Detection of Low Levels of Listeria monocytogenes Cells by Using a Fiber-Optic Immunosensor

Abstract

Biosensor technology has a great potential to meet the need for sensitive and nearly real-time microbial detection from foods. An antibody-based fiber-optic biosensor to detect low levels of Listeria monocytogenes cells following an enrichment step was developed. The principle of the sensor is a sandwich immunoassay where a rabbit polyclonal antibody was first immobilized on polystyrene fiber waveguides through a biotin-streptavidin reaction to capture Listeria cells on the fiber. Capture of cells on the fibers was confirmed by scanning electron microscopy. A cyanine 5-labeled murine monoclonal antibody, C11E9, was used to generate a specific fluorescent signal, which was acquired by launching a 635-nm laser light from an Analyte 2000 and collected by a photodetector at 670 to 710 nm. This immunosensor was specific for L. monocytogenes and showed a significantly higher signal strength than for other Listeria species or other microorganisms, including Escherichia coli, Enterococcus faecalis, Salmonella enterica, Lactobacillus plantarum, Carnobacterium gallinarum, Hafnia alvei, Corynebacterium glutamicum, Enterobacter aerogenes, Pseudomonas aeruginosa, and Serratia marcescens, in pure or in mixed-culture setup. Fiber-optic results could be obtained within 2.5 h of sampling. The sensitivity threshold was about 4.3 ؋ 10 3 CFU/ml for a pure culture of L. monocytogenes grown at 37°C. When L. monocytogenes was mixed with lactic acid bacteria or grown at 10°C with 3.5% NaCl, the detection threshold was 4

Biosensors Applications in Agri-food Industry

“…Its response in cold (4 °C) and salty conditions showed lower reaction rates due to "stress" of the monoclonal antibodies at low temperatures. The biosensor also showed a reduction in sensitivity at low L. monocytogenes concentrations when the medium contained other microbiota able to affect the antigen-antibody reaction (Geng et al, 2004). The fiber-optic biosensor detects concentrations from 10 7 to 10 8 CFU/ml (Geng et al, 2004).…”

“…A rapid detection of this pathogen is essential. Biosensors offer advantages over traditional methods that need longer test time and specific growth media before the pathogen is detected (Geng et al, 2004). The use of optical biosensors allows the reaction between receptor and analyte, providing confidence, specificity and less time for detection.…”

“…The biosensor also showed a reduction in sensitivity at low L. monocytogenes concentrations when the medium contained other microbiota able to affect the antigen-antibody reaction (Geng et al, 2004). The fiber-optic biosensor detects concentrations from 10 7 to 10 8 CFU/ml (Geng et al, 2004). In situations where the product is suspected to contain L. monocytogenes counts below 10 7 CFU/ml, an enrichment step prior to the biosensor detection is required.…”

“…In this way, real time data is used to identify bacteria, viruses or toxins. Moreover, these biosensors allow the identification of pathogens at low concentrations (Geng et al, 2004). A fiber-optic biosensor can be used for the detection of Listeria monocytogenes (Geng et al, 2004).…”

“…Moreover, these biosensors allow the identification of pathogens at low concentrations (Geng et al, 2004). A fiber-optic biosensor can be used for the detection of Listeria monocytogenes (Geng et al, 2004). It is based on the measurement of fluorescent light generated by a wave when there is a change in resonance.…”