Department of Food Science and Technology, Oregon State University, Corvallis, OR 97331, USA.
Franklin County Extension, College of Agricultural, Human, and Natural Resource Sciences, Washington State University, Pasco, WA 99301, USA.
J Food Prot. 2024 Sep;87(9):100326. doi: 10.1016/j.jfp.2024.100326. Epub 2024 Jul 6.
Two U.S. outbreaks of salmonellosis in 2020 and 2021 were epidemiologically linked to red onions. The 2020 outbreak investigation implicated the production of agricultural water as a likely contamination source. Field trials were designed to investigate the prevalence and survival of Escherichia coli (surrogate for Salmonella) on dry bulb onions after the application of contaminated irrigation water at the end of the growing period. Irrigation water was inoculated at 3 log most probable number (MPN)/100 mL (2022 and 2023) or 5 log MPN/100 mL (2023, drip only) with a cocktail of rifampin-resistant E. coli and applied with the final irrigation (0.4 acre-inch/0.4 ha-cm) to onions. Onion bulbs (40 or 80) were sampled immediately after irrigation and throughout field curing (4 weeks) and E. coli was enumerated using an MPN method. For drip irrigation, at 3 log MPN/100 mL E. coli was detected on 13% of onions at 24 h but not detected at 0 h; at 5 log MPN/100 mL for drip irrigation applied to saturated soil, E. coli was detected in 63% of onions at 0 h. Prevalence significantly (P < 0.05), decreased after 7 d of curing with cell densities of 1-1,400 MPN/onion. At the end of field curing in 2023, 1/80 of onions had detectable E. coli (2.04 MPN/onion). E. coli was detected in a significantly smaller percentage of onions (2022: 13%; 2023: 68%) after a contaminated drip irrigation event compared to overhead irrigation (98-100%; P < 0.05). After overhead irrigation, E. coli was detected in onions (1-1,000 MPN/onion) on day 0. Prevalence decreased significantly (P < 0.05) after 7 d of field curing in both years (2022: 15%; 2023: 7%). E. coli was not detected on Calibra onions (80/year) at the end of field curing in either year but was detected at <12 MPN/onion in 2.5-3.75% of onions (n = 80) for other cultivars. These data confirm limited contamination risk associated with drip irrigation water quality and begin to quantify contamination risks associated with overhead irrigation of dry bulb onions.
2020 年和 2021 年美国发生的两起沙门氏菌病疫情与红洋葱有关。2020 年的疫情调查表明，农业用水的生产可能是污染的来源。田间试验旨在调查在生长期末期用受污染的灌溉水灌溉后，干燥鳞茎洋葱上大肠杆菌（沙门氏菌的替代品）的流行率和存活情况。在 2022 年和 2023 年，灌溉水以 3 个最可能数 (MPN)/100 毫升（2023 年仅滴灌）或 5 个 MPN/100 毫升（2023 年，仅滴灌）的浓度接种利福平抗性大肠杆菌混合物，并在最后一次灌溉（0.4 英亩英寸/0.4 公顷厘米）时施加到洋葱上。在灌溉后立即和整个田间养护（4 周）期间，对 40 或 80 个洋葱球进行采样，并使用 MPN 方法对大肠杆菌进行计数。对于滴灌，在 3 log MPN/100 毫升时，24 小时时 13%的洋葱上检测到大肠杆菌，但 0 小时时未检测到；对于施加到饱和土壤的 5 log MPN/100 毫升滴灌，0 小时时 63%的洋葱上检测到大肠杆菌。在养护 7 天后，细胞密度为 1-1400 MPN/洋葱时，阳性率显著（P<0.05）下降。在 2023 年田间养护结束时，1/80 的洋葱中可检测到大肠杆菌（2.04 MPN/洋葱）。与喷灌相比，污染滴灌事件后，大肠杆菌在洋葱中的检出率明显较小（2022 年：13%；2023 年：68%；P<0.05）。喷灌后，0 天可在洋葱中检测到大肠杆菌（1-1000 MPN/洋葱）。在这两年中（2022 年：15%；2023 年：7%），田间养护 7 天后，阳性率显著（P<0.05）下降。在这两年的田间养护结束时，在 Calibra 洋葱（80/年）中均未检测到大肠杆菌，但在其他品种的 2.5-3.75%（n=80）洋葱中检测到大肠杆菌<12 MPN/洋葱。这些数据证实了与滴灌水质相关的有限污染风险，并开始量化与干燥鳞茎洋葱喷灌相关的污染风险。
