gyrA mutations in ciprofloxacin-resistant Bartonella bacilliformis strains obtained in vitro

Abstract

We isolated and characterized mutants of Bartonella bacilliformis that are resistant to the fluoroquinolone antibiotic ciprofloxacin, which targets the A subunit of DNA gyrase. Mutants had single point mutations in the gyrA gene that changed either Asp-90 to Gly or Asp-95 to Asn and had 3- or 16-fold higher resistance, respectively, to ciprofloxacin than did wild-type B. bacilliformis. Asp-95 is homologous to Asp-87 of Escherichia coli GyrA and is a common residue mutated in fluoroquinolone-resistant strains of other bacteria. This is the first report of a mutation at an Asp-90 homologue, which corresponds to Asp-82 in E. coli GyrA.

FIG. 1.

Linkage map of the B. bacilliformis gyrA locus, including two putative flanking genes encoding a single-stranded DNA binding protein (ssb) and phosphopantetheine adenylyltransferase (coaD).

FIG. 2.

Multiple-sequence alignment of B. bacilliformis GyrA (Bb) with GyrA proteins from Rhizobium meliloti (Rm) and Brucella melitensis (Bm). Identical amino acid residues are shown in black, conserved residues are shown in gray, and introduced gaps are indicated with hyphens. The GenBank accession numbers for the Rm and Bm homologues are NP385666 and NP539801, respectively. The QRDR is boxed and the nested ciprofloxacin resistance mutations observed at Asp-90 and Asp-95 are indicated by arrowheads. The highly conserved GyrA, A, and B boxes of the GyrA subunit are also shown.