The present invention provides a method of maintaining a gram negative bacterium plasmid without the use of antibiotic selection pressure. Further, the invention relates to the drugless plasmids produced including drugless plasmids containing a heterologous gene. The invention also provides formulations and/or compositions comprising the drugless plasmids comprising a heterologous gene, formulations and/or compositions comprising a protein or an immunogen expressed using the drugless plasmids, and methods of administering such formulations and/or compositions to a host. The invention relates to gram negative bacteria containing the drugless plasmids.
