The Mechanism Of Plasmid-mediated Multidrug Resistance Of Enterobacteriaceae Isolated From Food-producing Animals

Bacterial resistance from food-producing animals has become a global problem.To investigate the drug resistance of Enterobacteriaceae and the transmission evolution history of the IncI-complex plasmids,a total of more than 1000 bacterial strains were isolated and identified.They were collected from the local vegetable and aquatic product markets,livestock and poultry farms.The drug resistance analysis revealed that more than 400 isolates were multidrug-resistant.Among them,four representive strains were selected for further study and the genome of one isolate was sequenced.Bioinformatic analysis of plasmids carrying resistance genes were performed,and the molecular mechanism of plasmid-mediated resistance gene transfer of Enterobacteriaceae was elucidated finally.The comparative genomics analysis of the four sequenced IncI-complex plasmids was also carried out among and the evolutionary relationship among several IncI-complex plasmids was investigated.Based on their repZ nucleotide sequences,the IncI-complex plasmids were typed into four subgroups.The present study may contribute to the control of drug resistant microorganisms,and benifit to food safety and public health.Among the many interesting findings,Proteus mirabilis F160211 and Citrobacter freundii F160188 were the first mcr-1-carring isolates found in the world.The mcr-1-harboring plasmid of Klebsiella pneumonia F160070was identified as a novel IncY-like type plasmid.The Escherichia coli F160047 strain carrying mcr-1 had been reported previously.The minimum inhibitory concentration?MIC?test and resistance gene screening showed that the four above-mentioned isolates carried multiple drug resistance genes and were resistant to several classes of antibiotics.The genome sequencing of F160070 indicated that this isolates carried three resistant plasmids,p160070-catA,p160070-MCR and p160070-CTXM.These plasmids harbored mph?A?,catA2,dfr A12,aadA2,aph?3'?-Ia,sul1,and mcr-1,and fos A14,bla_CTX-M-65,aadA22 and lnu?F?,respectively,while the chromosome carrying bla_SHV-28,fos A2,oqxB and oqxA resistance genes.Nucleotide sequence analysis of the IncI-complex plasmids repZ can reclassify them into four subgroups,namely IncI2,IncI1/B/O,IncI?/K1 and IncK2/Z.These four sequenced plasmids belong to IncI?/K1 type.All the other three plasmids except for p205880-NR2 containing none of known resistance genes,contained bla_CTXM-14/65TXM-14/65 gene in an accessory module,named“the bla_CTXM-14/65TXM-14/65 region”.Some of the plasmids contained several mobile elements and accessory modules,such as?Tn6295 and two copies of?IS26in p61806-CTXM,the MDR region in p11011-CTXM,which included three copies of the bla_CTXM-65 region,and the aacC2-tmrB region carrying aacC2and tmr B genes in p14E509-CTXM.