Construction of the mutant strains.

<p>(A) The genes <i>ehx</i> and <i>ecf</i> were detected in EDL933 but not in ΔpO157. Lane M: marker; Lanes 1 and 3: EDL933; Lanes 2 and 4: ΔpO157 mutant. (B) Comparison of genomic DNA of EDL933 and ΔpO157 using PFGE of <i>Xba</i>I-digested. Lane M: marker; Lane 1: EDL933; Lane 2: ΔpO157 mutant. (C) Using primer <i>ehxA</i>-3,4, EDL933 was amplified as a ≈3.3 kb fragment. Δ<i>ehxA</i> and Δ<i>ehxA</i>/pehxA were amplified as a reduced fragment to ≈1.6 kb. Using primer <i>ehxA-</i>5,6, Δ<i>ehxA</i> showed no PCR product. EDL933 and Δ<i>ehxA</i>/pehxA were amplified as a ≈360 bp fragment. Lane 1: EDL933; Lane 2: Δ<i>ehxA</i>; Lane 3: Δ<i>ehxA</i>/pehxA.