Minimum inhibitory concentrations (MICs) and mutant prevention concentrations (MPCs) of
prulifloxacin against 30 strains of Escherichia coli isolated from
urinary tract infections as well as the '
biological cost' related to acquisition of resistance to the same
drug in 10 uropathogenic E. coli were assessed. In terms of MIC(90),
prulifloxacin was more potent than
ciprofloxacin and
levofloxacin.
Prulifloxacin produced lower or equal MPC values than the other two
fluoroquinolones (93.3% and 73.3% compared with
levofloxacin and
ciprofloxacin, respectively). Compared with susceptible strains,
prulifloxacin-resistant mutants showed a reduced rate of growth (ranging from 20.0% to 98.0% in different
culture media and incubation conditions) and a decreased fitness index (ranging from 0.959 to 0.999). They were also impaired in their ability to adhere to uroepithelial cells and
urinary catheters (11.7-66.4% and 16.3-78.3% reduction, respectively) and showed a lower surface hydrophobicity (51.2-76.0%). They were more susceptible to ultraviolet irradiation (30.6-93.8% excess mortality), showed increased resistance to
colicins and diminished transfer of plasmids (<1-8.5x10(-8) vs. 3.3x10(-7)-2.4x10(-4)). Synthesis of haemolysin and type I fimbriae and production of flagella were also adversely affected. This study demonstrates a strict relationship between acquisition of
prulifloxacin resistance and loss of important virulence traits. In this transition, E. coli pays a severe
biological cost that entails a general reduction of fitness, thus compromising competition with susceptible wild-type strains in the absence of the
drug.