Purpose: In this study we investigated the role and regulation of each catalase/peroxidase in the H2O2 resistance of a biofilm forming variant of strain EDL933 (43895OR) residing in a single-species biofilm.
Methods: We constructed mutants of isolate 43895OR with deletion of rpoS, oxyR, both oxyR/rpoS, or with deletions of 3 of the 4 peroxide scavenging enzymes. Strains bearing only katG, katP, ahpC or katE were compared to a strain with deletion of all four genes and to the wild-type for survival differences following H2O2 challenge. rpoS deletions constructed in each of the strains bearing a single catalase/peroxidase gene defined the regulatory influence of RpoS.
Results: Strain 43895OR survival was greater (P < 0.05) in biofilm than in planktonic cells, and full resistance required rpoS but not oxyR. In 72-h biofilms, katG and katE provided the most protection, with katG able to maintain full resistance. Each mutant bearing a single resistance gene survived under reduced O2 conditions, but their counts were significantly lowered (P < 0.05) in the absence of RpoS. In contrast, RpoS deletion was lethal in a strain missing all four resistance genes indicating that all four resistance genes provide some RpoS-independent peroxide resistance in biofilms.
Significance: This is the first study of the role and regulation of the major peroxide resistance genes in E. coli serotype O157:H7 biofilms. Understanding the mechanism and regulation of peroxide resistance in biofilms will aid in developing intervention strategies for the control of E. coli O157:H7.