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Biomedical subjects

D Law

Publications and source records attributed to D Law.

At least 19 recordsLinked to original sources
PubMed1992

The influence of salt concentration on the detection of methicillin resistance in coagulase-negative staphylococci.

The detection of methicillin resistance by the breakpoint method was examined using three different media containing varying quantities of added salt and 4 mg/L methicillin or 1 mg/L oxacillin. Three hundred clinical isolates of eight species of coagulase-negative staphylococci were tested. In 68 strains methicillin resistance was expressed only at certain salt concentrations and four distinct susceptibility phenotypes were observed. A correlation between the susceptibility phenotype and the species of the isolate was found. Testing on Columbia agar (CA) containing 4 mg/L methicillin with 0% and 4% added salt was required to detect resistance in all 68 strains. Resistance was detected less frequently using Balanced Sensitivity Test (BST) agar or Diagnostic Sensitivity Test (DST) agar containing methicillin or CA, BST or DST agar containing oxacillin. Increased production of beta-lactamase was shown to be an unlikely cause of MR in these strains. Disc sensitivity tests were performed on the 68 strains using five different media. Columbia agar gave optimum results as the other media gave enhanced zones of inhibition for some isolates. Further tests were performed on CA containing varying salt concentrations using both oxacillin and methicillin discs. A close relationship between the staphylococcal species, and the influence of increasing salt concentration on zone size was found. Discrepancies were noted between results obtained by breakpoint and the results obtained with methicillin discs particularly with Staphylococcus simulans and some Staphylococcus epidermidis strains. Results obtained with oxacillin discs more closely correlated with those obtained by breakpoint, but only when disc tests were performed on media with low and high salt content. To identify methicillin resistance in strains of CNS by disc tests, the use of Columbia agar with 0% and 5% added salt and oxacillin discs is recommended.

Coagulase↗
PubMed1992

Detection by ELISA of low numbers of Shiga-like toxin-producing Escherichia coli in mixed cultures after growth in the presence of mitomycin C.

Techniques currently available to detect Shiga-like toxin (SLT)-producing Escherichia coli lack sensitivity or require specialised equipment and facilities, and in some cases detect only strains belonging to serotype O157. We have used an ELISA technique, capable of detecting both SLTI and SLTII with crude P1 glycoprotein from hydatid cysts, in combination with enhancement of toxin production by culture with mitomycin C. Supernates of Tryptone Soya Broth cultures containing mitomycin C 200 ng/ml were tested for SLTII. For SLTI, cell lysates pre-treated with polymyxin B were tested. In tests with E. coli O157:H7 in mixed culture with E. coli strain C600 alone, or with E. coli C600, Proteus mirabilis and Enterococcus faecalis, SLTI could be detected when the proportion of toxigenic organisms represented 1% of the mixture, and SLTII when the proportion was 0.025%. When faecal samples with added E. coli O157:H7 were examined in this system, SLTII-producing strains were detected when they comprised less than 0.1% of the coliform population. This technique is a sensitive and specific assay for detecting low numbers of SLT-producing organisms in mixed culture such as occurs in cases of haemolytic uraemic syndrome and haemorrhagic colitis.

Bacterial Toxins↗
PubMed1992

The iron uptake mechanisms of enteropathogenic Escherichia coli: the use of haem and haemoglobin during growth in an iron-limited environment.

The iron uptake mechanisms of enteropathogenic Escherichia coli (EPEC) were examined and compared with those of control E. coli strains. The incidence of aerobactin production was similar (39% and 37% respectively) in the two groups. The quantities of enterochelin produced by aerobactin-negative EPEC and control strains were similar, as were the quantities of enterochelin produced by aerobactin-positive EPEC and control strains. The ability to use haem or haemoglobin as an iron source in an iron-restricted environment was found in 80.4% and 60.8% of EPEC strains respectively, and in 76.6% and 56.6% of control E. coli strains. The ability of E. coli strains to use these compounds was not related to the production of enterochelin or aerobactin or to the production of haemolysins, and may be an important characteristic of bowel organisms. When growing in an iron-limited environment, the iron contained in haemoglobin was used in preference to ovotransferrin-bound iron. During periods of haemoglobin-stimulated growth, the enterochelin uptake system was shown to be fully expressed and may be involved in transport of haemoglobin-derived iron into the cell. Uptake of ovotransferrin-bound iron took place immediately upon exhaustion of haemoglobin-derived iron. The ability to use iron derived from haem compounds represents an alternative iron uptake mechanism for organisms growing in an iron-limited environment and allows greater flexibility during growth in vivo.

