Preliminary investigations into fluoroquinolone resistance in Escherichia coli strains resistant to nalidixic acid isolated from animal faeces

Resistance to fluoroquinolones was evaluated in 17 nalidixic acid-resistant Escherichia coli strains isolated from animal faeces. Polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP), hybridisation and sequencing were used to reveal point mutations in DNA gyrase subunits A and B and the presence of the qnr gene as evidence of plasmid resistance. Chromosomal resistance and class 1 integrons were found in 10 of the 17 E. coli strains examined, while the qnr gene was not found in any of these. Mutation Ser83-Leu was found in six strains and in one strain mutation Ser83-Ala was found in gyrA. Mutations in gyrA Asp87 codons and in gyrB Asp426 or Lys 447 codons were not identified. Sequencing of the E. coli strain ATCC 25922 subjected to resistance induction revealed a gyrB mutation of the Lys 447 residue which had been replaced by arginine