Accumulation of ofloxacin and tosufloxacin in fluoroquinolone-resistant E coli.
OBJECTIVE
To make sure whether there is a difference in mechanism existed in the resistant E coli strains accumulated hydrophilic fluoroquinolone ofloxacin and hydrophobic fluoroquinoline tosufloxacin.


METHODS
Fluoroquinolone accumulation in bacteria and effect of active efflux were measured by fluorescence method. Analysis of outer membrane proteins was made by SDS-PAGE. E coli strains included JF701 and JF703 that are OmpC- or OmpF-deficient mutants of E coli K-12 respectively, and the susceptible strain Ecs and its in-vitro selected resistant strains R2, R256, and clinical resistant isolates R5, R6.


RESULTS
Ecs accumulated ofloxacin almost at the same concentration as JF701, but JF703 did about 1/2 of that lower than JF701. However, four resistant strains accumulated ofloxacin about 5 to 7-fold lower than those susceptible strains. On the other hand, there was no significant difference for the accumulation of tosufloxacin between fluoroquinolone-resistant and -susceptible strains. After addition of proton ionophore DNP for 5 min and 10 min, the accumulation of tosufloxacin slowly decreased in E coli strains, whereas the accumulation of ofloxacin was increased, especially in the resistant strains. A good relevance exists between the accumulation increment of ofloxacin and its MIC for each E coli strain after addition of DNP for 5 min and 10 min (r=0.9623 and 0.8006 respectively). Furthermore, both OmpF and OmpC in Ecs, OmpF-deficiency in R2, R256 and OmpC-deficiency in R5, R6 were observed.


CONCLUSIONS
The accumulation of ofloxacin other than tosufloxacin could be reduced by OmpF-deficiency and active efflux, and the latter may be an important factor in the development of resistance to hydrophilic fluoroquinolone in E coli.
Xia
P Y
PY
Department of Infectious Diseases, the First Affiliated Hospital, West China University of Medical Sciences, Chengdu 610041, China. xiapy63@netease.com
Feng
P
P
Zhong
L
L
Lv
X J
XJ
Lei
B J
BJ
D000890:Anti-Infective Agents / Q000378:metabolism*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000378:metabolism*; D024841:Fluoroquinolones / Q000008:administration & dosage / Q000494:pharmacology*; D009287:Naphthyridines / Q000378:metabolism*; D015242:Ofloxacin / Q000378:metabolism*
D000890:Anti-Infective Agents; D024841:Fluoroquinolones; D009287:Naphthyridines; D015242:Ofloxacin; C055185:tosufloxacin