Provided are: a method for blocking the biosynthesis of an outer membrane protein (OMP) necessary for the survival of Gram-negative bacteria by inhibiting the formation of a YaeT complex in the outer membrane of the bacteria and an agent therefor for the purpose of basically solving a problem of the development of multidrug resistance in Gram-negative bacteria. Specifically disclosed is an anti-Gram-negative bacteria agent, wherein the agent exerts a bactericidal action, a growth-inhibiting action, and/or a drug efflux-inhibiting action on Gram-negative bacteria by inhibiting the formation of a YaeT complex. The agent is preferably a peptide molecule comprising an amino acid sequence consisting of at least LTLR or a peptide molecule comprising an amino acid sequence consisting of at least FIRL.
