What is antimicrobial resistance and give an example of a resistant organism.

• A. The ability of microbes to withstand effects of an antimicrobial; example: methicillin-resistant Staphylococcus aureus (MRSA)
• B. The growth of microbes in the absence of antimicrobials
• C. The use of vaccines to prevent infections
• D. The modification of antibiotics by bacteria

Answer: (A)

Antimicrobial resistance means microbes survive or keep growing despite exposure to drugs that are meant to kill them or stop their growth. This happens when they acquire changes that reduce a drug’s effectiveness, such as altered drug targets, inactivating the drug, or pumping the drug out of the cell. An example is MRSA, a strain of Staphylococcus aureus that became resistant to methicillin because it carries the mecA gene, which makes a penicillin-binding protein with low affinity for beta-lactam antibiotics. That change means methicillin and related drugs can no longer effectively bind their target, so the bacteria aren’t killed. This is why resistant infections are harder to treat and may require different medications and longer therapy. Other statements either describe growth without drugs, which isn’t resistance, or vaccination for prevention, or describe a specific resistance mechanism rather than the general idea.