Vibrio parahaemolyticus and Vibrio vulnificus are food born pathogens that are commonly found in warm ocean waters. This bacterium concentrated in seafood and when ingested, can cause extreme food poisoning symptoms in healthy adults and can be deadly among immuno-compromised individuals. Both bacteria have had a significantly negative economic impact to the raw oyster industry in the Gulf Coast region of the US. This work examines the impact of alternating current electric field gradients on Vibrio parahaemolyticus cultures in salt-water media. The pathogen viability is assessed before and after electrical treatment via culturing and counting of colony forming units (CFUs).

Food-grade chemical treatments and temperature shock have previously been explored, but none have been able to reduce viable Vibrio colonies by the necessary 5 log magnitude. Therefore the scope of this research was to test whether dielectrophoretic fields could kill the pathogenic Vibrio bacterium in free solution. Dielectrophoresis (DEP) is the application of a non-uniform alternating current (AC) electric field to a conductive suspension of cells or particles. The goal of this research project was to experimentally determine if dielectrophoresis could be used to cause mechanical strain to the cell wall of the bacteria, thus lysing the cell and rendering it inert.

V. parahaemolyticus were cultured in a 37oC incubator in a Difco 70% NaCl nutrient enriched broth. Prior to DEP testing, the bacteria were isolated from the broth solution by centrifugation into a pellet. Broth was decanted off and replaced with a saltwater buffer solution (washed 2 more times) to 2.5% by weight. Control plates were streaked with this suspension, DEP tests were performed within a specially designed microdevice, and three additional plates were streaked with the treated solution. The number of viable cells was determined via standard plate culture counting techniques to determine the number of colony forming units (CFUs) after 16 hours. The average percent reduction was based on a mean of several experiments run as well as an average reduction of three samples taken from each experiment.

Results will demonstrate that viable Vibrio parahaemolyticus concentrations were reduced in the dielectrophoretic fields and depended greatly on the electric field frequency. From the experiments the greatest reduction in the Vibrio concentration was 91% ± 3% at 39 MHz. Through these preliminary tests we were able to establish a 3 log reduction of Vibrio para. at 39 MHz and 5 volts peak to peak using a square waveform. However, several other frequencies showed reduction between 15%-78%. In conclusion, it is possible to reduce the bacteria concentration in solution with the application of a non-uniform electric field (DEP). Further work is ongoing to determine if the necessary 5 log reduction can be achieved.