Detection of Salmonella Enterica Typhimurium in Chicken Meat Using Phage Coated Magnetoelastic Sensors

According to the Centers for Disease Control and Prevention (CDC), from 2011-2014, there were at least several outbreaks in the U.S. due to Salmonella associated with chicken.  Our goal was to improve food safety in this area, and develop a real time detection system. We developed and demonstrated the use of our phage C4-22 immobilized onto a rapid magnetoelastic (ME) biosensor system for use as a front-line detection ligand to detect all Salmonella enterica serotypes in TBS model.

Here, we confirm the phage peptide binding to Salmonella typhimurium cells by fluorescent imaging (Fig. 1 and 2.) Figure 1 showed the Salmonella cells only without C4-22 phages with magnification of 100x. In figure 2, it is the binding of fluorescent labeled phages (1x10¹¹ vir/ml) and Salmonella, viewing under fluorescent microscope with fluorescein isothiocyanate (FITC) filter and with magnification of 100x.

 Moreover, we show the construction of a chicken model to evaluate the detection of Salmonella on/in chicken meat using the phage coated sensor. In the surface detection system, S.  typhimurium solutions at four concentrations of 2.5x10⁶, 5x10⁶, 2.5x10⁷, and 5x10⁷ cfu/ml were inoculated on the surface of chicken breast. Three phage sensors as a test group were placed on the chicken surface for detection. Experiments were repeated twice. Phage sensors were prepared by coating the ME sensors with 1x10¹⁰ virons phage C4-22 in TBS. BSA (0.1%) was used as a blocking reagent on the sensor. Sensors coated with 0.1% BSA only served as controls. Cells of S. typhimurium detected on the sensor were eluted with 0.1M Glycine to break phage-Salmonella binding. The percent of Salmonella binding to the phage coated sensor was determined using a standard aerobic plate count method with TSA and BG plates. Phage C4-22 sensors demonstrated more than 12 times higher Salmonella binding capacity than the control sensors at the Salmonella loading concentration of 5x10⁷cfu (Fig.2).

During the experiments, it was found that the spiked Salmonella solution was quickly absorbed by the chicken meat. In the second chicken model, phage sensors were placed at different depths (0.1cm; 0.5cm; 1.0cm below the surface; Fig. 3) inside the chicken after inoculation of Salmonella for 15min. Our data show more than 30% of the inoculated Salmonella cells absorbed inside the chicken meat below 0.1cm of the chicken surface. The percentage of the biosensor captured Salmonella decreased while the detection depth increased.

In summary, phage C4-22 ME biosensors detect well when there are high concentrations of Salmonella on the chicken surface. The inside meat detection allow us to effectively monitor Salmonella cells which were absorbed into the chicken and unable to detect by the biosensors while using a surface detection method.