A chronic Pseudomonas aeruginosa lung infection is treated with tobramycin. Which resistance mechanism most directly allows the bacteria to persist despite initially effective antibiotic concentrations?

💡 Explanation

Upregulation of efflux pump expression directly reduces intracellular antibiotic concentration, because it actively transports tobramycin out of the bacterial cell. Therefore, the bacteria persist due to decreased drug effectiveness, rather than ribosomal modification, enzymatic inactivation, or limited drug entry.

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