The synthesis of novel chromogenic enzyme substrates for detection of bacterial glycosidases and their applications in diagnostic microbiology

The preparation and evaluation of chromogenic substrates for detecting bacterial glycosidase enzymes is reported. These substrates are monoglycoside derivatives of the metal chelators catechol, 2,3-dihydroxynaphthalene (DHN) and 6,7-dibromo-2,3-dihydroxynaphthalene (6,7-dibromo-DHN). When hydrolysed by appropriate bacterial enzymes these substrates produced coloured chelates in the presence of ammonium iron(III) citrate, thus enabling bacterial detection. A β-d-riboside of DHN and a β-d-glucuronide derivative of 6,7-dibromo-DHN were particularly effective for the detection of S. aureus and E. coli respectively.

Audit of near patient cholesterol testing in occupational health clinics

An audit of near patient cholesterol testing was carried out in occupational health clinics. The aims were to examine the statistical agreement between Reflotron and laboratory measurements of blood cholesterol and to formulate a policy for the use of Reflotrons in cholesterol testing. Three hundred and fifty-two staff members attending occupational health clinics over a period of 10 months had blood taken for both Reflotron and laboratory measurements. The correlation between the two methods was 0.95. The Reflotron had a negative bias compared to the laboratory, with the mean difference between the two methods of measurement being -0.21 mmol/l (95 per cent confidence interval -0.18 to -0.25 mmol/l). Despite the high correlation coefficient and small mean difference, the scatter of Reflotron-laboratory differences was broad, with 95 per cent of the differences lying in the range of 0.95 mmol/l below to 0.52 mmol/l above the laboratory result. For Reflotron results of 5.50 mmol/l and greater, the sensitivity and specificity of the Reflotron in detecting subjects with laboratory cholesterol levels greater than 6.5 mmol/l were 100 per cent and 70 per cent respectively. The laboratory participated in two external quality assessment schemes for cholesterol testing during the course of the audit and all the results of these fell within the acceptable limits. The audit demonstrated that the Reflotron was too imprecise to be used to give accurate measurements of blood cholesterol. However, providing a suitable Reflotron result above which patients were sent for confirmatory laboratory testing was selected, it was an acceptable screening device in the detection of hypercholesterolaemia. Other Reflotron users should consider carrying out similar audits.