Evaluation of DNA barcode abiotic surrogate as a predictor for inactivation of E. coli O157:H7 during spinach washing

Authors: BOLTON, SAMANTHA - Orise Fellow; Gu, Ganyu; GULBRONSON, CONNOR - Indiana University; Kramer, Matthew; Luo, Yaguang - Sunny; ZOGRAFOS, ANTHONY - Safetraces Inc; Nou, Xiangwu

Submitted to: Journal of Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2021
Publication Date: 3/16/2021
Citation: Bolton, S., Gu, G., Gulbronson, C., Kramer, M.H., Luo, Y., Zografos, A., Nou, X. 2021. Evaluation of DNA barcode abiotic surrogate as a predictor for inactivation of E. coli O157:H7 during spinach washing. Journal of Food Science and Technology. https://doi.org/10.1016/j.lwt.2021.111321.
DOI: https://doi.org/10.1016/j.lwt.2021.111321

Interpretive Summary: FDA regulations recently enacted in implementing Food Safety Modernization Act require food processors to specifically validate the efficacy of preventive interventions against targeted foodborne pathogens. In collaboration with SafeTraces Inc., ARS scientist evaluated a matrix containing embedded barcode DNA as abiotic surrogate for validating the performance of antimicrobial washing of spinach. This DNA-based abiotic surrogate was shown to have comparable inactivation patterns as foodborne pathogen E. coli when exposed the chlorinated wash water. This work provided the fresh produce industry a promising tool that can be used for validating preventive control processes.

Technical Abstract: Fresh-cut leafy greens are washed in water with antimicrobials such as free chlorine in order to mitigate risk of pathogen cross-contamination that may cause foodborne illness outbreaks. Verifying the efficacy of the washing process poses challenges, including the identification of effective surrogates that can be used directly on the processing line during commercial operation. The objective of this study was to evaluate the use of an abiotic, DNA-based indicator (DBAS) as a potential surrogate for Escherichia coli O157:H7 during the washing of spinach. E. coli O157:H7 and DBAS were inoculated onto spinach leaves and washed in wash water with free chlorine. E. coli O157:H7 and DBAS populations were enumerated by selective plate counting or qPCR, respectively, and by laser scanning confocal microscopy. DBAS displayed high sensitivity to free chlorine at concentrations =12.5 mg/L, similar to concentrations commonly used in leafy green washing. Linear regression analysis indicated that inactivation of E. coli O157:H7 and DBAS had comparable inactivation responses (r=0.89). Microscopy analysis also showed similar rates of decontamination between the two analytes from the surface of spinach. These results support that DBAS can be a promising abiotic surrogate for onsite validation of antimicrobial processes targeting foodborne pathogens such as E. coli O157:H7 on fresh produce.