Chlorine dioxide is a broad-spectrum disinfectant against Shiga toxin-producing Escherichia coli and Listeria monocytogenes in agricultural water

Authors: Van Blair, Jared; Lacombe, Alison; HARVEY, BEATRICE - Hispanic Association Of Colleges & Universities (HACU); Wu, Vivian

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2024
Publication Date: 10/25/2024
Citation: Van Blair, J.B., Lacombe, A.C., Harvey, B.L., Wu, V.C. 2024. Chlorine dioxide is a broad-spectrum disinfectant against Shiga toxin-producing Escherichia coli and Listeria monocytogenes in agricultural water. Frontiers in Microbiology. 15. Article 1469615. https://doi.org/10.3389/fmicb.2024.1469615.
DOI: https://doi.org/10.3389/fmicb.2024.1469615

Interpretive Summary: Water is necessary for the growth and preparation of produce. Water contacts raw produce during the irrigation and washing steps that typically occur at the processing facility. When contacting food, contaminated water can transfer human pathogens held in the water onto the surface of the food, making it unsafe to eat. This possibility of pathogen transfer makes water treatment an important step for industrial farming. Common water treatment methods utilize chlorine-based chemicals such as bleach; however, defining alternative methods for treating water is important to aid farmers in treating a wide range of water sources. In this study, Shiga toxin-producing Escherichia coli (STEC) and Listeria monocytogenes were exposed to chlorine dioxide (ClO2), a bleach alternative. We tested survivability following treatment in a range of water samples, including field samples taken from ground and surface water adjacent to farm operations in Salinas Valley, CA. Chlorine dioxide was able to reduce bacterial populations by 99.9% in all samples after 5 minutes of exposure in concentrations as low as 1.4 ppm. This is different from bleach, which is heavily influenced by water quality. Results here support the development of regulations for treating surface water that is increasingly used by farm operations as water becomes scarce.

Technical Abstract: Water in agriculture is commonly treated with chlorine-based disinfectants, which can be impacted by water quality. Understanding how water influences disinfectants such as chlorine dioxide (ClO2) against human pathogens is important for defining use in food processing. The minimum inhibitory concentration (MIC) of ClO2 to achieve 3-Log reduction against Shiga toxin-producing Escherichia coli (STEC) and Listeria monocytogenes was determined in water samples of varying quality. Sterile ddH¬2O served as a control to compare with environmental samples from Salinas Valley, CA, and laboratory standards. Field samples varied in pH, turbidity, conductivity, and total dissolved solids, ranging between the ddH2O control and laboratory standards. To test disinfection across dosages and water qualities, stock ClO2 was diluted in 24-well plates to 10, 5, 2.5, and 1.25 mg/L ClO2 using test water. Wells were inoculated with pathogens, and then plated and incubated to enumerate viable cells. Groundwater samples required the lowest concentration of disinfectant to achieve a 3-Log reduction, with an MIC value of <1.25 mg/L ClO2. Open-source surface water samples required a higher dosage of ClO2 to achieve similar results, with MIC for a 3-Log reduction range between 2.5-10 mg/L. Generally, STEC reached a 3-Log reduction between ~1.5-3 mg/L ClO2, while L. monocytogenes required a higher dosage of ClO2. L. monocytogenes had less predictable reduction across water samples compared to STEC. Importantly, there was no correlation between pH, turbidity, or conductivity/TDS and reduction for either STEC or L. monocytogenes, suggesting no individual water metric is driving reduction. Overall, these results indicate that ClO2 is a broad-spectrum disinfectant due to its demonstrated efficacy across a wide range of treatment conditions.