykinin (0.1 microM), ATP (10 microM) and ionophore A23187 (0.1 microM), each markedly elevated the cyclic GMP content of pig aortic endothelial cells, but acetylcholine (1 microM) had no effect. None of these agents had any effect on cyclic AMP content. 4. Two agents that potentiate the actions of EDRF; M & B 22948 (100 microM) and superoxide dismutase (30 units ml-1), each elevated the cyclic GMP content of pig aortic endothelial cells without affecting the cyclic AMP content. Pretreating cells with catalase (100 units ml-1) did not affect the rise in cyclic GMP content induced by superoxide dismutase (30 units ml-1). 5. Pretreatment of pig aortic endothelial cells with haemoglobin (10 microM) reduced the resting content of cyclic GMP and blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 microM), sodium azide (10 microM), bradykinin (0.1 microM), ATP (10 microM), ionophore A23187 (0.1 microM), M & B 22948 (100 microM) and superoxide dismutase (30 units ml-1), but not that induced by atriopeptin II (10 nM). 6. Pretreatment of pig aortic endothelial cells with an inhibitor of soluble guanylate cyclase, methylene blue (20 microM), had no effect on the resting content of cyclic GMP. Methylene blue (20 microM) blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 microM), M & B22948 (100 microM) and bradykinin (0.1 microM), but not that induced by atriopeptin II (10 nM). 7. The data show that soluble guanylate cyclase, particulate guanylate cyclase and adenylate cyclase are present in pig aortic endothelial cells. They further suggest that EDRF, produced spontaneously or in response to vasoactive agents, elevates endothelial cyclic GMP content by stimulating soluble guanylate cyclase. It is possible that this may serve as a feedback loop by which the endothelial cell modulates EDRF production.

Adenylyl Cyclases↗
PubMed1987

Effects of ischemic nerve block on the early and late components of the stretch reflex in the human forearm.

To investigate the peripheral afferent mechanisms which mediate the short latency (M1) and long latency (M2) components of the stretch reflex, we have recorded EMG responses to extension perturbations at the wrist before and following inflation of a blood pressure cuff around the upper arm. After approximately 30 min of ischemia, the reflexes had almost completely disappeared, although subjects were still able to activate the forearm muscles voluntarily. As the ischemic block developed, the M2 component began to decrease in amplitude sooner than M1, and up to the time of complete loss of reflex activity, the suppression of M2 was relatively greater than that of M1. These results suggest that M2 may be mediated by a population of afferent fibers different from the Ia afferents which are believed to generate the M1 response.

Adult↗
PubMed1987

Effects of teat dipping on intramammary infections by staphylococci other than Staphylococcus aureus.

Effects of intramammary infections in herds 1) either not teat dipping or postmilking teat dipping with either 2) linear dodecyl benzene sulfonic acid, 3) chlorhexidine, or 4) iodophor containing products were determined. Duplicate quarter foremilk samples were collected once from all lactating cows in 16 herds, four for each practice. Mean percentage of quarters infected with Staphylococcus species other than Staph. aureus was 11.0 in herds not teat dipping and 7.2 in herds teat dipping. Prevalence of Staphylococcus species intramammary infections in herds teat dipping with linear dodecyl benzene sulfonic acid was comparable to herds not teat dipping and greater than in herds using chlorhexidine and iodophor. The predominant Staphylococcus species in herds not teat dipping was Staph. epidermidis (37.1%). Staphylococcus hyicus constituted 48.5% of total Staphylococcus species intramammary infections in herds teat dipping and 12.4% in herds not teat dipping. Differences were not observed among SCC for quarters infected with different Staphylococcus species. Application of germicidal teat dips appeared to have selectively altered both prevalence and distribution of Staphylococcus species intramammary infections.

Animals↗
PubMed1986

Influence of endothelium on drug-induced relaxation of the rabbit aorta.

The influence of endothelium on relaxation induced by glyceryl trinitrate (GTN) and isoprenaline (I) has been studied in isolated rabbit aortic ring preparations, in the resting state and after constriction with 5-hydroxytryptamine (5HT). In resting preparations relaxant responses to GTN and I were smaller in the presence of endothelium. In preparations constricted with 5HT relaxant responses to GTN and I were conversely greater in the presence of endothelium. These paradoxical findings are discussed in relation to basal release of endothelium derived relaxant factor.

