Molecular Epidemiology Of ESBLs-and Carbapenemases-producing Enterobacteriaceae From Retail Meat And Vegetables

With the wide use of antimicrobial agents, antimicrobialresistance among Enterobacteriaceae hasbecome aserious problem in the world. The increasingantimicrobial resistance makes the infectious treatmentno longer effective, including the third and forth generation cephalosporins as well as carbapenems, producing ESBLs and carbapenemases are the major mechanisms for Enterobacteriaceae to exhibit resistance to above-mentioned antimicrobial agents. Previous studies about ESBLs and carbapenemases mainly focus on Enterobacteriaceae from human clinics and animals, however, studies about Enterobacteriaceae from food are still rare and needed to be investigated.The aim of this study was to investigate antibiotics resistance and the dissemination of ESBLs- and carbapenemases-producing genes among Enterobacteriaceaeisolates from vegetables and retail meat, to provide a basis for the rational use of antimicrobial agents and to prevent further spread of drug resistance.395vegetables and 200 raw chiken sampleswere randomly collected from different markets and supermarkets in Guangzhou between 2014 and2015, 60 and 134 E.coliwere recovered from vegetable and meat samples,respectively.33 ESBLs-producing Enterobacteriaceaeisolates were obtained from395 vegetable samplesselected by CHROM agar plates,including12 E.coliisolates,19 Klebsiella pneumoniaeisolates, 1Enterobacter cloacaeisolates, and 1 Citrobacter freundiiisolates. Antimicrobial susceptibility test of the E.colifrom vegetables and meat were performed by the agar dilution method. Escherichia coli from raw chickenshowed higher resistance rates compared to those from vegetables. All 33 ESBLs-producing Enterobacteriaceaeisolatesshowed resistance to ampicillin and cefotaxime, more than 50% of the 33 isolates were resistant to cefquinome, tetracycline, penicillin, doxycycline, olaquindox, and cotrimoxazole. All of the33 ESBLs-producing Enterobacteriaceaeisolateswere susceptible to imipenem. Seven types of CTX-M genes were detected from 33 ESBLs-producing Enterobacteriaceae, including bla^CTX-M-3,bla^CTX-M-15,bla^CTX-M-55,bla^CTX-M-14, bla^CTX-M-24, bla^CTX-M-38 and bla^CTX-M-65, among which bla^CTX-M-55（n=7）, bla^CTX-M-15（n=10） being most dominant types. The detection ratesof CTX-M genesfrom different vegetable types were: cucumbers, 10.4%（12/115）; tomatoes, 3.3%（3/90）; lettuces, 13%（13/100）; carrots, 5.6%（5/90）.Isolate TS79harbouringblaKPC-2belonged tosequence type ST877 by multilocussequence typingwasrecoverdfromlettuces, exhibiting resistance to all tested antimicrobial agents except colistin and tigecycline.blaKPC-2was located on a non-typable plasmidof roughly54-kb.THSJ02 recoveredfrom a chicken wing samplein the supermarketwasresistant to all tested antimicrobial drugsexcept doxycycline and tigecycline. THSJ02 belonged tosequence type ST167 by multilocussequence typing. PCR and Sangersequencing confirmed that this straincarried blaNDM-9, mcr-1, fos A3, rmt B, bla^CTX-M-65 and flo R.Conjugation,S1-pulse-field gelelectrophoresis, and southern hybridization results showed thatmcr-1was located on an Inc I2 plasmid, blaNDM-9 and fos A3 were carriedby a non-typable plasmid of roughly100-kb, whereas rmt B, bla^CTX-M-65, and asecond copy of fos A3 were located on a F33:A-:B-plasmid.The results demonstrated that the potential threats from resistant Enterobacteriaceae in vegetables and animal foods could not be neglected. CTX-M enzymes distributed in Enterobacteriaceaewith CTX-M-55 and CTX-M-15 being dominant and the CTX-Mproducing Enterobacteriaceae were multidrug resistant. It was the first detection of KPCproducing Escherichia coli in vegetables, this Escherichia colistrain showed resistance to most antibiotic except colistin and tigecycline. One Escherichia coliisolate recovered from chicken meat carryingblaNDM-9 and mcr-1was resistant to carbapenem and colistin. Thus, we should pay more attention to the antibiotics resistance of foodborne Enterobacteriaceae, to prevent it from becoming one main route to spread antimicrobial resistance genes throughout the world for the sake of public health.