Litmus Milk.pptx

Litmus Milk Test

1. SUBJECT: FOOD MICROBIOLOGY

SUBMITTED BY
DHIVYADHARSHINI RAMESH.
ll B.SC., - MICROBIOLOGY
DEPARTMENT OF MICROBIOLOGY

Sankagiri, Salem.
Tamil Nadu, India.

3. CONTENT

« Introduction
+ Application

+ Media preparation

+ Procedure
* Litmus milk test and result
\ y /e Uses

4. INTRODUCTION

ilk is an excellent medium for the growth of microorganisms
because it contains the milk protein casein, the sugar lactose,
vitamins, minerals and water.

7A, 2. Litmus milk is a milk-based medium used to distinguish
— between different species of bacteria.

3. The lactose (milk sugar), litmus (pH indicator), and casein (milk
protein) contained within the medium can all be metabolized by
different types of bacteria.
4. The test differentiates microorganisms based on various metabolic
reactions in litmus milk, including reduction, fermentation,
clot formation, digestion, and the formation of gas.

5. APPLICATION 2%

% The major milk substrates capable of transformation are the milk su
lactose and the milk proteins casein, lactalbumin, and lactoglo!

x To distinguish among the metabolic changes produced in milk, a pH
indicator, the oxidationreduction indicator litmus, Is incorporated into the
medium.

* Litmus milk then forms an excellent differential medium in which
microorganisms can metabolize milk substrates depending on their
enzymatic complement. A variety of different biochemical changes result.

* Fermentation of lactose is demonstrated when the litmus turns
pink as a result of acid production.

6. x If sufficient acid is produced, casein in the milk is coagulated
solidifying the milk.
* With some organisms, the curd shrinks and whey is formed
at the surface.

% Some bacteria hydrolyze casein, causing the milk to become
straw colored and resemble turbid serum.

x Additionally, some organisms reduce litmus, in which case
the medium becomes colorless in the bottom of the tube.

7. MEDIA PREPARATION

* Powdered skim milk (100 g) si
* litmus (0.5 g)

* sodium sulphite (0.5 g)
* per 1000 mL

* pH 6.8.

8. PROCEDURE

1.Inoculate with 4 drops of a 24-hour broth culture.
2. Incubate at 35°-37°C in ambient air.

3. Observe daily for seven days for acid clot, acid
reaction rennet clot, and peptonization.

4. Record all changes.

9. POSITIVE TEST

¢ Acid pH: pink to red color

¢ Alkaline pH: purplish- blue color

* peptonization - alkaline pH, supernatant brown
+ Gas production: bubbles in coagulated milk

+ Alkaline reaction - blus - Alkaligenes faccalis
NEGATIVE TEST

+ Color and consistency remain same.

11. USES "TE

1. The litmus milk test differentiates members of the Re
Enterobacteriacaeae from other gram-negative bacilli +
based on the enterics’ ability to reduce litmus.
2. It is commonly used to differentiate members
within the genus Clostridium.
3. It mainly aids intheidentification and
differentiation of Enterococcus, and Lactic acid
bacteria. The media may also be used to grow lactic

acid bacteria.
AO