Deciphering KPC Variant Resistance: Cross-Resistance Mechanisms to Last-Resort Antibiotics

Klebsiella pneumoniae carbapenemase (KPC) variants, predominantly KPC-2 and KPC-3, are a significant global resistance mechanism in K. pneumoniae. KPC-2 and KPC-3 confer resistance to a broad range of β-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 237–243 loop, and the 266–275 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 Klebsiella 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 266–275 loop. Cross-resistance to FPZ was observed in five KPC variants, particularly those with mutations in the 266–275 loop, although many omega loop and 237–243 loop mutants remained susceptible to FPZ. WGS of FDC-resistant subpopulations revealed additional mutations in genes such as ompC, rpoC, dksA, and cirA.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 blaKPC, cirA, and other novel genes highlights the importance of understanding the molecular mechanisms driving resistance to develop effective therapeutic strategies.肺炎克雷伯菌碳青霉烯酶（Klebsiella pneumoniae carbapenemase, KPC）变异株，以KPC-2与KPC-3为主要类型，是肺炎克雷伯菌（Klebsiella pneumoniae）中具有重要临床意义的全球性耐药机制。KPC-2和KPC-3可介导对包括碳青霉烯类在内的广谱β-内酰胺类抗菌药物耐药，但仍对头孢他啶-阿维巴坦（ceftazidime-avibactam, CZA）敏感。近年来，新型KPC变异株不断出现，其常通过Omega环、237–243环及266–275环等关键区域的突变、插入或缺失，获得对CZA的耐药性。 本研究旨在明确上述KPC相关突变在针对最后一线抗菌药物（如头孢地尔（cefiderocol, FDC）与头孢吡肟/齐多巴坦（cefepime/zidebactam, FPZ））的交叉耐药产生过程中的作用。本研究纳入15株产KPC的克雷伯菌属临床分离株，覆盖15种不同的KPC变异株。检测的15种KPC变异株中，有12株被证实对CZA耐药。8株分离株表现出对FDC的交叉耐药，其中5株存在自发耐药亚群，包括1株最初被归类为FDC敏感的菌株。6株FDC耐药菌株在266–275环区域携带突变。5种KPC变异株表现出对FPZ的交叉耐药，尤以266–275环存在突变的菌株为甚，尽管多数Omega环与237–243环突变株仍对FPZ敏感。 对FDC耐药亚群的全基因组测序（Whole Genome Sequencing, WGS）结果显示，ompC、rpoC、dksA及cirA等基因存在额外突变。本研究证实，KPC变异株可同时对CZA与FDC产生耐药，而对FPZ的交叉耐药发生率相对较低。在未暴露于上述抗菌药物的菌株中出现交叉耐药，这一现象引发了学界对耐药性传播的担忧。对blaKPC、cirA及其他新发现基因中突变的鉴定，凸显了阐明耐药分子机制以制定有效治疗策略的重要性。