Results : OMP analysis showed decreased expression, the absence of certain proteins or the presence of proteins with altered molecular weights when compared with wild-type strains. Most isolates possessed a smooth LPS phenotype. Isolates had double mutations in GyrA codons 83 and 87, in addition to a ParC alteration at Ser-80/Glu-84. Isolates accumulated varying levels of ciprofloxacin, and upon the addition of carbonyl cyanide m-chlorophenylhydrazone, increased accumulation was observed in all instances. E. coli isolates with a rough LPS phenotype appeared to accumulate higher levels of ciprofloxacin compared with those with a smooth LPS phenotype expressing OmpF normally, or even those not possessing OmpF. All E. coli isolates tested demonstrated active efflux of ciprofloxacin. Plasmid- mediated quinolone resistance (presence of the qnrA gene) was observed in 36.8% of isolates. Conclusions : A combination of target gene alterations, altered OM permeability, presence of the qnrA gene and active efflux appear to act together to produce a high-level, multiresistance phenotype. Keywords: fluoroquinolone resistance, OMP, LPS, GyrA and ParC alterations, energy-dependent efflux systems