PubMed Health⌕ Search

Biomedical subjects

K R Smith

Publications and source records attributed to K R Smith.

At least 19 recordsLinked to original sources
PubMed1992

Escherichia coli Rep protein and helicase IV. Distributive single-stranded DNA-dependent ATPases that catalyze a limited unwinding reaction in vitro.

Rep protein and helicase IV, two DNA-dependent adenosine 5'-triphosphatases with helicase activity, have been purified from Escherichia coli and characterized. Both enzymes exhibit a distributive interaction with single-stranded DNA as DNA-dependent ATPases in a reaction that is relatively resistant to increasing NaCl concentration and sensitive to the addition of E. coli single-stranded DNA binding protein (SSB). The helicase reaction catalyzed by each protein has been characterized using a direct unwinding assay and partial duplex DNA substrates. Both Rep protein and helicase IV catalyzed the unwinding of a duplex region 71 bp in length. However, unwinding of a 119-bp or 343-bp duplex region was substantially reduced compared to unwinding of the 71-bp substrate. At each concentration of protein examined, the number of base pairs unwound was greatest using the 71-bp substrate, intermediate with the 119-bp substrate and lowest using the 343-bp substrate. The addition of E. coli SSB did not increase the fraction of the 343-nucleotide fragment unwound by Rep protein. However, the addition of SSB did stimulate the unwinding reaction catalyzed by helicase IV approximately twofold. In addition, ionic strength conditions which stabilize duplex DNA (i.e. addition of MgCl2 or NaCl), markedly inhibited the helicase reaction catalyzed by either Rep protein or helicase IV while having little effect on the ATPase reaction. Thus, these two enzymes appear to share a common biochemical mechanism for unwinding duplex DNA which can be described as limited unwinding of duplex DNA. Taken together these data suggest that, in vitro, and in the absence of additional proteins, neither Rep protein nor helicase IV catalyzes a processive unwinding reaction.

Adenosine Triphosphatases↗
PubMed1992

In vitro activity of sparfloxacin and three other fluoroquinolones against methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis.

Fluoroquinolones are variably active against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE). The purpose of this study was to test the in vitro susceptibility of 50 isolates each of MRSA and MRSE to four of the new fluoroquinolones--sparfloxacin, ciprofloxacin, ofloxacin and norfloxacin--and to see if resistance could be induced in five susceptible strains of each species by serial passages with increasing concentrations of drug. A standard microdilution technique was used to determine minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of each drug for each isolate. Agar dilution plates were also prepared containing concentrations of drug varying from one-half of the reported MIC to 128 times the reported MIC, and microorganisms persisting were serially passaged. Initially, 98% of the strains of MRSA were susceptible to the fluoroquinolones. MBCs were essentially identical to MICs. Similarly, 96% of the strains of MRSE were susceptible. Following exposure to increasing concentrations of each fluoroquinolone, resistance appeared to emerge less rapidly to sparfloxacin and ofloxacin than to norfloxacin and ciprofloxacin.

Anti-Infective Agents↗
PubMed1992

Correct folding of alpha-lytic protease is required for its extracellular secretion from Escherichia coli.

alpha-Lytic protease is a bacterial serine protease of the trypsin family that is synthesized as a 39-kD preproenzyme (Silen, J. L., C. N. McGrath, K. R. Smith, and D. A. Agard. 1988. Gene (Amst.). 69: 237-244). The 198-amino acid mature protease is secreted into the culture medium by the native host, Lysobacter enzymogenes (Whitaker, D. R. 1970. Methods Enzymol. 19:599-613). Expression experiments in Escherichia coli revealed that the 166-amino acid pro region is transiently required either in cis (Silen, J. L., D. Frank, A. Fujishige, R. Bone, and D. A. Agard. 1989. J. Bacteriol. 171:1320-1325) or in trans (Silen, J. L., and D. A. Agard. 1989. Nature (Lond.). 341:462-464) for the proper folding and extracellular accumulation of the enzyme. The maturation process is temperature sensitive in E. coli; unprocessed precursor accumulates in the cells at temperatures above 30 degrees C (Silen, J. L., D. Frank, A. Fujishige, R. Bone, and D. A. Agard. 1989. J. Bacteriol. 171:1320-1325). Here we show that full-length precursor produced at nonpermissive temperatures is tightly associated with the E. coli outer membrane. The active site mutant Ser 195----Ala (SA195), which is incapable of self-processing, also accumulates as a precursor in the outer membrane, even when expressed at permissive temperatures. When the protease domain is expressed in the absence of the pro region, the misfolded, inactive protease also cofractionates with the outer membrane. However, when the folding requirement for either wild-type or mutant protease domains is provided by expressing the pro region in trans, both are efficiently secreted into the extracellular medium. Attempts to separate folding and secretion functions by extensive deletion mutagenesis within the pro region were unsuccessful. Taken together, these results suggest that only properly folded and processed forms of alpha-lytic protease are efficiently transported to the medium.

