In the present study, of the isolates assayed for ciprofloxacin accumulation, only isolates F14 and F18 demonstrated loss of OmpF, however, their LPS profiles were different and this may account for the difference in ciprofloxacin accumulation. Active efflux either singly or in tandem with OMP alterations would be responsible for the low accumulation of ciprofloxacin seen in isolates assayed (14–25 ng ciprofloxacin/mg cells) in the absence of CCCP