LONG-TERM, ONLINE MONITORING OF MICROBIAL BIOFILMS USING A QUARTZ CRYSTAL MICROBALANCE

A quartz crystal microbalance was used to nondestructively monitor the formation of Pseudomonas cepacia biofilms. These experiments involved long-term monitoring over days. Long-term monitoring initially encountered problems associated with baseline drift which were not observed in short-term electrochemical experiments or studies performed in vacuum or air. The extent of baseline drift produced by fluctuations in hydrostatic pressure and temperature was ascertained. Results showed that 5-MHz AT-cut quartz crystals sealed into flow cells and exposed to aqueous environments were more sensitive to pressure and temperature changes than crystals exposed to air. A test system was designed to eliminate these interferences in order to monitor the frequency shift caused by the attachment and surface growth of P. cepacia cells. A calibration curve for the frequency shift corresponding to a given number of bacteria within a biofilm was generated, and the detection limit of the technique was determined to be 3 x 10(5) cells.cm2. The calibration curve was utilized to produce graphs of the number of attached cells versus time, and the first derivative curves were used to study rates of biofilm formation.