A plasmid carries genes for resistance to tetracycline, penicillin (via a beta-lactamase), and a carbapenemase. If a clinician prescribes tetracycline, what is the most likely population-level consequence regarding carbapenem resistance encoded on the same plasmid?

• A. Use of tetracycline will co-select for the entire plasmid, increasing the frequency of carbapenem resistance in the population even though carbapenems were not used.
• B. Carbapenem resistance will decline because tetracycline induces a plasmid loss mechanism that specifically cures plasmids with beta-lactamase genes while leaving other resistance determinants unaffected.
• C. Tetracycline use will only select for tetracycline resistance and will actively reduce any carbapenem resistance because carbapenemase expression is repressed when tetracycline is present.
• D. Resistance dynamics are unaffected because co-selection requires simultaneous administration of all antibiotics encoded on the plasmid; single-drug exposure cannot drive selection for unrelated resistance genes on the same element.

Answer: (A)