Evaluation of phage-based magnetoelastic biosensors for direct detection of Salmonella Typhimurium on spinach leaves

For a phage-based magnetoelastic (ME) biosensor method to become accepted for evaluating foodborne contamination, the method of use must be objectively compared, evaluated and validated against more widely accepted standard methods. In this study, a ME biosensor method was evaluated by comparison with TaqMan-based quantitative PCR (qPCR) for the detection of Salmonella Typhimurium on spinach leaves. Limit of detection (LOD) was determined after serial inoculation of S. Typhimurium on spinach leaves. The LOD for the ME biosensor was 2.17 and 1.94 log CFU/spinach for adaxial and abaxial surface, respectively. The LOD for qPCR was 1.37 log CFU/spinach. The repeatability of both methods was measured over a three day period by inoculation of S. Typhimurium on spinach leaves. The repeatability of the ME biosensor method was determined to be 6.38%, competitive with qPCR at 1.92%. For the direct comparison of both methods, 3 log CFU/spinach of S. Typhimurium was grown on two groups of 25 spinach leaves for 24 h and the number of S. Typhimurium was quantified by both methods. After confirmation of the growth, S. Typhimurium was positively detected and the quantified numbers were 5.79 ± 0.88 and 6.11 ± 0.26 log CFU/spinach for the ME biosensor and the qPCR method, respectively. This study demonstrated that the ME biosensor method was competitive and promising as an on-site and in-field detection method for the detection of pathogens.