biochemical tests Flashcards
used to identify bacterial species based
on the differences in the biochemical reactions of each of
the different types of bacteria
Biochemical test
biochemical tests are especially useful in identifying this type of bacteria
It is useful to differentiate members of the family
Enterobacteriaceae.
is used to identify bacteria that
produce cytochrome c oxidase, an enzyme of the
bacterial electron transport chain (ETC).
oxidase test
It is based on the principle that
certain bacteria produce indophenol blue from the
oxidation of dimethyl-p-phenylenediamine and anaphthol.
Principle of Oxidase test
In presence of the enzyme cytochrome oxidase
(gram-negative bacteria), the N,N-dimethyl-pphenylenediamine oxalate and a-naphthol react to
indophenol blue.
- Oxidase POSITIVE bacteria:
o Pseudomonas
o Vibro cholerae
o Neisseriae
o Campylobacter
o Helicobacter / Haemophilus
o Aeromonas
o Alcaligenes
- Precaution while performing oxidase test:
o Do not use nickel-base alloy wires containing
chromium and iron wire (nichrome wire).
o Interpret test within 10 seconds.
o Perform test using 5% SBA or on a medium without
fermentable sugar.
To differentiate among and between the members of
Enterobacteriaceae.
Triple Sugar Iron (TSI)
- maintains osmotic pressure.
NaCl
are the fermentable
carbohydrates.
Lactose, Sucrose, and Dextrose
Triple Sugar Iron (TSI)
incubation and purpose
18 to 24 hours in order to detect the
presence of sugar fermentation, gas production, and H2S
production.
differentiates entoerobacteriae from other is the ability to
catabolize glucose, lactose, or sucrose, and to
liberate sulfides from ferrous ammonium sulfate or
sodium thiosulfate.
TSI agar slants contain a
1% concentration of
sucrose and lactose, and 0.1% glucose.
The pH indicator, phenol red, is also incorporated into
the medium to detect acid production from
carbohydrate fermentation
TSI RESULT INTERPRET
The indicator is pink at alkaline pH and yellow in acidic
pH, at neutral pH it remains red.
Yellow butt (A) and red slant (K)
due to fermentation
of glucose
- phenol indicator turns yellow due to
persisting acid formation in the butt - The slant remains red (alkaline) (K) because of
limited glucose in the medium. Therefore, limited
acid formation, which does not persist
yellow butt (A) and slant (A)
A due to fermentation of
lactose and/or sucrose
Yellow slant and butt due to high concentration of
these sugars leading to excessive acid formation
in the entire medium.
Red butt (K) and slant (K) introduces that
none of the
sugars were fermented and neither gas nor H2S
produced.
IN TSI. GAS FORMATION IS SHOWN BY
by splitting agar.
(may bubbles or cracks)
A SLANT AND A BUTT
EXAMPLE
Escherihia,
Klebsiella,
Enterobacter
K SLANT A BUTT
SHIGELLA, SERRATIA
K SLANT A BUTT
SALMONELLA, PROTEUS
K SLANT AND BUTT
pseudomonas
h2sd production is seen by
black precipitate
Amino acid decarboxylation
- If an Enterobacteriaceae contains amino acid
decarboxylase, amines produces by decarboxylae action
cause an alkaline pH, and bromcresol purple turns purple. - Lysine, ornithine and arginine are utilized.
- A base broth without amino acid is included in which
glucose fermentation acidifies the broth, turning the
bromcresol purple yellow
Decarboxylation patterns are essential for the genus
identification of Klebsiella, Enterobacter, Eschericia, and
Salmonella.
Klebsiella, Enterobacter, Eschericia, and
Salmonella.
Decarboxylation patterns are also essential for the species
identification of
Enterobacter aerogenes, E. cloacae,
Proteus mirabilis, and Shigella sonnei.
To differentiate gram-negative bacilli based on
decarboxylation or deamination of the lysine and the
formation of hydrogen sulfide (H2S).
Lysine Iron Agar
Lysine decarboxylation is indicated by an
alkaline (purple)
medium
di pa tapos. stopped at p. 2