Animals↗
PubMed1986

Evaluation of a rapid specific test for detecting colostral IgG1 in the neonatal calf.

A commercially available latex agglutination test was used to measure the concentration of IgG1 in bovine plasma and the results were compared with radial immunodiffusion and zinc sulphate turbidity methods. For concentrations of IgG1 up to 80 g/litre there were highly significant (P less than 0.001) correlation coefficients between the latex agglutination test and radial immunodiffusion, and between the latex agglutination test and zinc sulphate turbidity method (0.93 and 0.74 respectively). The coefficient of variation for the latex agglutination test ranged from 8.1 per cent to 17.9 per cent. IgG1 concentration was measured using the latex agglutination test in whole blood on a farm, in whole blood at a laboratory and in plasma at a laboratory. The correlation coefficients were highly significant (P less than 0.001) in all cases. The latex agglutination test is easy to use, rapid and specific. It is suitable for checking the colostral status of young calves on commercial farms.

Animals↗
PubMed1986

Identification of Naegleria fowleri in fresh isolates of environmental amoebae using a staphylococcal coagglutination technique.

A coagglutination test using Staphylococcus aureus Cowan strain 1 sensitized with specific antiserum successfully identified Naegleria fowleri in axenic and monoxenic culture by detection of a heat stable antigen released into the culture medium during growth. Strong coagglutination, visible to the naked eye, occurred within 30 sec when the sensitized reagent was mixed on a slide with medium from N. fowleri cultures. N. lovaniensis gave a weak cross-reaction which developed over one min clearly distinguishable from that of N.fowleri.N.gruberi and N. australiensis gave no reaction. The technique is proposed as part of a rapid and economical scheme for detecting N. fowleri in environmental samples very soon after primary isolation, with distinct advantages over conventional methods. Further development of the technique to detect other Naegleria spp. and the early diagnosis of primary amoebic meningoencephalitis are suggested as future applications.

Agglutination Tests↗
PubMed1986

Modification of motor output to compensate for unanticipated load conditions during rapid voluntary movements.

Mechanisms responsible for load compensation during fast voluntary movements were investigated in 20 normal subjects trained to carry out rapid wrist flexions against a standard load. When an unanticipated increase in load occurred, there was a compensatory increase in agonist EMG and decrease in antagonist EMG. Unanticipated decreases in load produced reciprocal changes with a decrease in agonist EMG and an increase in antagonist EMG. The latency of these EMG changes was quite short and compatible with a spinal reflex mechanism rather than a long loop response. The results suggest that mechanisms exist at the spinal level to allow rapid modification of motor programs when unanticipated load conditions are encountered on initiation of movement.

Adult↗
PubMed1986

Atriopeptin II-induced relaxation of rabbit aorta is potentiated by M&B 22,948 but not blocked by haemoglobin.

We examined the effects of haemoglobin (which inhibits the vascular responses to stimulation of soluble guanylate cyclase) and of M&B 22,948 (which selectively inhibits cyclic GMP phosphodiesterase) on the relaxation induced in rabbit aorta by the atrial natriuretic peptide, atriopeptin II (which stimulates particulate guanylate cyclase). Pretreatment with M&B 22,948 (100 microM) produced a 2.3 fold potentiation of atriopeptin II-induced relaxation of endothelium-denuded rings of rabbit aorta. Pretreatment with haemoglobin (10 microM) had no effect on the relaxation or the 10.9 fold increase in cyclic GMP content induced by atriopeptin II in endothelium-denuded rings of rabbit aorta. The potentiation by M&B 22,948 suggests a causal role for cyclic GMP in mediating atriopeptin II-induced vasodilatation of rabbit aorta. The inability of haemoglobin to block the atriopeptin II-induced rise in cyclic GMP suggests that it does not block stimulation of particulate guanylate cyclase. Thus, it is unlikely that a ferrous haem-containing receptor site is involved in the activation of the particulate form of guanylate cyclase as it is with soluble guanylate cyclase.

Animals↗
PubMed1986

The mechanisms by which haemoglobin inhibits the relaxation of rabbit aorta induced by nitrovasodilators, nitric oxide, or bovine retractor penis inhibitory factor.

