Field Evidence Supporting Conventional Onion Curing Practices as a Strategy To Mitigate Escherichia coli Contamination from Irrigation Water

Abstract

The Produce Safety Rule of the U.S. Food Safety Modernization Act includes restrictions on the use of agricultural water of poor microbiological quality. Mitigation options for poor water quality include the application of an irrigation-to-harvest interval of <4 days; however, dry bulb onion production includes an extended irrigation-to-harvest interval (<30 days). This study evaluated conventional curing practices for mitigating Escherichia coli contamination in a field setting. Well water inoculated with rifampin-resistant E. coli (1, 2, or 3 log CFU/mL) was applied to onion fields (randomized block design; n = 5) via drip tape on the final day of irrigation. Onions remained undisturbed for 7 days and were then lifted to the surface to cure for an additional 21 days before harvest. Water, onions, and soil were tested for presence of rifampin-resistant E. coli. One day after irrigation, 13.3% of onions (20 of 150) receiving the poorest quality water (3 log CFU/mL) tested positive for E. coli; this prevalence was reduced to 4% (6 of 150 onions) after 7 days. Regardless of inoculum level, E. coli was not detected on any onions beyond 15 days postirrigation. These results support conventional dry bulb onion curing practices as an effective strategy to mitigate microbiological concerns associated with poor quality irrigation water.

Assembly and Characterization of a Pathogen Strain Collection for Produce Safety Applications: Pre-growth Conditions Have a Larger Effect on Peroxyacetic Acid Tolerance Than Strain Diversity

“…In order to ensure inclusion of the non-O157 STEC serotypes, an additional two strains were included representing serotypes O45 and O103. The strain set also includes four surrogate organisms relevant for E. coli , including three generic E. coli isolated from the environment (FSL R9-4077, FSL R9-4078, FSL R9-4079), as well as a naturally occurring non-pathogenic E. coli O157:H7 (FSL R9-3467), all of which have been used previously as surrogates (Tomás-Callejas et al, 2011; Atwill et al, 2015; Weller et al, 2017a,b; Cai et al, 2018; Wright et al, 2018) (Table 1).…”

“…For example, produce-related STEC strains that were initially selected included E. coli O157 as well as two non-O157 STEC serotypes (i.e., O121, O26), these strains were supplemented with seven other STEC strains to represent the most common clinically associated serotypes in the United States (i.e., serotype O145, O111, O45 and O103 [Gould et al, 2013]). Surrogate organisms for inclusion in the initial draft strain collection were selected to include strains that had previously been used in produce-relevant validation or challenge studies, e.g., the rifampicin resistant E. coli strain TVS 353 (also designated W778), which has been used in a number of studies that assessed survival of E. coli on leafy greens (Tomás-Callejas et al, 2011; Weller et al, 2017a; Cai et al, 2018; Wright et al, 2018). The initial draft strain collection included 13 L. monocytogenes , 24 S. enterica , 10 STEC, as well as 10 surrogate organisms (5 additional E. coli , two Listeria innocua , one Listeria marthii , one Enterococcus faecalis , and one Enterococcus faecium ).…”

Recent Advances in Bioactive Compounds, Health Functions, and Safety Concerns of Onion (Allium cepa L.)

“…The use of sanitizer, sodium hypochlorite, combined with elevated CO 2 /reduced O 2 in package atmosphere was found beneficial for the safety and quality of fresh-cut onion, which showed effective inhibitory effects on the growth of Salmonella typhimurium, mesophilic aerobic bacteria, yeasts, and molds during storage (202). Moreover, the pathogenic microorganisms, including Listeria monocytogenes (21), Escherichia coli (203,204), Salmonella spp. (205), and mold (20) in onion infected by contaminated irrigation water or transferred from contaminated workplace are also considered as potential health risks.…”

A 2020 Vision of Subsurface Drip Irrigation in the U.S.

“…Three studies were in this subcategory (table 4) and included a study of plastic mulch effectiveness for tomato (Elsayed-Farag et al, 2018), evaluation of tomato varieties using unmanned aerial vehicles (UAVs) (Enciso et al, 2019), and evaluation of pathogen control with on-surface curing of onions when using SDI (Wright et al, 2018).…”