T10-01 Developing Methods to Identify Surrogates for E. coli O157:H7 in Validation of Fresh Produce Washing Processes

Wednesday, August 3, 2016: 8:30 AM
242 (America's Center - St. Louis)
Catherine Rolfe, Illinois Institute of Technology/IFSH, Bedford Park, IL
Arlette Shazer, U. S. Food and Drug Administration, Bedford Park, IL
Kaiping Deng, Illinois Institute of Technology/IFSH, Bedford Park, IL
Introduction: Cross-contamination during fresh produce washing is commonly prevented using chlorine inactivation treatment. Surrogate microorganisms can be used in validation of chlorine washing process. However, fresh produce washing incorporates physical, chemical, biological and kinetic factors which create an intricate process for which little is known regarding surrogate selection.

Purpose: The purpose of this study was to identify the important elements relevant to produce washing processes and identify methods that will be used in surrogate selection.

Methods: The behavior of three (3) non-pathogenic microorganisms (generic E. coli Nissle1917, Pediococcus pentosaceus and lettuce isolate 813-F1) were examined in comparison to E. coli O157:H7 based on phenotypic similarities. Chlorine inactivation kinetics of E. coli O157:H7 and the non-pathogenic strains were evaluated with varying pH levels (6.5 and 8.0) and exposure times (3-30 seconds). Detachment of leaf-bound E. coli O157:H7 and non-pathogenic strains at different inoculation levels (~2 log, 6 log) and drying conditions (aging time, temperature) in wash water was examined.

Results: Chlorine inactivation at pH 6.5 resulted in a range of viability corresponding to E. coli O157:H7 and the non-pathogenic strains; demonstrating a sharp inactivation curve for E. coli O157:H7, EcN and P. pentosaceus. Whereas, inactivation at pH 8.0 allowed more survival relating to exposure time for all microorganisms. Detachment from inoculated leaves at 2 log and 6 log inoculation showed steady survival levels in wash water at 0 ppm and significantly lower survival at 1 ppm for all strains excluding 813-F1; 813-F1 was consistently less chlorine-sensitive. Aging time was not seen to have remarkable effects on bacterial transfer during washing.

Significance: These results suggest assay methods of chlorine inactivation at pH 6.5 and detachment with 6 log initial inoculation may be useful in selecting appropriate surrogates for fresh produce washing.