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

Catalase test o 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 % H 2 O 2 (hydrogen peroxide). Interpretation: Rapid bubbling indicates oxygen production and a positive test. This test is used to differentiate between staphylococci (+Ve) and streptococci (-Ve).

Catalase Test

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.

Coagulase test

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.

Oxidase test

H 2 S test Principle: Production of H 2 S 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 H 2 S, a black color is formed. Examples: Proteus & Salmonella typhi.

H 2 S 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

H 2 S test Hydrogen Sulfide (H2S) Test Positive=black Neg= yellow or yellow with black line