The emergence of blaCTX-M-15-carrying Escherichia coli of ST131 and new sequence types in Western China

Background: bla(CTX-M-15), the most widely distributed gene encoding extended-spectrum beta-lactamases globally, was not common in China. This study was performed to characterize bla(CTX-M-15)-carrying Escherichia coli in western China. Findings: Out of 144 Escherichia coli isolates from 20 hospitals in western China, 8 were found carrying bla(CTX-M-15). bla(CTX-M-15) was carried by isolates of ST131and 5 new STs (ST3342, ST3513, ST3516, ST3517 and ST3518). The 5 new STs shared 5 identical alleles out of 7 but only had up to 2 alleles identical to ST131. blaCTX-M-15 was located on plasmids of IncI1 (ST16) or IncFII-related group (four replicon types). The co-transfer of a few antimicrobial resistance genes including qnrA, qnrB, qnrS, qepA, aac (6')-Ib-cr, aac (3)-II, tetA, bla(TEM) and bla(OXA-1) with bla(CTX-M-15) were examined but only bla(TEM-1) was found co-transferring with bla(CTX-M-15). Conclusions: Five new STs of E. coli and three new types of IncFII-related plasmids carrying bla(CTX-M-15) were identified. This study together with several reports suggested that bla(CTX-M-15) has emerged in China and the interruption of both vertical and horizontal transmission of bla(CTX-M-15) is required to hurdle its further spread.