Hybridization chain reaction-based flow cytometric bead sensor for the detection of emetic Bacillus cereus in milk

Emetic Bacillus cereus is a common foodborne pathogen that can cause vomiting after ingesting the contaminated food. Detection of emetic B. cereus plays an important role in food industry. In this study, a flow cytometric bead assay based on hybridization chain reaction (HCR) were developed to detect emetic B. cereus. Forward primer labeled magnetic beads (MBs) could capture single-strand DNA (ssDNA), which were generated through the asymmetric polymerase chain reaction from the partial cereulide-encoded gene of emetic B. cereus. Then the ssDNA initiated HCR to self-assemble with two fluorescent hairpin probes. Flow cytometry was then performed to monitor the HCR products of MBs. Under optimal experimental conditions, the limit of detection (LOD) for emetic B. cereus was 7.6 x 10(0) CFU/mL with a liner range from 7.6 x 10(0) CFU/mL to 7.6 x 10(6) CFU/mL in pure culture. The proposed strategy can be used in spiked milk with LOD of 9.2 x 10(2) CFU/mL without enrichment. The high specificity of the assay was verified using closely related strains, such as B. subtilis, non-emetic B. cereus. The proposed strategy offers a great promise for simple, low-cost, sensitive, and specific pathogen diagnosis in a real food matrix. (C) 2017 Elsevier B.V. All rights reserved.