The Research On The ?-Lactams Antibiotic Resistance Among Escherichia Coli From Chicken Broilers

The widespread use of antibiotics lead to antimicrobial resistance which renders antibiotics ineffective when human treat diseases with it.This has become a major threat to human health that has been widely acknowledged by scientists and.Of all the antibiotics,p-lactams received the most attention,not only because that the first discovered antibiotic penicillin is a ?-lactam,but also because that P-lactams(including cephalosporins and carbapenems)are still the most frequently prescribed antibiotics today.And Escherichia coli is one of the most important food pathogens that may lead to gastrointestinal and urinal track infections.The treatment of E.coli infection involves the use of antibiotics,but the rise of antimicrobial resistance in E.coli has hampered these efforts in recent years.In this work,we performed surveillance of resistance in E.coli isolated frombroiler chicken from China against the most common antibiotics ?-lactams,and performed further investigations on the mechanism and spread of ?-lactam resistance.Antimicrobial resistance profiles of 14 antibiotics for these strains were determined by the disk diffusion method.Nearly every strain was shown to be multi-drug resistant,and most of these strains were resistant to 10-13 antibiotics.For ?-lactams,almost 80%of the strains were resistant to at least 3 ?-lactams out of the 5 ?-lactams tested,while only 4 strains were sensitive to all p-lactams tested.These resuLts clearly suggested the strong antimicrobial resistance of these strains isolated from broiler chicken,particuLarly to ?-lactams.Furthermore,Integrons are important mobile genetic elements that were known to participate in the mobilization and transfer of antibiotic resistance genes.Among the 158 isolates,class 1 and 2 integrons were identificated in 135(85.44%)and 29(18.35%)isolates,respectively,while no class 3 integrons were detected.7 types of gene cassette arrays were identificated in the variable region of class 1 integrons:dfrA17-aadA5,derA12-orfF-aadA2,dfrAl-aadAl,catB3-arr3,aacA4-cmLA1-variant,dfrA17-aadA5/aacA4-cmLAl-variant,While only one type of class 2 integrons(dfrAl-sat2-aadAl)was identified.Further survey of ?-lactamase-coding genes showed that blaTEM(81%)and blaCTX-M(86.7%)genes that encode Class A ?-lactamases are widespread,although only blaeCTX-M was found statistically significantly correlated with ?-lactam resistance.A more detailed typing of the blaCTX-M.showed that 77 strains harbor blaCTX-M-1 and 60 strains harbor blaCTX-M-9.Of the blacTx-M-1 harboring strains,the majority(n=70)harbor the blaCTX-M-55 subtype and only 7 strains harbor the blaCTX-M-123 subtype.The blacrx-M-9 genes can be classified into the blaCTX-M-65(n=35),blaCTX-M-4(n=18)and blaCTX-M-27(n=7)subtypes,respectively.The AmpC type ?-lactamase-encoding blaCMY was found in 5 strains.They were all classified into the blaCMY-2 subtype.Although the blaCTX-M genes were highly homologous,they apparently lead to different levels of resistance against different ?-lactams.The blaCTX-M-55 gene leads to strong resistance against AMC,AMP,CAZ,CTX and CPE.The blaCTX-M-14,blaCTX-M-65 and blaCTX-M-123 genes lead to resistance against AMC,AMP,CTX,CPE,but not CAZ.The blaCTX-M-27 gene leads to strong resistance against AMC,moderate resistance against AMP and CTX,but not other ?-lactams.More investigations on the mobile genetic element integron showed that integrons are frequently observed in the E.coli strains,but the conjugative transfer of integrons is unlikely the cause for the spread of P-lactam resistance.Among the 158 isolates,the success rate of conjugative transfer of P-lactam resistant genes is higher than plasmid-mediated quinolone resistance genes and class 1 integrons?class 2 integrons.Finally,we performed mechanistic investigations on blaCMY-2 found on 5 isolated E.coli strains,and discovered a novel synergistic effect of blaCMY-2 together with blaCTX-M on the resistance of imipenem.These results provides evidence on the high prevalence of p-lactam resistant E.coli in meat products that could be a public health threat,identified the role of integrons in the spread of ?-lactam resistance among E.coli in broiler chicken,and lead to the discovery of alternative approaches for carbapenem resistance besides the use of carbapenemases such as blaNDM-1.These findings provide the basis for further mechanistic investigations,and serve to enhance food safety and finding solutions for antimicrobial resistance.