Distribution of drug-resistance and mechanism of fluoroqninolones-resistance of Shigella isolates in Dali Region, Yunnan Province, China.

Objective To investigate the distribution of drug-resistance and mechanism of fluoroqninolones-resistance of Shigella isolates in Dali Region,Yunnan Province,China.Methods Fecal specimens were collected from various hospitals in Dali Region in 2010 ～ 2011,from which Shigella strains were isolated,cultured and identified for serotype.The resistances of Shigella isolates to 12 routine antibacterial drugs were analyzed by K-B agar diffusion test.The minimal inhibitory concentrations(MICs) of ceflriaxome and nalidixic acid to drug-resistant Shigella strains were determined by E-test.The gene mutations of drug-resistant strains were analyzed by PCR and DNA sequencing.The relationship between resistance to fluoroqninolones and R plasmid mediation was evaluated by R plasmid conjugation test.Results A total of 68 Shigella strains were isolated,including 41 Shigella flexner strains,25 Shigella sonnei strains and 2 Shigella boydii strains.The resistance rate of Shigella to nalidixic acid was the highest,followed by those to sulfalene and nalidixic.The Shigella isolates were relatively sensitive to ceftriaxone and cefotaxime,while showed a certain resistance to fluoroquinolones.The MICs of ciprofloxacin to Shigella strains ranged from 0.008 to 32 μg / m1.However,all the MICs of nalidixic acid to Shigella strains were more than 1 μg / m1,of which those to 4 strains more than 256 μg / m1.Substitutions of Ser83 → Leu in gyrA gene and Ser80 → Ile in parC gene were observed in 6,while those of Asp87 → Asn in gyrA gene in 2,Asp87 → Gly of gyrA gene in 2,and Gln91 → His of parC gene in 3 fluoroquinolones-resistant strains.No evidence suggested that R plasmid mediated the resistance to fluoroquinolones.Conclusion Ceftriaxone and cefotaxime were the first choice for treatment of bacterial dysentery.The fluoroquinolone-resistance of Shigella was closely associated with the mutations of gyrA and parC genes,while was unassociated with R plasmid mediation.