Low cost bioluminescence imaging as an alternative to in vivo bioassays for quantifying biologically active staphylococcal enterotoxin type E

Staphylococcus aureus is a major causative agent implicated in outbreaks of food poisoning. It acts through the production of a range of toxins including staphylococcal enterotoxin type E which has been associated with foodborne outbreaks in the USA, UK and France. While tests such as ELISA exist to detect the toxin's molecules, existing methods to distinguish active toxin from inactivated are costly and require the use of live animal testing. In this study we constructed and evaluated a low cost CCD camera device in conjunction with a cell based assay for active SEE employing a genetically engineered T-cell line with a luciferase reporter regulated by nuclear factor of activated T-cells combined with a B-cell line for toxin presentation. The emitted light intensity from the T-cells is proportional to SEE concentration over an 8-log range and can discern the active form of toxin that sickens consumers, from toxin inactivated by heat treatment. The assay was verified in sample food matrices by spiking white grape and peach mango juices as well as apple cider. The low cost imaging device compared favorably against the expensive commercial luminometer plate reader using the same cell based assay. The low cost camera device should improve the availability of active toxin testing, especially in resource poor regions.