Objective: Escherichia coli is a common Gram-negative human pathogen. The emergence of E. coli with multiple-antibiotic-resistant phenotypes has become a serious health concern. This study reports the whole-genome sequences of third-generation cephalosporin-resistant (3GC-R) and multidrug-resistant (MDR) E. coli EC6868 and explores the acquired antibiotic-resistance genes (ARGs) as well as their genetic contexts.
Methods: E. coli EC6868 was isolated from a vaginal secretion sample of a pregnant patient in China. The antimicrobial susceptibility was assessed, and whole-genome sequencing was conducted. The acquired ARGs, insertion sequence (IS) elements, and integrons within the genome of E. coli EC6868 were identified, and the genetic contexts associated with the ARGs were analyzed systematically.
Results: E. coli EC6868 was determined to belong to ST69 and harbored a 144.9-kb IncF plasmid (pEC6868-1) with three replicons (Col156, IncFIB_AP001918, and IncFII). The ESBL gene bla_CTX-M-27 was located on the structure “∆ISEcp1-bla_CTX-M-27-IS 903B”, which was widely present in the species of Enterobacteriales. Other ARGs carried by plasmid pEC6868-1 were mainly located on the 18.9-kb IS 26-composite transposon (five copies of intact IS 26 and one copy of truncated IS 26) composing of IS 26-mphA-mrx(A)-mphR(A)-IS 6100, ∆TnAs3-eamA-tet(A)-tetR(A)-aph(6)-Id-aph(3”)-Ib-sul2-IS 26, and a class 1 integron, which was widely present on IncF plasmids of E. coli, mainly distributed in ST131, ST38, and ST405. Notably, pEC6868 in our study was the first report on a plasmid harboring the 18.9-kb structure in E. coli ST69 in China.
Conclusion: The 3GC-R E. coli ST69 strain with an MDR IncF plasmid carrying bla_CTX-M-27 and other ARGs, conferring resistance to aminoglycosides, macrolides, sulfonamides, tetracycline, and trimethoprim, was identified in a hospital in China. Mobile genetic elements including ISEcp1, IS 903B, IS 26, Tn 3, IS 6100 and class 1 integron were found within the MDR region, which could play important roles in the global dissemination of these resistance genes.

Keywords: Escherichia coli, vaginal secretion, plasmid, bla_CTX-M-27, genetic context