However, EM still offers tremendous advantages to the microbiologist, both in the speed of diagnosis and the potential for detecting, by a single test, any viral pathogen or even multiple pathogens present within a sample. Hence the role of EM in clinical virology is evolving with less emphasis on diagnosis and more on research, although this is likely only to be undertaken in specialist centres. Development of molecular techniques, which offer greater sensitivity and often the capacity to easily process large numbers of samples, has replaced EM in many areas of diagnostic virology. Electron microscopy has led to the discovery of many new viruses, most notably the various viruses associated with gastroenteritis, for which it remained the principal diagnostic method until fairly recent times. Subsequently, the technique was employed in the diagnosis of other viral infections, such as hepatitis B and parvovirus B19. Viruses from different families look different and these morphological variances are the basis for identification of viruses by EM.Įlectron microscopy initially came to prominence in diagnostic microbiology in the late 1960s when it was used in the rapid diagnosis of smallpox, by differentiating, on a morphological basis, poxviruses from the less problematic herpesviruses in skin lesions. Viruses are grouped into families based on their morphology. The 1000-fold improvement in resolution provided by electron microscopy (EM) has allowed visualization of viruses, the existence of which had previously only been suspected as the causative agents of transmissible infectious disease. This prohibits the use of the microscope to study living organisms which would evaporate and disintegrate under such conditions.Transmission electron microscopy has had a profound impact on our knowledge and understanding of viruses and bacteria. In Physics, it has been used in the investigation of atomic structure and structure of crystals in detail.Īn electron microscope is operated only in high vacuum. In medicine and biology, it is used to study virus, and bacteria.Ĥ. It is used in the industry, to study the structure of textile fibres, surface of metals, composition of paints etc.Ģ. Since, the electron beam operates in vacuum, the apparatus is mounted in a chamber which is completely evacuated.ġ. Sharp focusing is obtained by adjusting the intensity of magnetic fields produced by electro magnets. It can also be obtained on a suitable photographic plate for a permanent record. The image obtained on the fluorescent screen is made visible by scintillation for direct view. The electromagnet C (projector magnetic lens) focusses the electron beam from the part of the enlarged image on the fluorescent screen producing still greater magnification. The second electro magnet B (objective magnetic lens) causes the electron beam to diverge to produce enlarged image of the object. The transmitted beam will thus have the likeness of the object traversed by it. It should be noted that the electrons will be transmitted more through the transparent parts of the object and transmitted in less number through comparatively denser portions. The electrons get deflected to form a parallel beam which strikes the object to be magnified. The fine beam of electrons is made to pass through the centre of the doughnut shaped electromagnet A (condenser magnetic lens). An electron beam emitted by a filament is accelerated through a large potential difference in a device called electron gun. The modern electron microscope is usually of transmission type in which magnetic lenses of short focal length are used to obtain large magnification. An electron microscope is similar in principle to an optical microscope. The schematic diagram of an electron microscope is shown in Fig.
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