Cloning and nucleotide sequence of the Campylobacter jejuni gyrA gene and characterization of quinolone resistance mutations.

The gyrA gene of Campylobacter jejuni UA580, which encodes the A subunit of DNA gyrase, was cloned and its nucleotide sequence was determined. An open reading frame of 2,589 nucleotides was identified, which could code for a polypeptide of 863 amino acids with a M(r) of 97 kDa. Both the nucleotide sequence and the putative amino acid sequence show ca. 50% identity with those of other gyrA genes from gram-positive and gram-negative bacteria. The locations of the gyrA gene on genome maps of both C. jejuni UA580 and Campylobacter coli UA417 were determined. Six nalidixic acid-resistant isolates of C. jejuni were shown to carry mutations in gyrA. Three clinical isolates had Thr-86-to-Ile substitutions. Three laboratory mutants had substitutions of Thr-86 to Ile, Asp-90 to Ala, and Ala-70 to Thr, respectively. The mutation at Thr-86, which is homologous to Ser-83 in Escherichia coli, was associated with high-level resistance to ciprofloxacin in C. jejuni.