Study On The Association Of Mutations Of Efflux Pump AcrAB-TolC And Its Regulation Genes With Fluoroquinolone-resistance In Shigella

Shigella species. is the major causative agent of bacillary dysentery. Shigella infection is still the important issue of global public health. The endemic serotype of Shiglla isolated form the patients with bacillary dysentery varies with the time and geographical area. Bacterial resistance has become a significant clinical problem due to wildly use of antibiotics, and multidrug resistant Shigella has been increasing rapidly through years.Objective: To determine the major serotype of Shigella isolated from patients with bacillary dysentery over the past three years form three general hospitals in Tianjin, to investigate the state of antimicrobial resistance of Shigella strains on clinical applied antibiotics as well as the mechanism of resistance against Fluoroquinolones over the past three years form three general hospitals in Tianjin.Materials and methods: A total of 159 clinical isolated Shigella from 2009 to 2013 were collected from three hospitals in Tianjin. The serotype and subtype of Shigella were determined by serum agglutination test. We also tested the susceptibility of antibiotic by using the K-B disk diffusion method with 17 kinds of commonly used antibiotics. Five Fluoroquinolone-resistant Shigellas were selected by ciprofloxacin and levofloxacin. Moreover, gyrA、 parC,、acr A,、acrB, acrR、marOR and soxS genes were amplified and sequenced and compared our results on the gene bank..Results :There were 57 strains of Shigella flexneri and 102 strains of Shigella sonnei from the 159 tested samples. The susceptibility rates of Shigella, Streptomycin and Chlromycetin were 98.49%, 94.33%, and 93.71%, respectively. Imipenem resistant strains did not found. Among the Fluoroquinolones, the resistance rate of Ofloxacin, Ciprofloxacin and Norfloxacin were lower than 5.03%, the rate of Levofloxacin was 1.88%.gyrA and parC were positive in all tested strains. gyrA83(Ser�'Leu) and parC 80(Ser�'IIe) were found in 4 fluoroquinolones resistant strains,only parC(Ser�'IIe) was found in 1 fluoroquinolones resistant strains, 2fluoroquinolones resistant strains showed deletion of gyr A205 phenylalanine, and other 4 fluoroquinolones resistant strains showed no mutation in both gyrA and parC.Some random mutation in acrA, acrB and soxS were found in fluoroquinolones resistant strains as well as in fluoroquinolones susceptible strains. The deletion of CATT(position 36,37,38 and 39) of marOR were found in fluoroquinolones resistant strains, and did not in fluoroquinolones susceptible strains.Conclusion:The major endemic serotype of Shigella, which wrer isolated from patients with bacillary dysentery over the past three years form three general hospitals in Tianjin, is Shigella sonnei. The problem of antibiotic resistance is very serious in our district through years. The isolating rate of multidrug resistant Shigella is98.11 %.The deletion of CATT of in marOR, the regulating gene for efflux pump acrAB-tolC, may be associated with the fluoroquinolones resistance.