Question

Microbes are often identified using biochemical tests that detect specific enzymes of metabolic pathways. E. coli typically ferments lactose, whereas Shigella does not. If a pure culture of each bacterium was placed in a tube containing lactose as the only food source, and a chemical indicator changed color after a pH change, what would the tubes look like after the bacteria were incubated?

Answer 1

Answer: There will be change in the tube in which E.coli will be incubated and there will be no change in the test tube in which Shigella is incubated

Explanation:

Lactose Fermentation Test is done to see which bacteria ferments lactose. pH and color indicator is attached to observe the change. The pH goes slightly down because of formation of Acid and due to this reason a color change is also seen during this test.

As E.coli typically ferments lactose so there will change in color and pH in the test tube incubated with E.coli, while there will be no change in the test tube incubated with Shigella.