Bacterial Outer Membrane Proteins↗
PubMed1992

Taurine depletion and cardiovascular disease in adult cats fed a potassium-depleted acidified diet.

Although low plasma taurine concentrations have been associated with congestive cardiomyopathy in cats, the cause of taurine depletion in cats consuming adequate quantities of taurine is unknown. Taurine depletion and cardiovascular disease (cardiomyopathy and thromboembolism) developed unexpectedly in 3 of 6 healthy adult cats during a potassium-depletion study. Plasma taurine concentration decreased significantly (P less than 0.05) and rapidly over an 8-week period (from 98 to 36 nmol/ml) in 6 cats that consumed a potassium-deficient diet (0.20% potassium, dry matter basis) that was acidified with 0.8% ammonium chloride, despite containing dietary taurine concentrations (0.12% dry matter basis) in excess of amounts currently recommended. Taurine concentrations were significantly lower in cats fed the acidified diet than in 6 cats fed a potassium-deficient diet that was not acidified (36 nmol/ml vs 75 nmol/ml) after 8 weeks. In addition, plasma taurine concentrations did not decrease over a 6-month period in 8 cats that were fed a potassium-replete diet with acidifier. Plasma taurine concentrations were lowest in 3 cats that died of cardiovascular disease in the group receiving potassium-deficient, acidified diets. These data indicated an association between taurine and potassium balance in cats and suggested that development of taurine depletion and cardiovascular disease may be linked to concurrent potassium depletion.

Ammonium Chloride↗
PubMed1991

In vitro comparison of cilofungin alone and in combination with other antifungal agents against clinical isolates of Candida species.

Cilofungin, a lipopeptide antifungal agent, was tested for in vitro activity alone and in combination with ketoconazole, itraconazole, flucytosine and amphotericin B against 102 clinical isolates of Candida species. At 48 hours all isolates of Candida albicans, Candida tropicalis, Candida paratropicalis and Candida glabrata were inhibited by less than or equal to 5 meg/ml of cilofungin. In contrast, the MIC90 for Candida krusei was 10 mcg/ml and for Candida parapsilosis greater than 40 mcg/ml. The interaction of combinations of cilofungin with amphotericin B, itraconazole, ketoconazole and flucytosine was additive or indifferent at 48 hours for 100%, 88%, 78% and 70% of all Candida species isolates, respectively. Overall, cilofungin demonstrated good activity in vitro against most Candida species isolates.

Amphotericin B↗
PubMed1991

Cerebrospinal fluid endothelin-1 and endothelin-3 levels in normal and neurosurgical patients: a clinical study and literature review.

Endothelins are a family of structurally related, potent, long-lasting vasoconstrictor peptides. There are no established normal human levels of endothelin-1 or endothelin-3 in the cerebrospinal fluid. We measured cerebrospinal fluid endothelin-1 and endothelin-3 levels in five groups of patients: normal controls, patients with subarachnoid hemorrhage and cerebral vasospasm, patients with severe head injuries, patients undergoing temporal lobectomy for intractable epilepsy, and a patient with a gunshot injury to the thoracic spine. Endothelin-3 levels were significantly elevated in patients with subarachnoid hemorrhage and may participate in cerebral vasospasm and subsequent neurologic deterioration.

Adult↗
PubMed1991

Incidence of Listeria monocytogenes in meat production environments of a South Island (New Zealand) mutton slaughterhouse.

The results of a survey conducted at a South Island, New Zealand, abattoir are presented. Two-hundred-and-eighteen samples taken from ovine carcasses and the environment were analysed. The traditional cold enrichment, i.e. 4 degrees C for up to 16 weeks, was used. No isolations of listeriae were made from freshly dressed carcasses or from surfaces with which meat makes contact. However, seven isolates of Listeria monocytogenes were obtained from cold rooms operating at 5 degrees C and which are used to store carcasses. Also, a single isolate of L. ivanovii was obtained from a mesh screen strainer of the waste water treatment plant located near the works. The study indicates that ovine carcasses can be prepared free of L. monocytogenes, that cold rooms may be a source of these microorganisms and it also reconfirms that listeriae can be found in soil and fodder of animal paddocks adjacent to the abattoir.

