Beneficial Chromosomal Integration of the Genes for CTX-M Extended-Spectrum β-Lactamase in for Stable Propagation.

The acquired CTX-M-type extended-spectrum-β-lactamase (ESBL)-producing are of great concern in clinical settings because they limit therapeutic options for patients infected by the pathogens. An intriguing clonality of CTX-M ESBL-producing blood isolates was observed from a national cohort study, and comparative genomics were assessed for the 115 blood isolates carrying the gene. The plasmid preference of particular clones of a sequence type (ST) was assessed by liquid mating. A quarter of the gene-carrying blood isolates harbor the gene in their chromosome, and most of those with the built-in gene belonged either to ST307 or ST48. Notably, all 16 ST48 isolates harbored two copies of the gene in the chromosome. The chromosomal integration of the gene was mostly derived from the IS-targeting 5-bp AT-rich locus in the chromosome. The IS-mediated chromosomal integration occurred when the upstream IS from the gene was truncated, targeting the anchor IS copy in the chromosome. Higher transfer efficiency of the gene-carrying FIA:R plasmid was observed in ST17 than that of the gene-carrying FIB:FII plasmid. The transfer efficiency of the plasmid differed by isolate among the ST307 members. The clones ST307 and ST48 harboring the gene in the chromosome were able to disseminate stably in clinical settings regardless of the environmental pressure, and the current population of blood isolates was constructed. Further follow-up is needed for the epidemiology of this antimicrobial resistance. Dominant F-type plasmids harboring the gene have been pointed out to be responsible for the dissemination of the CTX-M extended-spectrum-β-lactamase (ESBL)-producing Recently, the emergence of isolates with the gene in their chromosomes has been reported occasionally worldwide. Such a chromosomal location of the resistance gene could be beneficial for stable propagation, as was the ST191 harboring chromosomal that is endemic to South Korea. Through the present study, particular clones were identified as having built-in resistance genes in their chromosomes, and the chromosomal integration events were tracked by assessing their genomes. The cefotaxime-resistant clones of this study were particularized as results of the fastidiousness for plasmids to acquire the gene for securing the diversity and of the chromosomal addiction of the gene for ensuring propagation.