Evaluation of Fourier transform infrared spectroscopy for the rapid identification of glycopeptide-intermediate Staphylococcus aureus

Objectives To evaluate Fourier transform infrared (FTIR) spectroscopy as a rapid method for distinguishing glycopeptide-intermediate Staphylococcus aureus (GISA) from glycopeptide-susceptible methicillin-resistant S. aureus (MRSA) and to compare three data analysis methods. Methods First-derivative normalized spectra of dried films of bacterial growth on Que-Bact® Universal Medium No. 2 were examined by singular value decomposition to identify key spectral regions. Region selection was analysed by principal component analysis (PCA), self-organizing maps (SOMs) and the K-nearest neighbour (KNN) algorithm. The initial data set included 35 GISA (including GISA Mu50 and heterogeneous GISA Mu3) and 25 epidemic MRSA. The regions were then tested using enlarged data sets that included 22 sporadic and 85 additional epidemic MRSA. Results Epidemic MRSA and GISA/hGISA were separated into two distinct clusters on the basis of spectral data from regions 1352-1315 and 1480-1460 cm−1, the former providing 100% correct classification by all three analyses and the latter providing 96.67% correct by PCA, 98.34% by SOM and 100% by KNN. The 1480-1460 cm−1 region was more effective for distinguishing GISA/hGISA from a set combining sporadic and epidemic MRSA, with two GISA/hGISA and four sporadic MRSA misclassified by PCA and SOM (92.69% correct), while the KNN method misclassified three of the four sporadic MRSA (93.90% correct). The addition of 85 other epidemic MRSA this set increased the fraction of correctly classified isolates to 96.41% and 97.01% by PCA, SOM and KNN, respectively. Conclusions As only 6 of 167 isolates were misclassified, FTIR spectroscopy may provide means of rapid and accurate identification of GISA and hGISA among isolates of MRS

Application of Fourier transform infrared spectroscopy in the analysis of edible fats and oil

The application of Fourier transform infrared (FTIR) spectroscopy in the assessment of oil quality and stability and the determination of the degree and type (cis or trans) of unsaturation of fats and oils was investigated. FTIR spectroscopy was shown to provide a rapid means of monitoring changes in oils undergoing oxidation or subjected to thermal stress. Absorption bands associated with common primary and secondary oxidation products were identified by relating them to those of spectroscopically representative reference compounds, and a quantitative approach based on the use of oils spiked with these reference compounds as calibration standards was proposed. A sample-handling accessory based on a heated 25-mum transmission flow cell and heated input and output lines was developed to facilitate the rapid analysis of oils and premelted fats in their neat form. Using this system, an FTIR edible oil analysis package was developed to simultaneously analyze for trans content, cis content, iodine value (IV), and saponification number (SN) of neat fats and oils, using partial-least-squares (PLS) calibrations based on pure triglycerides. An automated transmission-based peak height method for isolated trans isomer determination using the characteristic trans absorption band at 967 cm -1 in the spectrum of a neat fat or oil, ratioed against the spectrum of a trans-free oil, was also developed. A subsequent validation study involving the analysis of more than 100 oil samples demonstrated concurrence between the trans data obtained by the PLS and peak height FTIR methods as well as between IV results obtained by FTIR analysis and gas chromatography. In addition, the internal consistency of the IV, cis, and trans FTIR predictions provided strong experimental evidence that the FTIR edible oil analysis package measures all three parameters accurately. A PLS-based IV/trans method was developed for a heated single-bounce horizontal attenuated total reflectance (SB-HATR) sample

Evaluation of Fourier transform infrared spectroscopy for the rapid identification of glycopeptide-intermediate Staphylococcus aureus

OBJECTIVES: To evaluate Fourier transform infrared (FTIR) spectroscopy as a rapid method for distinguishing glycopeptide-intermediate Staphylococcus aureus (GISA) from glycopeptide-susceptible methicillin-resistant S. aureus (MRSA) and to compare three data analysis methods. METHODS: First-derivative normalized spectra of dried films of bacterial growth on Que-Bact Universal Medium No. 2 were examined by singular value decomposition to identify key spectral regions. Region selection was analysed by principal component analysis (PCA), self-organizing maps (SOMs) and the K-nearest neighbour (KNN) algorithm. The initial data set included 35 GISA (including GISA Mu50 and heterogeneous GISA Mu3) and 25 epidemic MRSA. The regions were then tested using enlarged data sets that included 22 sporadic and 85 additional epidemic MRSA. RESULTS: Epidemic MRSA and GISA/hGISA were separated into two distinct clusters on the basis of spectral data from regions 1352-1315 and 1480-1460 cm(-1), the former providing 100% correct classification by all three analyses and the latter providing 96.67% correct by PCA, 98.34% by SOM and 100% by KNN. The 1480-1460 cm(-1) region was more effective for distinguishing GISA/hGISA from a set combining sporadic and epidemic MRSA, with two GISA/hGISA and four sporadic MRSA misclassified by PCA and SOM (92.69% correct), while the KNN method misclassified three of the four sporadic MRSA (93.90% correct). The addition of 85 other epidemic MRSA this set increased the fraction of correctly classified isolates to 96.41% and 97.01% by PCA, SOM and KNN, respectively. CONCLUSIONS: As only 6 of 167 isolates were misclassified, FTIR spectroscopy may provide means of rapid and accurate identification of GISA and hGISA among isolates of MRSA