Resistance can occur without prior exposure to an antibiotic.

• A. Sometimes
• B. Not applicable
• C. True
• D. False

Answer: (C)

Antimicrobial resistance can exist even if the organism has never been exposed to the antibiotic in question. Some bacteria are intrinsically resistant due to their biology, such as impermeable membranes or efflux pumps, so resistance is built in rather than earned through exposure. Additionally, resistance genes can be carried on mobile genetic elements and spread between bacteria in the environment or within a host via horizontal gene transfer. This means a patient can be colonized or infected with a resistant strain without prior antibiotic exposure, and subsequent antibiotic use can select for that resistant population. Understanding this helps explain why treatment decisions rely on local resistance patterns and susceptibility testing, not just a patient’s history of prior antibiotic use.