Acquired resistance is when a bacterium undergoes spontaneous mutation of a gene or horizontal gene transfer.

• A. Acquired
• B. Intrinisc
• C. Transient
• D. Adaptive

Answer: (A)

The main concept here is how bacteria gain the ability to resist antibiotics. Acquired resistance arises when a bacterium either mutates an existing gene or picks up new genetic material from another organism. Spontaneous mutation can alter a drug’s target or increase mechanisms that push the drug out or inactivate it, while horizontal gene transfer lets resistance genes spread on plasmids, transposons, or other mobile elements between bacteria. This is different from intrinsic resistance, which is built into a species by its normal biology (for example, lacking a drug target or having an inherently impermeable cell envelope), and from adaptive resistance, which is a temporary, reversible change in response to antibiotic exposure rather than a permanent genetic change. Transient resistance is also not about stable genetic acquisition. Therefore, describing resistance as acquired aligns with how bacteria gain resistance through mutation or gene transfer.