Schumann Anna, Gaballa Ahmed, Yang Hyojik, Yu Di, Ernst Robert K, Wiedmann Martin
Department of Food Science, Cornell University, Ithaca, New York, USA.
Graduate Field of Biomedical and Biological Sciences, Cornell University, Ithaca, New York, USA.
mSphere. 2024 Dec 19;9(12):e0073124. doi: 10.1128/msphere.00731-24. Epub 2024 Nov 29.
Genes encoding lipid A modifying phosphoethanolamine transferases (PETs) are genetically diverse and can confer resistance to colistin and antimicrobial peptides. To better understand the functional diversity of PETs, we characterized three canonical mobile colistin resistance () alleles (, , ), one intrinsic (), and two -like genes (, ) in . Using an isogenic expression system, we show that and confer similar phenotypes of decreased colistin susceptibility with low fitness costs. , which is phylogenetically closely related to , and only provide fitness advantages in the presence of sub-inhibitory concentrations of colistin and significantly reduce fitness in media without colistin. PET-B and PET-C were phenotypically distinct from bonafide PETs; neither impacted colistin susceptibility nor caused considerable fitness cost. Strikingly, we found for the first time that different PETs selectively modify different phosphates of lipid A; MCR-1, MCR-3, and PET-C selectively modify the 4'-phosphate, whereas MCR-9 and EptA modify the 1-phosphate. However, 4'-phosphate modifications facilitated by MCR-1 and -3 are associated with lowered colistin susceptibility and low toxicity. Our results suggest that PETs have a wide phenotypic diversity and that increased colistin resistance is associated with specific lipid A modification patterns that have been largely unexplored thus far.
Rising levels of resistance to increasing numbers of antimicrobials have led to the revival of last resort antibiotic colistin. Unfortunately, resistance to colistin is also spreading in the form of genes, making it essential to (i) improve the identification of resistant bacteria to allow clinicians to prescribe effective drug regimens and (ii) develop new combination therapies effective at targeting resistant bacteria. Our results demonstrate that PETs, including MCR variants, are site-selective in and that site-selectivity correlates with the level of susceptibility and fitness costs conferred by certain PETs. Site selectivity associated with a given PET may not only help predict colistin resistance phenotypes but may also provide an avenue to (i) improve drug regimens and (ii) develop new combination therapies to better combat colistin-resistant bacteria.
编码脂质A修饰磷酸乙醇胺转移酶（PETs）的基因在遗传上具有多样性，并且可以赋予对黏菌素和抗菌肽的抗性。为了更好地理解PETs的功能多样性，我们对肺炎克雷伯菌中的三个典型可移动黏菌素抗性（mcr）等位基因（mcr - 1、mcr - 3、mcr - 9）、一个固有eptA基因以及两个eptA样基因（eptB、eptC）进行了表征。使用同基因表达系统，我们发现mcr - 1和mcr - 3赋予相似的表型，即黏菌素敏感性降低且适应性代价低。与mcr - 1系统发育密切相关的mcr - 9和eptA仅在亚抑制浓度的黏菌素存在时提供适应性优势，而在没有黏菌素的培养基中显著降低适应性。PET - B和PET - C在表型上与真正的PETs不同；它们既不影响黏菌素敏感性，也不会导致显著的适应性代价。令人惊讶的是，我们首次发现不同的PETs选择性修饰脂质A的不同磷酸基团；MCR - 1、MCR - 3和PET - C选择性修饰4'-磷酸基团，而MCR - 9和EptA修饰1-磷酸基团。然而，由MCR - 1和 - 3促进的4'-磷酸基团修饰与降低的黏菌素敏感性和低毒性相关。我们的结果表明PETs具有广泛的表型多样性，并且增加的黏菌素抗性与特定的脂质A修饰模式相关，而这些模式迄今为止在很大程度上尚未被探索。
对越来越多抗菌药物的耐药性水平上升导致了作为最后手段的抗生素黏菌素的复兴。不幸的是，对黏菌素的耐药性也以mcr基因的形式传播，这使得（i）改进耐药细菌的鉴定以允许临床医生开出有效的药物治疗方案以及（ii）开发针对耐药细菌有效的新联合疗法变得至关重要。我们的结果表明，包括MCR变体在内的PETs在脂质A修饰方面具有位点选择性，并且位点选择性与某些PETs赋予的敏感性水平和适应性代价相关。与给定PET相关的位点选择性不仅可能有助于预测黏菌素抗性表型，还可能为（i）改进药物治疗方案以及（ii）开发新的联合疗法以更好地对抗黏菌素耐药细菌提供一条途径。
