Question

Medium Reaction Interpretation Litmus milk a. Pink color throughout b. Curd formation C. Solid mass formed d. White color throughout Sulfide indole motility a. Blackening of the medium b. Red color formed with addition of Kovac's reagent c. Growth only on line of inoculation Triple sugar ion agar a. Yellow butt b. Yellowing of entire medium c. Large holes in agar Τ Τ Τ Arial 3 (12pt)

Answer 1

Litmus milk

a. When acid reaction takes place, litmus turns pink colour, due to fall in pH. Lactose fermentation occurs in which lactose sugar is converted to lactic acid with the help of beta galactosidase enzyme.

b. If sufficient acid is produced, casein in the milk is coagulated, solidifying the milk, and becomes curd.

c. Solidification is due to protein coagulation.

d. Culture becomes white when bacteria reduce the oxidation-reduction potential of medium.

Sulfide indole motility

a.  Hydrogen sulfide production is detected when ferrous sulfide, a black precipitate, is produced as a result of ferrous ammonium sulfate reacting with H₂ S gas.

b. Indole is detected upon the addition of Kovacs Reagent after the incubation of the inoculated medium. Indole combines with p-dimethylaminobenzaldehyde and produces a red band at the top of the medium.

c. Motile organisms extend from the stab line and produce turbidity or cloudiness throughout the medium.

Triple Sugar Ion agar

a. If lactose is not fermented but the small amount of glucose is, the oxygen-deficient butt will be yellow, since the butt has more glucose than slant. Slant will be red since it is alkaline as lactose fermentation did not occur.

b. If lactose is fermented, a large amount of acid is produced, which turns the phenol red indicator yellow both in the butt and in the slant.

c. If lactose is fermented, some organisms generate gases, which produces bubbles or large holes on the medium.