MOLECULAR CHARACTERIZATION OF PATHOGENS AND THEIR RESPONSES TO ENVIRONMENTAL FACTORS
Location: Molecular Characterization of Foodborne Pathogens
Title: KatP contributes to OxyR-regulated hydrogen peroxide resistance in Escherichia coli serotype O157:H7
Submitted to: Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 20, 2009
Publication Date: November 1, 2009
Citation: Uhlich, G.A. 2009. KatP contributes to OxyR-regulated hydrogen peroxide resistance in Escherichia coli serotype O157:H7. Microbiology. 155(11):3589-3598.
Interpretive Summary: Escherichia coli O157:H7 and other Shiga toxin-producing E. coli (STEC) are important food-borne pathogens. In slaughter and food processing plants, sanitizers and antimicrobial agents are used as part of the sanitation procedure to eliminate or control food-borne pathogens. One of the mechanisms that sanitizers, such as hydrogen peroxide (H2O2), utilize to inactivate microbes is the production of oxygen free radicals. To combat oxidative damage, E. coli produces enzymes that inactivate H2O2 and other peroxides, including three enzymes encoded by the genes katG, katE, and ahpC. Many STEC encode an additional gene, katP, which has not been fully investigated. In this study we characterized the function and regulation of katP, and its relationship to the other peroxide resistance genes. The results of the study indicate that katP plays an important role in H2O2 scavenging and contributes to growth of E. coli O157:H7 in oxygen-rich environments, but does not contribute to resistance during H2O2 challenge assays. We also determined that two global gene regulators, OxyR an RpoS, are also involved in regulating katP along with the other peroxide stress genes. These studies provide a baseline for future studies to determine how the peroxide resistance system enables STEC to survive in processing plants and will provide new strategies for inactivation of STEC.
Escherichia coli K12 defends against peroxide mediated oxidative damage using two catalases, hydroperoxidase I (katG) and hydroperoxidase II (katE) and the peroxiredoxin, alkyl hydroperoxide reductase (ahpC). In E. coli O157:H7 strain ATCC 43895 (EDL933), plasmid pO157 encodes for an additional catalase-peroxidase gene, katP. Although KatP has been shown to be a functional catalase-peroxidase, a plasmid-cured derivative of strain 43895 showed no deficit in peroxide resistance suggesting that katP may not participate in peroxide resistance. To explore the role of katP in strain 43895 peroxide resistance, we constructed mutant strains of 43895 bearing individual deletions of katG, katE, katP, and ahpC, as well as double, triple, and quadruple deletions encompassing all possible gene combinations there of. The wild-type and all 15 mutant strains were compared for differences in aerobic growth, ability to scavenge exogenous H2O2, and resistance to exogenous peroxides. Although katG scavenged the most exogenous H2O2, katP scavenged statistically greater amounts than either katE or ahpC during exponential growth. However, katG and ahpC together were sufficient for full peroxide resistance in disc diffusion assays. While ahpC and katG were most important for maintaining full aerobic growth in rich media at 37 C, katP and katE together could maintain full growth in the absence of ahpC and katG. Gene expression studies showed that katP is an OxyR regulated gene, but its expression is suppressed in stationary phase by RpoS. These studies indicate that pO157-encoded katP contributes to the complex gene network protecting strain 43895 from peroxide-mediated oxidative damage in an OxyR-dependant manner.