Description

Step one

His-tag purified phage tail tip conjugated to a colorometric enzyme is added to a water sample by drawing water into a syringe. The tail tip recognizes LamB, an outer membrane protein on E. coli and binds to any E. coli present in the sample.

Step two

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 prevents false positives by ridding the solution of excess phage tail for step three.

Step three

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.