Question

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?

(A) A patient must have become infected with MRSA from another community.

(B) In response to the drug, S. aureus began making drug-resistant versions of the protein targeted by the drug.

(C) Some drug-resistant bacteria were present at the start of treatment, and natural selection increased their frequency.

(D) S. aureus evolved to resist vaccines.

Short answer

1. The statement “A patient must have become infected with MRSA from another community” is false.
2. The statement “In response to the drug, S. aureus began making drug-resistant versions of the protein targeted by the drug” is false.
3. The statement “Some drug-resistant bacteria were present at the start of treatment, and natural selection increased their frequency” is true.
4. The statement “S. aureus evolved to resist vaccines” is false.

Step-by-step solution

S. aureus and MRSA

The bacterial community, Staphylococcus, is the bacterial genus that comprises spherical-shaped bacterial cells.The bacterial community belonging to the species S. aureus is a general residing community of the human skin. The MRSA is the antibiotic-resistant group of S. aureus.

Step 2: Explanation for option (A)

MRSA is a bacterial community that is a type of S. aureusbut is antibiotic-resistant. The MRSA, also known as methicillin-resistant S. aureus,developed due to regular exposure to methicillin and other similar antibiotics.

Thus, MRSA belongs to S. aureus.

Therefore, the given statement is false.

Step 3: Explanation for option (B)

The antibiotics cannot induce a new version or trait. The bacteria did not begin to produce drug-resistant versions of the proteins targeted by the drugs.

Thus, S. aureusdid not make drug-resistant versions.

Therefore, the given statement is false.

Step 4: Explanation for option (C)

Some S. aureushad drug-resistant traits.S aureusnaturally selected the traits for antibiotic resistance, and a portion of the bacterial species became methicillin-resistant.

Thus, the drug-resistant bacteria were naturally selected, which increased their population.

Therefore, the given statement is true.

Step 5: Explanation for option (D)

One cannot infer that S. aureusdeveloped resistance to the vaccine. Instead, the bacterial species grew resistant to antibiotics.

Thus, the bacteria did not develop resistance against the vaccine.

Therefore, the given statement is false.