Cross contamination of Escherichia coli O157:H7 between lettuce and wash water during home-scale washing Dane A. Jensen a , Loretta M. Friedrich b , Linda J. Harris c , Michelle D. Danyluk b, 1 , Donald W. Schaffner a, *, 1 a Department of Food Science, Rutgers University, 65 Dudley Rd., New Brunswick, NJ 08901-8520, USA b Department of Food Science and Human Nutrition, Citrus Research and Education Center, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA c Department of Food Science and Technology, University of California, One Shields Avenue, Davis, CA 95616-8598, USA article info Article history: Received 28 April 2014 Received in revised form 15 July 2014 Accepted 22 August 2014 Available online 18 September 2014 Keywords: Lettuce Washing Cross contamination Escherichia coli O157:H7 abstract Lettuce and leafy greens have been implicated in multiple foodborne disease outbreaks. This study quantifies cross contamination between lettuce pieces in a small-scale home environment. A five-strain cocktail of relevant Escherichia coli O157:H7 strains was used. Bacterial transfer between single inocu- lated lettuce leaf pieces to 10 non-inoculated lettuce leaf pieces that were washed in a stainless steel bowl of water for 30 s, 1 min, 2 min, and 5 min was quantified. Regardless of washing time, the wash water became contaminated with 90e99% of bacteria originally present on the inoculated lettuce leaf piece. The E. coli O157:H7 concentration on initially inoculated leaf pieces was reduced ~2 log CFU. Each initially uncontaminated lettuce leaf piece had ~1% of the E. coli O157:H7 from the inoculated lettuce piece transferred to it after washing, with more transfer occurring during the shortest (30 s) and longest (5 min) wash times. In all cases the log percent transfer rates were essentially normally distributed. In all scenarios, most of the E. coli O157:H7 (90e99%) transferred from the inoculated lettuce pieces to the wash water. Washing with plain tap water reduces levels of E. coli O157:H7 on the inoculated lettuce leaf pieces, but also spreads contamination to previously uncontaminated leaf pieces. © 2014 Elsevier Ltd. All rights reserved. Lettuce and leafy greens have been implicated in multiple foodborne disease outbreaks (Doyle and Erickson, 2008; Froder et al., 2007; Gorny et al., 2006; Lund and O'Brien, 2011; Smith et al., 2003). Pathogens, such as Campylobacter , Escherichia coli O157:H7, Listeria monocytogenes, Salmonella, Staphylococcus aureus, Shigella, and Yersinia enterocolitica have all been linked to lettuce, salad, and leafy green outbreaks (Beuchat, 1996; Froder et al., 2007; Gorny et al., 2006). Head lettuce can harbor bacteria even after washing due in part to its large surface area and layering of the leaves (Solomon et al., 2002), and lettuce leaves can often have high populations of non-pathogenic bacteria (Smith et al., 2003; Soriano et al., 2000; Vijayakumar and Wolf-Hall, 2002). Contamination of lettuce can occur at numerous points from food production through distribution including irrigation water, soil, harvesting, washing, packaging, storage, and in the kitchen (Beuchat, 1996; Froder et al., 2007; Gorny et al., 2006). Many pathogens, including E. coli O157:H7, survive and depending on temperature, grow on cut lettuce (Boyer et al., 2007; Gleeson and O'Beirne, 2005; Takeuchi et al., 2000; Wachtel et al., 2002). This is likely due to the cut leaf edges, which encourage attachment and contain nutrients that promote bacterial growth (Froder et al., 2007; Wachtel et al., 2002). A consumer or restaurant employee may wash lettuce with the intention of removing dirt, debris, bacteria, or pesticides that may have accumulated during cultivation or processing. Prior research has demonstrated that multiple washes with plain water may not significantly reduce bacterial concentration on contaminated let- tuce leaves or leaf pieces (Fink et al., 2012; Froder et al., 2007; Gil et al., 2009; Goularte et al., 2004; Nou and Luo, 2010; Wachtel et al., 2002; Zhang et al., 2009). A recent expert review of the literature concluded that washing ready-to-eat fresh cut leafy greens in the home was not likely to enhance safety but did significantly increase the risk for cross contamination (Palumbo et al., 2007). Microbial concentrations on some lettuce leaves or * Corresponding author. Tel.: þ1 732 982 7475. E-mail address: schaffner@aesop.rutgers.edu (D.W. Schaffner). 1 The last two authors contributed equally to the supervision of data collection and analysis. Contents lists available at ScienceDirect Food Microbiology journal homepage: www.elsevier.com/locate/fm http://dx.doi.org/10.1016/j.fm.2014.08.025 0740-0020/© 2014 Elsevier Ltd. All rights reserved. Food Microbiology 46 (2015) 428e433