Question

You have a tube of E. coli in nutrient broth that has been growing in a 37 degree C incubator. This culture is then inoculated into 3 tubes of media: Tube B is lactose broth, warmed to room temperature, inoculated, and then placed at 37oC. Tube C is nutrient broth taken right out of the refrigerator, inoculated, and then placed at 37oC. Tube D is nutrient broth, warmed to room temperature, inoculated, and then placed at 37oC. The original tube of E. coli (called tube A) is placed back into the 37oC for incubation. In the next one-half hour, which culture will grow the fastest and why?

(A) Tube A will grow fastest because it is the original culture and has already been growing.
(B) Tube B will grow fastest because lactose is a good nutrient for all bacterial species.
(C) Tube C will grow fastest because the medium has been stored cold, and is fresher than the other media used.
(D) Tube D will grow fastest because the nutrients and the temperature are optimal for a fast lag phase.

Answer 1

D

Step-by-step explanation:

E.coli will grow fastest when warmed to room temperature, inoculated, and then placed at 37°C because the nutrients and the temperature are optimal for a fast lag phase. it is important to allow media to equilibrate to room temperature before use to minimize the potential of thermal shock. The exposure of cells to heat stress leads to accumulation of partially and fully denatured proteins that interfere with normal cellular function. The growth of E.coli is inhibited in lactose broth, therefore lactose is not a good nutrient for E.coli.