Automatic detection of Staphylococcus aureus and Shigella dysenteriae with separated electrodes series piezoelectric sensing technique

The series piezoelectric quartz crystal (SPQC) sensing technique is a rapid and sensitive method for detection of microorganisms. In the present study, the detection device was composed of detecting system, signal generating system and data analyzing system. To magnify the amount of detection samples, eight independent SPQC sensors were parallel connected to form a muti-channel detecting unit. Electrodes were separated from the SPQC sensor and immersed into culture medium to detect the change of solution conductivity. The cell constant k was determined as 0.05 m, and the sensitivity interval of the device was from 550 to 600 μs. To maintain sensitivity of the SPQC sensor, a novel culture medium amino acid broth (AaB) was developed. It was nutrient with low conductivity and satisfied our detection device. For determining frequency detection time (FDT) expediently and accurately, FDT was defined afresh with fitting–differentiating method. Pathogens Staphylococcus aureus and Shigella dysenteriae were determined with an automated detecting device and the methods mentioned above. The calibration curves of FDT against density of bacteria showed a linear correlation coefficient (R ≥ 0.99) over the range of 10–10⁶ cells ml⁻¹. Detection results all fell inside the 95% confidence interval of a standard pour plate counting method. The reproducibility was also reviewed, and results showed that the device was stable and sensitive even after 180 days of employment.