Purpose: This study investigated use of DEUF-C in commercial-scale tests through the following two objectives: 1) comparison of pathogen detection probabilities using DEUF-C versus standard grab sampling in LWWs generated from a processing test line and 2) assessment of DEUF-C to concentrate pathogens spiked into commercially generated flume and centrifugation LWWs.
Methods: In objective 1, 2 to 4×104 CFU of Escherichia coli O157:H7 (Ec) and 3 to 9×105 CFU of Listeria monocytogenes (Lm) were spiked into one lettuce head and processed along with 907 kg of lettuce and sanitizer-free tap water. Two to four 40 liter volumes of LWW were processed by DEUF-C to generate 400 ml concentrated samples. Detection of probabilities for DEUF-C samples were compared to standard grab samples after 24 h enrichment/qPCR. In objective 2, flume and centrifuge LWW were collected from a commercial plant, treated with sodium thiosulfate (100 mg/liter) to neutralize the chlorine-based sanitizer, spiked with both Ec and Lm at ~102 CFU/ml and, then, processed by DEUF-C to determine total filterable volumes (TFVs). Detection (qPCR) probabilities in nonenriched DEUF-C and grab samples were determined to compare target organism recoveries. Experiments were repeated in quadruplicate.
Results: In objective 1, Ec and Lm were detected in 100% of DEUF-C samples (n=14) compared to 6.7% and 20%, respectively, in standard grab samples (n=15). In objective 2, TFVs for flume water were higher (n=4; 30.6+9.9 L) than those for centrifugation water (n=4; 9.9+2.0 L) (P=0.029, Mann-Whitney U Test). Ec and Lm were detected in 100% of DEUF-C samples compared to 11.1% and 16.7%, respectively, in standard grab samples.
Significance: DEUF-C offers improved probability of detection for E. coli and Listeria; however, TFV for commercial produce wash water needs to be further improved.