P1-27 Spread of Escherichia coli O157:H7 during Flume Washing and Drying of Fresh-cut Romaine Lettuce

Monday, August 1, 2016
America's Center - St. Louis
Siyi Wang, Michigan State University, East Lansing, MI
Haley Smolinski, Michigan State University, East Lansing, MI
Lin Ren, Michigan State University, East Lansing, MI
Yuhuan Chen, U.S. Food and Drug Administration-CFSAN, College Park, MD
Barbara Kowalcyk, RTI International, Research Triangle Park, NC
Ellen Thomas, RTI International, Raleigh, NC
Elliot Ryser, Michigan State University, East Lansing, MI
Introduction: The microbiological safety of leafy greens remains a concern as evidenced from recent outbreaks.

Purpose: Consequently, this study assessed the spread of Escherichia coli O157:H7 during pilot-scale washing and drying of fresh-cut Romaine lettuce.

Methods: Using inoculated radicchio as a colored surrogate for uninoculated Romaine lettuce, radicchio leaves (~5 x 5 cm) were spot-inoculated at ~10-1, 101 and 103 CFU/leaf and mixed with uninoculated Romaine lettuce leaves (~5 x 5 cm) to obtain 5 kg batches having inoculated:uninoculated product ratios of 0.5:100, 1:100, 5:100 and 10:100. After 2 minutes of flume washing in sanitizer-free water followed by shaker table dewatering and centrifugal drying in a pilot-scale processing line, all radicchio leaves were removed. Each batch was then divided into ~20 225-g samples which were analyzed for presence/absence of E. coli O157:H7 using the E. coli O157 GeneQuence method (Neogen Corp, Lansing, MI).  The percentage of E. coli O157:H7 lost from radicchio during processing was determined by direct plating before and after processing with E. coli O157:H7 populations also assessed in 50 ml water samples by membrane filtration.

Results: Based on triplicate experiments, lower radicchio inoculation levels led to decreased E. coli O157:H7 transfer to Romaine lettuce during processing (P<0.05). All lettuce samples yielded E. coli O157:H7 when radicchio was inoculated at 103 CFU/leaf. When radicchio was inoculated at 101 CFU/leaf, the percentage of positive samples decreased from 100-90.5% to 100-81.0%, 90.5-76.2% and 85.7-28.6% for inoculated:uninoculated ratios of 10:100, 5:100, 1:100 and 0.5:100 while at 10-1 CFU/leaf, 38.1-4.8%, 9.5-0%, 4.8% and 19-0% of the samples were similarly positive for the same inoculated:uninoculated ratios. Within each inoculation level, no significant differences (P>0.05) were found among the four inoculated:uninoculated product ratios. E. coli O157:H7 was non-quantifiable in the water samples.

Significance: These findings will provide important data for improving exposure assessment in risk assessments for leafy greens.