Exercise 8: intro and litmus milk

What agar plates (3) test for exoenzymes?

Lipase, Milk agar, and Starch agar

What tube media (3) tests for metabolic processes?

Litmus milk, sugar fermentation broth, and Kligler’s Iron agar

What does Litmus Milk contain?

lactose, casein and other peptones, and litmus pH indicator

What does Litmus Milk test for (4)?

fermentation of lactose, metabolism of proteins, degradation of casein, and litmus reduction

What are 5 possible reactions you can get in Litmus milk test? Reminder: there can be a combos

Acid production (fermentation), alkaline production (peptone deamination), curding, reduction (redox), and proteolysis

With litmus milk test, what does fermentation do to lactose?

Fermentation of lactose produces acids that reduce the pH of the litmus milk solution

With litmus milk test, what results will you see if an organism is able to ferment lactose (+)?

litmus milk turns pink

For litmus milk test, what is something to keep in mind when you are looking for lactose fermentation results? what does the varying degrees mean?

There are varying degrees, less intense pink means a weak acid and the more intense the more stronger the acid is

With litmus milk, what does deamination of peptones do?

Deamination of peptones releases ammonia into solution, this raises the pH of the litmus milk

With litmus milk test, what results will you see if an organism is able to deaminate peptones (+)?

litmus milk turns blue

With litmus milk, because peptone deamination is an oxygen dependent process, what is something to keep in mind when looking at results?

the color change may be limited to the top of the tube

Litmus milk can only function as a pH indicator in what state?

Oxidized state (lost electrons)

With litmus milk, what does reduction do to the solution (+)?

Reduction of solution will cause loss of color and be white

With litmus milk, what is something to keep in mind with the results of reduction?

A band of color may persist at the top of the media, this is because oxygen can penetrate and re-oxidize the litmus indicator

With litmus milk, what enzyme is needed to cause the degradation of casein and cause proteolysis (the breakdown of proteins)?

Caseinase

With litmus milk, if the organisms produces caseinase (+) what happens to the solution? Why?

Casein gives the milk its opacity, so degrading it will make the milk clear. Clear means no opacity, there is still color but it is clear and “able to see through”

With litmus milk, if enough acid is produced from lactose fermentation what may happen?

Proteins may become denatured

With litmus milk, what can protein denaturing result in (+)?

clumping or solidifying of milk (not always)