Use of endogenous host plasmids for generation of Escherichia coli O157:H7 and Shigella sonnei strains that stably express the green fluorescent protein.

The gfp gene was manipulated from a commercially available, high copy vector into endogenous plasmids of Escherichia coli O157:H7 and Shigella sonnei to yield stable GFP strains that required neither high copy number for visualization nor antibiotics for stable maintenance of the phenotype. The GFP phenotype of these strains remained stable after repeated passages in media and conditions that enhance plasmid instability and loss from bacterial cells. These results demonstrate the utility of the endogenous plasmids in selectively marking bacteria without altering host cellular function or biochemical properties.