Rapid Detection of Escherichia coli O157:H7 in Alfalfa Sprouts Using Liquid Crystal-based Immunoassay

Introduction: E. coli O157:H7 a major foodborne pathogen that has posed serious problems for food safety and public health. Although E. coli O157:H7 has been associated with various types of food, alfalfa sprouts are considered one of main food vehicles for E. coli O157:H7. A rapid and sensitive detection assay for this pathogen is critical to control outbreaks and ensure food safety.

Purpose:  The aim of this study was to evaluate a novel liquid crystal-based system as a rapid and sensitive assay for detection E. coli O157:H7 in alfalfa sprouts.

Methods: The liquid crystal-based immunoassay for E. coli O157:H7 was developed using immunomagnetic beads (IMB) and liquid crystal. When E. coli O157:H7 is present, formation of E. coli O157:H7-IMB aggregates distorts liquid crystal matrix and causes the bending of light, which is then detected by Crystal Diagnostics Xpress system. The assay was tested for its sensitivity using artificially inoculated alfalfa sprouts, and its specificity was tested with various non-O157 Shiga Toxin-producing E. coli (STEC) strains and common foodborne pathogens.

Results: The developed immunoassay was able to detect E. coli O157:H7 with detection limits of 10⁵ CFU/ml without any enrichment. When 6 h sample enrichment step was added, the assay could detect E. coli O157:H7 as low as 1 CFU in 100 g of alfalfa sprouts. The total assay was completed within 30 min. The developed assay was highly specific to E. coli O157:H7, and did not show any cross-reactivity with non-O157 STEC or with other common foodborne pathogens.

Significance: The novel immunoassay based on liquid crystal technology shows a great potential as a rapid and sensitive detection method for E. coli O157:H7 in food.