Rapid assessment of Escherichia coli by growth rate on piezoelectric-excited millimeter-sized cantilever (PEMC) sensors

A piezoelectric-excited millimeter sized glass cantilever with a 1 mm(2) sensing surface was fabricated for the purpose of detecting the growth of Escherichia coli (E. coli) JM101 in real-time. The resonance characteristic of the fundamental mode in air was 31.08 +/- 0.01 kHz. Upon the addition of the agar film to the cantilever sensing surface the fundamental resonance frequency decreased by 2 +/- 0.01 kHz. Upon subsequent inoculation of E. coli JM101, the fundamental frequency decreases an additional 0.1 +/- 0.01 kHz. The E. coli was grown at 29 degrees C in a temperature-controlled chamber. The E. coli went through a lag phase of 1 h followed by a continuous decrease in resonant frequency due to growth of the bacteria. The total change in resonant frequency during the growth phase was 5.08 +/- 0.01 kHz. After 6 h, the resonant frequency reached a constant Value as growth ended. A model was developed to relate resonant frequency to specific growth rate (mu). The E. coli exhibited exponential growth rate of 1.31 +/- 0.05 h(-1) and a late exponential growth rate of 0.55 +/- 0.05 h(-1) which compared favorably with growth rate obtained in submerged culture of 1.28 +/- 0.02 h(-1) at 29 degrees C. The significance of the results is that microbial contamination in food processing plants can be assessed rapidly (< 4 h) by measuring growth rate on piezoelectric-excited millimeter-sized glass cantilevers. Further, we compare its performance with QCM and find that PEMC is 1000 times more sensitive and 10 times quicker in establishing growth of bacteria. (c) 2005 Elsevier B.V. All rights reserved.