Within six months of effectively using methicillin to treat...

Within six months of effectively using methicillin to treat S. aureus infections in a community, all new $S$ . aureus infections were caused by MRSA. How can this best be explained? \begin{equation}\begin{array}{l}{\text { (A) A patient must have become infected with MRSA from }} \\ {\text { another community. }} \\ {\text { (B) In response to the drug, S. aureus began making drug- }} \\ {\text { resistant versions of the protein targeted by the drug. }} \\ {\text { (C) Some drug-resistant bacteria were present at the start }} \\ {\text { of treatment, and natural selection increased their }} \\ {\text { frequency. }} \\ {\text { (D) } S \text { . aureus evolved to resist vaccines. }}\end{array} \end{equation}

Within six months of effectively using methicillin to treat S. aureus infections in a community, all new $S$ . aureus infections were caused by MRSA. How can this best be explained?
\begin{equation}\begin{array}{l}{\text { (A) A patient must have become infected with MRSA from }} \\ {\text { another community. }} \\ {\text { (B) In response to the drug, S. aureus began making drug- }} \\ {\text { resistant versions of the protein targeted by the drug. }} \\ {\text { (C) Some drug-resistant bacteria were present at the start }} \\ {\text { of treatment, and natural selection increased their }} \\ {\text { frequency. }} \\ {\text { (D) } S \text { . aureus evolved to resist vaccines. }}\end{array}
\end{equation}

Labs

Want to see this concept in action?

NEW

Explore this concept interactively to see how it behaves as you change inputs.

View Labs

Key Concepts

Antibiotic Resistance

Antibiotic resistance is the ability of bacteria to withstand the effects of an antibiotic that would normally eliminate them. This resistance can be due to preexisting genetic differences, mutations, or acquired resistance mechanisms, and it is a classic example of evolution by natural selection in response to the selective pressure imposed by antibiotic use.

Natural Selection

Natural selection is the process by which organisms with traits that are better adapted to their environment survive and reproduce more than those without such traits. In the context of bacterial infections, when an antibiotic is introduced, bacteria that have or acquire resistance traits survive the treatment and multiply, eventually becoming the dominant strain.

Preexisting Genetic Variation

Preexisting genetic variation refers to the natural differences among individual bacteria in a population. Even before antibiotic treatment, some bacteria may inherently possess mutations or traits that confer resistance to a drug. When antibiotics are used, these resistant bacteria have a survival advantage, and their frequency in the population increases.

Transcript

Please give Ace some feedback