The mechanisms by which haemoglobin and methaemoglobin inhibit the vasodilator actions of glyceryl trinitrate, sodium azide, nitric oxide, and the bovine retractor penis inhibitory factor (IF) were studied on rabbit endothelium-denuded aortic rings. Methaemoglobin was less effective than haemoglobin against each vasodilator, it was more effective at inhibiting the relaxation to azide than that to glyceryl trinitrate. Glyceryl trinitrate was neither bound nor inactivated when passed through columns of haemoglobin-agarose or methaemoglobin-agarose. Azide was reversibly bound but less by haemoglobin-agarose than by methaemoglobin-agarose. Inhibition of the vasodilator actions of glyceryl trinitrate is not attributable therefore to a direct interaction with the haemoproteins, although a small part of the inhibition of azide-induced relaxation by methaemoglobin is likely to be due to a direct interaction. Columns of haemoglobin-agarose were more effective than columns of methaemoglobin-agarose in removing nitric oxide from solution. The greater ability of haemoglobin, compared to methaemoglobin, to inhibit vasodilatation induced by nitrovasodilators may therefore reflect the greater ability of haemoglobin to bind nitric oxide which is the active principle of the nitrovasodilators. Neither the acid-activated nor the inactive forms of IF were bound or inactivated when passed through columns of methaemoglobin-agarose. Neither form of IF was retained on passage through columns of haemoglobin-agarose, but the resulting activity in the eluates was less than control, was unstable and, unlike the original activity, decayed rapidly on ice. The greater ability of haemoglobin, compared to methaemoglobin, to inhibit vasodilatation induced by IF might therefore reflect the greater ability of haemoglobin to interact with this vasodilator and inactivate it.

Animals↗
PubMed1986

Effect of induced hypomagnesaemia on the toxicity of imidocarb in calves.

The hypothesis that the toxic effects of imidocarb mediated by reduced cholinesterase activity might be intensified by hypomagnesaemia was tested in calves. Hypomagnesaemia was induced in 12 males (50 kg) using an artificial milk based on a commercial nondairy coffee creamer. Although plasma magnesium levels reached 0.33 mmol litre-1 in two weeks no clinical signs were detected. In 12 control calves a daily magnesium supplement of 0.6 g was inadequate although the published requirement is 0.45 g; it was raised to 1.2 g to keep plasma magnesium normal. Lighter calves developed hypomagnesaemia more readily and fast-growing calves had lower plasma urea concentrations. Plasma calcium, but not plasma magnesium, showed significant positive correlation with plasma albumin. The only statistically significant effects of hypomagnesaemia were slight elevations of white cell count and plasma sodium. The hypomagnesaemic and normomagnesaemic calves were divided into two equal groups and treated with 3.3 mg kg-1 of imidocarb dipropionate or a placebo. The drug produced the expected clinical signs of mild toxicity and depression of cholinesterase but no other adverse effects. Transient slight depressions of plasma calcium and potassium concentration, a transient rise of plasma sodium and elevation of creatine kinase occurred. None of the effects of imidocarb treatment was intensified by hypomagnesaemia except, perhaps, constriction of the pupils; generally, hypomagnesaemic animals were affected less.

Animals↗
PubMed1985

Human parvovirus arthropathy.

19 of 153 patients attending an early-synovitis clinic were shown to have been recently infected by the human parvovirus (HPV). 5 other patients had evidence of some other closely preceding infection. HPV-infected patients typically presented with symmetrical peripheral polyarthropathy of sudden onset and moderate severity. Usually there was some improvement within 2 weeks, but in 17 patients symptoms persisted for more than 2 months, and in 3 for more than 4 years. Arthropathy in the absence of the facial rash that characterises HPV infection in children is a common presentation of the infection in adults.

Adolescent↗
PubMed1985

Rapid identification of thermophilic Naegleria, including Naegleria fowleri using API ZYM system.

The suitability of the API ZYM system for identifying thermophilic Naegleria species, based on enzyme presence and activity, was investigated. Replicate testing on strains of N fowleri, N lovaniensis, and N australiensis cultured in a monoxenic and an axenic medium showed that the system could provide a rapid and reproducible means of identifying the species soon after primary isolation. No single enzyme was found specific for any one species, but considerable differences were found in the patterns of activity of acid phosphatase and leucine arylamidase. When these were compared the species could be differentiated. Use of the system in conjunction with a simple culture method is proposed as a readily available means of monitoring environmental and public bathing sites to prevent primary amoebic meningoencephalitis.

Acid Phosphatase↗