Automated bacteriuria screening using the Berthold LB 950 luminescence analyser

Evaluation of enzyme linked immunosorbent assay for screening urinary tract infection in elderly people

AIMS

To evaluate the Uristat test, an indirect enzyme linked immunosorbent assay for the qualitative detection of antibodies in urine, as a screening, and in the diagnosis of urinary tract infection in the elderly.

METHODS

Semiquantitative culture was compared with conventional microscopy, dipstick analysis and the ELISA. In the ELISA, 371 urine samples were examined for antibodies to an antigen mixture of six common urinary pathogens.

RESULTS

The sensitivity was 91% and the specificity 25% for the ELISA. The negative predictive value was 81% and the positive predictive value was 43%.

CONCLUSIONS

In its present form the Uristat test has no clear advantages over conventional bacteriological techniques for screening urine samples for infection in an elderly population.

Evaluation of a bioluminescence assay for the detection of bacteriuria

Bacteriuria defined with urine culture as the reference method was compared with bacterial adenosine triphosphate (ATP) measurements of cystoscopical urine samples from 216 men. Discrepant samples were studied by reculturing and microscopy of the sediment. Results show a good correlation (sensitivity 1.0 and specificity 0.95) between bacteriuria greater than or equal to 10(4) cfu/ml and bacterial ATP greater than 10 nmol/l measured by bioluminescence. Samples with macroscopic hematuria may influence the ATP value and give false positive results.

Clinical and biochemical applications of luciferases and luciferins

Recent advances in the analytical applications of bacterial and firefly luciferases and firefly luciferin are reviewed. Luciferases have been used in soluble and immobilized/co-immobilized forms in assays for a variety of enzymes, substrates, and cofactors. The firefly luciferase reaction forms the basis of rapid microbiological tests which have found application in susceptibility testing, detection of bacteriuria, activated sludge analysis, and food testing. Rapid microbiological assays are also possible using bacteriophages containing the lux genes from Virbrio harveyi. Both the firefly and the bacterial luciferase reaction have been applied in immunoassay and DNA probe assays and the firefly luciferin phosphate substrate for alkaline phosphatase labels has proven particularly successful.

Evaluation of six screening methods for detecting significant bacteriuria

Six screening methods for the successful detection of significant bacteriuria--electrical impedance (Malthus), automated acridine-orange staining (Autotrak), particle counting (Ramus), bioluminescence, nitrite and leucocyte test strip (BM Nephur), and microscopy--were evaluated. All had excellent predictive values for a negative result (97%-100%) but were less accurate in predicting a positive result (31%-83%). All methods had high sensitivities (83%-100%) but lower levels of specificity (68%-79%). Bioluminescence was the method with the highest specificity (79%) and the lowest rate of false positive results (15%). It would be inappropriate to decide on treatment and management on the basis of the positive results achieved with any of the methods evaluated, but all methods tested could be used for screening out negative results.