Immunomagnetic detection of Bacillus stearothermophilus spores in food and environmental samples

There are currently no methods for the rapid and sensitive detection of bacterial spores that could be used to direct raw materials containing high spore loads away from products that pose a food safety risk. Existing methods require an overnight incubation, cannot detect spores below 10(5) CFU/ml, or are not specific to particular species. This work describes a method to specifically detect < 10(4) CFU of bacterial spores per ml within 2 h. Polyclonal antibodies to Bacillus stearothermophilus spores were attached to 2.8-micron-diameter magnetic polystyrene beads by using a polythreonine cross-linker via the antibody carbohydrate moiety. A biotin-avidin-amplified sandwich enzyme-linked immunosorbent assay coupled to a fluorescent substrate was used to quantitate captured spores. The concentration of B. stearothermophilus spores in samples was linearly correlated to fluorescent activity (r2 = 0.99) with a lower detection limit of 8 x 10(3) CFU/ml and an upper detection limit of 8 x 10(5) CFU/ml. The detection limits are not fixed and can be changed by varying the immunomagnetic bead concentration. Several food and environmental samples were tested to demonstrate the versatility of the assay.