Attenuated total reflectance spectroscopic(ATR-FT-IR) Technic is most use full for identification of bacteria up to 100% species level. Details of bacterial sample preparation relatively simple than other FTIR technique. Direct analysis of bacterial suspensions by ATR-FT-IR include direct transfer of bacterial colonies into small suspensions(20-200 µl), followed by drying onto optical surfaces as thin films; stamping techniques where optical plates were lightly pressed against bacterial colonies on agar plates. However after getting spectral data statistical analysis and correction of the spectral data is most important. From the bellow link hope help you lots.