Purpose: Two sets of loop-mediated isothermal amplification (LAMP) assays, (serogroup-independent and serogroup-specific) were evaluated for the detection of the seven major STEC serogroups in produce samples.
Methods: Lettuce, spinach and sprouts were surface-inoculated with low levels (1-10 CFU/25 g) of STEC strains of the major serogroups. The LAMP assays were used to detect the STEC strains in the produce samples after culture enrichment. Real-time quantitative PCR (qPCR) assays were performed in parallel as a comparison.
Results: The detection limits of the LAMP assays for the STEC ranged from 1 to 20 cells. No false-positive or false-negative results were generated when testing 120 bacterial strains. Sample preparations using centrifugation were efficient in extracting DNA template for LAMP amplifications. LAMP produced positive results in spiked samples in approximately 20 to 45 min after 6 h culture enrichment, whereas pPCR required 35 to 70 min after 6-8 h enrichment to produce the results in the same samples.
Significance: The LAMP assays were able to rapidly detect the seven major STEC serogroups in produce samples with excellent specificity and sensitivity, which could facilitate timely implementation of control measures concerning potential STEC contaminations in produce.