The Detection Of Plasmid-Mediated Mcr-1 And ESBLs Genes In Escherichia Coli Isolates From Food Animals In Sichuan Province

Escherichia coli?E.coli?is one of the most common pathogenic bacteria in veterinary clinical.With the wordwide use of antimicrobial agents,multi-drug resistant E.coli has increasing rapidly.The epidemic of plasmid-mediated colistin resistant gene mcr-1,particularly withincreasing prevalence of Extended-spectrum?-lactamases?ESBLs?producing strains has become a major threat to public health and veterinary.Therefore,the detection of E.coli resistance and research of molecular epidemiological of resistant genes have become urgent tasks.A total of 621 E.coli strains were isolated from animals in different farms of Sichuan province during 2008 to 2017 year.The MICs of 10 antimicrobials were determined by broth microdilution method.The results showed that the resistant rates of tested strains were between 27.5%⁹5.2%.Magnitude of resistant rates to E.coli isolated from 2008²017 were 12.2%⁴9.5%.More than 60%strains showed resistant to at least 5antimicrobials.Resistance rates of most antimicrobials to E.coli isolated from poultry?20.3⁹4.9%?were higher than them from swine?18.5%⁹5.8%?.The seriouscross resistance was showed between?-lactams?28.9%¹00%?as well as between colistin and?-lactams?47.8%⁹9.4%?.The results of detection of mcr-1 and ESBL genes in 621 E.coli strains show that the positive rates of mcr-1 and ESBL geneswere 22.1%?137/621?and 42.5%?264/621?,The genotypes of ESBL were bla_TEM?60.6%,160/264?,bla_CTX-M-1TX-M-1 group?50.0%,132/264?,bla_CTX-M-9TX-M-9 group?17.0%,45/621?and bla_OXA?3.4%,9/264?genes respectively,which were dominanted by blaTEM-1,blaCTX-M-55,blaCTX-M-65 and blaCTX-M-14.The blaCTX-M-2 group,bla_CTX-M-8/25 group and bla_SHV genes were not detected.MoreESBL variants were observed in E.coli isolated from poultry which had higher positive rates of mcr-1?27.3%?and ESBL genes?51.3%?than other animals.66.4%?91/137?mcr-1-positive E.coli harbored ESBL genes which were significantly higher than mcr-1-negetive E.coli which was 35.7%?173/484?.Conjugation experiment and ERIC-PCR were carried out among mcr-1-positive E.coli,which for evaluated horizontal transmissibility and genetic background of E.coli.The results show that mcr-1-positive plasmids could successfully transferred to recipient strains by conjugation,which conjugation rate was 47.1%?65/137?.And the resistant rates to transconjugants were 33.8%¹00%.88.5%transconjugants harbored at least one plasmid was>15kb in size.41.5%?27/65?transconjugants harbored bla _TEM and bla_CTX-MTX-M genes.The results of ERIC-PCR showed that 22 genotypes were detected in selected E.coli strains,which indicated that E.coli with the same resistant genes were different in genetic background.In conclusion,the resistance of E.coli isolates from food-producing animal of Sichuan province were in severe cases,and the cross resistance to different antimicrobials were obviously.The prevalent of resistant genes were on the rise with time,in which the spread of mcr-1 gene showed low-level and ESBLs gene showed high-level respectively.More complicated resistant phenotypes and genes were detected in the E.coli isolates from poultry.Mcr-1-positive E.coli isolates showed higher positive rate of ESBLs genes,and more serious resistant phenotypes.The mcr-1 and ESBLs genes were spread in complex genetic background and dominated by horizontal transmission.