Abstract: Abstract: Objective To investigate the role of AcrAB-TolC efflux pump in fluoroquinolones resistance by Shigella. spp and to explore the significance of AcrAB-TolC efflux pump on mutation of acrR, soxS and marOR as well as on drug re⁃ sistence. Methods Drug resistant bacteria were selected by Kirby-Bauer disk diffusion test. After addition of efflux pump inhibitor carbonylcyanide-m-chlorophenylhydrazone (CCCP), change of minimal inhibitory concentration (MIC)s of nilidixic acid, Levofloxacin, ofloxacin, ciprofloxacin and Norfloxacin were examined. The DNA binding region of acrA, acrB, soxS, acrR and marOR gene in these mutants were amplified by PCR and sequenced. Results Among the 159 clinical isolates of Shigella，11 strains are resistant to fluoroquinolone. After the addition of CCCP, MICs of 2 fluoroquinolone resistant strains decreased; the MICs of 7 fluoroquinolone resistant strains did not change; MICs of 2 fluoroquinolone resistant strains in⁃ creased. The corresponding nucleotides C, A, T, T on the 36th to 39th of marOR gene were missing, showing by sequencing, in fluoroquinolone resistent strains which might be regulated by the efflux pump gene AcrAB-TolC. Conclusion Efflux pump inhibitor could restrain the activity of efflux partially. The mutations of marOR might play an important role in fluoroquino⁃ lone resistent by shigella.

Key words: shigella, quinolones, drug resistance, bacterial, AcrAB-TolC efflux pump, marOR, carbonylcyanide-mchlorophenylhydrazone (CCCP)