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Biochemical Characterization of Bacteria

LECTURE 8:. Biochemical Characterization of Bacteria. Microbiology and Virology; 3 Credit hours Atta- ur - Rahman School of Applied Biosciences (ASAB) National University of Sciences and Technology (NUST). Catalase test. Principle :

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Biochemical Characterization of Bacteria

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  1. LECTURE 8: Biochemical Characterization of Bacteria Microbiology and Virology; 3 Credit hours Atta-ur-Rahman School of Applied Biosciences (ASAB) National University of Sciences and Technology (NUST)

  2. Catalase test • Principle: • Tests the ability of some bacteria to produce catalase enzyme. • Procedure: • Pick up the test colony on a platinum loop and immerse it in few drops of 3 % H2O2 (hydrogen peroxide). • Interpretation: • Rapid bubbling indicates oxygen production and a positive test. • This test is used to differentiate between staphylococci (+Ve) and streptococci (-Ve).

  3. Catalase Test

  4. Coagulase test • Detects the coagulase bound to the organism. • Procedure: • Homogenous suspension of the test organism is made in a drop of saline on a slide then mixed with a drop of undiluted human or rabbit plasma. • Staphylococcus aureus clumps within 15 sec. because coagulase enzyme precipitates the fibrin in the plasma on the cell surface.

  5. Coagulase test

  6. Oxidase test • Principle: • Some bacteria produce oxidase enzyme which reduces the oxidase reagent (tetramethyl-p-phenylene-diamine hydrochloride) to a deep purple color. • Procedure: • Done by picking up a portion of the colony tested and smearing it on a filter paper impregnated with oxidase reagent. • Interpretation: • The immediate development of a deep purple color indicates positive test. • Examples: Neisseria& Pseudomonas& Vibrios.

  7. Oxidase test

  8. H2S test • Principle: • Production of H2S from proteins. • Procedure: • Inoculate the organism on peptone water. • After incubation, put lead acetate paper at the mouth of the tube. • Interpretation: • If the organism produces H2S, a black color is formed. • Examples: Proteus & Salmonella typhi.

  9. H2S test • Tests for enzyme cysteine desul-furase bacteria with this enzyme can break down amino acid cysteine • Growth medium- SIM medium agar  • Positive= black • Negative= medium remains yellow or black line forms just below surface

  10. H2S test Hydrogen Sulfide (H2S) Test Positive=black Neg= yellow or yellow with black line 

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