(2S)-2-((4-((4-((1S)-1,2-dihydroxyethyl) phenyl) ethynyl) benzoyl) Ethyl) benzoyl) (methyl) amino)-N-hydroxy-2-methyl-2-((4-((4-((1S)-1-hydroxy-2-methoxyethyl) phenyl) ethynyl)-N, 2-dimethyl malonamide and (2S)-N-Benzoyl) (methyl) amino)-N , 2-dimethyl malonamide, or a salt thereof and an antimicrobial substance are useful for the treatment of gram-negative bacterial infection.(2S)-2-((4-((4-((1S)-1,2-디히드록시에틸)페닐)에티닐)벤조일)(메틸)아미노)-N-히드록시-N,2-디메틸말론아미드, (2S)-2-((4-((4-((1R)-1,2-디히드록시에틸)페닐)에티닐)벤조일)(메틸)아미노)-N-히드록시-N,2-디메틸말론아미드 및 (2S)-N-히드록시-2-((4-((4-((1S)-1-히드록시-2-메톡시에틸)페닐)에티닐)벤조일)(메틸)아미노)-N,2-디메틸말론아미드에서 선택되는 히드록삼산 유도체 또는 그 염 및 항균성 물질을 함유하는 의약 조성물은 그람 음성균 감염증의 처치에 유용하다.
