Infrared signals of microorganisms are highly specific fingerprint-like patterns that can be used for probing the identity of microorganisms. The simplicity and versatility of Fourier-transform infrared spectroscopy (FT-IR) makes it a versatile technique for rapid differentiation, classification, identification and large-scale screening at the subspecies level.

This study describes a computer-based technique for classifying and identifying bacterial samples using Fouriertransform infrared spectroscopy (FT-IR) patterns. Classification schemes were tested for selected series of bacterial strains and species from a variety of different genera. Dissimilarities between bacterial IR spectra were calculated using modified correlation coefficients. Dissimilarity matrices were used for cluster analysis, which yielded dendrograms broadly equated with conventional taxonomic classification schemes. Analyses were performed with selected strains of the taxa Staphylococcus, Streptococcus, Clostridium, Legionella and Escherichia coli in particular, and with a database containing 139 bacterial reference spectra. The latter covered a wide range of Gram-negative and Gram-positive bacteria. Unknown specimens could be identilied when included in an established cluster analysis. Thirty-six clinical isolates of Staphylococcus aureus and 24 of Streptococcus faecdis were tested and all were assigned to the correct species cluster. It is concluded that: (1) FT-IR patterns can be used to type bacteria; (2) FT-IR provides data which can be treated such that classifications are similar and/or complementary to conventional classification schemes; and (3) FT-IR can be used as an easy and safe method for the rapid identification of clinical isolates.

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Some particular cell components can be detected and identified by Fourier Transform infrared spectroscopy (FT-IR) of intact bacteria. Typical marker bands were used to identify these bacterial cell components. Polypeptide capsules were detected in several Bacillus species by a band typical for o-helical structures and by strong carboxylate stretching vibrations. Formation of endospores in clostridia and bacilli was discovered using marker bands for dipicolinic acid. Spectra of some Bacillus strains showed expression of poly+hydroxybutyric acid granules, capsules and endospores simultaneously.

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Some particular cell components can be detected and identified by Fourier Transform infrared spectroscopy (FT‐IR) of intact bacteria. Typical marker bands were used to identify these bacterial cell components. Polypeptide capsules were detected in several Bacillus species by a band typical for α‐helical structures and by strong carboxylate stretching vibrations. Formation of endospores in clostridia and bacilli was discovered using marker bands for dipicolinic acid. Spectra of some Bacillus strains showed expression of poly‐β‐hydroxybutyric acid granules, capsules and endospores simultaneously.