Plasmid-mediated acquisition and chromosomal integration of <i>bla</i> _CTX-M-14 in a subclade of <i>Escherichia coli</i> ST131- <i>H</i> 30 clade C1

<i>Escherichia coli</i> ST131 is a multidrug-resistant lineage associated with the global spread of extended-spectrum β-lactamase-producing organisms. Particularly, ST131 clade C1 is the most predominant clade in Japan, harboring <i>bla</i>_CTX-M-14 at a high frequency. However, the process of resistance gene acquisition and spread remains unclear. Here, we performed whole-genome sequencing of 19 <i>E. coli</i> strains belonging to 12 STs and 12 <i>fimH</i> types collected between 1997 and 2016. Additionally, we analyzed the full-length genome sequences of 96 ST131-<i>H</i>30 clade C0 and C1 strains, including those obtained from this study and those registered in public databases, to understand how ST131 clade C1 acquired and spread <i>bla</i>_CTX-M-14. We detected conjugative IncFII plasmids and IncB/O/K/Z plasmids carrying <i>bla</i>_CTX-M-14 in diverse genetic lineages of <i>E. coli</i> strains from the 1990s to the 2010s, suggesting that these plasmids played an important role in the spread of <i>bla</i>_CTX-M-14. Molecular phylogenetic and molecular clock analyses of the 96 ST131-<i>H</i>30 clade C0 and C1 strains identified 8 subclades. Strains harboring <i>bla</i>_CTX-M-14 were clustered in subclades 4 and 5, and it was inferred that clade C1 acquired <i>bla</i>_CTX-M-14 around 1993. All 34 strains belonging to subclade 5 possessed <i>bla</i>_CTX-M-14 with IS<i>Ecp1</i> upstream at the same chromosomal position, indicating their common ancestor acquired <i>bla</i>_CTX-M-14 in a single IS<i>Ecp1</i>-mediated transposition event during the early formation of the subclade around 1999. Therefore, both the horizontal transfer of plasmids carrying <i>bla</i>_CTX-M-14 to diverse genetic lineages and chromosomal integration in the predominant genetic lineage have contributed to the spread of <i>bla</i>_CTX-M-14.