A multiparameter chemical toxicity test using Salmonella typhimurium and Spirochaeta aurantia

A battery of measurements, including specific growth rate, intracellular ATP level, and respiration rate, was designed to measure the responses of Salmonella typhimurium and Spirochaeta aurantia to chemical toxicants. The test battery provided both a measure of relative toxicity and an indication of the biochemical mechanism of chemical toxicity. The utility of the battery was investigated using chemicals (cyanide, 2,4‐dinitrophenol, chloramphenicol, and dicyclohexylcarbodiimide) for which toxic mechanisms have been clearly established. Test battery results provided a reproducible “signature” for each model compound, which was useful for differentiating among compounds whose primary mechanism of toxicity involves (a) inhibition of catabolic activity leading to oxidative phosphorylation, (b) disruption of membrane integrity, and (c) interference with biosynthetic activity. The responses of the two test organisms to model inhibitors were qualitatively identical and paralleled predictions based on theoretical grounds. In theory, the test battery can measure toxicity among classes of compounds that alternative, single‐parameter microbial tests would classify as nontoxic. The microbial test battery described may eventually provide a theoretically superior and economically attractive alternative to established toxicity testing procedures.