SPIRAL SALMONELLA ASSAY - VALIDATION AGAINST THE STANDARD POUR-PLATE ASSAY

The spiral Ames assay, an automated approach to bacteriol mutagenicity testing which simplifies the test procedure and reduces the amount of drug required to generate mutagenic dose-response information, has be en evaluated and validated for routine screening. The spiral plater de livers the Salmonella bacteria, exogenous metabolic activation system and drug to the surface of a rotating agar plate one on top of another in such a way that a uniform density of bacteria is exposed to a loga rithmically decreasing volume of drug. Following an incubation of 48 h r at 37 degrees C, the plates are scanned by a loser counter, and the data are subjected to a computerized analysis. Petri plates of 15 cm d iameter were used to provide a concentration range of about 250-fold p er plate. The Salmonella were concentrated 20-fold to increase sensiti vity. Thirty-eight compounds from a variety of chemical classes, inclu ding both pharmaceuticals and known mutagens of moderate to strong pot ency, were tested in both the spiral and the standard pour-plate assay s. There was overall test agreement on positive or negative results Fo r 82% of the compounds tested. When only the results from strains TA98 plus TA100 were considered, the agreement was 87%. When positive resu lts were obtained, the fold increase over vehicle control was on avera ge twice as great for the spiral assay compared to the pour-plate assa y. If wets concluded that the two assay procedures generally provided comparable results, with the spiral assay being somewhat more sensitiv e in terms of dose-response than the pour-plate assay. (C) 1996 Wiley- Liss, Inc.