| With the widely use of antibiotics,bacterial resistance has been one of the most serious threatens to the human health in 21 century.At present,multi-drug resistant(MDR)Gram-negative bacterial infections is getting worse,especially after the emergence of the carbapenem-resistant bacterium,there is no medicine can be used for the infection by Gram-negative bacteria.Regarded as the last line to treat the MDR infections,colistin is becoming more and more significant.Before the mcr-1 was found,scholars commonly believed that colistin resistance spread mostly by chromosomal mutation and resisitant strains clone,but these two ways are not stable enough and can't transfer to other species of bacterium.In 2016,the plasmid-mediated colistin resistance gene mcr-1 was firsty found,it was also proved that this gene had spread all over the world,this situation threatened the clinical application of colistin.The aim of this study is to understand the mcr-1 prevalence in Chinese swine industry and research its communication mechanism.The main contents of this paper can be divided into the following five sections,the main contents and results are as follows.The first one is collection of swine faecal sample: strain isolation and identification.A total of 600 faecal samples were collected from 60 swine farms in 18 provinces of China.Faecal DNA was extracted and subjected to PCR screening to detect the presence of mcr-1.For further characterization of mcr-1-positive bacteria,mcr-1-positive samples from different provinces were randomLy selected for further bacterial isolation.A total of 152 mcr-1-positive E.coli strains were isolated.Then I investigaed the prevalence of mcr-1 in the Chinese swine industry: A total of 600 faecal samples DNA were screened for the presence of mcr-1 gene PCR,the result showed that the carriage rate was extremely high(457/600,76.2%),ranged from 45.0% to 100% in different provinces,which indicated that mcr-1 has been very common in Chinese swine industry.Then I investigated the resistance of mcr-1-positive strains in the Chinese swine industry: The minimal inhibitory concentrations(MICs)was took to test the resistance profiles of the 152 mcr-1-positive E.coli isolates from different provinces,susceptibility of 13 antibiotics including colistin were determined.The result showed that the 152 mcr-1-positive E.coli showed different resistance to these medicines,from the highest to the lowest was colistin(100%),tetracycline(94.74%),doxycycline(93.42%),ampicillin(79.60%),florfenicol(78.29%),and enrfloxacin(44.08%),ciprofloxacin(38.82%),ceftiofur(26.32%),cefoxitin(0.66%)and amikacin(0.66%),no resistant strain to meropenem,gentamicin and tigecycline was found.Then I researched the resistance gene mcr-1 communication mechanism between different animals in different regions: Using PFGE to analysis different swine isolate strains' homology.PFGE showed that we all gain 142 different finger types,and there is no obvious dominant clone strain.Combined with a large number of reports,the colistin resistance gene mcr-1 mainly relies on the horizontal transmission mediated by transferable elements such as plasmids and transposons in different regions.Finally I researched the resistance gene mcr-1 communication mechanism in intestinal microecological community of animals: Used “resisitant culturomics” technology isolates strains from just one swine faecal sample,a total of 245 mcr-1-positive stains were collected,and 196 strains of these were E.coli.Using PFGE to obtain 196 E.coli strains' finger types,then selecting the represent strain of each different strains and using S1-PFGE and Southern Blot to position the mcr-1.The result shows: 1.For most strains,mcr-1 are located in 5 different plasmids,one strain's locate at chromosome.2.There is dominant clone strain.This also suggested that the mechanism of mcr-1 gene transmission in the herd is not only due to plasmid-mediated lateral transfer,but also due to clonal propagation. |
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