Study Suggests Potential Utility of Bacteriophage as Supplemental Preharvest Agricultural Water Treatment
Contaminated irrigation water is a significant route by which foodborne pathogens are introduced to produce. In this context, a new study assessed the efficacy of a commercial preharvest water treatment, specifically, the SalmoFresh lytic bacteriophage cocktail, against Salmonella Infantis.
For their study, the researchers used a controlled test agricultural water (TAW) matrix at 6.5 and 8.4 pH and 4–100 nephelometric turbidity units (NTU), as well as natural pond water (both autoclaved and nonsterile) at temperatures of 12 °C and 32 °C. Both water setups were inoculated with nalidixic acid-resistant S. Infantis at 4 to 6-log colony forming units per milliliter (CFU/mL) and treated with SalmoFresh at 7 or 8-log plaque-forming units (PFU)/mL. Phage treatment times ranged between five and 30 minutes.
In TAW, a consistent 1-log CFU/mL reduction was observed after 5 minutes of treatment with 8-log PFU/mL, regardless of pH or turbidity. In pond water, significant reductions occurred only at the higher phage concentration (8-log PFU/mL), with mean reductions of up to 1.7-log CFU/mL after 30 minutes at 32 °C. Lower temperatures yielded slightly reduced efficacy, likely due to decreased bacterial metabolic activity.
The U.S. Environmental Protection Agency (EPA)/U.S. Food and Drug Administration (FDA) protocol requires a 3-log CFU/mL reduction within 5 minutes for antimicrobial approval, of which the maximum reduction achieved by SalmoFresh fell short in the study. Comparatively, chemical sanitizers such as chlorine and peracetic acid (PAA) have demonstrated greater than or equal to 3-log reductions under similar conditions. However, the phage treatments showed resilience across varying water qualities, including high coliform counts and organic matter, suggesting potential utility as a supplemental treatment.
Previous research supports a hurdle approach, combining phages with chemical sanitizers to enhance efficacy.
The study marks the first application of a lytic phage cocktail for preharvest water treatment, demonstrating modest but consistent reductions of S. Infantis across diverse water conditions. Although not meeting regulatory thresholds alone, phages may complement chemical sanitizers in integrated water safety strategies. Further research is required to optimize phage application methods and assess efficacy against different pathogens.
The U.S. Department of Agriculture’s Agricultural Research Service (USDA-ARS) supported the study, which was conducted by researchers affiliated with USDA-ARS, the University of Delaware, Texas State University, Alabama A&M, the University of Maryland, and Intralytix Inc. (the owner of SalmoFresh). The findings were published in the Journal of Food Protection.
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