Abstract: A rapid and sensitive assay for detecting Cronobacter sakazakii in powdered infant formula (PIF) was developed by utilizing immunomagnetic separation (IMS) combined with visual gold nanoparticle (GNP) hybridization probe. C. sakazakii was captured via antibody-functionalized magnetic particles (MPs) and the polymerase chain reaction amplicon of the target bacteria was analyzed by GNP instead of traditionally used electrophoresis. Immunomagnetic particles (IMPs) were obtained by mixing together 100 μL of MPs, 120 μL of carbodiimide hydrochloride (EDC) and 80 μL of monoclonal antibody against C. sakazakii with 0.02% (V/V) added Tween-20. Specificity test showed positive results only for C. sakazakii. C. sakazakii could be detected at 102 CFU/mL and 103 CFU/g in pure culture and artificially contaminated PIF without pre-enrichment, respectively. After 3 h of pre-enrichment, this assay was able to detect as low as 4.5 × 101 CFU/g of C. sakazakii in PIF. The results of the visual assay were consistent with those of electrophoresis and ultraviolet scanning spectroscopy. Therefore, the IMS-GNP probe assay proved to be an alternative to gel electrophoresis for the rapid detection of C. sakazakii in PIF samples.

Key words: Cronobacter sakazakii; immunomagnetic separation; gold nanoparticles; powdered infant formula; visual detection