A Rapid and Automated Fiber Optic–Based Biosensor Assay for the Detection ofSalmonella in Spent Irrigation Water Used in the Sprouting of Sprout Seeds

Abstract

Recent outbreaks of foodborne illness have been linked to the consumption of contaminated sprouts. The spent irrigation water used to irrigate sprouts can carry many microorganisms, including pathogenic strains ofEscherichia coli andSalmonella enterica. These pathogens are believed to originate from the seeds. The U.S. Food and Drug Administration recommends that sprout producers conduct microbiological testing of spent irrigation water from each production lot at least 48 h after seeds have germinated. Microbial analysis for the detection ofSalmonella is labor-intensive and takes days to complete. A rapid and automated fiber-optic biosensor assay for the detection ofSalmonella in sprout rinse water was developed in this study. Alfalfa seeds contaminated with various concentrations ofSalmonella Typhimurium were sprouted. The spent irrigation water was assayed 67 h after alfalfa seed germination with the RAPTOR (Research International, Monroe, Wash.), an automated fiber optic–based detector.Salmonella Typhimurium could be positively identified in spent irrigation water when seeds were contaminated with 50 CFU/g. ViableSalmonella Typhimurium cells were also recovered from the waveguides after the assay. This biosensor assay system has the potential to be directly connected to water lines within the sprout-processing facility and to operate automatically, requiring manual labor only for preventative maintenance. Therefore, the presence ofSalmonella Typhimurium in spent irrigation water could be continuously and rapidly detected 3 to 5 days before the completion of the sprouting process.