Exploring Biochemical Tests in Bacteriology
Catalase Test
Principle
The enzyme
catalase facilitates the decomposition of hydrogen peroxide into water and
oxygen.
Example
Staphylococcus Catalase Positive Bubbles
appear.
Streptococcus Catalase Negative Bubbles
not appear.
Coagulase Test
Principle
Coagulase is an
enzyme that turns a liquid called fibrinogen into a sticky substance called
fibrin.
It's used to
check if bacteria can make blood clot."
Example
Coagulase
Positive Staphylococcus
aureus.
Coagulase
Negative Staphylococcus epidermidis.
Oxidase Test
Principle
The oxidase test identifies the
presence of cytochrome c oxidase enzyme in bacteria.
Or
the oxidase
test is to detect the presence of the enzyme cytochrome c oxidase in bacteria.
This enzyme is involved in the electron transport chain of aerobic respiration
and catalyses the oxidation of cytochrome c by molecular oxygen.
Example
Oxidase Positive Pseudomonas
aeruginosa.
Oxidase Negative E.
coli.
Urease Test
Principle
The urease test
identifies bacteria that produce the enzyme urease, which breaks down urea into
ammonia, H2O and CO2.
Example
Urease Positive
àProteus and Nocardia
Urease Negativeà E. Coli
Triple Sugar Iron (TSI)
Principle
Microorganisms
break down carbohydrates, making the medium acidic and sometimes producing gas.
Iron salts combine with H2S to create a black solid (ferrous sulfide).
Example
E. coli: Ferments glucose and lactose,
producing yellow with gas.
S.
typhi: Ferments glucose
only, alkaline butt, acidic slant, no gas.
S.
flexneri: No
sugar fermentation, alkaline slant and butt, no gas.
DNASE Test
Principle
DNA binds with
methyl green dye. When microorganisms containing DNase are present, they break
down the DNA.
Example
Oxidase Positive
S. aureus
Oxidase Negative
S.epidermidis
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