Abattoirs↗
PubMed1991

Open depressed skull fracture missed on computed tomography: a case report.

A case of an open depressed skull fracture that was missed on standard computed tomographic (CT) scan is presented. The fracture was seen on a CT generated lateral scout film, and after repositioning the gantry, further CT images clearly showed the fracture and underlying brain injury. The authors recommend that all patients with head trauma undergoing head CT have either a CT generated lateral scout film or a lateral skull radiograph to assess the vertex of the skull, an area poorly visualized on standard axial images.

Adult↗
PubMed1991

Patterns of economic change surrounding the death of a spouse.

The timing of economic changes near the death of a spouse is not well understood. Using multiple regression analysis and longitudinal data from the Panel Study of Income Dynamics, the economic situations of middle-aged and older widows and widowers were compared to those of otherwise similar intact couples over an 11-year period. The analysis shows that all four widowed groups had fewer economic resources 5 years after the death than did their married counterparts. Yet, each group took very different economic paths to get to this point. For example, older widows and widowers begin the analysis with significantly lower income-to-needs ratios 5 years prior to the death, while middle-aged widows experience more economic change near the time of the death. These findings suggest that both middle-aged and older cohorts of widowed individuals may have made consumption choices over the life cycle that differ from those made by their intact counterparts.

Age Factors↗
PubMed1991

Solid waste scavenger community: an investigation in Bangkok, Thailand.

A solid waste scavenger community at On-Nooch dump site in Bangkok was investigated. The purpose was to identify the dimensions of the public health risk to this group of people and their community due to exposure to hazardous conditions from waste materials. A cross-sectional descriptive study utilizing field surveys and measurements was performed. The demographic, socioeconomic, health related and environmental characteristics of this community were examined. Health complaints and injuries were inventoried among scavengers. Prevalence of childhood respiratory illness was high especially in those households where smoking was present. Intestinal helminthic and protozoan infection in children were detected. Six individuals with possible HIV infection and a number of Hepatitis B anti-genemia were found among male respondents. An appreciable proportion of respondents fell below normal when tested for lung function. Air pollution measurements showed acceptable ambient air levels except for particulate matters. Water quality was low for both potable and nonpotable water.

Adolescent↗
PubMed1991

Remarriage patterns among recent widows and widowers.

Remarriage is one of the most important determinants of physical and economic well-being among the widowed. The goal of this study is to estimate how hazard rates for remarriage vary among widows and widowers on the basis of both observable and unobservable characteristics. The remarriage estimates rely on nationally representative samples of widows and widowers from the Panel Study of Income Dynamics. Continuous-time hazard rate regressions indicate strong age and duration dependence effects for middle-aged widows and widowers and for older widowers. Among middle-aged widows, blacks and those with dependent children in the home have lower rates of remarriage. For middle-aged widowers, living in urbanized areas limits the prospects of remarriage. For older widowers, education and, to some extent, economic status appear to have positive effects on the remarriage rates. Overall, age and time since widowhood have the strongest and most consistent effects on remarriage rates for different widowed groups.

Age Factors↗
PubMed1991

The effect of a stiff spinal implant on the bone-mineral content of the lumbar spine in dogs.

The response of canine lumbar vertebral bone to the application of a stiff transpedicular screw-plate implant from the third to the fifth lumbar vertebra, without arthrodesis, was investigated. Five groups of six dogs each were studied: dogs that had not had an operation (control group); dogs that had had a sham operation, with survival periods of three and six months; and dogs that had received an implant, with survival periods of three and six months. The results were the same in specimens from the control group and the group that had had a sham operation. In the groups that had received an implant, dual-photon absorptiometry revealed an insignificant decrease in bone-mineral content at the bypassed fourth lumbar segment (17 per cent at three months and 12 per cent at six months). When the data for the three and six-month intervals were pooled, the mean decrease in bone-mineral content of 14 per cent was significant. Histomorphic study yielded similar results; the mean decrease in bone-mineral content for the pooled three and six-month specimens was significant (16 per cent). Losses were similar for the ventral and dorsal columns. Histomorphometric analysis also showed a significant (13 per cent) loss of bone-mineral content at the adjacent caudad (sixth lumbar) vertebra for the pooled three and six-month groups. The results of the methods of analysis of loss of bone-mineral content correlated strongly. Under these experimental conditions, a stiff spinal implant caused loss of bone-mineral content of the bypassed vertebral segment, although the loss was less than anticipated and did not increase between three and six months.

