Abstract:

Objective     To study and discriminate the resistance and tolerance of P.aeruginosa to ciprofloxacin. Methods      MICs of fluoroquinolones against 33 strains of P.aeruginosa, isolated from farm and hospital together with P.aeruginosa ATCC 27853 and its high resistant mutant strain PA34 consecutively induced by ciprofloxacin and cefotaxime in vitro, were determined with broth microdilution method.Among the clinic strains,  and five multi-drug resistant strains were selected for the following study. The resistance-determining region (QRDR) was sequenced to determine the mutations for fluoroquinolone resistance. The activities of the efflux pump in different resistant phenotypes of P.aeruginosa were detected by fluorescent colorimetric method, also mRNA expression of the efflux pump, the transmembrane transporter protein and fluoroquinolones target enzymes were detected by the fluorescence quantitative PCR method.  Result    Compared with that of ATCC 27853, the activities of the efflux pumps of the five clinic resistant strains of P.aeruginosa remarkably increased(P＜0.01)， and efflux pumps and fluoroquinolones target enzymes were overexpressed while mRNA expression of the trans-membrane transporter protein comparatively declined. There was a point-mutation in gyrA at Thr83→Ile for each of the five resistance phenotypic strains. However, their MICs were far below that of the induced super high-esistant mutant strain PA34 in which the gyrA mutation occurred at Thr-83→Ile, parC mutations occurred at Glu-84→Gln、Gln-91→Lys and mRNA expression of the transmembrane transporter protein declined in the extreme.    ConclusionTo resist fluoroquinolones, P.aeruginosa can develop any possible  phenotype, which can be genitically disciiminated as resistance(gyrA, parC mutation) or tolerance(adaptive expression of efflux pumps protein, the tran-smembrane transporter protein and fluoroquinolones target enzymes).  The new evolutionary taxonomy facilitates the focus on the simplex study of resistance mutation.

Key words: Pseudomonas aeruginosa；  Fluoroquinolones； Resistance； Tolerance