ABSTRACT
We report the novel application of a herbicide-resistance-based dominant marker for the positive selection of expression plasmids in
Salmonella
serovar vaccines. The β-lactamase gene of the plasmid pTETnir15, which expresses fragment C of tetanus toxin (TetC), has been replaced with the
bar
gene marker. The new plasmid pBAT1 can be positively selected in vitro within
Salmonella
serovars in the presence of the herbicide
dl
-phosphinothricin. The expression of TetC remains unaltered, and the
Salmonella enterica
serovar Typhimurium vaccine strain is stable and immunogenic in vivo.