High-efficiency transformation of Listeria monocytogenes by electroporation of penicillin-treated cells

Abstract

A procedure has been developed for electroporation-mediated transformation of Listeria monocytogenes with plasmid DNA. The method was optimized for intact cells of L. monocytogenes 23074 by determining the effects of field strength, cell density, and plasmid DNA topology. Transformation efficiencies were dramatically increased when cells were treated with penicillin. Optimum frequencies of transformation (4 × 106 transformation/μg DNA) were obtained when cells were grown in 10 μg/ml of penicillin G and electroporated at a field strength of 10kV/cm. Using, this procedure, transformation of relaxedf plasmid DNA from ligation reactions provided 1 × 104 transformants/μg DNA, allowing direct molecular cloning of DNA into this organism. © 1990.