A rapid paper-disc test for penicillinase.

A practical acidimetric assay for penicillinase production using penicillin and phenol red impregnated in paper discs was developed. Blank discs were first impregnated with buffered penicillin G and, after drying, with 1% phenol red. For use, a disc was added to a bacterial suspension made in saline solution. A yellow color within 1 to 30 min of incubation indicated penicillinase production. These discs were tested against Staphylococcus aureus, Haemophilus influenzae, and Neisseria gonorrhoeae, and the assay was found to be a simple, rapid, and accurate method for detection of penicillinase.