A Suggested Sterility Test for Penicillin

The proposed sterility test for penicillin, which employs cysteine (in the form of its hydrochloride) rather than Clarase, has proven to be satisfactory in our laboratories. The use of cysteine is advantageous because it is a compound of known structure and is readily available at relatively small cost. Suitable samples of Clarase or bacterial penicillinases are not as reproducible and the latter require much time and effort in their preparation. Furthermore, cysteine solutions do not require filtration but may be sterilized by heat in the autoclave.