Thymidine Content in Commercially Prepared Media.

The thymidine content of a number of media now available commercially was determined, using Lactobacillus arabinosus ATCC 8014. The thymidine concentration in most liquid media was so high (greater than 0.01 microng/ml) that, without further treatment, these media could not be used for the testing of sulphonamides, trimethoprim or combinations thereof, more especially if bactericidal action was being investigated. Low and tolerable thymidine amounts were found in some agar media. Considerable variation was observed in the thymidine concentration in the same media produced by different manufacturers, as e.g; in Mueller Hinton Agar, as well as in different batches of one medium from the same manufacturer.