Abstract: Provided is a culture medium for microorganisms present in contaminated working fluids such as coolants. More particularly, said culture medium is particularly suitable for supporting growth of microorganisms colonizing metalworking fluids and allows for specific detection of both bacterial microorganisms and fungal microorganisms the latter depending on the added selective agents which can be antibiotics for the detection of fungal contamination or fungicides for the detection of bacterial contamination. Furthermore, devices and kits comprising the culture medium of the present invention are described as well as a method of detecting microbial contamination of metalworking fluids.