Within Six Months of Effectively Using Methicillin to Treat S

question 4

Multiple Choice

Within six months of effectively using methicillin to treat S. aureus infections in a community, all new infections were caused by MRSA. How can this result best be explained?

• A) S. aureus can resist vaccines.
• B) A patient must have become infected with MRSA from another community.
• C) In response to the drug, S. aureus began making drug-resistant versions of the protein targeted by the drug.
• D) Some drug-resistant bacteria were present at the start of treatment, and natural selection increased their frequency.
• E) The drug caused the S. aureus DNA to change.

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