The „Pseudomonas cell growth inhibition test“ is assessing the chronic toxicity of wastewater and water-soluble substances to bacteria. Pseudomonas putida is used as a representative of heterotrophic microorganisms in freshwaters. The test bacteria are exposed to a serial dilution of the test substance in a defined medium for several generations.
First, the toxic concentration range of the test substance is established in preliminary tests. In the main test, a serial dilution within the relevant concentration range is tested with three replicates per concentration and a negative control without the test substance as well as a positive control with 3,5-dichlorophenol are run in parallel. A defined bacterial suspension (corresponding to 10 formacine turbidity units) is added to each test line. After 16 ± 1 hours, the cell concentration is measured by means of turbidity measurement at 436 nm. The dose-effect relationship is calculated by a regression analysis with log-probit transformation of the parameter pairs, and from this the 10% and 50% effect concentration is determined as test result (EC10 and EC50).
The Committee on biological agents has recently reclassified the strain used in this test from risk group 1 to 2 (see TRBA 466). The test is therefore no longer offered by Hydrotox.