Rapid Detection of Single Viable Escherichia coli O157 Cells in Fresh Lettuce and Strawberry by Immunomagnetic Flow Cytometry in Combination with Pre-Enrichment

Enterohemorrhagic Escherichia coli are an important pathogen causing food poisoning. The rapid detection of viable E. coli O157 in vegetables and fruits at single-cell level is critical because of the low infective dose of this pathogen. In this study, an immunomagnetic flow cytometry (IMFC)-based method was developed to detect E. coli O157 in lettuce and strawberries inoculated with 1 CFU/25 g. This method developed immunomagnetic (IM)-beads to capture E. coli O157 cells. The pre-enrichment of E. coli O157 and IM-bead separation rapidly increased the concentration of cells to a detectable range for flow cytometry. Compared with the plate-based method, the diagnostic sensitivity and specificity of the IMFC-based method were 100% in 166 samples, including 100 artificially contaminated samples, 60 retail samples, and six O157-positive samples for proficiency testing. The developed IMFC-based method was found to be effective in detecting E. coli O157 at single-cell level in 25 g of lettuce or strawberry with relatively shorter associated time to results of 5.7 h. Therefore, the IMFC-based method could improve detection efficiency and also make early warnings in a short time.