Detection of Listeria monocytogenes Using a Liquid Crystal-based Immunoassay

Introduction: Patients infected with Listeria monocytogenes (L. monocytogenes) exhibit the highest mortality rate experienced with foodborne bacterial pathogens.  L. monocytogenes is additionally challenging because of its long persistence at low temperatures on surfaces and niches in food processing plants.   The current study developed a rapid (< 30 hours sampling to results), one step enrichment, liquid crystal (LC)-based screening test for detection of L. monocytogenes on surfaces.

Purpose: The LC assay was developed, tested for selectivity and specificity, and compared against two culture agars and the USDA reference method.

Methods: The LC assay selectivity and specificity was evaluated using four enrichment media. Surface testing on stainless steel and plastic was conducted 24 hours after the sample was inoculated and dried at room temperature.  Swab samples were collected, enriched and tested.  LC assay detection was compared against direct plating on Modified Oxford Agar (MOX) and Chromagar Listeria, and the USDA reference method.

Results: Foodchek Listeria and University of Vermont (UVM) media provided superior growth and selectivity when combined with the LC assay.  The LC assay detected 98% (54 of 55) of the L. monocytogenes and excluded 95% (38 of 40) of the non-L. monocytogenes tested. Detection by the LC assay was not statistically different (n=84, dPOD_c= 0.05 with a 95% confidence interval of (-0.10, 0.19)) when compared to MOX and Chromagar Listeria, and was not significantly different from the USDA reference method.

Significance: The liquid crystal-based immunoassay provides a rapid, one-step enrichment screening method for surface-associated L. monocytogenes.