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The infrared spectra of 14 bacteria were recorded by Fourier Transform Infrared (FTIR) spectroscopy. The effects of changes in growth conditions, such as temperature, growth medium, and incubation time, sampling conditions on the reproducibility of the spectra were investigated. The spectra of bacteria suspended in saline solution, in D$ sb2$O-saline and on plate films were obtained and stored in separate spectral libraries. The application of library search routines for differentiation and identification of the 14 bacteria was investigated. The spectral regions used for the library search include 1750-1560 cm$ sp{-1}$ and 1480-960 cm$ sp{-1}$, which contain bands mainly associated with proteins (secondary structure), lipids, and polysaccharides. An index produced by the library search, which indicates how much an "unknown spectrum" matches a library spectrum, is suggested as a criterion for the differentiation and identification of bacteria. A correct identification of five unknown samples shows the feasibility of using spectral library searching routines for identification of bacteria down to the species level by FTIR spectroscopy. This technique is rapid, easier, and more efficient than conventional microbiological and biochemical methods. Quantitative analysis of a mixture of Escherichia coli and Staphylococcus aureus by the partial-lest-square (PLS) technique was also evaluated. The analytical error was about 10%.