ABSTRACT: Piezoelectric biosensors have the potential to provide direct detection of food contaminants, such as pathogens. In this study, Protein A antibody immobilization was used for the activation of the piezoelectric biosensor to detect Salmonella typhimurium. The overall system consisted of a new design for a flow cell and flow injection analysis system. The flow cell made possible a baseline stability of ± 1 Hz out of 5 MHz for hours. The sensor had responses of 5 to 65 Hz in 30 min with R2= 0.95 for S. typhimurium concentrations of 107to 109 CFU/ml under continuous flow, and 3 to 75 Hz in 40 min with R2= 0.96 for S. typhimurium concentrations of 106 to 1010 CFU/ ml under stop flow. Cross-reactivity tests were performed with nonpathogenic Escherichia coli, Escherichia coli O157:H7, Listeria monocytogenes, and Vibrio parahaemolyticus and showed less than 10% response.