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Biomedical subjects

D Law

Publications and source records attributed to D Law.

10 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↗
PubMed1976

The continuing challenge of acute and perforated appendicitis.

A two year review of 216 patients with a preoperative diagnosis of appendicitis is used to help clarify the continuing points of controversy concerning appendicitis. Morbidity of perforated appendicitis by far exceeds that of nonperforated cases. Twenty-nine per cent of patients had perforation with a postoperative complication rate of 33 per cent. Rate of wound infection after perforation was 15 per cent despite antibiotics and delayed wound closure. Pediatric patients in this study did not experience a higher incidence of perforation or complication. A decision tree for management of acute appendicitis is presented.

Abscess↗
PubMed1976

Management of tracheobronchial foreign bodies in children: a reevaluation of postural drainage and bronchoscopy.

The efficacy of the inhalation-postural drainage technique for removal of aspirated foreign bodies was compared with that of bronchoscopy in 76 children. Twelve of 49 children on postural drainage coughed out the foreign body (25%); the other 37 required bronchoscopy. The foreign body was successfully removed in 56 of 63 children who were bronchoscoped (89%). Our experience suggests that a trial of inhalation-postural drainage, administered in a hospital, may be valuable in the initial management of aspirated foreign bodies. If unsuccessful after several treatments, however, the technique should be abandoned, and bronchoscopy performed. Delay of foreign body removal beyond 24 hours may be associated with increased morbidity and prolonged hospital stay. With recent improvements in pediatric endoscopic instruments, the efficacy of bronchoscopy exceeds 90%.

Bronchi↗