QUINOLONCARBONSÄUREDERIVAT

A quinolonecarboxylic acid derivative represented by general formula (1), its salt and an antibacterial agent containing the same as the active ingredient, wherein R represents hydrogen, alkyl, aralkyl or an ester residue which is hydrolyzable in vivo; R represents hydrogen or amino which may be substituted with one or two lower alkyl groups; X represents hydrogen or halogen; Y represents CH2, O, S, SO, SO2 or NR , wherein R represents hydrogen or lower alkyl; and Z represents an oxygen atom or two hydrogen atoms. This compound develops a potent antibacterial activity particularly against gram-positive bacteria, so that it is useful in preventing and treating various infectious diseases clinically.