Bacterial Outer Membrane Proteins↗
PubMed1992

Citrate transport in proximal cell line.

Citrate uptake into kidney proximal tubules occurs via an apical dicarboxylate transporter and a poorly characterized process in the basolateral membrane. We used OK cells, a cell line derived from opossum kidney, to study citrate transport in proximal tubule-like cells. Citrate uptake into cell monolayers was studied using [14C]citrate with [3H]mannitol as a volume marker. Citrate uptake into these cells was sodium dependent and saturable with increasing concentrations of citrate. In contrast to previous models, citrate transport was altered minimally by changes in pH from 6.2 to 7.0 and increased at pH 7.4 to 7.8. A variety of di- and tricarboxylates were tested for interaction with citrate transport. The dicarboxylates succinate, malate, and oxaloacetate at 1 mM concentration inhibited citrate uptake minimally (uptake at least 80% of control); one dicarboxylate, alpha-ketoglutarate, did inhibit citrate uptake significantly. In contrast, the tricarboxylates isocitrate and tricarballylate inhibited citrate uptake significantly, indicating probable competitive inhibition with the transport process. These characteristics are distinctly different from those of the apical membrane dicarboxylate transporter. 1,2,3-Benzenetricarboxylic acid, an inhibitor of the mitochondrial tricarboxylate transporter, did not alter citrate uptake. In conclusion, the OK proximal cell line exhibits a novel citrate transport process compared with the apical transport of citrate described in most proximal systems. This transport process probably involves the trivalent species of citrate in contrast to the usual predominant transport of divalent citrate. This transport process may represent a process similar to that in the basolateral membrane of the proximal tubule.

Animals↗
PubMed1992

Escherichia coli: rapid identification by chromogenic tests.

A system has been assessed for the identification of Esch. coli using a rapid triple chromogenic test which relies on the ability of the organism to produce a beta-galactosidase, a beta-glucuronidase, and indole. Coliforms which had been fully identified were tested by this system. Of 512 non-Esch. coli strains there were no false positives, whereas of 514 Esch. coli strains 486 (94.5%) were found to give positive results. Two hundred and twenty-one coliforms that had been isolated from blood cultures were also tested using the colistrip in advance of, or without knowledge of the API 20E result. The test was found to be 100% specific and 94% sensitive for the 105 Esch. coli strains. The test was rapid, simple to perform and economical.

Chromogenic Compounds↗
PubMed1991

Characterization and application of a murine monoclonal antibody that reacts specifically with the serogroup D1 Salmonella.

A murine hybridoma cell line that produces monoclonal antibody (mAb) against the serogroup D1 Salmonella lipopolysaccharide (LPS) antigen was established. The trisaccharide tyvelose alpha 1----3 mannose alpha 1----4 rhamnose was shown to be involved in the reactive epitope of the mAb since this mAb reacted strongly with strains of serogroup D1 Salmonella but not with Salmonella strains from the O serogroups of A, B, and D2, and sodium meta-periodate was found to destroy the reactivity of the serogroup D1 O-antigen with the mAb. As such this mAb was found to be a useful serotyping reagent for the identification of serogroup D1 Salmonella, and for the differentiation of strains of serogroups D1 and D2 Salmonella which have identical flagellar H antigens.

Animals↗
PubMed1991

Problems of thermonuclease detection for identifying Staphylococcus aureus in blood culture broths.

The detection of thermonuclease by the Oxford strain and eight clinical isolates of Staphylococcus aureus in a variety of bacteriological broths with and without added blood was examined using a toluidine blue-DNA-agar plate method. In Isosensitest, brain-heart infusion, tryptic soy, nutrient and gas-liquid chromatography broths (all of which do not contain liquoid) thermonuclease detection was uncomplicated. In Bactec broths (containing liquoid) detectable thermonuclease activity was greatly reduced in the absence of blood. The addition of 10% blood to the Bactec broths restored the activity. Liquoid was shown to be responsible for the inhibition of thermonuclease activity, and its effect could be neutralised by the addition of blood, albumin, or haemoglobin. In specimens containing no blood, or insufficient blood to neutralise the liquoid in culture broths, more has to be added to prevent false negative reporting of S aureus. This can be done after growth at the time of thermonuclease testing. Clinical consequences of delayed identification of S aureus in routine blood cultures may be serious. The application of the thermonuclease test to blood culture broths is both fast and specific.

