Quinolylpropylpiperidine derivatives of general formula (I) in which: R1 is NH2, alkylamino, dialkylamino, hydroxyamino, alkyl(alkyloxy)amino or alkyloxyamino, R2 is a carboxyl, carboxymethyl or hydroxymethyl radical, R3 is alkyl (1 to 6C) substituted by phenylthio which can itself carry 1 to 3 substituents selected from halogen, OH, alkyl, alkyloxy, CF3, OCF3, COOH, alkyloxycarbonyl, CN and NH2, by cycloalkylthio (3 to 7 members) or by heteroarylthio (5 to 6 members) comprising 1 to 4 heteroatoms selected from N, S and O and optionally itself substituted [by halogen, OH, alkyl, alkyloxy, CF3, OCF3, ═O, COOH, alkyloxycarbonyl, CN or NH2] or R3 is propargyl substituted by phenyl which can itself carry 1 to 3 substituents selected from halogen, OH, alkyl, alkyloxy, CF3, OCF3, COOH, alkyloxycarbonyl, CN and NH2 or substituted by cycloalkyl comprising 3 to 7 members or substituted by 5- to 6-membered heteroaryl comprising 1 to 4 heteroatoms chosen from N, O or S and optionally itself substituted by halogen, OH, alkyl, alkyloxy, CF3, OCF3, ═O, COOH, alkyloxycarbonyl, CN or NH2, and R4 is alkyl (1 to 6C), alkenyl-CH2—, alkynyl-CH2— (3 to 7C), cycloalkyl or (cycloalkyl)alkyl, in their diastereoisomeric forms or their mixtures, and their pharmaceutically acceptable salts. These novel derivatives are particularly advantageous antimicrobial agents.