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  VIRUS IDENTIFICATION AND QUANTIFICATION   Briefing: ·       Virus isolation in cell cultures, immunofluorescence-based assay and molecular techniques to determine nucleic acid, have all been used successfully to detect and identify the viruses. ·       On the other hand, the most commonly used methods to quantify viruses can be subdivided into three broader categories: 1.    Techniques measuring viral infectivity (viral plaque assay, TCID50 and immunofluorescence foci assay) 2.    Those that examine viral nucleic acid and protein (q-PCR, immune-blotting, immune-precipitation, ELISA and hemagglutination assay) 3.    Those that rely on direct counting of physical viral particles (viral flow cytometry and transmission electron microscopy) Methods of Virus Identification: Microscopy in Cell Culture: ·       Main Categories 1.    Viruses that ca...

    HEMAGGLUTINATION INHIBITION TEST   Briefing: ·       The nucleic acids of various viruses encode surface proteins (e.g. hemagglutinin (HA) of influenza virus) that agglutinate red blood cells (RBC) of a variety of species. ·       Agglutinated cells settle in a compact button. This process is known as hemagglutination. ·       Hem agglutination occurs when measles viruses and red blood cells are mixed (see image). But, if the serum of a person infected with measles virus is mixed with RBC and measles virus, there won’t be any agglutination of RBC. This phenomenon is known as hemagglutination inhibition. ·       This arises because antibodies present in the serum of that infected person reacts with the measles viruses and neutralize them (positive result). HAI Titer: ·       The highest dilution of serum (Abs) that prevents hema...

  PLAQUE ASSAY FOR VIRUSES:   Definition: ·       Plaque assay is a quantitative method of measuring infectious viruses by quantifying the plaques formed in cell culture upon infection with serial dilutions of a virus specimen. ·       As such, plaque assays remain the gold standard in quantifying concentrations of replication‐competent lytic virions. Cultivation and Enumeration of Bacteriophages: Principle: ·       This exercise demonstrates the ability of viruses to replicate inside a susceptible host cell. ·       For this purpose, you will be provided with a virulent phage and a susceptible host cell culture. ·       This technique also enables you to enumerate phage particles on the basis of plaque formation in a solid agar medium. ·       Plaques are clear areas in an agar medium previously seeded with a...

                        ELECTRON MICROSCOPE   Briefing: ·       The electron microscopes use electron beams and magnetic fields to produce the image instead of light waves and glass lenses used in the light microscopes. ·       The resolving   power of EM is far greater than that of any other compound microscope. ·       This is due to shorter wavelengths of electrons. ·       The wavelength of electrons is about 100,000 times smaller than the wavelength of visible light. Unique possibilities: ·       Structure ·       Topology ·       Morphology ·       Composition of materials Electron microscopy usage: ·       In the 1920s it was discovered that accele...