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Biomedical subjects

S M Stevens

Publications and source records attributed to S M Stevens.

At least 19 recordsLinked to original sources
PubMed2000

The flagellar filament of Rhodobacter sphaeroides: pH-induced polymorphic transitions and analysis of the fliC gene.

Flagellar motility in Rhodobacter sphaeroides is notably different from that in other bacteria. R. sphaeroides moves in a series of runs and stops produced by the intermittent rotation of the flagellar motor. R. sphaeroides has a single, plain filament whose conformation changes according to flagellar motor activity. Conformations adopted during swimming include coiled, helical, and apparently straight forms. This range of morphological transitions is larger than that in other bacteria, where filaments alternate between left- and right-handed helical forms. The polymorphic ability of isolated R. sphaeroides filaments was tested in vitro by varying pH and ionic strength. The isolated filaments could form open-coiled, straight, normal, or curly conformations. The range of transitions made by the R. sphaeroides filament differs from that reported for Salmonella enterica serovar Typhimurium. The sequence of the R. sphaeroides fliC gene, which encodes the flagellin protein, was determined. The gene appears to be controlled by a sigma(28)-dependent promoter. It encodes a predicted peptide of 493 amino acids. Serovar Typhimurium mutants with altered polymorphic ability usually have amino acid changes at the terminal portions of flagellin or a deletion in the central region. There are no obvious major differences in the central regions to explain the difference in polymorphic ability. In serovar Typhimurium filaments, the termini of flagellin monomers have a coiled-coil conformation. The termini of R. sphaeroides flagellin are predicted to have a lower probability of coiled coils than are those of serovar Typhimurium flagellin. This may be one reason for the differences in polymorphic ability between the two filaments.

Amino Acid Sequence↗
PubMed1997

Medical savings accounts (MSAs)--big benefits for small business.

The Health Insurance Portability and Accountability Act, passed by Congress last year, implemented a four-year pilot project that allows employees of small businesses to set up tax-free interest-bearing medical savings accounts. These accounts offer advantages for both employees and employers

Career Mobility↗
PubMed1994

Rectal spirochaetosis in homosexual men: the association with sexual practices, HIV infection and enteric flora.

OBJECTIVE: To determine the prevalence of rectal spirochaetosis in homosexual men attending a sexually transmissible diseases clinic and investigate the association between their presence and sexual practices, HIV infection and enteric flora. DESIGN: The study included 144 male homosexual subjects who each completed a questionnaire, underwent physical examination, proctoscopy and investigations for STD and HIV screening, rectal biopsies and collection of faecal samples. SETTING: The Sexual Health Centre, Sydney Hospital, Sydney, Australia. RESULTS: Spirochaetes were detected in 39% of the rectal biopsies, using histological criteria. Logistic regression analysis showed that rectal spirochaetosis was significantly associated with: oral-anal contact. (P < 0.05, OR 3.45, 95% CI 1.48-8.05); detection of 3-5 different non-pathogenic protozoa in faeces (P < 0.01, OR 11.68, 95% C.I. 2.33-58) and a positive HIV antibody test (P < 0.01) OR 4.48, 95% C.I. 1.28-15.72). CONCLUSIONS: These findings indicate that rectal spirochaetosis is relatively common in homosexual men. The association with non-pathogenic protozoa is most likely attributable to the common mode of transmission viz oral-anal contact. However it is difficult to determine whether the association with HIV infection is cause or effect because of the limitations in the study design. Further information is required to determine the clinical significance of infection with these organisms.

Adult↗
PubMed1994

Estimating neonatal mortality risk: an analysis of clinicians' judgments.

BACKGROUND: Clinicians' estimates of mortality risk in the neonatal intensive care unit (NICU) have implications for patient triage, transfer, initiation and termination of life support, and allocation of medical resources. The accuracy of these judgments has not been studied, nor the differences between nurses and attending physicians. OBJECTIVES: 1) evaluate the accuracy of subjective judgments of NICU unit mortality risk, 2) identify the key components of clinician judgments, 3) compare accuracy between attending physicians and nurses, and 4) examine the utility of combining an objectively computed risk and clinician judgments to improve predictions. METHODS: We obtained estimates of mortality risk on 544 admissions to two NICUs on the day of admission from the attending physician and primary nurse. These were compared with an objective computed mortality risk based on birth weight and the Score for Neonatal Acute Physiology (SNAP) using a linear judgment analysis model, as well as with actual outcomes. RESULTS: Physicians and nurses had good discriminating power with actual mortality rates ranging from 0% among low risk patients to 67% among those with the highest mortality estimates. Physicians had a tendency to overestimate mortality risk. Clinicians base their estimates on the same factors and similar judgment weights as the empiric mortality risk model (22% birth weight, 62% illness severity (SNAP), 13% low Apgar, and 3% for intrauterine growth restriction). Clinicians place additional emphasis on therapeutic as well as physiologic factors. When the computed risk and physician judgment were combined, both made significant contributions in a logistic mortality risk model. CONCLUSIONS: Clinician judgments of mortality risk are fairly accurate and similar to an objective illness severity index. This simple method provides insight into clinical decision making and has important applications in improving direct patient care, appropriate allocation of medical resources, and medical training.

