Wild-type MIC Distribution and Epidemiological Cut-off Value and Resistant Characteristics of Colistin Against Escherichia Coli from Chickens

The aim of the present study was to investigate minimum inhibitory concentration （MIC） distributions by broth microdilution （BMD） method and to determine the preliminary epidemiological cut-off value （ECV） of colistin by epidemiologicalcut-off （ECOFF） finder against E.coli from chickens in China.Anal swabs were collected from chicken farms in China.BMD method was used to measure MIC50 and MIC90 of colistin which were 2 and 4 μg ? mL^-1,respectively.MIC frequency distributions for colistin were used to estimate preliminary ECV (8 μg ? mL^-1).High percentages of resistance to ampicillin （94.12%）,nalidixic acid （94.12%）,enrofloxacin （94.12%）,tetracycline （94.12%）,ciprofloxacin （88.24%）,florfenicol （88.24%）,neomycin （64.71%）,gentamicin （58.82%）,levofloxacin （58.82%）,doxycycline （88.24%） and cefalexin （76.47%） were found.In addition,low percentages of resistance to amikacin （5.88%）,spectinomycin （17.65%） and fosfomycin （41.18%） were noted.Notably,amoxicillin,sulfisoxazole and trimethoprim resulted in a 100 % resistance generation efficacy rate.Prevalence of mcr-1 in E.coli （9/17） in chromosomal DNA was higher than mcr-4 （2/17） gene,and mcr-1 （5/17） was higher than mcr-4 （3/17） in plasmid.