Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, Cologne, Germany.
School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.
Antimicrob Agents Chemother. 2019 Feb 26;63(3). doi: 10.1128/AAC.01586-18. Print 2019 Mar.
Colistin resistance in is of great concern and is a threat to human health. In this study, we investigate the mechanisms of colistin resistance in four isogenic pairs of isolates displaying an increase in colistin MICs. A mutation in was detected in each colistin-resistant isolate, three of which were novel (A28V, I232T, and ΔL9-G12). Increased expression of was shown by semi-quantitative reverse transcription-PCR (qRT-PCR) for three colistin-resistant isolates, and the addition of phosphoethanolamine (PEtN) to lipid A by PmrC was revealed by mass spectrometry. Interestingly, PEtN addition was also observed in some colistin-susceptible isolates, indicating that this resistance mechanism might be strain specific and that other factors could contribute to colistin resistance. Furthermore, the introduction of carrying the short amino acid deletion ΔL9-G12 into a knockout strain resulted in increased expression and lipid A modification, but colistin MICs remained unchanged, further supporting the strain specificity of this colistin resistance mechanism. Of note, a mutation in the homologue and a point mutation in IS upstream of were associated with colistin resistance and increased expression, which is a hitherto undescribed resistance mechanism. Moreover, no cost of fitness was observed for colistin-resistant isolates, while the virulence of these isolates was increased in a infection model. Although the mutations in were associated with colistin resistance, PEtN addition appears not to be the sole factor leading to colistin resistance, indicating that the mechanism of colistin resistance is far more complex than previously suspected and is potentially strain specific.
黏菌素耐药性令人高度关注，对人类健康构成威胁。在这项研究中，我们调查了四对显示黏菌素 MIC 值升高的同源性肺炎克雷伯菌分离株中黏菌素耐药的机制。每个耐药分离株均检测到 基因中的突变，其中 3 个为新突变（A28V、I232T 和 ΔL9-G12）。通过半定量逆转录-PCR（qRT-PCR）显示三种耐药分离株的 表达增加，通过质谱法显示 PmrC 将磷酸乙醇胺（PEtN）添加到脂 A 中。有趣的是，在一些敏感的分离株中也观察到 PEtN 添加，表明这种耐药机制可能具有菌株特异性，并且其他因素可能导致黏菌素耐药。此外，将携带短氨基酸缺失 ΔL9-G12 的 基因导入 基因敲除菌株中，导致 表达增加和脂 A 修饰，但黏菌素 MIC 值保持不变，进一步支持这种黏菌素耐药机制的菌株特异性。值得注意的是， 基因的突变和 IS 上游的点突变与黏菌素耐药和 表达增加相关，这是一种以前未描述的耐药机制。此外，耐药分离株没有观察到适应性成本，而这些分离株在 感染模型中的毒力增加。虽然 基因中的突变与黏菌素耐药性相关，但 PEtN 添加似乎不是导致黏菌素耐药的唯一因素，这表明黏菌素耐药机制远比以前怀疑的要复杂，并且可能具有菌株特异性。
