OBSERVATIONS SUR LES COULEURS DE LA FLUORESCENCE PRIMAIRE DES MICROORGANISMES

Abstract

Primary fluorescence of microbial cells may show contrasting colors. According to our results, 36 species were divided in two groups: (1) 30 presenting exclusively a yellow-green fluorescence, (2) the 6 others for which reddish cells were observed among yellow-green cells. The species of the second group were: Candida albicans, Pseudomonas aeruginosa, Saccharomyces cerevisiae, Salmonella typhimurium, Sarcina lutea, and Serratia marcescens. In this work, we have deliberately excluded any staining (with fluorochrome or other stain) to avoid possible confusion on the precise meaning of primary fluorescence.These observations were completed by (a) examining, with a "pupillary spectroscope", the light which emerged from the microscope. All the wavelengths of the visible spectrum were, thus, found to be present in the primary fluorescence of the 36 species; (b) verifying macroscopically, under the Wood lamp, the resulting dominant color of the fluorescence of washed microorganisms and of their extracts in alcohol, acetone, or water. Thus was confirmed the presence of yellow, green, or reddish fluorescent substances, already found by the previously mentioned methods.In our experimental conditions (bright condenser, dry objective, and OGI yellow secondary filter), the blue fluorescence was eliminated.The color of the fluorescence of each species examined could be influenced by culture media, temperature, pH, and age of the cultures, but no reddish fluorescence was observed in the first group. After the smears were prepared, the colors were stable and did not fade for months.The color variations of the primary fluorescence is suggestive that between microbial cells there are very discreet metabolic differences which could hardly be observed otherwise.For the classification and the identification of microorganisms, our preliminary findings suggest that the color of primary fluorescence could be a supplementary method, at least for the minority of species producing the reddish fluorescence.