Transfer Potential of Plasmids Conferring Extended-Spectrum-Cephalosporin Resistance in Escherichia coli from Poultry

Escherichia coli strains resistant to extended-spectrum cephalosporins (ESC) are widely distributed in Norwegian broiler production, and the majority harbor transferable IncK or IncI1 plasmids carrying bla(CMY-2). Persistent occurrence in broiler farms may occur through the survival of ESC-resistant E. coli strains in the farm environment, or by transfer and maintenance of resistance plasmids within a population of environmental bacteria with high survival abilities. The aim of this study was to determine the transferability of two successful bla(CMY-2)-carrying plasmids belonging to the incompatibility groups IncK and IncI1 into E. coli and Serratia species recipients. Initially, conjugative plasmid transfer from two E. coli donors to potential recipients was tested in an agar assay. Conjugation was further investigated for selected mating pairs in surface and planktonic assays at temperatures from 12°C to 37°C. Transfer of plasmids was observed on agar, in broth, and in biofilm at temperatures down to 25°C. The IncK plasmid was able to transfer into Serratia marcescens, and transconjugants were able to act as secondary plasmid donors to different E. coli and Serratia species recipients. All transconjugants displayed an AmpC phenotype corresponding to the acquisition of bla(CMY-2). In summary, the results indicate that the IncK plasmid may transfer between E. coli and Serratia spp. under conditions relevant for broiler production. IMPORTANCE Certain bla(CMY-2)-carrying plasmids are successful and disseminated in European broiler production. Traditionally, plasmid transferability has been studied under conditions that are optimal for bacterial growth. Plasmid transfer has previously been reported between E. coli bacteria in biofilms at 37°C and in broth at temperatures ranging from 8 to 37°C. However, intergenus transfer of bla(CMY-2)-carrying plasmids from E. coli to environmental bacteria in the food-processing chain has not been previously studied. We demonstrate that bla(CMY-2)-carrying plasmids are capable of conjugative transfer between different poultry-associated bacterial genera under conditions relevant for broiler production. Transfer to Serratia spp. and to hosts with good biofilm-forming abilities and with the potential to act as secondary plasmid donors to new hosts might contribute to the persistence of these resistance plasmids. These results contribute to increased knowledge of factors affecting the persistence of ESC resistance in broiler production and can provide a basis for improvement of routines and preventive measures.