Mutation in the DNA gyrase A Gene of Escherichia coli that expands the quinolone resistance-determining region

Abstract

In three Escherichia coli mutants, a change (Ala-51 to Val) in the gyrase A protein outside the standard quinolone resistance-determining region (QRDR) lowered the level of quinolone susceptibility more than changes at amino acids 67, 82, 84, and 106 did. Revision of the QRDR to include amino acid 51 is indicated.

FIG. 1

Relative susceptibilites of gyrase mutants to fluoroquinolones. The MIC₉₉s (see text) of ciprofloxacin (A) and gatifloxacin (B) were determined for a series of GyrA variants and are indicated above each bar (each determination was made twice with similar results). For illustrative purposes, the results for the mutant with the Ala-51-to-Val substitution are shown in white and are indicated by the arrows. All strains are gyrA Nal^r transductants of wild-type strain DM4100, as described in the text or elsewhere (8). Amino acid changes in the GyrA QRDR and strain numbers (in parentheses) are as follows: S83L (KD66), A51V (KD1721), A67S (KD1911), G81C (KD1915), S83W (KD1909), D87N (KD1913), Q106H (KD1917), D82A (KD1973), A84P (KD1975), and D87Y (KD1977).

FIG. 2

Structure of the GyrA59 dimer. The figure shows a ribbon representation (generated in RasMol) of the GyrA59 fragment (10), courtesy of J. G. Heddle (John Innes Centre, Norwich, United Kingdom). (A) The entire GyrA59 dimer. (B) An enlargement of the boxed region in panel A. Amino acids that change to confer quinolone resistance are indicated in black and by the amino acid numbers. Amino acid 51 is in helix 2, amino acid 67 is in helix 3, and amino acids 83 and 87 are in helix 4.