Fluorescent Ca2+ Indicator-based B Cells Biosensor for Rapid Detection of Escherichia coli O157:H7 in Foods

Introduction: Escherichia coli O157:H7 is one of the leading bacterial pathogens causing foodborne illness, infecting an estimated 73,000 people in the US each year and having an infective dose as low as 10 cells. A rapid, sensitive, and specific detection method for E. coli O157:H7 is continuing needed.

Purpose: The objective of the present study was to develop a fluorescent Ca²⁺ indicator based B cells biosensor with better combined speed and sensitivity than current methods for rapid detection of E. coli O157:H7 in foods.

Methods: The B cell membrane was firstly engineered with antibodies specifically against E. coli O157:H7. Then, a fluorescent Ca²⁺ indicator (Fura-2) was transferred into the B cell, which had an emission wavelength at 510 nm. When the target pathogen was attached to its specific antibodies on B cell surface, it produced a signal, and the signaling pathways were activated, resulting in the release of Ca²⁺ within seconds. The elevated intracellular Ca²⁺concentration activated Fura-2 to report the fluorescence signal change and indicated the presence of target pathogen.

Results: The developed B cells biosensor was able to detect E. coli O157:H7 at the concentration as low as 70 cells in a sample with a volume of 100 µl and a detection range from 10² to 10⁸ CFU ml^-1 was obtained. The total detection time from sampling to detection was within 30 min. The attachment of target E. coli O157:H7 on the surface of B cells were further confirmed by SEM (Scanning electron microscope) images.

Significance: The outcome of this study will make the detection of E. coli O157:H7 easier, faster, more sensitive and more suited for the ongoing transition from fundamental analytical science to the early diagnosis and detection of pathogens.