A QUANTITATIVE MICROASSAY FOR ENDOTOXIN AND CORRELATION WITH BACTERIAL DENSITY IN URINE

Endotoxin concentrations in urine samples from patients with chronic Gram-negative bacteriuria were measured using a Limulus amoebocyte lysate (LAL) assay modified to overcome the obstacles to the quantitative assay of endotoxin in urine. With this modified LAL assay, in which kinetic readings of optical density change are made and heat treated 10% plasma may be used as a substitute for the chromogenic reagent, endotoxin concentrations could be measured over a range of at least four log10 fold in a microassay format. The concentration of endotoxin correlated with the number of colony forming units (CFU) of bacteria in the urine and the presence of heat treated 10% plasma was found to improve this correlation. In urine infected with one of the Enterobacteriaceae, 20 ng of endotoxin was equivalent to approximately 10(6) CFU and the concentration was 2-3 times higher for a given CFU count than in urine infected with Pseudomonas species.