Detection of bacteria with low-resolution Raman spectroscopy

Bacteria detection methods that are presently used in laboratories and quality control inspections, such as serological testing, biological enrichment, culturing, and gas chromatograph mass spectroscopy (GCMS), are expensive, labor intensive, and time consuming. Therefore, in order to ensure that consumers receive a safe and high-quality product, rapid and reliable methods need to be developed for detection of pathogens. Raman spectroscopy, an optical technique based on light scattering, was investigated as a means of rapid on-site produce safety, assessment. In this study, a dispersive system spectrophotometer, with a 785 nm diode laser, was employed. Chemometric methods such as partial least squares (PLS) regression and classification analysis were used to evaluate low- concentration suspensions of Erwinia carotovora pv. carotovora (ECC) and Clavibacter michiganense (CBM). The pathogens chosen represent Gram-positive and Gram-negative bacteria. A clear distinction between samples containing bacteria and clean samples was obtained by this method. The system was able to determine bacterial concentrations within 2% of the level in the basic bacteria suspension, based on PLS regression models. Classification analysis enables researchers to detect the presence of each of the tested bacteria in mixed-bacteria suspensions that contain between 10 and 100 cells/mL of ECC and CBM.