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 application_number US 201013377057 A description as described above the anti gram negative bacteria agent of the present invention is characterized by exerting a bactericidal action a growth inhibiting action and or a drug efflux inhibiting action on gram negative bacteria by inhibiting the formation of the yaet complex for the purpose of the present invention the term u201c gram negative bacteria u201d is used in the commonly used sense thus it is a generic term applied to bacteria whose crystal violet stain is decolorized in gram staining typical gram negative bacteria include proteobacteria such as escherichia coli salmonella pseudomonas and helicobacter and cyanobacteria when classified in connection with medicine they include bacilli such as pseudomonas aeruginosa and hemophilus influenzae causing the disturbance of the respiratory system escherichia coli and proteus mirabilis causing the disturbance of the urinary.