Resistance mechanisms of Pseudomonas aeruginosa to ceftolozane/tazobactam (C/T) were assessed on a collection of 420 nonredundant strains nonsusceptible to ceftazidime (MIC > 8 μg/ml) and/or imipenem (>4 μg/ml), collected by 36 French hospital laboratories over a one-month period (the GERPA study). Rates of C/T resistance (MIC > 4/4 μg/ml) were equal to 10% in this population (42/420 strains), and 23.2% (26/112) among the isolates resistant to both ceftazidime and imipenem. A first group of 21 strains (50%) was found to harbor various extended-spectrum β-lactamases (1 OXA-14; 2 OXA-19; 1 OXA-35; 1 GES-9; and 3 PER-1), carbapenemases (2 GES-5; 1 IMP-8; and 8 VIM-2), or both (1 VIM-2/OXA-35 and 1 VIM-4/SHV-2a). All the strains of this group belonged to widely distributed epidemic clones (ST111, ST175, CC235, ST244, ST348, and ST654), and were highly resistant to almost all the antibiotics tested except colistin. A second group was composed of 16 (38%) isolates moderately resistant to C/T (MICs from 8/4 to 16/4 μg/ml), of which 7 were related to international clones (ST111, ST253, CC274, ST352, and ST386). As demonstrated by targeted mass spectrometry, cloxacillin-based inhibition tests, and gene bla_PDC deletion experiments, this resistance phenotype was correlated with an extremely high production of cephalosporinase PDC. In part accounting for this strong PDC upregulation, genomic analyses revealed the presence of mutations in the regulator AmpR (D135N/G in 6 strains) and enzymes of the peptidoglycan recycling pathway, such as AmpD, PBP4, and Mpl (9 strains). Finally, all of the 5 (12%) remaining C/T-resistant strains (group 3) appeared to encode PDC variants with mutations known to improve the hydrolytic activity of the β-lactamase toward ceftazidime and C/T (F147L, ΔL223-Y226, E247K, and N373I). Collectively, our results highlight the importance of both intrinsic and transferable mechanisms in C/T-resistant P. aeruginosa. Which mutational events lead some clinical strains to massively produce the natural cephalosporinase PDC remains incompletely understood.

中文翻译：

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铜绿假单胞菌对头孢洛赞/他唑巴坦的耐药机制：GERPA多中心研究的结果

铜绿假单胞菌的耐药机制由36家法国医院实验室收集的420份对头孢他啶（MIC> 8μg/ ml）和/或亚胺培南（> 4μg/ ml）不敏感的非冗余菌株的评估对头孢洛氮/他唑巴坦（C / T）进行评估个月（GERPA研究）。在该人群（42/420株）中，C / T耐药率（MIC> 4/4μg/ ml）等于10％，在对头孢他啶和亚胺培南均耐药的菌株中，其C / T耐药率等于10％。发现第一组21株（50％）含有各种广谱β-内酰胺酶（1 OXA-14; 2 OXA-19; 1 OXA-35; 1 GES-9;和3 PER-1），碳青霉烯酶（2个GES-5； 1个IMP-8；和8个VIM-2），或两者（1个VIM-2 / OXA-35和1个VIM-4 / SHV-2a）。该组的所有菌株均属于广泛分布的流行克隆（ST111，ST175，CC235，ST244，ST348和ST654），除粘菌素外，几乎对所有测试的抗生素都具有高度抗性。第二组由16种（38％）对C / T有中等抵抗力的分离株（MIC从8/4至16/4μg/ ml）组成，其中7种与国际克隆有关（ST111，ST253，CC274，ST352，和ST386）。如靶向质谱法，基于氯氧西林的抑制试验和基因所证明在bla _PDC缺失实验中，这种抗性表型与头孢菌素酶PDC的极高产量相关。部分地解释了这种强烈的PDC上调，基因组分析揭示了调节剂AmpR（6个菌株中的D135N / G）和肽聚糖回收途径的酶（如AmpD，PBP4和Mpl）（9个菌株）中存在突变。最后，剩下的5个（12％）的C / T耐药菌株（第3组）似乎都编码具有已知可提高β-内酰胺酶对头孢他啶和C / T水解活性的突变的PDC变体（F147L，ΔL223- Y226，E247K和N373I）。总的来说，我们的结果突出了耐C / T的铜绿假单胞菌内在和可转移机制的重要性。。哪些突变事件导致某些临床菌株大量产生天然的头孢菌素酶PDC，目前尚不完全清楚。