A rapid and automated method for the determination of bacterial growth contamination is proposed and Escherichia coli was used as a model microorganism. The methodology involves the use of a piezoelectric quartz crystal (PQC) sensor connected to a flow injection (FI) system. The sample was introduced through the FI system and the resonant frequency change of PQC is related to the bacterial contamination in the sample. The method allows the successful determination of bacteria in residual water and several food samples