Rapid Quantification of <i>Escherichia coli</i> O157:H7 and <i>Salmonella</i> Typhimurium in Lettuce Using Immunomagnetic Separation and a Microfluidic System

Escherichia coli O157:H7 and Salmonella spp. are common foodborne pathogens. Simple, rapid and accurate methods to detect and enumerate these pathogens are required to prevent outbreaks of foodborne illness. Here, a microfluidic system with on-chip staining and semi-automated counting functionality was combined with the use of immunomagnetic separation to collect E. coli O157:H7 and Salmonella Typhimurium without an enrichment step. The recovery of bacteria from lettuce at different spiking ratios of the two species was 61-83%. In the range 3.5 × 10² to 3.3 × 10⁵ cells/g of lettuce, there was a good linear relationship (R² = 0.9997-0.9998) between the average counts from the microfluidic quantification method and conventional immunofluorescence microscopy. Detection took <3 h. The limit of detection of the microfluidic device was 4 × 10¹ cells/g, comparable to that of plate culture and real-time PCR methods. Our microfluidic approach has potential for rapid on-site detection of multiple pathogenic bacteria in foods.