Plasmid-mediated mcr-1 gene in Acinetobacter baumannii and Pseudomonas aeruginosa: first report from Pakistan

Abstract INTRODUCTION: The increased use of colistin against infections caused by Acinetobacter baumannii and Pseudomonas aeruginosa has resulted in colistin resistance. The purpose of this study was to detect plasmid-mediated mcr-1 gene in colistin-resistant A. baumannii and P. aeruginosa isolates. METHODS: A total of 146 clinical isolates of A. baumannii (n = 62) and P. aeruginosa (n = 84) were collected from the four largest tertiary care hospitals in Peshawar, Pakistan. All bacterial isolates were phenotypically screened for multidrug resistance using the Kirby-Baur disc diffusion method. The minimum inhibitory concentration (MIC) of colistin in all isolates was phenotypically performed using dilution methods. mcr-1 gene was detected through polymerase chain reaction and the nucleotide sequence of amplicon was determined using Sanger sequencing. RESULTS: Approximately 96.7% A. baumannii and 83.3% P. aeruginosa isolates were resistant to multiple antibiotics. Colistin resistance was found in 9.6% (6/62) of A. baumannii and 11.9% (10/84) of P. aeruginosa isolates. Among 16 colistin resistant isolates, the mcr-1 gene was detected in one A. baumannii (1.61% of total isolates; 16.6% of colistin resistant isolates) and one P. aeruginosa strain (1.19% of total isolates; 10% of colistin resistant isolates). Nucleotide BLAST showed 98-99% sequence similarity to sequences of the mcr-1 gene in GenBank. CONCLUSIONS: Our study reports, for the first time, the emergence of plasmid-mediated mcr-1-encoded colistin resistance in multidrug resistant strains of A. baumannii and P. aeruginosa. Further large scales studies are recommended to investigate the prevalence of this mode of resistance in these highly pathogenic bacteria.

摘要：随着黏菌素（colistin）在治疗鲍曼不动杆菌（Acinetobacter baumannii）与铜绿假单胞菌（Pseudomonas aeruginosa）感染中的应用增多，黏菌素耐药性问题日益凸显。本研究旨在检测黏菌素耐药鲍曼不动杆菌及铜绿假单胞菌分离株中的质粒介导mcr-1基因。
方法：本研究从巴基斯坦白沙瓦市四所最大的三级医院收集了146株临床分离菌，其中鲍曼不动杆菌62株、铜绿假单胞菌84株。采用柯比-鲍尔（Kirby-Bauer）纸片扩散法对所有细菌分离株进行多药耐药性表型筛选；通过稀释法测定所有分离株对黏菌素的最低抑菌浓度（minimum inhibitory concentration, MIC）；采用聚合酶链式反应（polymerase chain reaction, PCR）检测mcr-1基因，并通过桑格测序（Sanger sequencing）确定扩增产物的核苷酸序列。
结果：约96.7%的鲍曼不动杆菌分离株与83.3%的铜绿假单胞菌分离株表现出多药耐药性。黏菌素耐药株在鲍曼不动杆菌中占比9.6%（6/62），在铜绿假单胞菌中占比11.9%（10/84）。在16株黏菌素耐药分离株中，1株鲍曼不动杆菌（占总分离株的1.61%，占黏菌素耐药株的16.6%）与1株铜绿假单胞菌菌株（占总分离株的1.19%，占黏菌素耐药株的10%）检出mcr-1基因。核苷酸BLAST比对显示，该扩增序列与GenBank中mcr-1基因序列的相似性为98%~99%。
结论：本研究首次报道了多药耐药鲍曼不动杆菌与铜绿假单胞菌菌株中出现质粒介导的mcr-1基因编码的黏菌素耐药性。建议开展更大规模的研究，以探究这类高致病性细菌中该耐药模式的流行情况。