Biomedical subjects

D Ami

Publications and source records attributed to D Ami.

3 recordsLinked to original sources

PubMed2001

Investigating microbial (micro)colony heterogeneity by vibrational spectroscopy.

Fourier transform infrared and Raman microspectroscopy are currently being developed as new methods for the rapid identification of clinically relevant microorganisms. These methods involve measuring spectra from microcolonies which have been cultured for as little as 6 h, followed by the nonsubjective identification of microorganisms through the use of multivariate statistical analyses. To examine the biological heterogeneity of microorganism growth which is reflected in the spectra, measurements were acquired from various positions within (micro)colonies cultured for 6, 12, and 24 h. The studies reveal that there is little spectral variance in 6-h microcolonies. In contrast, the 12- and 24-h cultures exhibited a significant amount of heterogeneity. Hierarchical cluster analysis of the spectra from the various positions and depths reveals the presence of different layers in the colonies. Further analysis indicates that spectra acquired from the surface of the colonies exhibit higher levels of glycogen than do the deeper layers of the colony. Additionally, the spectra from the deeper layers present with higher RNA levels than the surface layers. Therefore, the 6-h colonies with their limited heterogeneity are more suitable for inclusion in a spectral database to be used for classification purposes. These results also demonstrate that vibrational spectroscopic techniques can be useful tools for studying the nature of colony development and biofilm formation.

Candida albicans↗

PubMed2001

Classification and identification of enterococci: a comparative phenotypic, genotypic, and vibrational spectroscopic study.

Rapid and accurate identification of enterococci at the species level is an essential task in clinical microbiology since these organisms have emerged as one of the leading causes of nosocomial infections worldwide. Vibrational spectroscopic techniques (infrared [IR] and Raman) could provide potential alternatives to conventional typing methods, because they are fast, easy to perform, and economical. We present a comparative study using phenotypic, genotypic, and vibrational spectroscopic techniques for typing a collection of 18 Enterococcus strains comprising six different species. Classification of the bacteria by Fourier transform (FT)-IR spectroscopy in combination with hierarchical cluster analysis revealed discrepancies for certain strains when compared with results obtained from automated phenotypic systems, such as API and MicroScan. Further diagnostic evaluation using genotypic methods-i.e., PCR of the species-specific ligase and glycopeptide resistance genes, which is limited to the identification of only four Enterococcus species and 16S RNA sequencing, the "gold standard" for identification of enterococci-confirmed the results obtained by the FT-IR classification. These results were later reproduced by three different laboratories, using confocal Raman microspectroscopy, FT-IR attenuated total reflectance spectroscopy, and FT-IR microspectroscopy, demonstrating the discriminative capacity and the reproducibility of the technique. It is concluded that vibrational spectroscopic techniques have great potential as routine methods in clinical microbiology.

Bacterial Typing Techniques↗

PubMed2000

FT-IR microspectroscopy for microbiological studies.

In this article we present an infrared microspectroscopic investigation on Candida albicans microcolonies, taken as a model system for studies on other microorganisms. Excellent Fourier transform infrared (FT-IR) absorption spectra from 4000 to 850 cm(-1) have been collected in only 20 s from sampling areas of 100x100 microm(2) in microcolonies, which had been transferred from the agar plate onto zinc selenide (ZnSe) windows. When different regions within a single microcolony were investigated, absorption spectra with important differences in the carbohydrate absorption (from 1200 to 850 cm(-1)) were detected for the cells in the center and in the periphery of the colony. Results obtained on microcolonies grown on solid agar with increasing dextrose concentrations indicated that the observed spectral heterogeneity was related to differences in dextrose uptake, which was lower for the old cells in the center of the colony than for the metabolically active cells at the periphery. Although it is otherwise difficult to quantitatively evaluate the dextrose uptake in a microcolony, FT-IR absorption microspectroscopy offers a new and rapid method for the analysis of this process. The possibility of studying highly absorbing colonies by attenuated total reflection (ATR) by means of an ATR microscope germanium objective is also presented here for the first time. An evaluation of the contact area sampled by this technique is reported with a discussion of the spatial resolution, the quality and the potential of the ATR measurements.

Candida albicans↗