Genetic context diversity of plasmid-borne blaCTX-M-55 in Escherichia coli isolated from waterfowl

Abstract

The aim of this study was to explore the prevalence of blaCTX-M and elucidate the characteristics of transferable blaCTX-M-55 plasmids. Escherichia coli were isolated from 10 large-scale duck farms from nine counties and cities in Guizhou Province. They were identified, subjected to antimicrobial susceptibility testing and screened for antibiotic resistance genes. blaCTX-M-positive strains were subtyped, and blaCTX-M-55-containing strains were further analysed by multilocus sequence typing, conjugation experiments and polymerase chain reaction-based replicon typing. Three transferable plasmids were selected for whole genome sequencing sequencing and further analysis of genetic context. In total, 128 E. coli strains were identified, and 23 were blaCTX-M-positive. Subtype analysis of blaCTX-M-positive strains revealed that 23 were blaCTX-M-55 and one of the strains contained both blaCTX-M-65 and blaCTX-M-55. They were divided into 12 multilocus sequence typing types, and 6 were undetermined. blaCTX-M-55-bearing plasmids in seven were transferred to E. coli C600 at frequencies between 10-6 and 10-9, and blaCTX-M-55 was found to be located on IncN, IncFⅡ and IncFII-N fusion type plasmids. Three plasmids (IncFⅡ plasmids pEC99_Plas3 and pS1_Plas2 and IncFII-N plasmid pD2_plas2) shared a homologous region of IS26-ARGs-IS26-blaTEM-orf477-blaCTX-M-55-ISEcp1△-IS26. Our study demonstrates the environmental presence of blaCTX-M-55 harbouring E. coli in Guizhou. Analysis of the genetic context of blaCTX-M-55 aids in understanding possible dissemination routes of ESBL genes and controlling widespread antibiotic resistance.