Detection of Salmonella typhimurium Grown Directly on Tomato Surface Using Phage-Based Magnetoelastic Biosensors

A phage-based magnetoelastic (ME) biosensor method is being developed for on-site pathogen detection in fresh fruits and vegetables. Salmonella typhimurium was directly grown with minimal nutrients on tomato surfaces in order to mimic natural environmental conditions. S. typhimurium was inoculated on the surface of fresh tomatoes, and ME biosensors were used to detect the bacteria. The populations of S. typhimurium after 24-h incubation time at 37°C and 100% relative humidity were 6.1 and 7.8 logCFU/cm 2 after starting with initial inoculations of 3.0 and 5.0 logCFU/cm 2 , respectively. After evident growth, measurement sensors with E2 phage immobilized on their surfaces and control sensors devoid of E2 phage were placed on the inoculated tomato surfaces and the resonant frequency shifts were measured. As the population of S. typhimurium increased, the resonant frequency shifts of the measurement sensors significantly increased ( P