Editing Infection (section)

===Microscopy===
Another principal tool in the diagnosis of infectious disease is [[microscopy]].<ref>{{cite book |last1=Murray |first1=Patrick R. |title=Medical Microbiology |date=2021 |publisher=Elsevier |location=Philadelphia |isbn=978-0-323-67450-8 |edition=9th |chapter=Microscopy and In Vitro Culture}}</ref> Virtually all of the culture techniques discussed above rely, at some point, on microscopic examination for definitive identification of the infectious agent. Microscopy may be carried out with simple instruments, such as the compound [[light microscope]], or with instruments as complex as an [[electron microscope]]. Samples obtained from patients may be viewed directly under the light microscope, and can often rapidly lead to identification. Microscopy is often also used in conjunction with [[biochemical]] [[staining]] techniques, and can be made exquisitely specific when used in combination with [[antibody]] based techniques. For example, the use of antibodies made artificially [[fluorescent]] (fluorescently labeled antibodies) can be directed to bind to and identify a specific [[antigen]]s present on a pathogen. A [[fluorescence microscope]] is then used to detect fluorescently labeled antibodies bound to internalized antigens within clinical samples or cultured cells. This technique is especially useful in the diagnosis of viral diseases, where the light microscope is incapable of identifying a virus directly.<ref>{{Cite journal |last1=Parveen |first1=Nagma |last2=Borrenberghs |first2=Doortje |last3=Rocha |first3=Susana |last4=Hendrix |first4=Jelle |date=2018-05-10 |title=Single Viruses on the Fluorescence Microscope: Imaging Molecular Mobility, Interactions and Structure Sheds New Light on Viral Replication |journal=Viruses |volume=10 |issue=5 |pages=250 |doi=10.3390/v10050250 |issn=1999-4915 |pmc=5977243 |pmid=29748498|doi-access=free }}</ref>

Other microscopic procedures may also aid in identifying infectious agents. Almost all cells readily stain with a number of basic [[dye]]s due to the [[electrostatic]] attraction between negatively charged cellular molecules and the positive charge on the dye. A cell is normally transparent under a microscope, and using a stain increases the contrast of a cell with its background. Staining a cell with a dye such as [[Giemsa]] stain or [[crystal violet]] allows a microscopist to describe its size, shape, internal and external components and its associations with other cells. The response of bacteria to different staining procedures is used in the [[taxonomic classification]] of microbes as well. Two methods, the [[Gram stain]] and the [[acid-fast]] stain, are the standard approaches used to classify bacteria and to diagnosis of disease. The Gram stain identifies the bacterial groups [[Bacillota]] and [[Actinomycetota]], both of which contain many significant human pathogens. The acid-fast staining procedure identifies the Actinomycetota genera ''[[Mycobacterium]]'' and ''[[Nocardia]]''.<ref>{{Cite journal |last1=Saubolle |first1=Michael A. |last2=Sussland |first2=Den |date=2003 |title=Nocardiosis |journal=Journal of Clinical Microbiology |volume=41 |issue=10 |pages=4497–4501 |doi=10.1128/JCM.41.10.4497-4501.2003 |issn=0095-1137 |pmid=14532173|pmc=254378 }}</ref>