Emerging Resistance to Novel b-Lactam b-Lactamase Inhibitor Combinations in Klebsiella pneumoniae bearing KPC Variants

<p><em><span><span>Klebsiella pneumoniae</span></span></em><span><span>&nbsp;carbapenemase (KPC) variants, predominantly KPC-2 and KPC-3, are a significant global resistance mechanism in&nbsp;<em><span>K. pneumoniae</span></em>. KPC-2 and KPC-3 confer resistance to a broad range of &beta;-lactams, including carbapenems, while remaining susceptible to ceftazidime-avibactam (CZA). Lately, new KPC variants have emerged and developed resistance to CZA, often through mutations, insertions, or deletions in key regions such as the Omega loop, the 237&ndash;243 loop, and the 266&ndash;275 loop. In the present work we aim to understand the role of these mutations in KPC in the emergence of cross-resistance to last-resort antibiotics like cefiderocol (FDC) and cefepime/zidebactam (FPZ). Fifteen clinical isolates of KPC-producing&nbsp;<em><span>Klebsiella</span></em>&nbsp;spp. were analyzed, representing 15 distinct KPC variants. CZA resistance was confirmed in 12 of the 15 KPC variants tested. Cross-resistance to FDC was observed in eight isolates, with five of these exhibiting spontaneous resistant subpopulations, including one originally categorized as FDC-susceptible. Six FDC-resistant strains carried mutations in the 266&ndash;275 loop. Cross-resistance to FPZ was observed in five KPC variants, particularly those with mutations in the 266&ndash;275 loop, although many omega loop and 237&ndash;243 loop mutants remained susceptible to FPZ. WGS of FDC-resistant subpopulations revealed additional mutations in genes such as&nbsp;<em><span>ompC</span></em>,&nbsp;<em><span>rpoC</span></em>,&nbsp;<em><span>dksA</span></em>, and&nbsp;<em><span>cirA</span></em>.<br>This study demonstrates that KPC variants show resistance to both CZA and FDC, with cross-resistance to FPZ observed to a lesser degree. The emergence of cross-resistance in strains that had not been exposed to these antibiotics raises concerns about the spread of resistance. The identification of mutations in&nbsp;<em><span>bla</span></em>_KPC,&nbsp;<em><span>cirA</span></em>, and other novel genes highlights the importance of understanding the molecular mechanisms driving resistance to develop effective therapeutic strategies. </span></span></p>