Analysis of the upstream genetic structures of the ISEcp1-bla_CTX-M transposition units in Escherichia coli isolates carrying bla_CTX-M obtained from the Indonesian and Vietnamese communities

Extended spectrum β-lactamase (ESBL)-producing Escherichia coli have been found in healthy individuals in Indonesia and Vietnam. The ISEcp1-bla_CTX-M transposition unit of ESBL-producing bacterial isolates has been considered responsible for the production of CTX-M type ESBL and it is important for the dissemination of bla_CTX-M . This study aimed to characterize the upstream genetic structure (UGS) of E. coli isolates possessing bla_CTX-M-1 group and/or bla_CTX-M-9 group genes obtained from healthy individuals in Indonesia and Vietnam. A total of 501 CTX-M type ESBL-producing E. coli isolates possessing bla_CTX-M-1 group and/or bla_CTX-M-9 group genes were obtained from healthy individuals of the two countries in 2018. The UGSs of the ISEcp1-bla_CTX-M transposition unit of the 501 ESBL-producing E. coli isolates were amplified by barcode-adaptor-ligation-mediated PCR and analyzed using the Nanopore sequencer. The obtained sequence information was used to classify the UGSs of the ISEcp1-bla_CTX-M transposition unit. From the 501 ESBL-producing E. coli isolates, 502 UGSs were obtained, which were classified into 85 UGS types based on the sequence. ISEcp1 of 359 (71.5%) of the 502 UGSs was disrupted by gene insertion, and ISEcp1-bla_CTX-M transposition unit of most (87.1%) of the determined UGSs was confirmed as plasmidic. Only 6 (7.1%) of the 85 UGS types were common to both countries. Our results indicated that many different UGSs of ISEcp1-bla_CTX-M transposition units were detected in Indonesia and Vietnam; hence, we suggest that structurally different kinds of plasmids harboring bla_CTX-M were separately distributed in the two countries.