Absorptiometry, Photon↗
PubMed1991

Asymptomatic versus symptomatic herniated thoracic discs: their frequency and characteristics as detected by computed tomography after myelography.

We retrospectively reviewed the myelograms of 433 patients and identified those who had no symptoms or signs referable to the thoracic cord, roots, or nerves. By post-myelography computed tomographic scan criteria, our frequency of asymptomatic thoracic herniated discs (ATHDs) was calculated. Post-myelography computed tomographic scans of 68 ATHDs were analyzed. Their imaging characteristics were compared with our own series of 5 symptomatic thoracic herniated discs and symptomatic thoracic herniated discs in the literature. We were unable to identify any imaging features that could reliably classify a disc as an ATHD or a symptomatic thoracic herniated disc. Our results call into question the propriety of prophylactic surgery for ATHDs, even when the lesions are radiographically impressive.

Adult↗
PubMed1978

A stereotaxic method based on ventricular radiography in the cat (with special reference to the stereotaxic topography of the substantia nigra).

A method based on an intracerebral coordinate system and contrast ventriculography was developed for stereotaxic surgery in the cat. The intercommissural (CA-CP) line was used as the principal reference because its length showed little variability in animals within a wide weight range. The stereotaxic coordinates of the substantia nigra (SN) in relation to the CA-CP line and the midline were evaluated in serail sections. Stereotaxic operations with the use of ventricular radiography were performed in different parts of the SN in 18 cats. Histological verification showed that the selected target regions within the SN were very accurately reached in all animals operated with this method. The precision of the stereotaxic method based on the intracerebral coordinate system compared to the Horsley-clarke method is discussed.

Animals↗
PubMed1978

Nigrothalamic pathway in the cat demonstrated by autoradiography and electron microscopy.

Light microscopic autoradiography and electron microscopy were used to trace the nigrothalamic projections and to study the sites of termination of this pathway in the cat. Injections of tritiated amino acids or electrolytic lesions were placed in the substantia nigra pars reticularis (SNr). An accumulation of radioactivity was found in the ventral medial nucleus and in the ventromedial part of the ventral anterior nucleus. At the ultrastructural level degenerating medium size synaptic boutons and medium size myelinated fibers were observed in these nuclei. The boutons contained clear pleomorphic veiscles and formed symmetrical type synaptic contacts with regular type dendrites and vesicel-containing dendrites. The present findings indicate that the ventral medial nucleus is the principal site of termination of nigrothalamic projections in the cat.

Animals↗
PubMed1978

Primary leptomeningeal melanoma: an ultrastructural study.

A primary leptomeningeal melanoma in a 19-year-old white women has been shown by electron microscopy to contain light and dark cells. The light cells fill the subarachnoid space, contain mature melanosomes and exhibit intracytoplasmic fine fibrils. The dark cells are found within the collagen network of pia-arachnoid. They possess a small rim of ribosomal-rich cytoplasms, occasional premelanosomes and no intracytoplasmic fibrils. The tumor cells appear to arise from these dark activated melanoblasts in the pia-arachnoid and proliferate into more differentiated light cells. A similar pattern of two types of cells has not been described in primary CNS melanomas. The possibility of differentiation from cutaneous melanoma is discussed.

Adult↗
PubMed1978

Diverticular disease of the colon: surgical management at a military hospital.

A recent review of the surgical management of diverticular disease of the colon included 73 patients. One-stage resections were accomplished in 67%, primarily in patients operated on electively for recurrent diverticulitis or fistula, and in the group of patients with cecal diverticulitis operated on for presumed appendicitis. Single-stage resection with ileorectal anastomosis is also preferred in patients with massive diverticular bleeding. For patients with large abscesses or diffuse peritonitis a two-stage procedure which removes the site of disease in the initial operation is recommended. There were no deaths and a lower incidence of complications in the group of patients who had elective operations for recurrent diverticulitis and fistula.

Adult↗