Epidemiology Of Antibiotics Resistance Among Escherichia Coli Isolates From A Chicken Farm And Its Surrounding Environment In Guangdong

In scale farming,the increasing use of antimicrobial agents promotes the emergence of antimicrobial resistance in Escherichia coli that brings great challenges to clinical treatment.Antibiotic-resistant bacteria genenated in the farms may be deposited into the surrounding environment,polluting the water and crops.In this paper,we investigated the molecular epidemiology of antimicrobial resistance and associated resistance genes among E.coli in a chicken farm and its surrounding environment in Guangzhou in order to offer guidance for the rational use of antibiotics in chicken farms and to provide a theoretical basis for exploring the transmission route of E.coli resistance.During 2016-2017,329 and 36 E.coli isolates were collected from 440 chicken fecal samples and 108 drinking water samples,respectively,in a chicken farm in Guangzhou.From the fish pond and vegetable field near the chicken farm,7,13,13 and 7 E.coli isolates were recovered from 35 fish pond sludge samples,27 pond water samples,60 vegetable samples and 17 vegetable soil samples,respectively.In addition,from a farmland far away from the chicken farm in Guangzhou,12,11,5 and 2 E.coli isolates were collected from 30pond water samples,22 soil samples,5 suldge samples and 15 vegetable samples,respectively.Antimicrobial susceptibility testing of E coli isolates were determined with the agar dilution method.For chicken fecal E.coli isolates,the resistance rates of ampicillin,streptomycin,tetracycline and cotrimoxazole were all higher than 90%,and the resistance rate of cefquinoxime and cefotaxime was 65.05%and 74.47%,respectively,but they were all sensitive to cefoxitin.Strains collected from chicken drinking water samples presented similar antimicrobial resistance as fecal samples,except that their resistance to cephalosporins is more serious.For,the resistance rates of isolates from the environment near the farms were lower than those of E.coli strains of chicken sources,but they were significantly higher than those of E.coli strains from the farmland far away from the chicken farm.All strains were sensitive to imipenem.The presence of bla _{CT X-M-1G},bla_{CT X-M-9G},mcr-1,floR,oqx AB,bla_CMY-2,rmt B and fosA3 were detected by PCR amplification and sequencing.The results showed that 157strains,including 144 strains obtained from chicken farm and 13 strains isolates from the environment near the chicken farm,were for bla_{CT X-M-1G}.Among them,bla_{CT X-M-55}demonstrated the highest detection rates?133?,followed by bla_{CT X-M123}?17?,bla_{CT X-M-64}?6?and bla_{CT X-M-3}?1?.93 isolates,including 92 chicken farm original strains and 1 strain from the environment near the farm,were positive for bla_{CT X-M-9G},consisting of 44 bla_{CT X-M-14}and 46 bla_{CT X-M-65};In addition,there were 46 mcr-1 positive strains,317 flo R positive strains,21 oqx AB positive strains,2 bla_CMY-2 positive strains,40 strains of rmt B positive strains and 66 fosA3 positive strains were detected.The clonal relationship of bla_{CT X-M-55} and bla_{CT X-M-123} positive E.coli isolates was determined by pulsed-field gel electrophoresis?PFGE?.A total of 64 bla_{CT X-M-55} and 17bla_{CT X-M-123} positive E.coli strains were randomly selected for PFGE analysis.Seventy-two strains were successfully typed but 9 strains failed.The 58 bla_{CT X-M-55} positive isolates had40 different PFGE types while the 14 bla_{CT X-M-123} positive E.coli strains were divided into8 different PFGE types.These results indicated the presence of clonal transfer of bla_{CT X-M-55} and bla_{CT X-M-123} positive E.coli strains between chicken farm and the environment.In summary,the antimicrobial resistance of E.coli obtained from chicken farm is very serious,in particular,the resistance rates of third-generation cephalosporins were more than70%.The bla_{CT X-M-55} gene is the most prevalent ESBLs gene in the farm and its surrounding environment.At the same time,we should monitor and control the dissemination of bla_{CT X-M},fosA3,floR and other drug-resistant genes in the chicken farm and its surrounding environment,and use antimicrobial drugs scientifically and rationally to prevent the spread of drug-resistant bacteria.