Biochemical ID Testing

Sawsan felmban

Different kinds of bacteria are distinguished through….

Enzymes using biochemical tests

Biochemical tests

Test the ability, activity or the presence of an

enzyme

Biochemical ID Testing

• Catalase test.

• Coagulase test.

• Oxidase test.

Catalase Test

• Reagents: H2O2

• Reaction :

• 2H2O2 2H2O + O2 (bubbles)

• Aim: to differentiate bacteria that produce catalase enzyme.

resu

lts

Bubbles +ve(staphylococcus)

No bubbles -ve

(NOT staph.)

Test QC:+ve cont.: Staphylococci spp.-ve cont.: Streptococci spp.

catalase

Coagulase Test• Types of Coagulase:

• Free coagulase.

• Bound coagulase.

Reagent:

• Free coagulase: plasma containing coagulase reacting factor (CRF).

• Bound coagulase: plasma

• Principle:

fibrinogen fibrin clot

Aim: to ID S. aureaus

coagulase

• Results:

• Free coagulase: fibrin clot (within 2hrs, 4hrs and 24 hrs) +ve

• Bound coagulase: fibrin clot 10 sec +ve.

• No fibrin clot: -ve

• Test QC:

• +ve Cont.: Staph. aureus

• -ve Cont.: Staph. epidermidis

Free coagulase

Bound coagulase

negative

posetive

posetive

negative

Oxidase Test

• Reagent:

• 1% tetramethyl-p-phenylenediaminedihydrochloride.

• Principle:

• tetramethyl-p-phenylenediaminedihydrochloride + reduced cytochrome c

oxidized cytochrome c (Purple) + H2O

• Aim:

to ID cytochrome oxidase producing bacteria

oxidase

Oxidase Test

resu

lts Dark purple : +ve

Pseudomonas

Colorless : - ve others