Susceptibility of foodborne pathogens to sanitizers in produce rinse water and potential induction of viable but non-culturable state

Authors: GU, GANYU - ORISE FELLOW; BOLTEN, SAMANTHA - ORISE FELLOW; MOWERY, JOSEPH - U.S. DEPARTMENT OF AGRICULTURE (USDA); MOWERY, JOSEPH; Luo, Yaguang - Sunny; Nou, Xiangwu

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2020
Publication Date: 1/24/2020
Citation: Gu, G., Bolten, S., Mowery, J., Mowery, J.D., Luo, Y., Nou, X. 2020. Susceptibility of foodborne pathogens to sanitizers in produce rinse water and potential induction of viable but non-culturable state. Food Control. 112:107138.

Interpretive Summary: Chlorine and peracetic acid (PAA) are chemical disinfectants (sanitizers) commonly used by fresh produce industry for protecting the products from contamination by harmful microorganisms that may cause foodborne infections. USDA-ARS scientists evaluated the susceptibility of three common foodborne pathogens to the sanitizers in simulated leafy green wash water. While it was shown that both sanitizers were effective in killing foodborne pathogens, the treatment with PAA might induce some of the treated pathogens to enter a viable but non-culturable (VBNC) state. However, efforts for resuscitating the potential VBNC cells have not been successful, necessitating additional studies to evaluate the risks of VBNC. The information is useful for fresh produce industry to improve produce sanitation practices.

Technical Abstract: Chemical sanitizers are commonly used for fresh produce washing to remove field dirt and exudates at cut surface, to decontaminate potential foodborne pathogens and spoilage bacteria, and to prevent cross-contamination. In this study, we evaluated the susceptibility of foodborne pathogens, including Shiga-toxigenic Escherichia coli, Salmonella enterica, and Listeria monocytogenes, to free chlorine (FC) and peracetic acid (PAA) in spinach and romaine lettuce rinsates as simulated leafy green wash water. All inoculated pathogens exhibited significantly enhanced tolerance to FC, but not to PAA, when treated in fresh produce rinsates in comparison to that in water. Both FC and PAA effectively inactivated the inoculated foodborne pathogens, rendering them undetectable after 30 s exposure to 10 mg/L FC or 30 mg/L PAA, by selective plating or non-selective enrichment. However, potentially viable cells for all the inoculated foodborne pathogenic species were detected by PMA-qPCR, especially in wash water samples treated with PAA at concentrations up to 100 mg/L. While laser confocal microscopy after differential staining suggested significant presence of viable but non-culturable (VBNC) populations in PAA treated wash water samples, resuscitation in vitro of the potentially VBNC cells was not achieved. Further research is necessary to determine the food safety risks of potentially sanitizer induced VBNC of foodborne pathogens.