Emergence and Characterization of Tigecycline Resistance Gene (X4) in ST609 Escherichia coli Isolates from Wastewater in Turkey.

Emergence of pathogens harboring tigecycline resistance genes incurs great concerns. Wastewater is recognized as the important reservoir of antimicrobial resistance genes. Here we characterized the phenotypes and genotypes of bacteria carrying (X4) from wastewater in Turkey for the first time. Four (X4)-positive Escherichia coli isolates were identified and characterized by PCR, Sanger sequencing, antimicrobial susceptibility testing, conjugation assays, Illumina sequencing, nanopore sequencing and bioinformatic analysis. Four (X4)-harboring isolates were multidrug-resistant (MDR) bacteria and the (X4) gene was nontransferable in four isolates. Genetic analysis revealed that (X4) genes in four isolates were located on plasmids co-harboring two replicons IncFIA(HI1) and IncFIB(K). However, none of the four plasmids carried genes associated with horizontal transfer of plasmids. The coexistence of -bearing IncX3-type plasmid and (X4)-harboring plasmid was also found in one isolate. These findings indicate that continuous surveillance of the (X4)-bearing isolates in different environments worldwide should be strengthened. The emergence of tigecycline resistance genes in humans and animals in China seriously threatens the clinical utility of tigecycline, but the molecular epidemiology of tigecycline-resistant bacteria in other countries remained largely unknown. Therefore, it is necessary to learn the prevalence and molecular characteristics of bacteria carrying tigecycline resistance genes, particularly the mobilizable (X4), in other countries. In the study, we first described the presence and molecular characteristics of the (X4)-positive E. coli isolates from wastewater in Turkey. Four (X4)-bearing isolates belonged to ST609, an E. coli clone commonly found from humans, animals and the environment. These findings highlight the importance of monitoring the (X4) gene in different settings globally.