P3-31 Evaluation of Loop-mediated Isothermal Amplification for the Rapid, Reliable, and Robust Detection of Salmonella in Produce

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Qianru Yang, Louisiana State University, Baton Rouge, LA
Fei Wang, University of Maryland-College Park, College Park, MD
Kelly Johns, U.S. Food and Drug Administration, Laurel, MD
Jianghong Meng, University of Maryland-College Park, College Park, MD
Witoon Prinyawiwatkul, Louisiana State University, Baton Rouge, LA
Beilei Ge, U.S. Food and Drug Administration, Laurel, MD
Introduction: Salmonella is a leading bacterial pathogen involved in produce-associated outbreaks. Rapid, reliable, and robust detection methods are needed to better ensure produce safety. Loop-mediated isothermal amplification (LAMP) was recently adopted to detect Salmonella in produce. However, the assay has not been evaluated using an extensive collection of strains or complex produce matrices.

Purpose: The purpose of this study was to further evaluate LAMP performance in comparison with real-time quantitative PCR (qPCR) using a large panel of strains, and to validate the method for the rapid, reliable, and robust detection of Salmonella in various produce items. 

Methods: The specificity of the assay was evaluated with 180 bacterial strains. The sensitivity of the assay was tested with ten Salmonella strains of different serovars in pure culture and spiked produce samples (cantaloupe, lettuce, pepper, sprout, and tomato). The same produce items were surface-inoculated with low levels (1-20 cells per 25 g of produce) of Salmonella and detected after aging at 4oC for 48 h. All samples were tested by both LAMP and qPCR.

Results: No false-positive or false-negative results were observed among 180 strains used to evaluate assay specificity. The limits of detection of various Salmonella strains belonging to various serovars were 1 to 10 cells/reaction in pure culture and 104 to 106 CFU/25 g in spiked produce samples, which were superior to qPCR. In produce samples spiked with low levels of respective Salmonella strains, LAMP consistently achieved accurate detection after 6 to 8 h of enrichment, with the exception of sprouts.

Significance: The LAMP assay was demonstrated to be a rapid, reliable, and robust method for the detection of Salmonella in produce. The difficult with sprouts detection by both LAMP and qPCR warrant further studies.