They put this DNA, along with an immune system stimulant, into a ring of genetic material, called a plasmid, from a bacterium.

In the pig bacteria, though, the resistance gene was on a small loop of DNA that lives outside a chromosome, called a plasmid.

This is called a plasmid; it's a unit of DNA that can be easily copied, then broken and is an important tool for molecular biologists.

DNA vaccines are a simpler version, made of just the virus' genes placed into a circular DNA structure called a plasmid, then grown in bacteria.