Bacterial tests such as growth inhibition tests are the only convenient investigation method to detect the impacts of water soluble drugs, e.g. antibiotics, on bacteria. These are cumbersome methods for determining the inhibiting effect of toxic components. The principle of these inhibition tests is the detection of cell numbers by measuring the optical density. With this time-consuming and complicate method only endpoint detection and no monitoring of cell growth is possible, which is obviously a drawback. Furthermore, coloured and turbid components cannot be tested. © 2005 IEEE.