The Total Coliform / E. coli Indicator Bacteria Test Kit (Code 4-3616-UV) includes five tubes, each with a nutrient tablet. The five tubes are inoculated with 10 mL of sample water each and incubated for 24 to 48 hours depending on the ambient temperature. A change in the color due to acid production and the formation of gas bubbles in the reconstituted gel indicates the presence of coliforms. The nutrient tablet contains MUG (4-methylumbelliferyl D- glucuronide), a fluorogenic substrate. A non-fluorescent material is acted upon by a bacterial enzyme to produce a fluorescent compound. If E. coli is present the sample will fluoresce with exposure to UV light (365 nm) from the UV penlight (included). E. coli is an indicator of fecal contamination. Further confirmation by a laboratory for the presence of E. coli is recommended.