| Salmonellosis has always been recognized as a major public health problem worldwide.To against or treat Salmonella infections, antimicrobial agents were usually used. However,the increasing emergence of multidrug-resistant Salmonella has become worldwide health concerns over the past decades. Mutations and over expression of efflux pump genes are the main resistance mechanisms to fluoroquinolones. The main purpose of this study is to explore the variation of Salmonella under inducement of different fluoroquinolones agents and the drug resistance rate of induced Salmonella to these antimicrobial agents as well as other ones.The main results are as follows:(1) After Salmonella ATCC 14028 s was laboratory-induced with increasing concentrations of nalidixic acid, ciprofloxacin, gatifloxacin, levofloxacin and delafloxacin,antimicrobial resistance of the induced Salmonella to fluoroquinolones were all increased as well as resistance to other five classs of antimicrobial agens including amikacin, ampicillin,sulfamethoxazole, chloramphenicol and tetracycline. The minimurium inhibitory concentrations of the 7th generational strains were 64 folds to those of the original one.(2) DNA sequencing results revealed that a single mutation was found in quinolone resistance determination region(QRDR) of gyrA with the Asparticacid was substituted by Asparagine in the 83 th animo acid in GryA in the 5-7 generational nalidixic acid induced strains. No mutation was detected in the QRDR of gyrB, parC, parE. Gene mutations of QRDR were likely to be found among long-used fluoquinolones like nalidixic acid and ciprofloxacin induced Salmonella.(3) The expression level of acr A, acrB, and tolC of nalidixic acid, ciprofloxacin,gatifloxacin, levofloxacin and delafloxacin induced substrains were significantly and consistently increased compared with those of S.typhimurium ATCC 14028 s. No mutation was detected in acrA, acrB, and tolC genes in all fluoroquinolones induced strains... |
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