The purpose of the present invention is to provide a method and an agent to efficiently inhibit the function of the drug efflux pump of Pseudomonas aeruginosa. The invention provides a method to inhibit the function of the drug efflux pump of Pseudomonas aeruginosa, comprising modifying any amino acid residue selected from 100th to 109th or 311th to 320th amino acid residues in the amino acid sequence of mature OprM protein. The invention also provides an agent having such inhibitory effect, and a screening method thereof.
