IAME, UMR 1137, INSERM, Université de Paris, AP-HP, France.
IAME, UMR 1137, INSERM, Université de Paris, AP-HP, France; Laboratoire de Microbiologie, Hôpital Robert Debré, AP-HP, 75019 Paris, France.
Clin Microbiol Infect. 2021 Aug;27(8):1172.e7-1172.e10. doi: 10.1016/j.cmi.2021.04.016. Epub 2021 Apr 26.
Ceftazidime-avibactam (CZA) and cefiderocol are recently commercialized molecules active against highly drug-resistant bacteria, including carbapenem-resistant members of the Enterobacteriaceae. Mutants resistant to CZA have been described, notably in Klebsiella pneumoniae carbapenemase (KPC) producers. Considering the structural similarities between ceftazidime and cefiderocol, we hypothesized that resistance to CZA in KPC-producing members of the Enterobacterales may lead to cross-resistance to cefiderocol.
CZA-resistant mutants from three clinical isolates of the Enterobacterales carrying either bla or bla were selected in vitro. Mutants with increased MIC to CZA compared to the ancestral allele were cloned in a pBR322 plasmid and expressed in Escherichia coli TOP10. We evaluated the impact of these mutations on cefiderocol MICs and minimal bactericidal concentrations (MBCs), and we assessed the impact of bacterial inoculum size on cefiderocol MICs.
We used 37 KPC mutants with increased CZA MICs. Of these, six have been described previously in clinical isolates. Compared to the wild-type alleles, increases in the cefiderocol MICs of 4- to 32-fold were observed for 75.6% of tested mutants (28/37), MICs reaching up to 4 mg/L in E. coli TOP10 for KPC-31 (D179Y-H274Y mutations). MBCs and MICs of cefiderocol were similar, confirming the bactericidal activity of this drug. Finally, when using higher inocula (10 CFU/mL), a large increase in cefiderocol MIC was observed, and all isolates were categorized as resistant.
We observed that most of the CZA-resistant KPC variants have a possible impact on cefiderocol by increasing the cefiderocol MICs. In addition, cefiderocol is greatly impacted by the inoculum effect, suggesting that precautions should be taken when treating infections with a suspected high inoculum.
头孢他啶-阿维巴坦（CZA）和头孢地尔可用于治疗多种耐药菌，包括产碳青霉烯酶的肠杆菌科细菌。已经描述了对 CZA 耐药的突变体，特别是在产肺炎克雷伯菌碳青霉烯酶（KPC）的细菌中。鉴于头孢他啶和头孢地尔结构相似，我们假设产 KPC 的肠杆菌科细菌对 CZA 的耐药性可能导致对头孢地尔的交叉耐药性。
从携带 bla 或 bla 的 3 株肠杆菌科临床分离株中筛选出体外 CZA 耐药突变株。将与野生型等位基因相比 MIC 升高的突变株克隆到 pBR322 质粒中，并在大肠杆菌 TOP10 中表达。我们评估了这些突变对头孢地尔 MIC 和最小杀菌浓度（MBC）的影响，并评估了细菌接种量对头孢地尔 MIC 的影响。
我们使用了 37 株 CZA MIC 升高的 KPC 突变株。其中，有 6 株在临床分离株中已有报道。与野生型等位基因相比，75.6%（28/37）的测试突变株对头孢地尔 MIC 升高 4-32 倍，大肠杆菌 TOP10 中 KPC-31（D179Y-H274Y 突变）的 MIC 最高可达 4mg/L。MBC 和头孢地尔 MIC 相似，证实了该药物的杀菌活性。最后，当使用更高的接种量（10 CFU/mL）时，头孢地尔 MIC 显著升高，所有分离株均被归类为耐药。
我们观察到，大多数 CZA 耐药的 KPC 变体可能通过增加头孢地尔 MIC 对头孢地尔产生影响。此外，头孢地尔受接种量效应的影响很大，这表明在治疗疑似高接种量感染时应谨慎用药。
