Emergence of an ST1326 (CG258) Multi-Drug Resistant Co-harboring , ESBL Genes, and the Resistance-Nodulation-Division Efflux Pump Gene Cluster in China.

CG258 is the dominant carbapenemase-producing clone worldwide and treatment of infections caused by this clone relies largely on the last-line antibiotics, colistin, and tigecycline. However, the emergence and global dissemination of and - genes have significantly compromised their clinical applications. CG258 carrying both and - have not been reported. A colistin-resistant strain T698-1 belonging to ST1326, a member of CG258, was isolated from the intestinal sample of a patient and characterized by the antimicrobial susceptibility testing, conjugation assay, WGS and bioinformatics analysis. It was resistant to colistin, tetracycline, aminoglycoside, fluoroqinolone, phenicols, sulfonamide, and some β-lactams, and positive for , -, and ESBL genes ( and ). The - gene cluster was located in an multi-drug resistant (MDR) region flanked by Tn elements on an IncHI1B/FIB plasmid. The genetic context of - was slightly distinct from previously reported Tn-like structures, with an IS element disrupting the upstream Tn and its adjacent genetic elements. The gene was inserted into the backbone of an IncFII/FIA plasmid with the genetic context of IS---IS. To our knowledge, this is the first report of co-occurrence of and - in a CG258 strain. Though this strain is tigecycline sensitive, the acquisition of colistin and tigecycline resistance determinants by the endemic CG258 clone still poses a serious public health concern. CG258, which became resistant to multiple last resort antibiotics, would be the next emerging superbug.