FIG. 1.
Dam overproduction (DamOP) results in motility defects in Salmonella strain 14028 but not in strain LT2. dam+, dam mutant, and DamOP derivatives of the Typhimurium pathogenic strain, 14028, and the avirulent laboratory strain, LT2, were inoculated into the center of soft agar motility plates (38). Motility was assessed by measuring the growth diameter of the swarm after 7 h of incubation at 37°C. Cells recovered from the outermost motility zone of the swarm generated by DamOP cells were shown to be motile escape mutants selected during the assay (data not shown). FlhC− (flhC5456::MudJ) strains TH3928 and MT2425 were used as nonmotile controls (21).