## 1 Introduction  
Fresh produce is consumed widely and has been associated with human illnesses due to contamination by pathogens [1, 2]. Of all foodborne illnesses linked to identified pathogens that occurred in the U.S. between 1998 and 2020, 9.18% are linked to leafy greens. Romaine lettuce, iceberg lettuce, and other lettuces account for 60.8% of leafy green-associated outbreaks, and 75.7% of leafy green-associated illnesses [2]. It is estimated that 19.8% of Shiga toxin-producing _E. coli_ (STEC) outbreaks from 1998 to 2020 have been associated with Romaine lettuce, resulting in more than 12,000 illnesses annually in the United States [2]. In recent years, multiple STEC outbreaks attributed to Romaine lettuce have been reported [3; 4; 5; 6; 7; 8; 9; 10], and some strains associated with these outbreaks have recently been classified as recurring, emerging, or persistent by the CDC [6]. _Latuca sativa_ L. (lettuce) is the third most consumed crop in the U.S. [11]. The production of leafy greens in the U.S. largely occurs in Arizona (~30%) and California (~70%) [12; 13]. After harvesting, lettuce is transported to cooling centers and is chilled [14; 15]. Once cooled, field-packed lettuce is transported for distribution and sale. Lettuce designated for further processing is transported to a processing facility and differences in transportation time can occur prior to processing [16; 17]. For lettuce processing facilities located outside the West Coast, long haul transportation is used, where the truck temperature is maintained at <5 \({}^{\circ}\)C [16; 17]. When lettuce is stored at <8 \({}^{\circ}\)C, with low relative humidity (<55%), STEC O157:H7 is unable to grow, although it can survive [18; 19; 20]. STEC O157:H7 can tolerate cold stress when present on lettuce, surviving at 5-6 \({}^{\circ}\)C for 10-14 days [21; 22], which is within the expected shelf-life of romaine lettuce (12-16 days) [23]. In addition to cold stress, STEC present on lettuce experiences multiple stresses during post-harvest handling. Once lettuce arrives at a processing facility, it is trimmed, cored, cut, washed, centrifuged, and then packaged for further distribution and sale [24]. Sanitizers are included in wash water to reduce cross contamination. Commonly used sanitizers for fresh produce wash water are chlorine, peroxyacetic acid (PAA), and ozone [25; 26; 27]. All three of these sanitizers pose oxidative stress to microbes, and PAA also poses a low pH stress [26]. STEC O157:H7 levels on lettuce can be reduced by approximately 1.5 to 5 log CFU/g due to sanitizer treatment; this variability is likely due to differences in organic load in the wash water, as well as the potential for bacterial adherence and/or internalization [28; 29; 30]. STEC O157:H7 that survives on lettuce after washing with sanitizers can persist during cold storage [31]. While studies have shown that STEC on lettuce can survive refrigeration temperatures and exposure to sanitizers during washing, it is not known if the length of time in cold storage prior to washing influences STEC tolerance to wash water sanitizers. Under unfavorable conditions for prolonged periods of time, bacteria can transition to dormant states, where metabolic activity is reduced [23]. The process of dormancy involves a spectrum of physiological transformations, spanning from actively proliferating cells to stationary phase cells, and culminating in the formation of persister cells or VBNC cells [23]. Persister cells can be formed during the exponential or stationary phase and have the potential to transition out of the persister state or into the VBNC state [23]. _E. coli_ can enter into dormant states during heat treatment [32], which can further induce protein aggregation [33]. Studies have shown that STEC O157:H7 can transform into dormant states such as persister and VBNC cells under pre-harvest conditions on leafy greens [34; 35].