What is a resistant bacteria?

• A. A strain of bacteria that isn't affected by a particular antibiotic.
• B. A bacteria that only grows in antibiotics.
• C. A virus that resists antibiotics.
• D. A fungus that is resistant.

Answer: (A)

Antibiotic resistance means some bacteria can survive exposure to an antibiotic that would normally kill or stop them. A resistant bacterium is a strain of bacteria that isn't affected by a particular antibiotic, so that drug won’t effectively treat infections caused by it. This happens when bacteria acquire mutations or resistance genes that change the drug’s target, produce enzymes that inactivate the drug, or use efflux pumps to push the drug out of the cell. These traits can be passed between bacteria, spreading resistance and making treatments harder.

Other options don’t fit because antibiotics target bacteria, so a virus wouldn’t be described as resisting antibiotics, and a fungus is a different organism class. The idea of a bacterium that “only grows in antibiotics” isn’t accurate—the presence of the antibiotic ideally halts growth or kills, and resistant strains simply keep growing despite it.