Phase noise generated by vibration of bacteria adhered to a quartz resonator
Ward L. Johnson, Danielle C. France, F L. Walls, William T. Cordell, Nikki S. Rentz
An approach is presented for sensing mechanical fluctuations of bacteria, with potential application in monitoring microbial responses to changes in chemical environment, such as antimicrobial intervention. Bacteria are tethered to a quartz crystal resonator that is incorporated in an electronic bridge and driven by a high-stability frequency source. Power spectral densities of phase noise of the output of the bridge are collected in the absence and presence of antibiotic. Measurements on Escherichia coli before and after exposure to ampicillin demonstrate that resonator phase noise is closely correlated with cell density. Power spectral densities of the cell-driven noise are found to decrease with increasing offset frequency over the measured range of 1 Hz to 100 Hz. Response to antibiotic is seen in less than one hour, offering the potential for definitive antimicrobial selection within actionable time frames in clinical environments.