Coagulase Test Coagulase bacterial virulence factor Enzyme that catalyzes the

Coagulase test coagulase bacterial virulence factor

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Coagulase Test Coagulase (bacterial virulence factor) Enzyme that catalyzes the conversion of fibrinogen to fibrin, forming an insoluble clot Purpose = Protection (Bacteria can coat themselves with the host proteins in order to hide from host immune system) Two forms of coagulase Bound (clumping factor) - Attached to cell walls & reacts directly with fibrinogen in plasma which leads to precipitation – cells clump together in a visible mass Free - Released from the cell (extracellular) & reacts with a plasma component called (CRF – coagulase reacting factor) – precipitation of fibrin – clumping Used to differentiate S. aureus from other Gm + cocci Slide Test : Detects bound coagulase - Two drops saline are placed on slide - Bacteria emulsified - Drop of plasma is added to each inoculated saline drop - Positive : clumping will be observed - Negative : no clumping ( S. epidermidis ) Tube Test : Detects both bound & free coagulase -Inoculate 0.5 ml of diluted (1:4) rabbit plasma with loopful of culture -Check tubes at 2-4 hrs for clot - Positive : plasma will coagulate and form clot - Negative : plasma remains liquid
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Antibiotics Antibiotic = chemotherapeutic agent that inhibits or abolishes the growth of micro-organisms Bacteria Fungi Protozoa The first widely used antibiotic compounds used in modern medicine were produced and isolated from living organisms Penicillin, streptomycin Many antibiotics are now also obtained by chemical synthesis Most antibiotics are relatively small molecules Antibiotics-Bacitracin Susceptibility Test Bacitracin = natural antibiotic produced by Bacillis lichenformis Inhibits cell wall synthesis Only works on bacteria that have cell walls Bacteria must be in the growth process for successful application Disc is placed on inoculated blood agar where it can then diffuse into the media Inhibition of growth will result in a clearing around the disc Used to differentiate β-hemolytic S. pyogenes (R) from other β-hemolytic Streptococcus species; also, Staphylococcus (R) from Micrococcus and Stomatococcus (S) Antibiotics-Optochin Susceptibility Test Optochin = antibiotic Detergent like ability causing lysis
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