Sun Fengqiang, Yu Xiaomei, Zhang Fengli, Ma Jie, Ji Ping
Department of Clinical Laboratory, Weifang People's Hospital, Weifang, China.
Department of Obstetrics, Weifang People's Hospital, Weifang, China.
J Glob Antimicrob Resist. 2025 Jun 6;44:95-102. doi: 10.1016/j.jgar.2025.05.027.
We aimed to characterize the molecular characteristics and clinical features of carbapenem-resistant Citrobacter braakii carrying bla, bla, and mcr-9.1 using whole-genome sequencing.
The susceptibility of C. braakii (WF0082) to 22 antimicrobial drugs was tested by an automated microbiology system. Whole-genome sequencing was performed using the Illumina and Nanopore platforms. Resistance genes and plasmid replicon types were determined. Gene structure was compared between strains to analyse the plasmid properties and gene environments of carbapenem (bla and bla) and mobilized colistin resistance genes (mcr-9.1). The core single-nucleotide polymorphisms were used to construct an evolutionary tree.
WF0082 was resistant to all antibiotics excluding colistin. bla was located on the truncated transposon Tn125 in the IncX3 plasmid. bla was located in the IncP6/IncX6 plasmid, a novel conjugative plasmid whose core bla platform (ISKpn27-bla-bla-ΔISKpn6-korC-klcA-orf279-orf396-ΔrepB) was derived mainly from the transposon Tn6296. The mcr-9.1 core region consisted of rcnR-rcnA-pcoE-ΔpcoS-IS903B-mcr-9.1-wbuC-IS26, and it was similar to the Tn6725 remnant. Based on phylogenetic analysis, the present strain was categorized into the C1 clade, and it was highly homologous to C. braakii isolates from Australia and China.
The results of this study showed that C. braakii strain WF0082 carrying bla, bla, and mcr-9.1 located on three plasmids was highly resistant to antimicrobial drugs. The ability of C. braakii to easily integrate foreign genes has the potential to seriously undermine clinical therapy, and it is urgent that the surveillance of strains harbouring multiple resistant genes is strengthened.
我们旨在通过全基因组测序来表征携带bla、bla和mcr-9.1的耐碳青霉烯类布氏柠檬酸杆菌的分子特征和临床特征。
使用自动化微生物系统检测布氏柠檬酸杆菌（WF0082）对22种抗菌药物的敏感性。采用Illumina和Nanopore平台进行全基因组测序。确定耐药基因和质粒复制子类型。比较菌株间的基因结构，以分析碳青霉烯类（bla和bla）和可移动黏菌素耐药基因（mcr-9.1）的质粒特性和基因环境。利用核心单核苷酸多态性构建进化树。
WF0082对除黏菌素外的所有抗生素均耐药。bla位于IncX3质粒的截短转座子Tn125上。bla位于IncP6/IncX6质粒中，IncP6/IncX6是一种新型接合质粒，其核心bla平台（ISKpn27-bla-bla-ΔISKpn6-korC-klcA-orf279-orf396-ΔrepB）主要来源于转座子Tn6296。mcr-9.1核心区域由rcnR-rcnA-pcoE-ΔpcoS-IS903B-mcr-9.1-wbuC-IS26组成，与Tn6725残余相似。基于系统发育分析，本菌株被归类为C1分支，与来自澳大利亚和中国的布氏柠檬酸杆菌分离株高度同源。
本研究结果表明，携带位于三种质粒上的bla、bla和mcr-9.1的布氏柠檬酸杆菌菌株WF0082对抗菌药物具有高度耐药性。布氏柠檬酸杆菌易于整合外源基因的能力有可能严重破坏临床治疗，因此迫切需要加强对携带多种耐药基因菌株的监测。
