Molecular Characteristics Of Plasmid-mediated ESBLs Genes In Escherichia Coli Isolated From Animals, Retail Meat And Humans

Resitance to extended-spectrum cephalosporins in Gram-negetive bacteria is mainly caused by extended-spectrum ?-lactamases?ESBLs? and plasmid-mediated AmpC ?-lactamases?p AmpC?. CTX-M-producing Escherichia coli can hydrolyze extended-spectrum cephalosporins. Escherichia coli carried the ESBLs genes in food and animal sources can be transfered to human directly or indirectly by food chain, which could quicken the transmission of ESBL genes and pose great threat to human and animals healthy. The aim of this study was to compare the molecular characterization of ESBL-producing E. coli isolates of different origins, so as to provide a basis for risk evaluation of the use of cephalosporins in food animals.931 cefotaxime-non- susceptible strains were isolated from different sources?animal, food and human? in Guangzhou during 2010-2014. Genes encoding CTX-M, SHV, CMY, and DHA enzymes were analyzed by PCR amplification and sequencing among the 931 E. coli isolates. The results showed that 92.8%?864/931? of the isolates carried bla_CTX-M?blaSHV?blaDHA and/or blaCMY genes, with bla_CTX-M-14?251??bla_CTX-M-55?150? and bla_CTX-M-65?124? be the most predominant genes. Also 73 isolates carried bla CMY gene. bla _CTX-M-1G ?bla CMY?bla _CTX-M-55 and bla_{CTX-M-24 a} were most prevalent in animal origin strains, followed by food origin isolates and human origin isolates.The prevalence of bla_CTX-M and bla_CTX-M-65 genes were detected highest in food original strains, which could illustrate meat food were seriously contaminated by drug-resistant strains. bla_CTX-M-14 and bla_CTX-M-15 genes were detected highest in human strains, followed by animal isolates and food isolates.Antimicrobial susceptibility testing of the 931 isolates to 20 antimicrobial agents was performed with the agar dilution method. The results showed most of the isolates?>70%? showed resistance to ampicillin, cefotaxime, streptomycin, sulfamethoxazole/trimethoprim and tetracycline. All of the isolates were susceptible to imipenem. Isolates of different sources showed different resistance patterns.Pulsed field gel electrphores?PFGE? and phylogenetic group methods to analysis the polygenentic and clonal relationship of 100 bla_CTX-M-55 positive isolates. Most of _CTX-M-55-producing E. coli isolates belong to phylogenentic group A?45.0%?,none belong to B2 group. PFGE typing revealed that most bla_CTX-M-55 positive E. coli clonally unrelated.Conjugation and transformation experiments were performed to determine the transferability of bla_CTX-M-55 genes. 60 out of 100 transconjugants/transformants were obtained. PCR based plasmid replicon typing results showed that most of bla _CTX-M-55-positive plasmids from animal isolates belong to Inc FII, while most bla _CTX-M-55-positive plasmids from human and food isolates belonged to Inc FII and Inc I1.In conclution, E. coli carried ESBLs genes were widely spread in human, animal and animal foods. The spread of bla_CTX-M-55 gene was mainly caused by horizonal transmission of Inc FII plasmids, indicating the possibility of the transfer of bla_CTX-M-55 gene by food chain.