Persistent use of a drug against disease-causing bacteria can result in populations that are resistant to the drug. Which of the following is the best explanation for the appearance of these drug-resistant bacterial strains?
A) The bacteria learn to excrete the drug so that they are not affected by it.
B) The drug increases the rate of cell division until the bacteria are reproducing faster than they are being killed.
C) The drug causes a mutation that confers resistance.
D) The bacteria produce membrane proteins which prevent the drug from entering the cell.
E) Drug-resistant bacteria already exist within the population. Application of the drug kills the non-resistant bacteria, so that only resistant bacteria survive to contribute to the gene pool of subsequent generations.

Question

Quizplus · Accepted Answer

Drug-resistant bacteria often pre-exist within a population. When a drug is applied, it selectively kills the non-resistant individuals, allowing the resistant ones to survive and reproduce, thereby increasing their proportion in the population over time. This process is an example of natural selection.

Persistent Use of a Drug Against Disease-Causing Bacteria Can Result