1, Briefly discuss how the Gram stain works, Not the steps but the biochemical basis, what...

1, Briefly discuss how the Gram stain works, Not the steps but the biochemical basis, what leads to the differential staining? Name one organism (genus and species) that is a Gram positive coccus, and one that the Gram stain will not work on.

2, Choose 2 of these diagnostic tests and briefly describe how each works. Your answer should include what is used and what a positive result would look like. Catalase test, hemagglutinin assay, coagulase test, IF test, virus neutralization assay.

Expert Solution

1. Gram staining is based on the ability of an bacterial cell wall to retain the crystal violet dye during the solvent treatment. The bacteria which contain higher peptidoglycan and lower lipid in their cell wall ,retain the crystal violet dye and are called as Gram positive bacteria and vice-a-versa.

The use of two dyes i.e; Crystal violet and Safranin during Gram staining leads to differential staining. Differential staining involves use of more than one chemical stain.

Example of Gram positive coccus is Staphylococcus aureus and Gram negative is Neisseria gonorrhea.

2. Catalase test- In this test, hydrogen peroxide is used. Catalase is an enzyme, that breaks down hydrogen peroxide into water and oxygen. If an organism can produce catalase, oxygen bubbles are formed when hydrogen peroxide is added to it. If an organism can not produce catalase, oxygen bubbles are not formed on adding the hydrogen peroxide.

Hemagglutinin assay- The basis of this assay is that antibodies to influenza virus will prevent attachment of the virus to RBC. Thus hemagglutination is inhibited when antibodies are present. If antibodies are absent,then hemagglutination is stimulated causing attachment of the virus to RBC.

Coagulase test- This test causes the cells to agglutinate and creates a clump like appearance of the cells to show a positive coagulase test. Coagulase when bound to the bacterial cell wall and reacts directly with fibrinogen which results in an alteration of the fibrinogen so that it precipitates on the cell causing the cells to clump when a bacterial suspension is mixed with plasma.

Virus Neutralization assay- It works by detecting the antibody which is capable of inhibiting virus replication. It does not detect all antigen-antibody reactions.

gladiator answered 2 years ago

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