Study on cytotoxicity and nucleotide sequences of enterotoxin FM of Bacillus cereus isolated from various food sources.

OBJECTIVE: To determine the cytotoxicity of the crude culture broth containing enterotoxins of B. cereus and investigate the nucleotide sequences of ent FM among various isolates B. cereus. MATERIAL AND METHOD: The 1.2 kb fragment of ent FM of B. cereus was amplified, cloned, sequenced, and compared with published sequences. The biological activity of crude culture broth containing enterotoxins with and without monoclonal antibodies against HBL, NHE, and EntFM enterotoxins was tested using Vero cells assay. RESULTS: A percentage homology of nucleotide sequences and deduced amino acid sequences among test isolates and published strains were 90-99% and 88-99%, respectively. An assays for cytotoxic activity revealed that seven and three of B. cereus isolates were positive for NHE enterotoxin and EntFM enterotoxin, respectively. In addition, the 4-repeating sequences "TCAAAC" of ent FM were found, which may or may not be probably correlated with cytotoxicity of B. cereus. CONCLUSION: The enterotoxin FM from B. cereus isolates is cytotoxic and the degree of cytotoxicity depends on the bacterial strain.