Rapid microbiological identification and characterization are very important in dentistry and medicine. In addition to
dental diseases, pathogens are directly linked to cases of endocarditis, premature delivery, low birth weight, and loss of
organ transplants. Fourier Transform Infrared Spectroscopy (FTIR) was used to analyze oral pathogens Aggregatibacter
actinomycetemcomitans ATCC 29523, Aggregatibacter actinomycetemcomitans-JP2, and Aggregatibacter
actinomycetemcomitans which was clinically isolated from the human blood-CI. Significant spectra differences were
found among each organism allowing the identification and characterization of each bacterial species. Vibrational modes
in the regions of 3500-2800 cm<sup>-1</sup>, the 1484-1420 cm<sup>-1</sup>, and 1000-750 cm<sup>-1</sup> were used in this differentiation. The
identification and classification of each strain were performed by cluster analysis achieving 100% separation of strains.
This study demonstrated that FTIR can be used to decrease the identification time, compared to the traditional methods,
of fastidious buccal microorganisms associated with the etiology of the manifestation of periodontitis.
Paracoccidioides brasiliensis the etiological agent of paracoccidioidomycosis, is a dimorphic fungus existing as mycelia
in the environment (or at 25 °C in vitro) and as yeast cells in the human host (or at 37°C in vitro). The most prominent
difference between both forms is probably the cell wall polysaccharide, being 1,3-β-glucan usually found in mycelia and
1,3-α-glucan found in yeasts, but a plethora of other differences have already been described. In this work, we performed
a Fourier Transform Infrared Spectroscopy analysis to compare the yeast and mycelia forms of P. brasiliensis and found
additional biochemical differences. The analysis of the spectra showed that differences were distributed in chemical
bonds of proteins, lipids and carbohydrates.