Magnetic Nanoparticle-Antibody Conjugates for the Separation of Escherichia coli O157:H7 in Ground Beef

Abstract

The immunomagnetic separation with magnetic nanoparticle-antibody conjugates (MNCs) was investigated and evaluated for the detection of Escherichia coli O157:H7 in ground beef samples. MNCs were prepared by immobilizing biotin-labeled polyclonal goat anti-E. coli antibodies onto streptavidin-coated magnetic nanoparticles. For bacterial separation, MNCs were mixed with inoculated ground beef samples, then nanoparticle-antibody-E. coli O157:H7 complexes were separated from food matrix with a magnet, washed, and surface plated for microbial enumeration. The capture efficiency was determined by plating cells bound to nanoparticles and unbound cells in the supernatant onto sorbitol MacConkey agar. Key parameters, including the amount of nanoparticles and immunoreaction time, were optimized with different concentrations of E. coli O157:H7 in phosphate-buffered saline. MNCs presented a minimum capture efficiency of 94% for E. coli O157:H7 ranging from 1.6 x 10(1) to 7.2 x 10(7) CFU/ml with an immunoreaction time of 15 min without any enrichment. Capture of E. coli O157:H7 by MNCs did not interfere with other bacteria, including Salmonella enteritidis, Citrobacter freundii, and Listeria monocytogenes. The capture efficiency values of MNCs increased from 69 to 94.5% as E. coli O157:H7 decreased from 3.4 x 10(7) to 8.0 x 10(0) CFU/ml in the ground beef samples prepared with minimal steps (without filtration and centrifugation). An enrichment of 6 h was done for 8.0 x 10(0) and 8.0 x 10(1) CFU/ml of E. coli O157:H7 in ground beef to increase the number of cells in the sample to a detectable level. The results also indicated that capture efficiencies of MNCs for E. coli O157:H7 with and without mechanical mixing during immunoreaction were not significantly different (P > 0.05). Compared with microbeads based immunomagnetic separation, the magnetic nanoparticles showed their advantages in terms of higher capture efficiency, no need for mechanical mixing, and minimal sample preparation.

Biosensors and their Applications in Food Safety: A Review

“…Recently, a new method that is referred to as immunomagnetic separation was developed to effectively isolate pathogens from food matrices using magnetic pellets to functionalize antibodies against target pathogens (Varshney et al, 2005). A similar technique was reported that is based on magnetic nanoparticles with a diameter of 30 nm functionalized with anti-L. monocytogenes antibodies via biotin-streptavidin bonds to generate immunomagnetic nanoparticles that were shown to capture L. monocytogenes during a 2-h immunoreaction (Damira et al, 2012).…”

“…Mass-sensitive biosensors are utilized less frequently than optical and electrochemical biosensors (Su and Li, 2005). Also known as piezoelectric biosensors, they use piezoelectric crystals that are highly sensitive and can detect small changes in mass.…”

Magnetite (Fe3O4) - Synthesis, Functionalization and its Application

“…When attached to antibodies these are used for immunogenic separation of bacteria, viruses, proteins and nucleic acid. Li and his co-workers used antibody conjugated nanoparticles to isolate Escherichia.coli O157:H7 from ground beef (Varshney, Yang, Su, & Li, 2005). Magnetic nanoparticles conjugates with proteins and microbes are used in detoxification of bio fluids, tissue repair, immuno-assay cell separation, and hyperthermia and drug delivery.…”

Biosensors for On-the-spot Detection of Bacteria from Foods

“…CFU/ml in ground beef [37] Amperometric E. coli, L. monocytogenes, and C. jejuni Without pre-enrichment 10-50 Cells/ml in milk and ground chicken [38] Amperometric Vibrio After 24hrs pre-enrichment 7.3 × 10 4 CFU/ml in culture media [39] Amperometric E. coli After 24hrs pre-enrichment 5 × 10 4 CFU/ml in wastewater [40] Amperometric E. coli Without pre-enrichment 55 Cells/ml, 100 Cells/ml in buffer solution and milk, respectively [41] Potentiometric E. coli O157:H7 After 24hrs pre-enrichment 10 4 CFU/ml in buffer solution [42] Potentiometric E. coli After 30hrs pre-enrichment 10 Cells/ml in ground vegetable [32] Impedimetric E. coli O157:H7 After 24hrs pre-enrichment 2 CFU/ml in culture media [43] Impedimetric E. coli O157:H7 Without pre-enrichment 83.7 CFU/ml in milk [44] Impedimetric Listeria…”