Purpose: The study evaluated a rapid, multiplexed liquid crystal-based immunoassay as compared to the USDA and FDA reference methods for detection of the 7 USDA mandated STEC serotypes (O26, O45, O103, O111, O121, O145 and O157) in various food matrices.
Methods: The assay involved screening different antibody coated microsphere panels against pathogens and examining their detection in a liquid crystal media. Selectivity was validated using 54 pure culture STEC strains and 52 pure culture non-STEC strains. Finally, the assay was optimized for the raw ground beef, beef trim and spinach food matrices and tested in parallel against the USDA/FSIS-MLG 5B.05 and FDA BAM4A reference methods, using multiple STEC strains.
Results: Two assay panels of antibody were designed to detect the 7 STEC serotypes. The liquid crystal-based assay selectively detected 98% (53 of 54) of the STEC while excluding 96% (50 of 52) of the non-STEC strains. Assay detection of 1 - 4 CFU of an individual STEC strain in 325 g of raw ground beef or trim, or 200 g of spinach, was statistically equivalent (95% CI) to the respective USDA and FDA reference methods, after a pre-enrichment for as short as 9.5 h (N = 30 for each matrix, dPOD of -0.10 with 95% CI (-0.33, 0.14) for ground beef and trim, and dPOD of 0.13 (-0.11, 0.36) for spinach).
Significance: This liquid crystal-based immunoassay provides a major time reduction from sample to detection compared to the reference methods, and appreciably reduces the risk for exposure to STEC contaminated food.