Ceftazidime-avibactam drives mutations, insertion, or overexpression in blaKPC-2 and enhances biofilm-forming ability of KPC-producing Klebsiella pneumoniae.

Although ceftazidime-avibactam (CZA) has known effectiveness against carbapenem-resistant Klebsiella pneumoniae (CRKP), its resistance is increasingly being reported. In this study, we explored the mechanisms behind this emerging resistance in CZA-resistant strains generated from 40 clinical K. pneumoniae carbapenemase (KPC)-producing CRKP through in vitro multipassage resistance selection with 1/2 MICs CZA. Of these, 12 strains developed CZA resistance, three of which displayed increased susceptibility to carbapenems, whereas the strain C23 demonstrated heightened susceptibility to tigecycline (TGC) after CZA exposure. blaKPC-2 in strains C108 and C115 was mutated to blaKPC-33 (D179Y), whereas, in C23, it was mutated to blaKPC-136 [P173L, with a 15-amino acid insertion (YTRAPNKDDKHSEAV) after position 276]. In the remaining strains, the blaKPC-2 sequence remained intact, as assessed by RT-PCR, albeit its expression increased by over threefold. In addition, C23 exhibited enhanced biofilm-forming ability after CZA exposure, which may be closely related to the lsrR-mediated quorum-sensing (QS) system through c-di-GMP. The increased sensitivity of C23 to TGC induced by CZA may be closely related to the decreased expression of efflux pumps acrB and acrR. These findings cumulatively suggest that CZA resistance in KPC-producing K. pneumoniae may result from mutations, insertions, or overexpression in blaKPC-2. The induction of CZA may reverse the sensitivity of certain antibiotics, providing a potential combination therapy for such drug-resistant bacterial infections. The biofilm-forming ability of a strain may be enhanced after CZA induction, which improves its adaptability to the environment.