An antibiotic is given repeatedly to treat a recurrent ear infection. It worked initially but now is no longer effective. This indicates that the Streptococcus bacterium
A) is infectious only if it is sensitive to the antibiotic.
B) is very sensitive to the antibiotic.
C) is being treated with an antibiotic that has experienced a manufacturing error, making it infective.
D) experienced natural selection that has allowed the resistant Streptococcus to survive and multiply.

Question

Quizplus · Accepted Answer

The antibiotic initially worked, suggesting that the Streptococcus bacterium was sensitive to it. However, over time, the bacteria that were resistant to the antibiotic survived and multiplied, leading to a population of bacteria that the same antibiotic could no longer effectively treat. This is an example of natural selection, where the resistant bacteria have a survival advantage in the presence of the antibiotic.

An Antibiotic Is Given Repeatedly to Treat a Recurrent Ear