OPTICAL DETECTION OF FOOD SAFETY AND FOOD DEFENSE HAZARDS
Location: Quality and Safety Assessment Research Unit
Title: Identification and characterization of salmonella serotypes using DNA spectral characteristics by fourier transform infrared
Submitted to: Proceedings of SPIE
Publication Type: Proceedings
Publication Acceptance Date: December 17, 2011
Publication Date: April 23, 2012
Citation: Sundaram, J., Park, B., Hinton Jr, A., Yoon, S.C., Windham, W.R., Lawrence, K.C. 2012. Identification and characterization of salmonella serotypes using DNA spectral characteristics by fourier transform infrared (FT-IR) spectroscopy. Proceedings of SPIE. 8369. DOI:10.1117/12.918585.
Interpretive Summary: Detection, identification and differentiation of different bacteria and their serotypes takes long time in conventional microbiological methods. Rapid pathogen detection is still needed in food processing to avoid or minimize foodborne pathogenic illness from contaminated food. In recent years, optical methods using spectroscopy for identifying the organisms rapidly and its characterization are getting significant attraction. In this work, Fourier transform infrared spectroscopy (FT-IR) method was investigated to detect and differentiate various serotypes of Salmonella (Salmonella Typhimurium, Salmonella Enteritidis, Salmonella Infantis, Salmonella Heidelberg and Salmonella Kentucky) foodborne pathogen using their DNA sample extracted from each serotypes. The DNA of Salmonella cells were scanned using FT-IR spectroscopy and spectral data of each serotypes were collected. Statistical analysis was carried out on the spectral data to develop a model that can differentiate Salmonella serotypes. Salmonella cells were classified with 100 % accuracy. Thus, FT-IR spectroscopy method can distinguish five different serotypes of Salmonella cells quickly within 30 minutes after DNA extraction without any extensive sample preparation. This information is useful for developing rapid methods to detect pathogens.
Analysis of DNA samples of Salmonella serotypes (Salmonella Typhimurium, Salmonella Enteritidis, Salmonella Infantis, Salmonella Heidelberg and Salmonella Kentucky) were performed using Fourier transform infrared spectroscopy (FT-IR) spectrometer by placing directly in contact with a diamond attenuated total reflection (ATR) crystal. Spectra were recorded from 4000 cm-1 to 525 cm-1 wavenumber with the resolution of 4 cm-1 and data spacing of 1.928 cm-1. Collected spectra were subtracted from the background spectra of empty diamond crystal surface. Principal Component Analysis (PCA) was conducted at four different spectral frequency regions (1200-800 cm-1, 1800-1200 cm-1, 2200-1800 cm-1 and 3000-4000 cm-1) to differentiate the different serotypes of Salmonella on the basis of difference in their spectral features of DNA structure macromolecules. PCA was used to show the natural clusters in the data set and to describe the difference between the sample clusters. At the region 1800 – 1200 cm-1, PC1 distinguished 93 % and PC2 distinguished 7 % of the serotypes, resulted in maximum classification of 100 %. For all the five different serotypes of Salmonella, the frequency between 1000-1150 cm-1 and 1170 -1280 cm-1 had higher loading values which showed their significant contribution in the serotype classification.