Transfer and Redistribution of Salmonella Typhimurium LT2 and Escherichia coli O157:H7 during Pilot-Scale Processing of Baby Spinach, Cilantro, and Romaine Lettuce

Abstract

Several outbreaks of foodborne illness traced to leafy greens and culinary herbs have been hypothesized to involve cross-contamination during washing and processing. This study aimed to assess the redistribution of Salmonella Typhimurium LT2 during pilot-scale production of baby spinach and cilantro and redistribution of Escherichia coli O157:H7 during pilot-scale production of romaine lettuce. Four inoculated surrogate:uninoculated product weight ratios (10:100, 5:100, 1:100, and 0.5:100) and three inoculation levels (10, 10, and 10 CFU/g) were used for the three commodities. For each of three trials per condition, 5-kg batches containing uninoculated product and spot-inoculated surrogate products at each ratio and inoculation level were washed for 90 s in a 3.6-m-long flume tank through which 890 L of sanitizer-free, filtered tap water was circulated. After washing and removing the inoculated surrogate products, washed product (∼23, 225-g samples per trial) was analyzed for presence or absence of Salmonella Typhimurium or E. coli O157:H7 by using the GeneQuence Assay. For baby spinach, cilantro, and romaine lettuce, no significant differences ( P > 0.05) in the percentage of positive samples were observed at the same inoculation level and inoculated:uninoculated weight ratio. For each pathogen product evaluated (triplicate trials), inoculation level had a significant impact on the percentage of positive samples after processing, with the percentage of positive samples decreasing, as the initial surrogate inoculation level decreased. The weight ratio of contaminated:noncontaminated product plays an important role: positive samples ranged from 0% to 11.6% ± 2.05% and from 68.1% ± 33.6% to 100% among the four ratios at inoculation of 10 and 10 CFU/g, respectively. To our knowledge, this study is the first to assess the redistribution of low levels of pathogens from incoming product to leafy greens during processing and should provide important data for microbial risk assessments and other types of food safety analyses related to fresh-cut leafy greens.

Antimicrobial-Loaded Polymeric Micelles Inhibit Enteric Bacterial Pathogens on Spinach Leaf Surfaces During Multiple Simulated Pathogen Contamination Events

“…Antimicrobial treatments, nonetheless, reduced pathogens on treated samples, with geraniol-using treatments (GPN, UG) being more effective for reducing pathogen numbers as compared to HOCl and Control treatments. While the potential for multiple crosscontamination events should be low for produce packed and held in a sanitary environment, research has demonstrated the opportunity for post-harvest contamination of pathogens to occur even when sanitizing treatments are applied (Pao et al, 2012;Singh et al, 2018;Smolinski et al, 2018). This occurrence is one the FDA's final rule on produce safety aims to prevent by the mandatory application of food safety hazard reduction strategies (FDA, 2020).…”

“…Organisms were selected to accommodate biosafety needs for already published research conducted simultaneous to data collection in the current study (Yegin et al, 2016). Previous research has indicated these and other similar virulence-attenuated organisms functioned effectively as pathogen surrogates for evaluating decontamination of stone fruit (Yun et al, 2013), or have demonstrated utility for discerning pathogen spread during leafy vegetable packing in research pilot facilities (Smolinski et al, 2018).…”

Evaluation of Potential Impacts of Free Chlorine during Washing of Fresh‐Cut Leafy Greens on Escherichia coli O157:H7 Cross‐Contamination and Risk of Illness

“…To ensure a minimum free chlorine level in wash water, it may be necessary to increase the average free chlorine level during washing above the minimum to replenish free chlorine loss due to natural decay and depletion. In the FDA-LGRAM, washing parameter X S, which represents the fraction of pathogens remaining on lettuce pieces during washing, was estimated based on the study published by Smolinski et al (2018), which was not specific to E. coli O157:H7 on lettuce (but rather for Salmonella on lettuce and E. coli O157:H7 on radicchio). As data become available on the proportion of E. coli O157:H7 remaining on lettuce pieces during washing, the model can be updated accordingly.…”

A Mathematical Model for Pathogen Cross‐Contamination Dynamics during the Postharvest Processing of Leafy Greens

“…had minimal impact on the final results. Using the same processing line design as the one discussed in Buchholz et al ., we also used data generated by Smolinski et al . on spread of E. coli O157:H7 during flume washing and drying of fresh‐cut romaine lettuce to calibrate the pathogen binding rate ( β LW ) in Equations and (data and results not shown here).…”