Phage tail tip conjugated to a colorometric enzyme is added to a water sample by drawing water into the syringe. The tail tip recognizes LamB, an outer membrane protein on E. coli and binds to any E. coli present in the sample.
The solution is syringe filtered through a 0.45 micrometer filter to trap bacteria bound to phage tails and allow any unbound phage tail through. This is followed by a series of washes which prevents false positives by ridding the solution of excess phage tails.
Substrate is added to the filter which will be cleaved by the enzyme. Color change occurs if E. coli is present. Note, each E. coli cell can bind hundreds of phage tail and each tail may bind several enzyme, which allows for high sensitivity.