Centre for Research and Development of Medical Diagnostic Laboratories (CMDL), Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen 40002, Thailand.
Clinical Microbiology Laboratory, Srinagarind Hospital, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand.
Infect Genet Evol. 2020 Nov;85:104577. doi: 10.1016/j.meegid.2020.104577. Epub 2020 Sep 30.
The global emergence of colistin resistance in carbapenem-resistant Acinetobacter baumannii (CRAB) clinical isolates is a serious public health concern. We therefore aimed to investigate colistin resistance mechanisms in 5 colistin-resistant (COL-R) CRAB isolates collected from Thai patients in 2016 by whole genome sequencing (WGS) compared with those of 5 colistin-intermediate (COL-I) CRAB isolates from the same period. All isolates were subjected to antimicrobial susceptibility testing, efflux pump inhibitor-based test and WGS. Mutations in known genes associated with colistin resistance were analyzed and deleterious mutations were then predicted by PROVEAN tool. The 10 CRAB isolates carried bla with the addition of bla in 1 isolate. All COL-R isolates exhibited colistin MICs of 4 μg/mL except for 1 isolate with that of 16 μg/mL. They belonged to ST2, ST16, ST23, ST164 and ST215, whereas the COL-I isolates with colistin MICs of ≤0.25-1 μg/mL were ST2, ST164 and ST215. Neither increased efflux pump activity nor mcr gene was found in any COL-R isolate. Three COL-R isolates contained different PmrB variants: a novel 10-amino acid (aa) repeat sequence insertion, VILGCILIFS between positions 27 and 28 (S27_A28insVILGCILIFS) in transmembrane domain (TM); a 1-aa insertion, alanine between positions 162 and 163 (A162_I163insA) in TM; and a 1-aa substitution, A226T in histidine kinase domain. One COL-R isolate possessed PmrA variant with A80V substitution. These alterations were predicted as deleterious. Mechanisms of colistin resistance in the remaining COL-R isolate were still unknown. In conclusion, the alterations in both PmrB and PmrA were predicted and suggested as initial mutations responsible for low-level colistin resistance in our CRAB isolates. Under selective pressure, these isolates may exhibit higher level colistin resistance by the additional mutations, leading to more therapeutic difficulties.
碳青霉烯类耐药鲍曼不动杆菌（CRAB）临床分离株中黏菌素耐药的全球出现是一个严重的公共卫生关注问题。因此，我们旨在通过全基因组测序（WGS）比较 2016 年从泰国患者中收集的 5 株黏菌素耐药（COL-R）CRAB 分离株与同期的 5 株黏菌素中介（COL-I）CRAB 分离株的黏菌素耐药机制。所有分离株均进行了抗菌药物敏感性试验、外排泵抑制剂试验和 WGS。分析了与黏菌素耐药相关的已知基因的突变，并通过 PROVEAN 工具预测了有害突变。10 株 CRAB 分离株均携带 bla，其中 1 株携带 bla。除 1 株分离株的 MIC 为 16μg/mL 外，所有 COL-R 分离株的 MIC 均为 4μg/mL。它们属于 ST2、ST16、ST23、ST164 和 ST215，而 MIC 为 ≤0.25-1μg/mL 的 COL-I 分离株为 ST2、ST164 和 ST215。在任何 COL-R 分离株中均未发现增加的外排泵活性或 mcr 基因。3 株 COL-R 分离株含有不同的 PmrB 变异体：第 27 和 28 位（S27_A28insVILGCILIFS）之间的 10 个氨基酸（aa）重复序列插入、跨膜域（TM）中的 1 个 aa 插入（A162_I163insA）和 TM 中的 1 个 aa 取代（A226T 在组氨酸激酶域中）。1 株 COL-R 分离株含有 PmrA 变异体，A80V 取代。这些改变被预测为有害的。其余 COL-R 分离株的黏菌素耐药机制尚不清楚。总之，我们预测并认为 PmrB 和 PmrA 的改变是导致我们的 CRAB 分离株产生低水平黏菌素耐药的初始突变。在选择压力下，这些分离株可能通过额外的突变表现出更高水平的黏菌素耐药性，从而导致更多的治疗困难。
