Development of an optimized system for electroporation of Listeria species.

Electroporation was used to facilitate transformation of Listeria species with plasmid DNA. Optimal conditions for transformation of L. monocytogenes were a field strength of 8.5 kV/cm, 200 Ohms resistance, 25 microF capacitor with a time constant of 5 ms. With these conditions, 3.9 x 10(6) transformants/micrograms DNA were obtained. Under the same conditions, L. innocua and L. ivanovii exhibited a frequency of transformation similar to that of L. monocytogenes but a somewhat lower level was obtained with L. seeligeri.