Protein FT-IR amide bands are beneficial to bacterial typing

Bacterial FT-IR signals are extremely specific and highly reproducible, making FT-IR an efficient tool for bacterial typing at the subspecies level. The polysaccharide and nucleic acid FT-IR regions (1200-900 cm^-1) are recommended as a precise and reproducible pattern for bacterial typing. However, proteins are the major macromolecules present in bacteria, and the FT-IR spectral region of proteins (1800-1300 cm^-1) is conceivably an important factor in bacterial typing. In this study, we investigated the influence of water on bacterial protein amide bands by comparing spectra obtained with and without FT-IR system dehydration. Eight Escherichia coli, ten Klebsiella pneumoniae, and eleven Staphylococcus aureus strains were typed by FT-IR under different conditions in a blinded experimental setup. Hierarchical clustering analysis (HCA) showed that, when protein signals were included (1800-900 cm^-1), the typing accuracies for select E. coli, K. pn and S. aureus strains without system dehydration were 50%, 30% and 18.2%, respectively. However, the accuracies greatly improved to 100%, 90% and 90.9% when the FT-IR system was dehydrated. These results indicate that the FT-IR signals of protein amide bands are beneficial for bacterial typing.