Clinical Competence↗
PubMed1992

Rheological changes in the prodromal and established phases of sickle cell vaso-occlusive crisis.

A rheological study has been made in 20 patients with sickle cell anaemia in the steady state and in the prodromal and established phases of 12 vaso-occlusive crises. Rheology of sickle cells was studied by discontinuous density gradient fractionation and by filtration through pores of 5 microns diameter. The prodromal phase of crisis (day 1), when compared with mean steady state values, was associated with the development of a sub-population of poorly deformable dense cells. This sub-population appeared 1 or more days before the acute-phase rise in C-reactive protein, orosomucoid, fibrinogen, plasma viscosity and leucocytes, and before the rise in serum lactate dehydrogenase. As crisis evolved, the sub-population decreased to steady-state values, or below, by days 6-7. Identification of the prodromal phase of sickle cell crisis has allowed the detection of rheological changes of potential aetiological significance.

Acute-Phase Reaction↗
PubMed1992

Subclinical ischaemic episodes during the steady state of sickle cell anaemia.

AIMS: To determine the clinical, haematological, biochemical and rheological changes that occur in the asymptomatic steady state of sickle cell anaemia. METHODS: Patient self-assessment visual analogue scores (for wellbeing and tiredness), the blood concentration of acute phase proteins (C-reactive protein, orosomucoid, and fibrinogen), and blood rheology (percentage of dense cells and the number of sickled cells that occluded pores 5 microns in diameter) were studied longitudinally on 10 occasions in each of 20 outpatients with sickle cell anaemia. RESULTS: Patients in the steady state showed fluctuation in visual analogue scores, in concentration of acute phase proteins, and in rheological parameters consistent with minor episodes of tissue injury. Significantly more variation in acute phase proteins occurred in the steady state of 14 of the 20 patients who developed one or more vaso-occlusive crises during the 16 month study period. Rheological fluctuation in the steady state simulated rheological change during crisis, namely a transient rise and then fall in the number of dense and poorly filterable cells. CONCLUSIONS: The term "steady state" is a misnomer, being characterised by biochemical and rheological fluctuation consistent with minor episodes of microvascular occlusion that are insufficient to cause the overt tissue infarction of painful crisis.

Acute-Phase Proteins↗
PubMed1992

Concurrent zidovudine-induced myopathy and hepatoxicity in patients treated for human immunodeficiency virus (HIV) infection.

Myopathy and hepatic toxicity are important complications of zidovudine (3'-azido-3'-deoxythymidine therapy) in patients infected with the human immunodeficiency virus (HIV) both may also occur in HIV infection in the absence of zidovudine therapy. We report 2 cases of myopathy caused by zidovudine, occurring within 16 wks of initiation of therapy, and a case of concurrent hepatic and muscle toxicity. In one case, electron microscopy demonstrated characteristic enlarged mitochondria with paracrystalline inclusions. This technique can distinguish the myopathies caused by either HIV or zidovudine. Both zidovudine-induced myopathy and hepatoxicity require discontinuation of the drug if severe.

Adult↗
PubMed1990

The effects of anthranilic acid on gene expression.

1. A Drosophila pseudoobscura amylase gene cloned in Escherichia coli is expressed at high levels. The expression of this gene is repressed when glucose (0.5% final concentration) is added to a starch minimal medium culture of E. coli cells containing the amylase plasmid. 2. Addition of anthranilic acid (5 and 7 mM final exogenous concentration) to catabolite repressed cells mimics the action of adenosine 3'5' cyclic monophosphate (cAMP) by depressing the expression of the amylase. 3. The results suggest that anthranilic acid acts either indirectly, possibly through the glucose transport system, or directly, by way of an intercalative model of initiation, to alter the levels of transcription.

Amylases↗
PubMed1989

Effect of polymerization tendency on haematological, rheological and clinical parameters in sickle cell anaemia.

The polymerization tendency of sickle haemoglobin was estimated as a function of oxygen saturation in 30 patients with homozygous sickle cell anaemia. The deformability of their erythrocytes was also measured, by initial-flow-rate filtration at 37 degrees C through pores of 5 microns diameter, and clinical severity was assessed using a visual analogue scale. By means of partial correlation analysis, it was found that correlations between haematological, rheological, and clinical parameters in sickle cell anaemia could be explained on the basis of an association of each variable with polymerization tendency. Patients with the greatest tendency to form polymer had the least deformable erythrocytes and perceived their disease to be more severe as judged by the visual analogue scale. Polymer formation also appeared to be a determinant of the number of dense cells which, in turn, determine haemolytic rate and erythrocyte deformability.

Anemia, Sickle Cell↗
PubMed1987

An amylase gene from Drosophila pseudoobscura is expressed in Escherichia coli. Functional selection and biochemical comparisons of the fly- and clone-produced amylases.

