Measurement of microbial alpha-amylases with p-nitrophenyl glycosides as the substrate complex.

The detection of alpha-amylase is commonly used in clinical microbiology laboratories to aid in differentiating Streptococcus bovis from other streptococci. It is also useful in identifying Eikenella corrodens and the gravis subspecies of Corynebacterium diphtheriae and in separating species of the genera Bacteroides, Clostridium, Actinomyces, and Bacillus. Currently, the most frequently used procedure utilizes starch as the substrate and iodine as the indicator. Starch is incorporated into a agar medium, the isolate is inoculated on the surface, and the medium is incubated for 24 to 48 h. A 15-min test containing p-nitrophenyl polyglycosides as the substrate complex was developed to yield results comparable with the agar-based starch test. The reagent was made in liquid form, 0.20 ml per tube, and could be incubated either in ambient air or at 35 degrees C. When dried, the p-nitrophenyl polyglycoside reagent could be stored at 0 degrees C for 4 weeks.