Examination of the Dielectrophoretic Reduction of Vibrio Parahaemolyticus and Vibrio Vulnificus

Vibrio parahaemolyticus and Vibrio vulnificus are food born pathogens that are commonly found in raw seafood. This bacterium causes 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. The warm waters in the Gulf of Mexico are more conducive to the growth of these bacteria than the Chesapeake Bay region, but both regions are susceptible to bacterial infection and solutions for the destruction of Vibrio is being sought.

A variety of common food treatments and temperature shock have been examined, but none have been able to reduce the bacterium concentrations by the necessary 5 log magnitude [www.cdc.gov]. This work examines the application of a dielectrophoretic field to reduce Vibrio concentrations in an aqueous suspension. Dielectrophoresis (DEP) is the application of a non-uniform alternating current (AC) electric field to a suspension of polarizable cells or particles. This research project sought to experimentally determine a frequency at which the bacterial membrane could be compromised, thus lysing the cell and rendering it unviable.

A DEP frequency range of 10 kHz to 80 MHz was tested to determine a frequency (or set of frequencies) favorable to membrane instability while simultaneously monitoring culturing viability. The frequency range around 40 MHz was most closely examined. The Vibrio para. viability was reduced in the dielectrophoretic fields and depended greatly on the field frequency. From the experiments the greatest reduction in the Vibrio concentration was 98.4% ± 3.23% at 39.25 MHz. Through these tests we were able to establish a 3 log reduction of Vibrio para. at 5 volts peak to peak amplitude using a sinusoidal waveform. However, several other frequencies showed reduction between 0%-96% with 13 peaks over 60% reduction of CFUs (colony forming units).

A comparison study was also conducted using DC fields within the original electrode configuration. Although it has been reported that DC electric fields can effectively lyse Vibrio para. bacteria in a NaCl solution, the dynamics of a DC device suggest that lysis only occurs at the electrode surface and not in solution. In conclusion, it is possible to reduce the bacteria concentration in solution with the application of a non-uniform electric field (DEP). However, further work is needed to determine if the necessary 5 log reduction can be achieved.