Location: Produce Safety and Microbiology ResearchTitle: Fundamental differences in inactivation mechanisms of Escherichia coli O157:H7 between chlorine dioxide and sodium hypochlorite
Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2022
Publication Date: 6/17/2022
Citation: Bridges, D.F., Lacombe, A.C., Wu, V.C. 2022. Fundamental differences in inactivation mechanisms of Escherichia coli O157:H7 between chlorine dioxide and sodium hypochlorite. Frontiers in Microbiology. 13. Article 923964. https://doi.org/10.3389/fmicb.2022.923964.
Interpretive Summary: Both sodium hypochlorite (NaOCl) and chlorine dioxide (ClO2) are commonly used antimicrobials in wastewater and food processing systems. While the mechanisms in which NaOCl inactivates microorganisms have been widely studied, the amount of literature pertaining to the inactivation mechanisms of ClO2 is relatively minimal. Therefore, the objective of this study was to observe how ClO2 inactivates bacterial in comparison to NaOCl using Escherichia coli O157:H7 as a model organism. This study demonstrates that NaOCl and ClO2 affect E. coli O157:H7 in fundamentally different ways and cause significantly distinct changes in gene expression and levels of internal reactive oxygen species (ROS) and relatively similar levels of microbial inactivation. These data are important because they show that while both NaOCl and ClO2 are chlorinous oxidizers, they inactivate bacterial in measurably different mechanisms, which helps to better understand commonly used antimicrobial treatments.
Technical Abstract: Chlorine dioxide (ClO2) and sodium hypochlorite (NaOCl) are two chlorinous oxidizers that are implemented in water treatment and postharvest processing of fresh produce. While the antibacterial mechanisms of NaOCl have been thoroughly studied, there are comparatively few studies that have looked at how ClO2 kills bacteria. Therefore, the objective of this study was to investigate how ClO2 inactivates Escherichia coli O157:H7 in comparison to NaOCl. Treatments consisted of 2.5, 5, and 10 ppm ClO2 or 50, 100, and 200 ppm NaOCl for 5, 10, and 15 min. Metrics measured after treatment include bacterial log reductions, intracellular reactive oxygen species (ROS) using with 2’,7’–dichlorofluorescin diacetate (DCFDA) or aminophenyl fluorescein (APF) probes, expression of key genes involved in ROS-defense or general stress responses, and relative values of NAD+, NADH, NADP+, and NADPH cofactors. Maximum log reductions of E. coli O157:H7 were 5.5 and 5.1 after treatment with ClO2 or NaOCl, respectively. Levels of intracellular ROS after ClO2 treatment were substantially higher than those found after treatment in NaOCl. Additionally, NaOCl treatment resulted in upregulation of ROS-defense genes, while expression of the same genes was typically at base levels or downregulated after ClO2 treatment. As the concentrations of both treatments increased the NADP+:NADPH ratio shifted to the cofactor being predominantly present as NADP+. These data demonstrate that ClO2 and NaOCl affect E. coli O157:H7 using measurably different mechanisms and that ClO2 does not appear to directly cause substantial oxidative stress to E. coli O157:H7.