Plasmid-mediated complementation of gyrA and gyrB in fluoroquinolone-resistant Bacteroides fragilis.
OBJECTIVE
To identify whether mutations in gyrA and gyrB confer fluoroquinolone resistance in Bacteroides fragilis.


METHODS
Eight fluoroquinolone-resistant (FQR) strains were complemented with plasmid-mediated B. fragilis wild-type gyrA (pMP1) and gyrB (pMP2), and MICs determined. Sequence analysis of the gyrA and gyrB quinolone resistance determining region (QRDR) was performed for all strains.


RESULTS
MICs of fluoroquinolones were two- to 32-fold higher than wild-type for all mutants. Five mutants had a substitution in GyrA (Ser-82-->Phe), one mutant had a substitution in GyrA (Asp-81-->Gly), one mutant had a substitution in GyrB (Glu-478-->Lys), and one resistant strain did not contain mutations in the QRDR of gyrA or gyrB. Following complementation with pMP1 or pMP2, the MICs of fluoroquinolones were reduced two- to 32-fold for the mutants.


CONCLUSIONS
These studies verify that substitutions in GyrA and GyrB confer resistance in B. fragilis. Other mechanisms are also responsible for resistance since not all resistant strains fully complemented to the wild-type phenotype.
Peterson
M L
ML
University of Minnesota, Minneapolis, MN, USA.
Rotschafer
J C
JC
Piddock
L J V
LJ
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001441:Bacteroides fragilis / Q000187:drug effects* / Q000235:genetics*; D027081:DNA Gyrase / Q000235:genetics*; D024881:Drug Resistance, Bacterial; D024841:Fluoroquinolones / Q000494:pharmacology*; D005816:Genetic Complementation Test; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010957:Plasmids / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D027081:DNA Gyrase