Ch 15 Litmus Milk Reactions - Micro Lab

Front 1

What is Litmus Milk used to test for?

Back 1

used to distinguish between different species of bacteria depending on their ability to transform "milk" (lactose) into different metabolic end products

Front 2

Litmus Milk

Back 2

• undefined, differential medium
• made of skim milk and pH indicator litmus (azolitmin)
• both a pH and reduction-oxidation indicator
• pink below pH 4.5
• purple intermediate pH
• blue above pH 8.3

Front 3

What are the 2 main ingredients in Litmus Milk that can be metabolized by bacteria?

Back 3

1. lactose (milk sugar)
2. casein (protein)

litmus cannot be used nutritionally by the bacteria

Front 4

What are the 4 basic reactions that occur in Litmus Milk?

Back 4

1. lactose fermentation
2. litmus reduction
3. casein coagulation
4. casein hydrolysis

Front 5

In Litmus Milk what does a pink color result indicate?

Back 5

acid production

Front 6

In Litmus Milk what does a pink and solid white in the lower portion with an immovable clot result indicate?

Back 6

acid curd

white indicates that the lower portion of the litmus is reduced

Front 7

In Litmus Milk what do fissures in the clot indicate?

Back 7

gas production occured

Front 8

In Litmus Milk what does a white colored result indicate?

Back 8

reduction of litmus

Front 9

In Litmus Milk what does a not pink and semisolid clot that is moveable indicate?

Back 9

Rennet curd

Front 10

In Litmus Milk what does a blue colored result indicate?

Back 10

alkaline reaction

Front 11

In Litmus Milk what does clarification of the medium indicate?

Back 11

proteolysis occured

Front 12

If an alkaline reaction occurs in Litmus Milk what would you expect it to look like?

Back 12

unchanged or deep blue

Front 13

If proteolysis occurs in Litmus Milk what would you expect it to look like?

Back 13

deep purple band at the top

whey-like brownish translucent medium in the remainder of the tube

Front 14

If a litmus reduction occurs in Litmus Milk what would you expect it to look like?

Back 14

a purple band at the top

the remainder of the tube is white

Front 15

If lactose fermentation occurs in Litmus Milk what would you expect it to look like?

Back 15

pink = acidic

Front 16

If lactose fermentation followed by reduction occurs in Litmus Milk what would you expect it to look like?

Back 16

pink band at the top

the remainder of the tube is white

Front 17

If lactose fermentation followed by reduction and curd formation occurs in Litmus Milk what would you expect it to look like?

Back 17

a pink band at the top

the remainder of the tube is white and solid

Front 18

If lactose fermentation followed by reduction, curd formation, and gas production occurs in Litmus Milk what would you expect it to look like?

Back 18

a pink band at the top

the remainder of the tube is white and solid

there will be fissures in the curd

Front 19

Which bacteria are able to ferment lactose?

Back 19

only bacteria that posses the lac operon

Front 20

lactose fermentation

Back 20

• lac operon required to ferment lactose
• contains the lac Z gene that codes for the inducible enzyme β-galactosidase (cleaves lactose → glucose + galactose)
• glucose enters the E-M pathway → pyruvic acid which gets reduced → lactic acid
• medium gets acidified = pink result

Front 21

What is the final product of lactose fermentation?

Back 21

lactic acid

Front 22

What causes a clot or curd to form?

Back 22

accumulating acid may cause the casein to precipitate solidifying the medium

can be pink or white depending on the oxidation-reduction status of litmus

Front 23

What color is reduced litmus?

Back 23

white

Front 24

What color is oxidized litmus?

Back 24

purple

Front 25

What is evidence gas production during fermentation of litmus milk?

Back 25

fissures in the curd

Front 26

proteolysis or peptonization

Back 26

occurs when microorganisms break down the milk proteins, mainly casein, to amino acids

produces ammonia

alkaline reaction (blue)

the medium will loose body because the proteins are hydrolyzed producing a translucent brownish color with a blue band at the top

Front 27

alkaline reaction

Back 27

when the microorganism partially degrades casein into shorter polypeptides

produces ammonia

alkaline reaction (blue) ; raises the pH of the medium

Front 28

What type of inoculation is used in this lab?

Back 28

stab inoculation

Front 29

What are the 5 bacteria used in this lab?

Back 29

1. E. coli
2. Lactococcus lactis
3. Alcaligenes faecalis
4. Pseudomonas aeruginosa
5. Klebsiella pneumoniae