Phosphoethanolamine Modification of Lipid A in Colistin-Resistant Variants of Acinetobacter baumannii Mediated by the pmrAB Two-Component Regulatory System
Phosphoethanolamine Modification of Lipid A in Colistin-Resistant Variants of Acinetobacter baumannii Mediated by the pmrAB Two-Component Regulatory System
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DOI：
10.1128/aac.00079-11
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发表时间：
2011-07-01
影响因子：
4.9
通讯作者：
Woodford, Neil
中科院分区：
文献类型：
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作者：
Beceiro, Alejandro;Llobet, Enrique;Woodford, Neil
鲍曼不动杆菌对黏菌素的耐药性很少见，其耐药机制尚不清楚。我们研究了PmrCAB在这一性状中的作用，使用（i）耐药和敏感的临床菌株，（ii）实验室选择的模式菌株ATCC 19606和临床分离株ABRIM的突变体，和（iii）从同一患者分离的一对敏感/耐药的同基因临床分离株Ab 15/133和Ab 15/132。所有粘菌素敏感分离株中的pmrAB序列与参考序列相同，而耐药临床分离株在PmrB中具有一个或两个不同位置的氨基酸替换。在菌株ATCC 19606和ABRIM的耐药突变体以及耐药临床分离株Ab 15/132中也发现了PmrB中的单一取代。未发现PmrA或PmrC突变。逆转录酶（RT）-PCR鉴定了耐药微生物与敏感微生物中pmrA（4- 13倍）、pmrB（2- 7倍）和pmrC（1- 3倍）的表达增加。基质辅助激光解吸电离-飞行时间（MALDI-TOF）质谱显示，在抗性变体和在低Mg 2+诱导条件下生长的菌株ATCC 19606中，磷酸乙醇胺被添加到七酰化形式的脂质A中。粘菌素抗性ATCC 19606衍生物的pmrB基因敲除突变体显示对粘菌素的敏感性增加>100倍，pmrC的表达降低5倍;它们还缺乏向脂质A中添加磷酸乙醇胺。我们的结论是，发展一个中等水平的粘菌素耐药性在A。鲍曼不动杆菌需要不同的遗传事件，包括（i）pmrB中的至少一个点突变，（ii）pmrAB的上调，和（iii）pmrC的表达，这导致磷酸乙醇胺添加到脂质A中。
Colistin resistance is rare in Acinetobacter baumannii, and little is known about its mechanism. We investigated the role of PmrCAB in this trait, using (i) resistant and susceptible clinical strains, (ii) laboratory-selected mutants of the type strain ATCC 19606 and of the clinical isolate ABRIM, and (iii) a susceptible/resistant pair of isogenic clinical isolates, Ab15/133 and Ab15/132, isolated from the same patient. pmrAB sequences in all the colistin-susceptible isolates were identical to reference sequences, whereas resistant clinical isolates harbored one or two amino acid replacements variously located in PmrB. Single substitutions in PmrB were also found in resistant mutants of strains ATCC 19606 and ABRIM and in the resistant clinical isolate Ab15/132. No mutations in PmrA or PmrC were found. Reverse transcriptase (RT)-PCR identified increased expression of pmrA (4- to 13-fold), pmrB (2- to 7-fold), and pmrC (1- to 3-fold) in resistant versus susceptible organisms. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry showed the addition of phosphoethanolamine to the hepta-acylated form of lipid A in the resistant variants and in strain ATCC 19606 grown under low-Mg2+ induction conditions. pmrB gene knockout mutants of the colistin-resistant ATCC 19606 derivative showed >100-fold increased susceptibility to colistin and 5-fold decreased expression of pmrC; they also lacked the addition of phosphoethanolamine to lipid A. We conclude that the development of a moderate level of colistin resistance in A. baumannii requires distinct genetic events, including (i) at least one point mutation in pmrB, (ii) upregulation of pmrAB, and (iii) expression of pmrC, which lead to addition of phosphoethanolamine to lipid A.