Characterization of IncI1/ST71 and IncF18:A-:B1 multidrug-resistance plasmids from an avian Escherichia coli isolate.

ABSTRACT

To characterize IncI1 and IncF18A-B1 multidrug-resistance plasmids from an avian Escherichia coli isolate, antibiotic susceptibility testing, conjugation assays, transformation assays, S1-PFGE, and WGS analysis were performed. The 119,457-bp plasmid pEC014-1 with a multidrug-resistance region (MRR) containing four different segments interspersed with six IS26 elements, belonged to incompatibility group I1 and sequence type 71. The 154,516-bp plasmid pEC014-2 with two replicons, typed as FII-18 and FIB-1, carried 14 resistance determinants including blaTEM-1b, blaOXA-1, oqxAB, dfrA17, aac(6')-Ib-cr, sul1, sul2, tet(A), floR, catB3, hph(aph(4)-Ia), aacC4(aac(3)-IV), aadA5, arr-3, and a merEDACPTR loci in MRR, and additionally encoded three virulence loci iroNEDCB, sitABCD, and iucABCD-iutA. Plasmid stability assays showed that pEC014-1 and pEC014-2 were stable in recipient E. coli C600 for at least 15 days of passage. Competition assays were carried out to evaluate the fitness impact of pEC014-2 carriage in vitro, revealing a decrease in host fitness. Growth kinetics showed that the growth rate for pEC014-1 or/and pEC014-2 bearing cells was significantly slower than that of the E. coli C600 host strain in the exponential stage (p < 0.01), with only cells carrying pEC014-1 sustaining rapid growth after 6 h of exponential growth. Our findings highlight the mosaic structures of epidemic plasmid IncI1/ST71 and F18A-B1 lineages and contribute to a better understanding of the evolution and dissemination of these multidrug resistance and virulence plasmids.