Differentiation of microorganisms by means of the infrared spectra of their acetone extracts.

Recent investigations give an optimistic view that infrared absorption spectra can be very useful in the rapid identification and differentiation of microorganisms. However, it is admitted that such identifications will have to be based on very small differences, often not much above the reproducibility with which the spectra can be measured. Blout and Lenormant (1953) compared the spectra of Lactobacillus arabinosus in D20 suspension with the spectra of proteins, nucleic acid, and nucleoproteins and pointed out the possibilities of identification by means of the infrared absorption spectra of whole organisms. Stevenson and Bolduan (1952) investigated the infrared spectra of whole bacteria for identification purposes and demonstrated that, while exhibiting quantitative differences because of variations in the thickness and physical homogeneity of the films, the procedure would produce spectra from replicate cultures which were qualitatively very similar. Although "the differences were somewhat subtle in some cases," they concluded that "the use of infrared absorption spectra as an aid to identification appears promising." Stevenson and Levine (1952) investigated eight types of pneumococcal polysaccharides and showed that, while the spectra of some types are quite distinctive and easily identified, the spectra of others are very similar. Experiments designed to identify specific coIlstituents in the microorganisms have indicated that considerably greater differentiation can be obtained by use of a series of extracts. Levine et al. (1953a, b, c) resorted to chemical fractionation to make correlations between absorption bands appearing in the spectra of intact bacterial cells