Rapid identification of Bacillus cereus based on the detection of a 28.5-kilodalton cell surface antigen

Conventional procedures for the identification of suspect Bacillus cereus isolated on mannitol-egg yolk-polymyxin (MYP) agar may need several days. To facilitate the identification of the bacterium, an enzyme-linked immunosorbent assay (ELISA) was developed. The assay was based on the detection of a 28.5-kDa cell surface antigen of B. cereus. Bacterial colonies grown on MYP agar or nutrient agar were suspended in phosphate-buffered saline (pH 7.2) containing 0.1% Teepol. The cell suspensions were heated at 100 degrees C for 5 min and added to the microtiter plates coated with antibodies against the 28.5-kDa antigen. After washing, the same antibodies labeled with horseradish peroxidase were used as secondary antibodies to reveal the signal of antigen-antibody reaction. For 38 strains of B. cereus and 127 strains of non-B. cereus bacteria (including 79 isolates of Bacillus spp.) tested, the sensitivity and specificity of the ELISA were 100 and 88.2%, respectively. Strains producing false-positive results were members of the B. cereus group (i.e., Bacillus anthracis, Bacillus mycoides, and Bacillus thuringiensis), which are genetically and biochemically similar to B. cereus. Similar ELISA results were obtained by using antibodies against another cell surface antigen with a molecular mass of 20 kDa. If members of the B. cereus group were recognized as a single species, the sensitivity and specificity of the ELISA were 100 and 99.1%, respectively. The ELISA could be used as a rapid method for presumptive identification of B. cereus grown on MYP agar.