Electrotransformation in Salmonella

Enteric bacteria are not naturally competent for DNA-mediated transformation, but methods derived from the Ca²⁺ -shock method of Mandel and Higa (1 ) permit uptake of DNA at levels adequate for molecular cloning. Transformation frequencies using Ca²⁺ -shock methods with selected strains of E. coli K-12 range from 10⁶ to 10⁸ transformants/�g of covalently closed circular plasmid DNA, but efficiency is frequently lower because these methods are very sensitive to purity of reagents, cleanliness and quality of glassware and plasticware, and methods of cell handling (2 ).