Text Box: 10:30 AM Text Box: MICROBIOLOGY Text Box: Differentiation of Lactobacillus spp. and Streptococcus spp. using Fourier Transform Infrared spectroscopy Text Box: Geng Chen and Dr. Rodriguez-Saona Text Box: Lactobacillus spp. and Streptococcus spp. are commonly used as starter cultures in cheese manufacture and are often present in the cheese as non-starter strains. The identification of the strains is essential for understanding their role on the cheese quality. Comparing to the conventional methods, infrared spectroscopy (FTIR) provides information about structural properties of cellular compounds and allows for rapid classification of closely related Lactobacillus strains and Streptococcus strains. The objective was to build a classification model for the differentiation of starter and non-starter Lactobacillus strains and starter Streptococcus strains using infrared spectroscopy and multivariate analysis. Twenty-two non-starter strains, 18 commercial starter Lactobacillus strains and 15 commercial starter Streptococcus were evaluated. The bacteria were cultivated and a single colony was suspended in distilled water. The cells were then sonicated, centrifuged, resuspended in 10 μl water and applied onto an ATR ZnSe crystal, dried and analyzed by FTIR. A classification model was built by Soft Independent Modeling of Class Analogy. The spectral region between 1020 and 1090 cm-1 was found to be the effective area for differentiation of non-starter strains from starter Lactobacillus strains. The complex sequences of bands in this region are mainly due to C-O-C and C-O-P stretching vibration of cell components involving polysaccharide components of the cell membrane. An infrared spectroscopy method was developed for the differentiation at the strains level. The generation of FTIR spectral libraries for starter and nonstarter cultures will allow for rapid, accurate and cost-efficient monitoring of culture composition during cheese manufacture and storage.