Research Service, Louis Stokes Cleveland Department of Veterans Affairs, Cleveland, Ohio, USA.
Department of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
Antimicrob Agents Chemother. 2018 Sep 24;62(10). doi: 10.1128/AAC.01140-18. Print 2018 Oct.
is a member of the complex, a group of >20 related species of nosocomial pathogens that commonly infect individuals suffering from cystic fibrosis. β-Lactam antibiotics are recommended as therapy for infections due to , which possesses two β-lactamase genes, and PenA is a carbapenemase with a substrate profile similar to that of the carbapenemase (KPC); in addition, expression of PenA is inducible by β-lactams in Here, we characterize AmpC from ATCC 17616. AmpC possesses only 38 to 46% protein identity with non- AmpC proteins (e.g., PDC-1 and CMY-2). Among 49 clinical isolates of , we identified 27 different AmpC variants. Some variants possessed single amino acid substitutions within critical active-site motifs (Ω loop and R2 loop). Purified AmpC1 demonstrated minimal measurable catalytic activity toward β-lactams (i.e., nitrocefin and cephalothin). Moreover, avibactam was a poor inhibitor of AmpC1 ( > 600 μM), and acyl-enzyme complex formation with AmpC1 was slow, likely due to lack of productive interactions with active-site residues. Interestingly, immunoblotting using a polyclonal anti-AmpC antibody revealed that protein expression of AmpC1 was inducible in ATCC 17616 after growth in subinhibitory concentrations of imipenem (1 μg/ml). AmpC is a unique inducible class C cephalosporinase that may play an ancillary role in compared to PenA, which is the dominant β-lactamase in ATCC 17616.
是 复合体的一个成员，该复合体是一组 >20 种与医院获得性病原体相关的物种，通常感染囊性纤维化患者。β-内酰胺类抗生素被推荐用于治疗 感染，该菌具有两个β-内酰胺酶基因 和 PenA 是一种碳青霉烯酶，其底物谱与 碳青霉烯酶（KPC）相似；此外，PenA 的表达可被 中的β-内酰胺诱导。在这里，我们对 ATCC 17616 中的 AmpC 进行了表征。AmpC 与非 AmpC 蛋白（例如 PDC-1 和 CMY-2）的蛋白质同一性仅为 38%至 46%。在 49 株 的临床分离株中，我们鉴定出 27 种不同的 AmpC 变体。一些变体在关键活性位点模体（Ω环和 R2 环）内具有单个氨基酸取代。纯化的 AmpC1 对β-内酰胺（即硝头孢菌素和头孢噻吩）表现出最小的可测量催化活性。此外，阿维巴坦对 AmpC1 的抑制作用很差（>600 μM），并且 AmpC1 与酰基-酶复合物的形成缓慢，可能是由于与活性位点残基缺乏有效相互作用所致。有趣的是，使用多克隆抗 AmpC 抗体进行免疫印迹显示，在亚抑菌浓度的亚胺培南（1 μg/ml）中生长后，AmpC1 在 ATCC 17616 中的蛋白表达可被诱导。AmpC 是一种独特的可诱导的 C 类头孢菌素酶，与 中的 PenA 相比，它可能在 中起辅助作用，而 PenA 是 ATCC 17616 中的主要β-内酰胺酶。
