染色體之fosA與運輸蛋白在碳青黴烯抗藥性克雷伯氏肺炎桿菌造成之磷黴素抗藥性

Abstract

碳青黴烯抗藥性克雷伯氏肺炎桿菌(carbapenem resistant Klebsiella pneumoniae)造成全世界臨床上極大的問題。磷黴素(fosfomycin)是少數的治療選擇之一。然而碳青黴烯抗藥性克雷伯氏肺炎桿菌對磷黴素的抗藥性也被觀察到。在本研究中，我們目標為找出碳青黴烯抗藥性克雷伯氏肺炎桿菌對磷黴素抗藥的機轉。我們蒐集台灣四家醫學中心2010年至2018年間對磷黴素抗藥性的克雷伯氏肺炎桿菌。我們將磷黴素抗藥性相關的基因擴增並且定序。並且利用碳水化合物攝取試驗以及基因突變試驗以確認基因突變與抗藥性的關聯。我們總共蒐集到了40株磷黴素抗藥性的碳青黴烯抗藥性克雷伯氏肺炎桿菌做分析，其中14株為低度抗藥性(最小抑菌濃度256-512mg/dl)，26株為高度抗藥性(最小抑菌濃度大等於1024mg/dl)。其中位於染色體上fosAKP點突變I91V在40株碳青黴烯抗藥性克雷伯氏肺炎桿菌當中的39株被發現。基因突變試驗發現I91V使得克雷伯氏肺炎桿菌對磷黴素最小抑菌濃度增加8倍，並且是低度抗藥性菌株唯一被找到的機轉。在26高度抗藥性株中同時找到了額外的機轉。多種不同的基因突變導致G3P和G6P運輸蛋白的缺陷在其中19株被找到，其中有三種造成過去未被發現過的氨基酸替換。(glpT E299D, glpT D274V and uhpC A393V)。其中7株發現質體中帶有的fosA3磷黴素分解酶基因。在本研究中，我們發現染色體上fosAKP點突變I91V造成低度抗藥性，而額外的磷黴素運輸蛋白(19/26, 73.1%)缺陷及磷黴素分解酶(7/26, 26.9%)造成了高度抗藥性。

Infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP) are of significant clinical concern worldwide. Fosfomycin is one of the limited treatment options for CRKP. However, resistance to fosfomycin in CRKP has been observed. In this study, we aimed to investigate the fosfomycin resistance mechanism of CRKP. Fosfomycin-resistant Klebsiella pneumoniae isolates were collected from four medical centers in Taiwan from 2010 to 2018. The genes that contributed to fosfomycin resistance were amplified and sequenced. Carbohydrate utilization assays and mutagenesis studies were performed to determine the mechanisms underlying fosfomycin resistance. Forty fosfomycin-resistant CRKP strains were collected and used for further analysis. Fourteen strains exhibited low-level resistance (MIC = 256–512 mg/dl), while 26 strains showed high-level resistance (MIC ≥ 1024 mg/dl). Chromosomal fosAKP I91V was detected in 39/40 fosfomycin-resistant CRKP strains. We observed that amino acid substitution of chromosomal fosAKP I91V increased the MIC of fosfomycin by approximately 8 folds, and this was the only mechanism elucidated for low-level fosfomycin resistance. Among the 26 high-level resistance strains, fosAKP I91V combined with transporter deficiencies (18/26, 69.2%) was the most common resistant mechanism, and one strain showed transporter deficiency only. Plasmid-borne fosA3 accounted for 27.0% (7/26) of high-level resistance. Various G3P and G6P transporter gene mutations, including three novel single amino acid mutations (glpT E299D, glpT D274V, and uhpC A393V) were detected in 19 strains. No murA mutation was found in this study. Our study highlights the need for new therapeutic agents for CRKP infections in Taiwan.