Quinolone-resistance determining region (QRDR) of Gyrase A gene was sequenced in 54 Salmonella strains of pig origin that have different quinolone-resistance patterns. Those strains accounted for 12 different serotypes. Mutations at Ser83 or Asp87 were predominant in the studied isolates. However, for serotypes Anatum and Virchow, resistance to quinolones seemed to be linked to specific mutations, namely, Ser83 → Tyr and Ser83 → Phe, respectively. Other mutations found in different positions did not seem to have clinical significance except for changes at Asp82. © 2005 Elsevier B.V. All rights reserved.