Caring for .

The bacterial strain K-12 has played an indisputably important role over the past century-in biology overall and in molecular biology in particular. Strains of (either untransformed or transformed with a plasmid) are usually sent through the mail as agar stab cultures. All strains must be validated as soon as they enter the laboratory, before they are used in experiments. This protocol provides guidelines for validation and storage of and plasmids.