US research aims to reduce Salmonella risks for bulb onions

Joy Waite-Cusic from Oregon State University is heading a project titled “Assessing the potential for production practices to impact dry bulb onion safety.” Vijay Joshi with Texas A&M AgriLife Research is leading a project titled “Strategic approaches to mitigate Salmonella contamination of bulb onions.” Both are hoping to develop recommendations on onion crop management, harvesting, curing, storage and distribution that will help the industry minimize the risk of Salmonella contamination.

“We’re just trying to figure out what possibly occurred so we’re able to understand the risks,” Waite-Cusic said, referring to Salmonella outbreaks in 2020 and 2021 linked to bulb onions. This year, the researchers conducted onion field trials in Pasco, Washington, and Ontario, Oregon, using a three-strain E. coli cocktail as a Salmonella surrogate. In both trials, the researchers monitored pathogen levels after application as the onions matured and cured in the field for 30 days.

“Spoiler alert — we just collected the last samples, and everything died. Over both field trials, only one onion out of 440 tested at the end of field curing was still positive for E. coli." Field curing did a great job of mitigating any contamination that happened in any of those water applications. This doesn’t tell us the answer to the outbreaks, but it’s great news for the industry and food safety.”

Texas research
Joshi’s project seeks to better understand how Salmonella colonizes and internalizes in onion bulbs. He also plans to identify production practices that may reduce plant susceptibility. Characterizing the genetic background and chemical and physical factors influencing Salmonella internalization also will help describe the dynamics involved.

With this information in hand, the researchers plan to conduct field trials to determine how bulb quality traits — including nitrogen content, moisture level, and macro- and micro-elements — influence Salmonella internalization.


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