Characterization of a new transposon, Tn7772, on a novel plasmid from multidrug-resistant Escherichia coli in China

• We identified a novel transposon in module one of the MDR regions in pQL57EC-1, designated Tn7772 in the Tn Number Registry. • Tn7772 comprised a sul3-type class 1 integron and multiple drug resistance genes may be formed through the homologous recombination of Tn7772–1 with Tn7772–2. • Tn7772 has been detected both in E. coli sourced from healthy pigs and in S. enterica sourced from human patients. The emergence of multidrug-resistant (MDR) Escherichia coli causes a serious threat to human and animal health. To characterize the genetic environments of a novel plasmid pQL57EC-1 in an MDR E. coli strain QL57EC from feces of a healthy swine in China. The plasmid pQL57EC-1 was characterized by antimicrobial susceptibility testing, whole genome sequencing and bioinformatic analysis. The transferability of pQL57EC-1 was verified by conjugation experiments and transformation experiments. E. coli QL57EC carries two plasmids. pQL57EC-1 belongs to the incompatibility groups IncF-FIB/IncX1, while plasmid pQL57EC-2 belongs to the incompatibility group IncF-FIB. Notably, pQL57EC-1 was a novel plasmid, containing a novel Tn7772 transposon flanked by two copies of IS26 at both ends, which can also be found on plasmids from Salmonella enterica isolated from human feces. Conjugation assays for E. coli QL57EC were unsuccessful. However, pQL57EC-1 could be transferred into E. coli DH5α by transformation experiments. This study reported a novel plasmid pQL57EC-1 harboring a novel Tn7772 transposon from swine derived E. coli QL57EC.This finding suggests that Tn7772 may pose a threat to both human and animal health by acting as a reservoir for antibiotic resistance genes (ARGs) and facilitating cross-species transmission.