A catheterized patient develops a persistent urinary tract infection despite antibiotic treatment. Which mechanism explains why the *E. coli* biofilm exhibits resistance when planktonic bacteria are susceptible?

💡 Explanation

The biofilm enhances antibiotic resistance in *E. coli* because it upregulates efflux pump expression, actively pumping antibiotics out of the biofilm matrix. This reduces intracellular antibiotic concentration, therefore resistance develops in the biofilm, rather than increased permeability or target site affinity.

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