Bacteriophage-linked superparamagnetic nanoparticle for sensitive and simple detection of pathogenic Escherichia coli O157:H7 bacteria

An easy-to-use and highly-sensitive magnetic nanoprobe to detect veratoxin-producing Escherichia coli O157:H7 was developed. The bacteriophage that targets E. coli O157:H7 was chemically linked to chitosan-coated iron oxide nanoparticles (5–50 nm) to form a nanoprobe for the detection of E. coli O157:H7 in aqueous samples. The nanoprobes had a limit of detection of 2 log CFU/mL in samples with pH from 5 to 8 at 25 °C, and temperatures from 25 to 40 °C at pH 7. In the beef and cabbage liquid extracts, the nanoprobe had a detection limit of 2 log CFU/mL at 25 °C and pH 7. The nanoprobe was highly specific and retrieved only E. coli O157:H7 from a sample of bacterial mixture. Gram staining method was used with the nanoprobe to visualize the bacterial cells captured from bacterial suspensions at 7 pH and 25 °C. Visualization of the bacterial cells captured from suspensions with a concentration of 2 log CFU/mL was achieved. To detect the presence of bacteria, the use of the magnetic nanoprobes and Gram staining took less than 30 min to complete. The system developed in this study offers a fast and operator-friendly alternative for highly-specific bacterial detection.