Dynabeads protein G antibody conjugates combined with modified brain heart infusion broth for the enrichment and separation of Bacillus cereus in artificially contaminated vegetables.

ABSTRACT

A modified brain heart infusion (MBHI) broth and a protocol of immunomagnetic separation (IMS) using antibody-coated Dynabeads® protein G were developed for the enrichment and separation of Bacillus cereus in artificially contaminated vegetable samples. The MBHI consisted of BHI and 0.34 g/L magnesium sulfate, 12.08 g/L sodium pyruvate, 1.82 g/L yeast extract, and polymyxin B. The amount of immunomagnetic beads (IMBs) and immunoreaction time were optimized. The capture efficiency was 58.32% with 0.4 mg IMBs when the immunoreaction time was 20 min. Capture of B. cereus by IMBs did not interfere with competing flora. Pre-enrichment IMS was validated with four B. cereus strains in artificially contaminated baby sprouts, bean sprouts, lettuce, and spinach at two levels (∼0.1 and ∼1 CFU/g). We were able to detect and isolate B. cereus in 40/40 samples of vegetables contaminated at 0.1 CFU/g with IMS after 6 h of enrichment in MBHI.