Lahiri Sushmita D, Walkup Grant K, Whiteaker James D, Palmer Tiffany, McCormack Kathy, Tanudra M Angela, Nash Tory J, Thresher Jason, Johnstone Michele R, Hajec Laurie, Livchak Stephania, McLaughlin Robert E, Alm Richard A
Infection Innovative Medicines Unit, AstraZeneca R & D Boston, Waltham, MA, USA
Infection Innovative Medicines Unit, AstraZeneca R & D Boston, Waltham, MA, USA.
J Antimicrob Chemother. 2015;70(6):1650-8. doi: 10.1093/jac/dkv004. Epub 2015 Feb 1.
Pseudomonas aeruginosa is an important nosocomial pathogen that can cause a wide range of infections resulting in significant morbidity and mortality. Avibactam, a novel non-β-lactam β-lactamase inhibitor, is being developed in combination with ceftazidime and has the potential to be a valuable addition to the treatment options for the infectious diseases practitioner. We compared the frequency of resistance development to ceftazidime/avibactam in three P. aeruginosa strains that carried derepressed ampC alleles.
The strains were incubated in the presence of increasing concentrations of ceftazidime with a fixed concentration (4 mg/L) of avibactam to calculate the frequency of spontaneous resistance. The mutants were characterized by WGS to identify the underlying mechanism of resistance. A representative mutant protein was characterized biochemically.
The resistance frequency was very low in all strains. The resistant variants isolated exhibited ceftazidime/avibactam MIC values that ranged from 64 to 256 mg/L. All of the mutants exhibited changes in the chromosomal ampC gene, the majority of which were deletions of various sizes in the Ω-loop region of AmpC. The mutant enzyme that carried the smallest Ω-loop deletion, which formed a part of the avibactam-binding pocket, was characterized biochemically and found to be less effectively inhibited by avibactam as well as exhibiting increased hydrolysis of ceftazidime.
The development of high-level resistance to ceftazidime/avibactam appears to occur at low frequency, but structural modifications in AmpC can occur that impact the ability of avibactam to inhibit the enzyme and thereby protect ceftazidime from hydrolysis.
铜绿假单胞菌是一种重要的医院病原体，可引起多种感染，导致显著的发病率和死亡率。阿维巴坦是一种新型非β-内酰胺β-内酰胺酶抑制剂，正与头孢他啶联合开发，有可能成为传染病医生治疗选择中的一个有价值的补充。我们比较了携带去阻遏ampC等位基因的三株铜绿假单胞菌对头孢他啶/阿维巴坦耐药性产生的频率。
将菌株在固定浓度（4mg/L）阿维巴坦存在下，与浓度不断增加的头孢他啶一起孵育，以计算自发耐药频率。通过全基因组测序对突变体进行表征，以确定耐药的潜在机制。对一种代表性的突变蛋白进行生化表征。
所有菌株的耐药频率都非常低。分离出的耐药变体对头孢他啶/阿维巴坦的最低抑菌浓度值范围为64至256mg/L。所有突变体的染色体ampC基因均发生了变化，其中大多数是AmpC的Ω环区域出现各种大小的缺失。对携带最小Ω环缺失的突变酶进行了生化表征，该缺失形成了阿维巴坦结合口袋的一部分，发现其受阿维巴坦抑制的效果较差，同时对头孢他啶的水解作用增强。
对头孢他啶/阿维巴坦产生高水平耐药性的情况似乎很少发生，但AmpC的结构修饰可能会影响阿维巴坦抑制该酶的能力，从而保护头孢他啶不被水解。
