| With the expansion of dairy farm scale,bacterial diseases have become the main diseases that harm animal husbandry.Escherichia coli(E.coli),the most common disease of dairy cows,brings great potential harm to animal husbandry in China.In the prevention and treatment of this disease,beta-lactam antibiotics are the first and most widely used drugs,which play an extremely important role.However,with the unreasonable abuse of this kind of drugs,the resistance of E.coli to this kind of drugs gradually aggravates,which has become a hot spot and a difficult problem that researchers around the world must solve.There are some researches show that Extended specturn β-lactamerses(ESBLs)is the main mechanism of E.coli’s resistance to beta-lactam drugs,especially the widespread abuse of third-generation cephalosporins(such as cefotaxime),which affects the detection rate of ESBLs-producing bacteria.At present,there are few studies on the epidemic distribution and transmission mode of ESBLs resistance genes E.coli isolated from dairy cows.Consequently,on the basis of the previous research,sources of E.coli to cows ESBLs resistance gene evolution study,reveal the cow source E.coli ESBLs popular distribution and transmission mode of drug resistance gene,and the main existing forms and transmission modes of ESBLs resistance genes in dairy cow derived E.coli.In this study,1950 strains of E.coli were isolated from 4536 cow source samples collected from 52 large-scale pastures in 11 regions of China,including 687 strains of milk source,1144 strains of feces source and 119 strains of other source samples.Among them,the isolation rate of dairy cow source E.coli was the highest in Beijing(38.72%)and the lowest in Liaoning(3.59%).The sensitivity test of 18 antimicrobial drug to E.coli was carried out with the agar dilution method recommended by CLSI.The results showed that the main drug resistance was ampicillin,streptomycin and doxycycline.And the drug resistance to kamikaze,ampromycin,polymyxin,imipenem and meropenem was highest sensitive.The E.coli from dairy cows in Guiyang and Ningxia were highest resistant to antibiotics.Among them,340 strains(17.44%)of strains(including 144 strains of milk sources,178 strains of fecal sources and 18 strains of other sources)of E.coli were preliminary screened for drug resistance to cefotaxime(CTX).The drug resistance rate of E.coli to CTX was higher in Guiyang(40.14%)and lower in Xinjiang(5.86%).PCR and electrophoretic analysis were used to detect and analyze ESBLs resistancegenes.The results showed that 170 strains of E.coli(including 89 strains from milk source,74 strains from feces source and 7 strains from other sources)contained at least one ESBLs gene.Among them,92 strains of E.coli detected bla CTX-M-1 gene,69 strains detected bla CTX-M-9 gene,3 strains were positive for bla CTX-M-1 and bla CTX-M-9 genes,14 strains detected bla CMY-2 gene,and 2 strains were positive for bla CTX-M-9 and bla CMY-2 genes.The detection rate of ESBLs gene was the highest in Ningxia(100%)and the lowest in Xinjiang(14.29%).The detection rate of bla CTX-M-1 gene was the highest in Ningxia(68.18%)and the lowest in Tianjin(4.35%).The detection rate of bla CTX-M-9 gene was the highest in Ningxia(31.82%)and the lowest in Xinjiang(7.14%).The detection rate of bla CMY-2 gene was extremely low,with the highest rate in Jilin(2.52%)and 0% in 6 provinces.The plasmid DNA from E.coli was extracted and transferred to DH5α cells for transformation to obtain single-purpose plasmid DNA.The results showed that E.coli with the bla CTX-M-1 gene had the highest number of transformants.Among them,the milk source E.coli with the bla CTX-M-1 gene obtained the most transformants.Fecal source E.coli with the bla CTX-M-9 gene had the highest number of transformants.E.coli from cow faecal sources that carried the bla CMY-2 gene had the highest number of transformants.In addition,electrophoretic analysis was used to detect whether the plasmid DNA of the transformed E.coli was single-purpose,and the results showed that they were all single-purpose plasmid DNA.The results of this study suggest that,E.coli from large-scale dairy cows in key areas of the country was widely found in feces.CTX-M ESBLs are mainly include CTX-M-1 and CTX-M-9. |
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