Microtox is an in vitro testing system which uses bioluminescent bacteria (Allivibrio fischeri, formerly known as Vibrio fischeri) to detect toxic substances in different substrates such as water, air, soils and sediments.[1] Allivibrio fischeri are non-pathogenic, marine, bacteria that luminesce as a natural part of their metabolism.[2] When exposed to a toxic substance, the respiratory process of the bacteria is disrupted, reducing light output.[2] Allivibrio fischeri have demonstrated high sensitivity across a wide variety of toxic substances.