High frequency of virulence genes among Escherichia coli with the blaCTX-M genotype from diarrheic piglets in China.

The purpose of this study was to characterize the virulence potential and determine the molecular epidemiology of extended-spectrum β-lactamases (ESBLs) in CTX-M-producing Escherichia coli isolated from piglets with diarrhea in China. A total of 62 E. coli isolates were obtained among which 49 and 13 were collected from diarrheic and healthy piglets, respectively. Cefotaxime resistant strains were screened for the presence of ESBL, adhesin and exotoxin genes as well as for their biofilm-forming ability. Characterization of blaCTX-M plasmids was determined by conjugation along with the determination of genetic relatedness and plasmid replicon type. CTX-M producers were found in 36 isolates with 6 different subtypes: blaCTX-M-14,27,65 from CTX-M-9G (n=27) and blaCTX-M-55, 15,79 from CTX-M-1G (n=22). This also included 13 isolates that carried two different CTX-M genes. Thirty of 36 CTX-M producers and 12 of 13 multiple CTX-M alleles were confirmed from diarrheic piglets. The presence of the iron regulatory gene irp2 as well as EAST1 was found in 83.3% (25/30) of CTX-M-producing isolates from diarrheic piglets and these were significantly better biofilm formers. PFGE profiles of CTX-M-positive isolates indicated the spread of multidrug resistance was primarily horizontal and spread via transferable plasmids. Most blaCTX-M-9G genes (10/17) were located on the IncFIB type plasmid with sizes of 40-145 kb, while the blaCTX-M-1G (11/16) genes were located on the ∼ 100 kb IncN-type plasmid. Together, our findings demonstrate that CTX-M ESBL-producing E. coli from diarrheic piglets were associated with serious multidrug resistance, increased biofilm-forming ability and the irp2 gene of HPI. Our findings highlight the need to urgent control the spread of resistant strains through food chain.