Fig 5. Induction of relE increases tolerance to ciprofloxacin, relE-3 to hydrogen peroxide, and relE-5 to pH 3.5.

(A) Cells carrying plasmids containing toxins as indicated were grown in M9-Glucose until late log phase and then exposed to 0.2% (12 mM) L-arabinose for 2 hours, followed by 2 hour challenge with ciprofloxacin, 0.2 μg/ml. (B) Dose response. Cells bearing prelE were induced with 0.1–10 mM L-arabinose followed by challenge with ciprofloxacin (0.2 μg/mL) for 2 hours. (C—E) As in (A), but challenged with hydrogen peroxide (1.25 mM), pH 3.5, or pH 3.0. Survival was monitored by plating for CFU and results are shown as log₁₀ survival after stress, normalized to vector control. Mean of > 4 independent experiments performed in triplicate are shown; error bars denote SEM. A Student's t-test was used to calculate significance comparing each toxin to vector; P<0.05 was considered significant. P < 0.0001 (***), P < 0.001 (**), P <0.05 (*).