An amylase gene from Drosophila pseudoobscura was isolated from a genomic library constructed in pBR322 and cloned in Escherichia coli by selecting for the ability of its product to hydrolyze starch, a carbon source not normally utilized by E. coli. Hybridization of pAMY17F to D. pseudoobscura polytene chromosomes shows a positive signal at the amylase pseudogene locus (bank 78, chromosome 3). The chimeric plasmid pAMY17F, has been altered in such a way as to increase amylase expression. Southern and Northern hybridizations to the cloned amylase DNA indicate that the source of the gene is from D. pseudoobscura. Biochemical properties such as pH optima, substrate specificities, electrophoretic analyses, inhibitor sensitivities, heat stabilities, temperature responsiveness and molecular weights indicate that the amylases produced by the fly and bacterial clone are similar and have similar properties. It appears that E. coli/pAMY17F is producing an amylase like that found in D. pseudoobscura.

Amylases↗
PubMed1986

Primary cerebral neuroblastomas. A clinicopathological study of one adolescent and five adult patients.

Neuronal differentiation was demonstrated by light microscopy, immunohistochemistry and electron microscopy in the cerebral neoplasms of one adolescent and five adult patients. The tumours exhibited a wide spectrum of cellular differentiation from low to high grade malignancy which seems to correlate well with their biological behaviour. The natural history of these 6 cerebral neuroblastomas is rather long compared to that of other malignant primary cerebral neoplasms of adulthood; however, 2 patients died, one survived about 5 yr after initial symptoms whilst an untreated patient survived more than 12 yr. It is suggested that morphological grading along the lines of Kernohan's system may be useful in determining the prognosis and postoperative management of patients with cerebral neuroblastomas.

Adolescent↗
PubMed1985

Round-headed spermatozoa: a case report.

A case is presented of a patient in whom over 90% of spermatozoa had distinctive round heads as seen by light microscopy. Other features of his semen were only slightly abnormal. Electron microscopy revealed spermatozoa with no acrosome confirming the sterility of the patient. With such men other means of achieving a family must be considered.

Adult↗
PubMed1985

Atypical polypoid adenomyoma: a case report with ultrastructural examination.

A case of atypical polypoid adenomyoma occurring in a 40 yr-old female is reported. The lesion was composed of irregular glands lined by atypical epithelium lying in a spindle cell stroma containing smooth muscle cells. The mitotic count of the stroma was less than 1 per 10 high power fields. Squamous metaplasia was present in the glandular elements. Ultrastructural examination of the stroma confirmed the presence of smooth muscle cells. The lesion is compared with similar cases previously reported. The differential diagnosis is considered, including endometrial adenocarcinoma, adenomyosis, endometrial polyps and mixed Mullerian tumours. Atypical polypoid adenomyoma is a benign lesion, and conservative management is recommended.

Adult↗
PubMed1982

Neuronal ceroid lipofuscinosis in the amaurotic retardate: electron microscopic confirmation.

The clinical features of two cases of blindness with pigmentary retinopathy in young retardates are presented. The diagnosis of neuronal ceroid lipofuscinosis (Batten's Disease) was suspected. This was confirmed in both cases by electron microscopic examination of blood and skin with demonstration of fingerprint and curvilinear inclusions. These inclusions are present in cells other than neurons; circulating lymphocytes, smooth muscle cells and eccrine sweat glands suggesting a more widespread pathological process. Less invasive procedures namely venepuncture and skin biopsy may be preferred to brain and rectal biopsy in the absence of a practical biochemical analysis at the present time.

Adolescent↗
PubMed1982

Crigler-Najjar Type 1 syndrome: absence of hepatic bilirubin UDP-glucuronyl transferase activity and therapeutic responses to light.

A 16-year-old boy with severe congenital unconjugated hyperbilirubinaemia is described in whom mental retardation occurred as an isolated neurological deficit. The diagnosis of Crigler-Najjar type 1 syndrome was supported by an extreme and persistent elevation of serum unconjugated bilirubin (650 mumol/l), failure of administered phenobarbitone to lower serum bilirubin concentration and family history of a similarly affected sibling. Hepatic bilirubin UDP-glucuronyl transferase activity determined in vitro by a sensitive new enzyme assay was found to be absent using bilirubin or bilirubin monoglucuronide as substrate. Phototherapy for 12 hours each night produced a partial but highly significant reduction in serum bilirubin concentration, which was not influenced further by the administration of cholestyramine.

Adolescent↗
PubMed1976

Necrotizing and giant cell granulomatous phlebitis of caecum and ascending colon.

A distinctive form of necrotizing and granulomatous phlebitis of a segment of large intestine is described in a previously healthy 36-year-old woman who presented with sudden severe abdominal pain and diarrhoea. At operation the caecum and ascending colon were oedematous and inflamed and right hemicolectomy was performed. Microscopically there was striking involvement of veins in all coats of the bowel ranging from recent fibrinoid necrosis of the whole vessel wall in the case of the caecum, to more chronic giant cell granulomas in parts of the vessel wall with partial or complete occlusion of the lumen in ascending colon. Arteries and lymphatics were entirely spared of these changes. The aitiology of this condition has not been elucidated but the histological appearances and site of involvement suggest an immunological reaction to material absorbed from the bowel. No evidence of food or other allergies or of infection has been obtained. The patient remains symptom free after 18 months. This form of phlebitis does not appear to have been previously described.

Adult↗