Luminescence inhibition test with Vibrio (Aliivibrio) fischeri (ISO 11348-1: 2007/Amd 1:2018). Determination of the inhibitory effect of water samples on the luminescence of Vibrio fischeri (luminescent bacteria assay).

This test is performed according to ISO 11348-1: 2007. The test determines the inhibition of luminescence produced in freshly prepared cultures of Aliivibrio fischeri. There are other similar tests carried out with lyophilized or dehydrated suspensions of Aliivibrio fischeri, which can give different results when there are heavy metals in the samples, or when the light emission by this bacterium is modified as a consequence of the preservative substances introduced for conservation of such suspensions, so in our laboratory we use the test with recently prepared suspensions of bacteria. This method is applicable to wastewater, marine and brackish water, sediment eluates from any of them, substances diluted in water, etc. To carry out the test, suspensions of the bacteria must be confronted with dilutions of the sample under test, and the effect of the sample on the emission of light (luminescence) by Aliivibrio fischeri must be observed. Luminescence should be measured after contact times of 15 min and 30 min, and optionally 5 min. It is necessary to take into account a correction factor (fkt) which is a measure of the changes in the intensity of the control samples during the exposure time. The inhibitory effect of the water sample can be determined in the form of dilution values of minimal no effect (DMSE), or as the values of the effective concentrations (EC₂₀ and/or EC₅₀) through a series of dilutions. Insoluble, sparingly soluble or volatile substances can hinder the interpretation of the results, in the same way that occurs with the presence of colored substances, or the turbidity of the sample. The decrease in oxygen concentration, or the decrease in pH can be inhibitory, so it must be adjusted during the test. Chemicals are used for the test as inhibition controls (zinc sulphate, dichlorophenol, or potassium dichromate).