The 1492V BI utilizes the a-glucosidase enzyme system, which is generated naturally within growing cells of Geobacillus stearothermophilus. The a-glucosidase in its active state is detected by measuring the fluorescence produced by the enzymatic hydrolysis of a non-fluorescent substrate, 4-methylumbelliferyl-a-D-gl ucoside (MUG). The resultant fluorescent by-product, 4-methylumbelliferone (MU), is detected in the 490 Auto-reader. The presence of fluorescence within 1 hour of incubation of the 1492V BI in the 490 Auto-reader indicates a steam sterilization process failure.