a You inoculate an organism into phenol red lactose broth Th

(a) You inoculate an organism into phenol red lactose broth. The organism ferments lactose. What color is the medium?________ What does this tell you about the pH of the medium?__________ (b) The organism ferments lactose and produces gases. What do you use to detect gas production ?__________? What do you see that indicates that gases are produced? In what test is Kovac\'s reagent used? _______What molecule does Kovac\'s reagent detect? ______________To do this test, why do you have to grow the organism in medium containing tryptophan? __________ In the urea test, what happens to the pH of the medium when an organism breaks down urea? What molecule causes this pH change?__________

Solution

Ans 3 a. If the organism is able to ferment lactose and produce energy out of it the colour of medium changes to yellow from red. This means it has produced acid so the ph of broth becomes less than 7 ( acidic)

B. If the organism ferments lactose and produces gas, durham tube is used to detect gas production. An air bubble gets trapped inside the durham tube, indicating that organism is fermenting lactose and producing gas as well.