Study of antibodies to stress induced cellular antigens of Listeria monocytogenes and its detection using a fiber -optic biosensor in food
Abstract
Listeria monocytogenes is a food-borne pathogen that causes listeriosis particularly in immunocompromised populations with the highest death rates among the food-borne bacteria in the United States. Detection of L. monocytogenes by conventional methodology usually takes 3–5 days and more rapid detection methods are in great demand. Antibody based immunoassays for this pathogen might be rapid, specific and sensitive, but detection could be affected by antigenic expression due to environmental stresses, resuscitation in enrichment broths, and the sensitivity and the specificity of immunoassay methods used. To address above problems, first, the expression of cellular antigens of L. monocytogenes that react with monoclonal antibodies C11E9 and EM-7G1 under acid, salt or temperature-induced stress environments was studied. Results indicated that MAb C11E9 or EM-7G1 could detect L. monocytogenes from cold or acid-stress environments; however, they may show weaker reactions with heat or osmotically stressed cells or cells grown at 4°C. Second, the expression of surface antigens of healthy or stressed L. monocytogenes grown in selective enrichment broths was investigated by using an anti-Listeria polyclonal antibody and a MAb CI I E9. Cells grown in buffered Listeria enrichment broth (BLEB) showed overall highest reaction to antibodies and Fraser broth (FB) gave the lowest growth, recovery and reaction to antibodies. Finally, a fiber-optic biosensor was used directly to detect healthy or stressed L. monocytogenes from buffer or from food by using an enrichment step. Results showed 10 CFU/ml cells in hotdog could be detected by this setup after 20 h pre-enrichment by BLEB. With high concentration of competitive microflora (107 CFU/ml), L. monocytogenes could be detected at 10 3 CFU/ml in hotdog samples. In direct detection, 4.3 × 10 3 CFU/ml healthy cells, 4.1 × 104 CFU/ml healthy cells with high concentration of competitive microflora or 2.8 × 10 7 CFU/ml stressed cells could be detected within two and half hours.
Degree
Ph.D.
Advisors
Bhunia, Purdue University.
Subject Area
Food science|Microbiology|Biomedical research
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