Simplified determination of bacterial contamination by Escherichia coli using a flow injection system with piezoelectric detection

A rapid and automated method was developed for the determination of bacterial contamination and using Escherichia coli as a model microorganism. The method involves the use of a sensor connected to a flow injection (FI) system. The sample is introduced through a flow injection system into a piezoelectric quartz crystal (PQC) flow-cell. The resulting change of the resonance frequency is related to the bacterial contamination in the sample. The parameters associated with the flow system and the conditions for introducing the sample culture were optimized. Calibration curves are linear in the range from 3.2 × 10⁷ to 3.2 × 10⁹ cfu per mL⁻¹, with a correlation coefficient of 0.997. The reproducibility was between 3.1 and 7.6%, and the detection limit is 1.1 × 10⁷ cfu per mL⁻¹. The method allowed the determination of bacterial contamination in residual water and in samples of milk and chicken stock within 5 h, while the conventional plate count method requires 24 to 48 h. The results obtained by these two methods are in good agreement. [graphic removed]