Abstract: Abstract Objectives: To investigate the antimicrobial resistance characteristics of shigella in Tianjin, and the mechanism of fluoroquinolone-resistance. Methods: A total of 119 clinical isolates of shigella identified in Tianjin from 2009 to 2010 were analysed by K-B disk diffusion method for their antimicrobial susceptibility. The gyrA and parC in fluoroquinolone-resistant stains and plasmid mediated quinolone resistant (PMQR) determinants (qnrA, qnrB, qnrS, aac(6’)-ib-cr and qepA) were amplified and sequenced. Conjugation test was performed for PMQR determinant positive strains. The antimicrobial-susceptibility of E.coli J53AZR was compared before and after conjugation test. Results: The susceptibility rate of 119 shigella strains to nalidixic acid was the lowest (1.72 %), followed was ampicillin (2.52 %) and sulfamethoxazole (3.36 %). There were significant differences in sensitive rates to fluoroquinolone between shigella sonnei and shigella flexneri. Five isolates of Shigella flexneri were resistant to fluoroquinolone, in which 2 isolates were resistant to ciprofloxacin, 2 isolates were resistant to levofloxacin and 4 to double mutations (gyrA83,87 and parC80).There were 3 PMQR positive strains, including 1 strain qnrS，2 strains of aac（6’）-ib-cr. E.coli J53AZR showed decreased susceptibility to many antimicrobial after conjugation. Conclusion: Shigella clinical isolates show high resistance rate to many antibiotic，but low resistance rate to fluoroquinolone (<5%). The mechanisms of fluoroquinolone resistance in shigella include both sense mutations at target enzyme in quinolone-resistance determining regions and harboring plasmid mediate quinolone-resistance gene.

Key words: shigella, fluoroquinolone, drug-resistance