FIG 4.

Characterization of E. coli and E. cloacae ΔiprA mutant strains. (A) A ΔiprA mutation was constructed in E. coli and transferred to E. coli strain TOP10. The percent survival of the ΔiprA mutant upon exposure to oxidative stress was measured and calculated for a ratio to the survival of the corresponding WT strain. TOP10 ΔiprA mutant strains containing plasmid vector and vector plus S. Typhimurium (ST) iprA were assayed for oxidative stress survival and compared to the corresponding WT strain. The S. Typhimurium iprA gene is the WT iprA gene cloned from S. Typhimurium. (B) Catalase activity was measured in the WT and E. coli TOP10 ΔiprA mutant strains and plotted as the ratio of the activity of each sample to that of the corresponding WT strain. (C) An ΔiprA mutation was constructed in E. cloacae, and the mutant was assayed for oxidative stress survival, as performed for the E. coli strains. Data in each panel are shown as the mean plus standard deviation, and the observed differences from the WT were found to be significant (as indicated by an asterisk) at a P value of <0.05 for all panels using a t test to compare the WT and the indicated mutant sample. For panel A, a t test comparison was also performed between vector and vector plus iprA.