FIG. 5.
Multicopy suppression of St46 antibiotic resistance by wild-type soxRS. (A and B) Specific suppression of quinolone resistance in St46. The multicopy soxRS plasmid pEM300 or the empty vector was transformed into S. enterica St46 (soxRC), and the resulting strains were tested in gradient plates for resistance to nalidixic acid (Nal [panel A]) or ciprofloxacin (Cpx [panel B]). Growth was measured after incubation at 37°C for 18 to 24 h. (C and D) Multicopy soxRS+ does not decrease quinolone resistance in St45. St45 was transformed with plasmids and tested for resistance as described for panels A and B. The maximum level of antibiotic in each plate is indicated above an arrow (μg, micrograms), indicating the direction of the gradient.