hooa” and Specimen Preparatio Heat filte otabo08A7heC Figure212 Fluorescence Microscopy.The principles of operation of from the light emitted when they fluoresce (figure 2 13)A har afer the lenses removes any re. es such orange and DAPI (diamidin contrast. ce orange or green and can be detected en in the mids in the caus of tu eatment with a special mi xture of stains (figure 2.Thus atively undisturbed ecol al niche. directlyco bodies using immunofluorescence procedures.In ecological Prescott−Harley−Klein: Microbiology, Fifth Edition I. Introduction to Microbiology 2. The Study of Microbial Structure: Microscopy and Specimen Preparation © The McGraw−Hill Companies, 2002 from the light emitted when they fluoresce (figure 2.13). A bar￾rier filter positioned after the objective lenses removes any re￾maining ultraviolet light, which could damage the viewer’s eyes, or blue and violet light, which would reduce the image’s contrast. The fluorescence microscope has become an essential tool in medical microbiology and microbial ecology. Bacterial pathogens (e.g., Mycobacterium tuberculosis, the cause of tu￾berculosis) can be identified after staining them with fluo￾rochromes or specifically labeling them with fluorescent anti￾bodies using immunofluorescence procedures. In ecological studies the fluorescence microscope is used to observe microor￾ganisms stained with fluorochrome-labeled probes or fluo￾rochromes such as acridine orange and DAPI (diamidino-2- phenylindole, a DNA-specific stain). The stained organisms will fluoresce orange or green and can be detected even in the midst of other particulate material. It is even possible to distinguish live bacteria from dead bacteria by the color they fluoresce after treatment with a special mixture of stains (figure 2.13d). Thus the microorganisms can be viewed and directly counted in a rel￾atively undisturbed ecological niche. Immunofluorescence and diag￾nostic microbiology (pp. 781, 831–32). 26 Chapter 2 The Study of Microbial Structure: Microscopy and Specimen Preparation 6. Barrier filter Removes any remaining exciter wavelengths (up to about 500 nm) without absorbing longer wavelengths of fluorescing objects 5. Specimen stained with fluorochrome Emits fluorescence when activated by exciting wavelength of light 4. Dark-field condenser Provides dark background for fluorescence Mirror 3. Exciter filter Allows only short wavelength light (about 400 nm ) through 2. Heat filter 1. Mercury vapor arc lamp Eyepiece Objective lens Figure 2.12 Fluorescence Microscopy. The principles of operation of a fluorescence microscope