The disclosure relates to the compounds of formula I (I) wherein A is N or CH； and n is 0 or 1； or the pharmaceutically acceptable salts thereof, for preventing or treating intestinal diseases which are caused by bacteria selected from Clostridium difficile, Clostridium perfringens or Staphylococcus aureus. Examples of these compounds include: 1-cyclopropyl-6-fluoro-7-{ 4-[2-fluoro-4-((R)-5-hydroxymethyl-2-oxo-oxazolidin-3-yl)-phenoxymethyl]-4-hydroxy-piperidin-1-yl} -4-oxo-1,4-dihydro-quinoline-3-carboxylic acid； 1-cyclopropyl-6-fluoro-7-{ 4-[2-fluoro-4-((R)-5-hydroxymethyl-2-oxo-oxazolidin-3-yl)phenoxymethyl]-4-hydroxy-piperidin-1-yl} -4-oxo-1,4-dihydro-[1,8]naphthyridine-3-carboxylic acid and 1-cyclopropyl-6-fluoro-7-{ 3-[2-fluoro-4-((R)-5-hydroxymethyl-2-oxo-oxazolidin-3-yl)-phenoxymethyl]-3-hydroxy-pyrrolidin-1-yl} -4-oxo-1,4-dihydro-quinoline-3-carboxylic acid.