Culture Media↗
PubMed1990

Comparison of the NES and CNS/B neuropsychological screening batteries.

Computer and hand administered neuropsychological tests are utilized in the evaluation of central nervous system changes associated with environmental or occupational exposure to neurotoxicants. This study compares the computerized Neurobehavioral Evaluation System (NES) developed by Baker et al., 1985, with the hand administered California Neuropsychological Screening Battery (CNS/B) developed by Bowler et al., 1986. Both batteries were designed for screening of the effects of neurotoxicants on the central nervous system and require less than one hr to administer. Both screening batteries consist of tests of: mood, word knowledge, attention, concentration, learning and memory and psychomotor and visuomotor and visuospatial abilities. They were administered in a standardized fashion to 106 subjects. Results indicate strong positive correlations for tests of word knowledge, moderate correlations for attention and concentration, while weaker correlations were obtained for tests of memory, psychomotor and visuomotor and visuospatial ability. The NES may be more useful for large epidemiological studies while the CNS/B appears more useful for individual screening and clinical studies.

Anxiety Disorders↗
PubMed1989

Cross-sectional neurotoxicology study of lead-exposed cohort.

Although the toxic effects of lead have been known for centuries, lead intoxication is still widespread in the United States. Without baseline tests of neuropsychological, neurobehavioral and neurophysiological testing it may be difficult to detect subtle changes in neurological function after lead exposure. This may be further confounded by partial chelation treatment and exposure to neurotoxic mixtures or inability to quantitate alcohol consumption. We undertook a cross-sectional study to address these problems in 24 exposed and 29 control subjects in a plant that manufactured electrical components using fritted leaded glass to coat capacitors and transistors. Potentially exposed workers had blood lead levels ranging between 3 micrograms/dL to 135 micrograms/dL. Industrial hygiene monitoring revealed the plant's air lead levels ranged from 61 micrograms/m3 to 1,700 micrograms/m3 in excess of OSHA permissible exposure limits of 40 micrograms/m3/10 hr day. Using a specially designed battery of neurophysiological, neurobehavioral and neuropsychological screening tests, we demonstrated a significant difference from controls in measures of psychomotor speed, motor strength and verbal memory. Although limited by the cross-sectional design, these findings support the hypothesis that the battery of neurophysiological, neuropsychological and neurobehavioral tests can detect a significant inter-group differences between lead-exposed and control subjects.

Adult↗
PubMed1989

Functional electrical stimulation for upper limb strengthening in traumatic quadriplegia.

The hypothesis of this study was that the functional electrical stimulation (FES)-assisted exercise of partially paralyzed arm muscles would result in significantly greater muscle strength in the arms of spinal cord injured quadriplegics than equal periods of conventional isotonic exercise. Single muscles were studied in seven subjects in a crossover design consisting of equal periods of FES-assisted exercise and conventional exercise. It was concluded that for these subjects using this exercise regime, neither FES-assisted exercise nor conventional exercise produced improvements in maximum voluntary force that were either statistically or functionally significant. The results, although disappointing, have helped these subjects to be more realistic about the potential therapeutic benefits of FES.

Adult↗
PubMed1988

Aspiration cytology in the management of breast lesions.

In a group of patients with breast lumps, diagnosis made by pre-operative aspiration cytology was compared with that obtained by histological section of excised specimens. Results showed that aspiration cytology correctly diagnosed 89% of malignant lesions and 92.6% of benign lesions based upon histological diagnosis. Cytological diagnosis of benign disease had a false negative rate of 6% while cytological diagnosis of malignant disease had a 2.7% false positive rate. Only 3.5% of cytologies returned an inadequate diagnosis. This study shows that aspiration cytology should be useful in allowing a better psychological preparation of patients before surgery as well as better utilization of operation theatre facilities.

Biopsy, Needle↗
PubMed1987

Examination of enteropathogenic Escherichia coli strains for an adenylcyclase stimulating factor.

Enteropathogenic Escherichia coli strains are a common cause of infantile diarrhoea but do not produce recognised enterotoxins. Three strains of proven virulence were examined for toxins which may be missed in conventional tests. Cell lysates and concentrated culture supernates of organisms grown in five different media gave negative results when examined for adenylcyclase stimulating activity. The additions of zinc ions or lincomycin to these media or the use of iron-depleted media also gave negative results. The significance of these findings and the possible role of other toxins in diarrhoea due to enteropathogenic E. coli are discussed.

Adenylyl Cyclases↗