Question

A penicillin sensitive Escherichia coli population is exposed to a lethal dose (200 µg/ml) of penicillin. Assuming density-independent mortality, which one of the following relationships would describe the number of surviving bacteria (N) over time (T)?
 

• A. Exponential
• B. Linear
• C. Sigmoidal
• D. Parabolic

Hint:

In bacterial population dynamics, exposure to a lethal dose of antibiotics often leads to exponential decay in the number of survivors. This is a result of density-independent mortality where each individual has the same probability of dying, regardless of population density.

Answer 1

The Correct Option is A

When a population of bacteria, such as Escherichia coli, is exposed to a lethal dose of penicillin, the number of surviving bacteria typically decreases in an exponential manner if the mortality is density-independent. This means that the bacteria die at a constant rate, and the number of survivors decreases exponentially over time, assuming no other limiting factors. Therefore, the correct relationship is exponential. 
- (B): A linear relationship would imply that the number of surviving bacteria decreases at a constant rate per unit of time. However, bacterial death due to a lethal dose of penicillin is typically more rapid initially, so a linear relationship is not accurate. Hence, statement (B) is incorrect. 
- (C): A sigmoidal curve describes population growth under favorable conditions with carrying capacity, not a situation involving density-independent mortality. Hence, statement (C) is incorrect. 
- (D): A parabolic relationship would imply a quadratic pattern of change, which is not typical for bacterial death under these conditions. Hence, statement (D) is incorrect. 
Thus, the correct answer is (A), exponential decay.