Evolution of ceftazidime-avibactam resistance driven by mutations in double-copy to during treatment of ST11 carbapenem-resistant .

UNLABELLED

carbapenemase (KPC) variants can contribute to resistance to ceftazidime-avibactam (CZA) in (KP). However, two-copy KPC variant-mediated resistance to CZA has rarely been reported to date. Here, we aimed to clarify the evolutionary trajectory of CZA resistance driven by mutations in double-copy to carried by the tandem core structure (IS-IS-IS) during treatment of ST11 carbapenem-resistant (CRKP). The CZA-resistant KP strain carried double-copy , a variant with alanine-threonine and aspartate-tyrosine substitutions at Ambler amino acid positions 172 (A172T) and 179 (D179Y) of . Clone experiments confirmed that, compared with that of the wild-type clone strain, the minimum inhibitory concentration of CZA increased 16-fold in the -mutant strain. Furthermore, protein structure analysis revealed the A172T and D179Y mutations of can have a direct effect on the binding affinity of CAZ and AVI for KPC. Sequence comparison revealed that was mutated in a double-copy format upon CZA exposure, which was carried by the IS-mediated tandem core structure IS-IS. This tandem core structure apparently evolves during infection, although not by self-transferring, and multiple IS-IS copy numbers could mediate transferable CZA resistance upon mobilization. In addition, compared with the wild-type gene, the gene had no fitness cost. In summary, our study highlighted the emergence of CZA-resistant variants in the ST11 clone and the presence of a double-copy in the IncFII-type plasmid, which is carried by a tandem core structure (ISIS-IS-IS).

IMPORTANCE

To date, ceftazidime-avibactam (CZA) resistance caused by double-copy carbapenemase (KPC) variants has not been elucidated. The multicopy forms of carbapenem resistance genes carried by the same plasmid are relatively rare in most carbapenem-resistant . In this study, we elucidate the evolutionary trajectory of CZA resistance in ST11 carbapenem-resistant harboring a double-copy blaKPC and provide new insights into the mechanisms of acquired resistance to CZA.