Which antibiotic is NOT indicated for treating MRSA?

The correct answer is amoxicillin, as it is not indicated for treating Methicillin-resistant Staphylococcus aureus (MRSA). MRSA is a type of staph bacteria resistant to many antibiotics, including methicillin and, by extension, other related beta-lactam antibiotics like penicillin, of which amoxicillin is a derivative.

In contrast, linezolid and tedizolid are both oxazolidinone antibiotics that are effective against MRSA and are specifically used to treat infections caused by this resistant strain. Delafloxacin, being a fluoroquinolone, has been shown to be effective against a variety of resistant bacteria, including MRSA.

Thus, the distinctive characteristic of amoxicillin's ineffectiveness against MRSA, due to the bacterium's resistance mechanisms, is why it is the correct choice in this context.