Table_3_Emergence of Aeromonas veronii strain co-harboring blaKPC–2, mcr-3.17, and tmexC3.2-tmexD3.3-toprJ1b cluster from hospital sewage in China.XLSX

IntroductionThe raise of multi-drug resistant bacteria involving carbapenem, colistin, or tigecycline resistance constitutes a threat to public health, which partly results from the transmission of corresponding mobile resistance genes, such as blaKPC and blaNDM for carbapenem, mcr for colistin, and tmexCD-toprJ gene cluster for tigecycline. Herein, we described the emergence of an Aeromonas veronii strain HD6454 co-harboring blaKPC–2, mcr-3.17, and tmexC3.2-tmexD3.3-toprJ1b gene cluster from hospital sewage.
MethodsWhole genome sequencing (WGS) was used to determine the genome sequence of HD6454, and the detailed genomic analysis of genetic elements or regions carrying key antimicrobial resistance genes (ARGs) from HD6454 were performed. Cloning experiment was conducted to confirm the function of key ARGs in mediating antimicrobial resistance. Conjugation experiment was conducted to determine the mobility of the plasmid.
ResultsThe results showed that this strain belonged to a novel sequence type (ST) variant ST1016, and carried 18 important ARGs. Among them, the blaKPC–2 was carried by non-self-transmissible IncP-6 plasmid, while tmexC3.2-tmexD3.3-toprJ1b gene cluster and mcr-3.17 were carried by integrative and mobilizable element (IME) or IME-related region in chromosome. The mcr-3.17, mcr-3.6, and mcr-3-like3 genes were further inferred to originate from IMEs of Aeromonas species. Additionally, for the first time, the mcr-3.17 was confirmed to confer low-level resistance to colistin under inducible expression, while tmexC3.2-tmexD3.3-toprJ1b gene cluster was confirmed to confer low-level resistance to tigecycline.
DiscussionThis is the first report of a strain co-harboring blaKPC–2, mcr-3.17, and tmexC3.2-tmexD3.3-toprJ1b gene cluster. Although the resistance and/or mobility of these ARGs are limited in this strain, the emergence of this multiple important ARGs-carrying strain deserves further attention.

引言：耐碳青霉烯类、黏菌素或替加环素的多重耐药细菌的出现对公共卫生构成威胁，其部分诱因是相应移动耐药基因的传播，例如针对碳青霉烯类的blaKPC与blaNDM、针对黏菌素的mcr，以及针对替加环素的tmexCD-toprJ基因簇。本研究报道了一株从医院污水中分离得到的维氏气单胞菌（Aeromonas veronii）HD6454菌株，该菌株同时携带blaKPC–2、mcr-3.17及tmexC3.2-tmexD3.3-toprJ1b基因簇。
方法：采用全基因组测序（WGS）确定HD6454的基因组序列，并对该菌株中携带关键抗菌药物耐药基因（antimicrobial resistance genes, ARGs）的遗传元件或区域开展详细基因组分析。通过克隆实验验证关键抗菌耐药基因介导抗菌耐药性的功能，借助接合实验确定质粒的迁移能力。
结果：结果显示，该菌株属于新型序列型（sequence type, ST）变体ST1016，共携带18种重要抗菌耐药基因。其中，blaKPC–2位于不可自主转移的IncP-6型质粒上，而tmexC3.2-tmexD3.3-toprJ1b基因簇与mcr-3.17则位于染色体上的整合可移动元件（integrative and mobilizable element, IME）或IME相关区域中。进一步推断，mcr-3.17、mcr-3.6及mcr-3-like3基因起源于气单胞菌属的整合可移动元件。此外，本研究首次证实，mcr-3.17在诱导表达条件下可介导低水平黏菌素耐药性，而tmexC3.2-tmexD3.3-toprJ1b基因簇可介导低水平替加环素耐药性。
讨论：本研究首次报道同时携带blaKPC–2、mcr-3.17及tmexC3.2-tmexD3.3-toprJ1b基因簇的菌株。尽管该菌株中这些抗菌耐药基因的耐药性和/或迁移能力有限，但这种携带多种重要抗菌耐药基因菌株的出现值得进一步关注。