Evaluation of the Oxoid BCET-RPLA Kit for the Detection of Bacillus cereus Diarrheal Enterotoxin as Compared to Cell Culture Cytotonicity

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Abstract
The relationship between detection of heat-labile enterotoxin production by Bacillus cereus using the Oxoid BCET-RPLA kit and the production of a cytotonic response in HEp-2 and CHO cells was evaluated using 12 isolates. The strains were cultured in brain heart infusion + 0.1% glucose for 5 h at 37°C on a rotary shaker. Cell-free supernatants were prepared by filtration and tested using the two cell lines and the immunoassay. The primary biological response noted with the cell lines was cytotonicity, with the CHO cells being consistently more sensitive than the HEp-2 cells. While there was general agreement between the cell culture tests and the immunoassay, differences were noted for specific strains. Further, while activity in cell cultures was lost when cell-free supernatants were heated to 80°C for 5 min, the BCET-RPLA kits continued to detect significant levels of enterotoxin. The results suggest that confirmation of B. cereus enterotoxin using a suitable biological response may be warranted until additional research can clarify the specificity of the BCET-RPLA assay.