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 testo 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).

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

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.

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

H2S test

Hydrogen Sulfide (H2S) TestPositive=blackNeg= yellow or yellow with black line