Abstract
A phage-based magnetoelastic (ME) biosensor method was compared with a TaqMan-based quantitative real- time PCR (Q-PCR) method for the detection of Salmonella typhimurium on tomato surfaces. This ME biosensor method utilizes magnetoelastic resonators coated with E2 filamentous phage to bind with and measure the concentration of S. typhimurium . In this study, standard curves, correlations, and limits of detection (LOD) for the ME biosensor and Q-PCR methods were determined by inoculating tomato surfaces with S. typhimurium suspensions in concentrations ranging from 1 to 8 log CFU/tomato. The LOD for the ME biosensor method and Q-PCR were 3 and 2 log CFU/tomato, respectively. In a direct comparison of the detection methods, S. typhimurium suspensions (3 log CFU/tomato) were inoculated on 65 tomato surfaces, then incubated at 37°C and 100% RH for 24 h. After 24 h, S. typhimurium was positively detected by both methods and the quantified concentrations were nearly the same, (6.35 ± 2.03) and (6.34 ± 0.17) log CFU/tomato respectively for the ME biosensor method and the Q-PCR method, which were significantly greater than the concentration determined by the BGS-plate count method (5.33 ± 0.21). Scanning electron microscopy (SEM) was used to confirm the growth of S. typhimurium on the tomato surfaces and the binding of S. typhimurium on the measurement sensors. This study demonstrated that the ME biosensor method was robust and competitive with Q-PCR for S. typhimurium detection on fresh produce.
Highlights
Outbreaks of Salmonella infection have recently occurred in a wide variety of fresh fruits and vegetables including lettuce, tomatoes, alfalfa sprouts, alfalfa seeds, artichokes, bean sprouts, cabbage, cilantro, lettuce, parsley and tomatoes, etc. [2]
The Limit of detection (LOD) in this study is defined as the lowest concentration of S. typhimurium that can be detected by quantitative real-time polymerase chain reaction (PCR) (Q-PCR) or ME biosensor methods [7]
A phage-based ME biosensor method was compared with Q-PCR
Summary
Outbreaks of Salmonella infection have recently occurred in a wide variety of fresh fruits and vegetables including lettuce, tomatoes, alfalfa sprouts, alfalfa seeds, artichokes, bean sprouts, cabbage, cilantro, lettuce, parsley and tomatoes, etc. [2]. From 1996 to 2008, eighty-two foodborne illness outbreaks were associated with the consumption of fresh produce (FDA, 2009). Of these outbreaks, 14 outbreaks (17.1%) were associated with the consumption of tomatoes and led to 1,927 illnesses and 3 deaths in the United States (FDA, 2009). Tomatoes have been one of the most common of fresh produce items implicated with Salmonella outbreaks [3]. Rapid and direct detection of Salmonella on fresh produce will decrease the number of illness outbreaks by providing timely data on the identification and quantification of Salmonella in contaminated foods [3]
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