Optical immunosensors for detection of Listeria monocytogenes and Salmonella Enteritidis from food

摘要

Listeria monocytogenes and Salmonella are two major foodborne pathogens of significant concern. Two optical evanescent wave immunosensors were evaluated for detection: Antibody-coupled fiber-optic biosensor and a surface plasmon resonant (SPR) immunosensor. In the fiber-optic sensor, polyclonal antibodies for the test organisms were immobilized on polystyrene fiber wave-guides using streptavidin-biotin chemistry. Cyanine 5 -labeled monoclonal antibodies C1 1E9 (for L. monocytogenes) and SF-11 (for Salmonella Enteritidis) were used to generate a specific fluorescent signal. Signal acquisition was performed by launching a laser-light (635 nm) from an Analyte-2000. This immunosensor was able to detect 10~3 - 10~9 cfu/ml of L monocytogenes or 10~6-10~9 cfu/ml of Salmonella Enteritidis and the assays were conducted at near real-time with results obtained within one hour of sampling. The assays were specific and showed signal even in the presence of other microorganisms such as E. coli, Enterococcus faecalis or Salmonella Typhimurium. In the SPR system, IAsys instrument (resonant mirror sensor) was used. Monoclonal antibody-C1 1E9 was directly immobilized onto a carboxylate cuvette. Whole Listeria cells at various concentrations did not yield any signal while surface protein extracts did. Crude protein extracts from L. monocytogenes and L innocua had average binding responses of around 150 arc sec (0.25 ng/mm~2), which was significantly different from L. grayi, L ivanovii, or L. welshimeri with average responses of <48 arc sec. Both fiber-optic and SPR sensors show promise in near real-time detection of foodborne L monocytogenes and Salmonella Enteritidis.