R. Bachoual et al., Roles of gyrA mutations in resistance of clinical isolates and in vitro mutants of Bacteroides fragilis to the new fluoroquinolone trovafloxacin, ANTIM AG CH, 44(7), 2000, pp. 1842-1845
We determined whether gyrA mutations were present in fluoroquinolone-resist
ant laboratory mutants derived from the Bacteroides fragilis reference stra
in ATCC 25285 and in clinical isolates of B. fragilis. The two first-step m
utants selected on ciprofloxacin (CIP) were devoid of gyrA mutations, where
as two of the three CIP-selected second-step mutants studied presented the
same gyrA mutation leading to a Ser82Phe change. Unusual GyrA alterations,
Asp81Asn or Ala118Val, were detected in two of the three first step mutants
selected on trovafloxacin (TRO), Mt3 and Mt1, respectively. The Ala118Val
change had no effect on the susceptibility of Mt1 to CIP, No second-step mu
tant could be obtained with TRO as a selector. For the 12 clinical isolates
studied, a Ser82Phe change in GyrA was found only in the 3 strains which s
howed the highest levels of TRO resistance (MIC, 4 mu g/ml). Thus, the resi
stance phenotypes and genotypes observed in fluoroquinolone-resistant clini
cal isolates of B. fragilis were similar to those found in CIP-selected lab
oratory mutants, whereas peculiar mutational events could be selected in vi
tro with TRO.