5-Amino-7-((3S,4S)-3-amino-4-methyl (or ethyl)-1-pyrrolidinyl)-1-cyclopropyl-6-fluoro-1,4-dihydro-8-methyl-4-oxoqu inoline-3-carboxylic acid or a pharmacologically acceptable salt thereof represented by the following formula wherein asymmetric carbon atoms marked with asterisks are in the S-configurations and R.sup.1 represents methyl group or ethyl group; and an antibacterial agent comprising said compound as an active ingredient. ##STR1##
5-
氨基-7-((3S,4S)-3-
氨基-4-甲基(或乙基)-1-
吡咯啉基)-1-环丙基-6-
氟-1,4-二氢-8-甲基-4-氧基
喹啉-3-羧酸,或其药理学上可接受的盐,如下式所示,其中用星号标记的不对称碳原子处于S构型,R.sup.1代表甲基或乙基基团;以及包含所述化合物作为活性成分的抗菌剂。